Problem/ Lit. Review/ Objectives/ Procedures/ Previous Work/ Cooperative Research/ References

BREEDING AND GENETICS FOR THE IMPROVEMENT OF POTATO (SOLANUM TUBEROSUM L.) FOR YIELD, QUALITY AND PEST RESISTANCE

David S. Douches
Department of Crop and Soil Sciences

1.  NATURE AND IMPORTANCE OF THE PROBLEM

     The cultivated potato, Solanum tuberosum (2n=4x=48) is the most important vegetable crop and the fourth most important food crop in the world.  The potato is an important food for the fresh market and it is also the raw material for the french fry, chipping, and starch processing industries.  The Michigan potato industry has had a variable history but its survival as one of the major potato producing states in the U.S. can be attributed to its ability to adjust to shifting market trends.  At the turn of the century the entire Michigan potato crop was marketed fresh and seed.   Today, the Michigan potato industry is dominated by the chip processing sector that accounts for about 80% of the approximately 45,000 acres in production.  The Michigan potato industry ranks as the largest northern supplier of potatoes to the chipping industry.  The 2004 Michigan potato harvest had a farmgate value of $100 million that increases to well over half a billion dollars after marketing.  Michigan is one of the few major potato producing states that are strategically located to ship potatoes to the East Coast market for potato chip processing. The ability to store and supply chip potatoes into June offers expanded market opportunities for the industry.  The tablestock market can expand with the changes in transportation costs. 

     New varieties are central to the health and growth of the Michigan potato industry.  With the breeding program we continue to address market and production limiting traits.  These key traits are chip quality (low reducing sugars) from storage, scab resistance, late blight resistance, beetle resistance, bruise resistance, starch content, abiotic stress and nutritional enhancement.  If host plant resistance can be increased for both insects and pathogens, pest control costs can be reduced and production management strategies may be simplified.  [top]

2.  LITERATURE REVIEW

     The cultivated potato is the most important vegetable crop and produces, on average, more food energy and protein than cereals, and the lysine content of potato complements cereal based diets that are deficient in this essential amino acid.  Not only is the potato an important food for the fresh market, but also it is the raw material for the french fry, chipping, and starch processing industries. It is highly productive on a per acre basis and, because of its adaptability, can be grown commercially in any of the 50 states. In fact, the United States produces 22 million metric tons of potatoes annually on approximately 1.3 million acres, with a farmgate value of greater than $2.7 billion (National Potato Council 2004).  In addition, the per capita consumption of potatoes is approximately 143 lbs. in the United States.

     Given the significance of the potato, research on the genetic improvement of this crop is important. Potato breeders are challenged by an autotetraploid genome, asexual propagation, and breeding principles and practices that are quite different from those employed for the majority of diploid (or allopolyploid), seed-propagated crops and numerous market limiting traits.  Tarn et al. (1992) have identified 18 traits related to fresh and processing uses, 17 pathogen and 6 pest resistance traits, and numerous agronomic traits that need to be considered in a potato breeding program.  Moreover, the genetic base of the cultivated potato is considered to be narrow (Mendoza and Haynes 1974) and yield stasis exists within the potato germplasm of North America (Douches et al. 1996).  However, the potato has an extremely rich gene pool with seven cultivated and 199 wild species.  To broaden the genetic base of the cultivated potato and introduce new traits, North and South American potato species have been used as a source of new genes (Haynes 1972; Hermundstad and Peloquin 1985).

     The Colorado potato beetle, Leptinotarsa decemlineata Say is one of the most economically significant pests of potato in northern latitudes.  From 12.5% to 25% defoliation can significantly decrease potato yields (Mailloux and Bostanian 1989) and complete defoliation of a crop can reduce potato yields by as much as two-thirds (Hare 1980).  However, the Colorado potato beetle led to the first large-scale use of insecticides in 1864 (Gauthier et al. 1981) and insecticides remain the primary means of Colorado potato beetle control (Casagrande 1987).  About 1.3 million lbs. of active ingredients of the insecticides are applied to potato crops to control Colorado potato beetle in the top eight potato-producing states (Wiese et al. 1998). However, the Colorado potato beetle has shown a remarkable ability to develop resistance to every insecticide used for its control (Bishop and Grafius 1996) and has done so at an increasingly fast rate (Ioannidis et al. 1991; Heim et al. 1990). 

     Colorado potato beetle caused Michigan potato growers crop losses and control costs of $10 to 14 million/year during the early 1990s, when insecticide resistance problems were severe (Grafius 1997).  The first neonicotinoid insecticide (imidacloprid) was registered in 1995; as the result, control costs were reduced to $3-4 million/year, crop losses were reduced to near zero, and insecticide use was reduced by 200,000 lb active ingredient (MPIC 1993, 1994).  Since 1995, neonicotinoid insecticides (including thiamethoxam, registered in 2002) have been critical for control of Colorado potato beetle.  72% of Michigan’s potato acreage is treated annually with imidacloprid or thiamethoxam as in furrow or seed treatment.  It would be very costly and difficult for Michigan growers to manage Colorado potato beetle without neonicotinoid insecticides.  The Michigan potato industry is beginning to see high levels of resistance to imidacloprid in Colorado potato beetle.  Resistance to imidacloprid first appeared in Michigan in 2004 (Grafius, pers. comm.)  In 2005, beetles from one field were 100 times more resistant to imidacloprid than susceptible beetles. 

     Potato cultivars resistant to Colorado potato beetle, developed through traditional breeding or genetic engineering, could form a critical part of a pest management system and reduce the reliance on insecticides if they could be incorporated into the management system.  Effective host plant resistance could reduce cost to growers and consumers. This strategy can be used to breed future varieties with additional host plant resistance to Colorado potato beetle.

     Bacillus thuringiensis (Bt) is an aerobic, gram-positive, soil bacterium that accumulates high levels of insecticidal crystal proteins during sporulation (McGaughey and Whalon 1992; Barton and Miller 1993). These crystalline protein inclusions, or -endotoxins, are the principal active ingredients in Bt formulations (McGaughey and Whalon 1992).  The advantage of the Bt toxin over conventional chemical insecticides is host specificity.  The Bt bacteria produce insecticidal crystal proteins that are encoded by single genes.  Transgenic plants are the most effective means to deliver Bt-based insecticides.  The major advantages to this delivery system are increased efficacy, reduced application costs and minimal scouting needs (Lambert and Peferoen 1992) compared with conventional insecticide sprays.  The efficacy of codon-modified Bt genes such as Bt-cry1 and Bt-cry3A were demonstrated to be greater than the wild type Bt genes in crop plants (Perlak et al. 1991; Wünn et al. 1996).  Many strategies for managing Bt crops have been discussed including the following:  1) high level of a single toxin; 2) mixture of non-resistant and resistant plants in the field; 3) the use of low level toxins and biocontrol agents; 4) toxins deployed sequentially; 5) pyramiding multiple toxins (Gould 1986).  NewLeaf potatoes (Monsanto Corp.) contain Bt-cry3A genes imparting very high levels of resistance to potato beetles.  They were registered and available for commercial use from 1995-2000 but were taken off the market because of processor concerns about genetically modified foods in international sales.  Other Bt-cry3A potato lines have been developed by the MSU Potato Breeding Program (Coombs et al. 2002). 

     Currently, there are two defined host plant resistance factors available in the Solanum gene pool that contributes to plant defenses against insects: glandular trichomes and leptine steroid glycoalkaloids.  Small insects exhibit modified behavior in the presence of trichomes including host avoidance and restlessness, reduced feeding, delayed development, and diminished longevity (Tingey 1991).  Three wild Solanum species, S. berthaultii, S. polyadenium, and S. tarijense, have high densities of glandular trichomes (Tingey et al. 1984) that have been bred into cultivated potato.  Breeding line NYL235-4 has glandular trichomes derived from S. berthaultii and is available for further research and breeding (Plaisted et al., 1992).  Glycoalkaloids are the most common form of antibiosis in potato (Sinden et al., 1986) and have been shown to inhibit acetyl cholinesterase (Bushway et al. 1987).  They have also demonstrated membrane disruption by lysis of sterol-containing liposomes.  Acetylated glycoalkaloids are the most active form of steroid glycoalkaloids present in potato.  Leptines are acetylated analogs of the common potato steroid glycoalkaloids, solanine and chaconine.  Leptines such as those found in USDA8380-1, and other acetylated steroid glycoalkaloids are only reported to be synthesized by some accessions of S. chacoense and are synthesized only in leaves and not the tubers (Sanford et al. 1996). 

     Biotin is an essential co-enzyme required for all insect growth and development.  Without this co-enzyme, an insect’s growth is severely stunted, eventually leading to death (Markwick  et al. 2001). Avidin is a protein found in chicken egg whites; this protein protects the chicken embryo by sequestering biotin from diseasing causing organisms (Hood et al. 1997).  The gene for avidin production have been cloned (Hood et al. 1997). The avidin gene has also been inserted and expressed in a few crops, including maize and tobacco and has demonstrated resistance to a wide spectrum of insect pests (Kramer et al. 2000, Markwick et al. 2001, Burgess et al. 2002).  All insects need biotin; therefore avidin is a more broad-spectrum toxin than Bacillus thuringiensis crystal proteins.  Avidin could be used not only to delay resistance of Colorado potato beetle to Bt-cry3A, but it may also be useful to control other pests such as potato leafhopper, aphids and European corn borer.  

     Another key tactic to resistance management is the development of alternative modes of action in the Bt-transgenic potato. No single form of resistance, either genetically engineered or classically bred, is likely to provide long-term control to such highly adaptable insects, particularly if other mortality factors, such as crop rotation or biological control, are not included in the management system.  More durable strategies than single factor Bt-based host plant resistance must be developed.  Host plant resistance management combining genetically engineered resistance with traditionally bred host plant resistance has the potential to be much more sustainable and easily implemented.  Combining host plant resistance factors as a resistance management strategy does not require grower cooperation or regulatory monitoring or enforcement. Potential pest resistance mechanisms to the different resistance factors will likely be completely different, as is probably the case with our research on leptines and Bt-based resistance for management of Colorado potato beetle (Cooper et al. 2004). Incorporation of host plant resistance into an integrated pest management system involving multiple biological, cultural, and chemical controls will further increase the sustainability of a pest management system.

     Potato late blight (Phytophthora infestans Mont. de Bary) is a significant global constraint to potato production and due to conducive climatic conditions and growing practices the mid western states of the US are particularly vulnerable.  During recent years in North America, potato late blight has re-emerged as the most important pathogen of the potato crop. The disease is characterized by haulm destruction and decay of the tubers.  The late blight pathogen most common in North America until 1994 was the US-1 genotype (Goodwin et al. 1995). Since then, the most commonly reported genotype of late blight is US-8. The US-8 genotype of P. infestans is characterized by reduced sensitivity to metalaxyl and the A2 mating type (Deahl et al. 1993).  The mid-west states produce about 10 million tons of potato from 150,000 planted hectares, which represents about 40% of total US production.  Potato late blight affects the health of foliage and tubers limiting profitable potato production.  Significant financial costs in terms of crop protection (up to $700/ha) and crop losses (up to $5,000/ha) are incurred when intervention measures to control potato late blight are unsuccessful.  One aspect of late blight disease management in the field is the use of resistant cultivars.  It is important to draw upon many germplasm resources to develop a broad genetic base and identify differences in expression of single components of field resistance (i.e. resistance to infection, spread and sporulation), then hybridize according to complementary components.  Concurrently, the high standards demanded by the industry and consumers for yield, maturity, class, quality and multiple resistances must be met.

     Jiang and Helgeson (USDA/ARS and University of Wisconsin, Madison) cloned the late blight resistance gene (RB) from S. bulbocastanum, a Mexican diploid potato species (Song et al. 2003).  This RB gene offers the unique opportunity to directly introduce a late blight resistance gene, cloned from a potato species, into all current potato cultivars and future advanced germplasm.  We have obtained the RB gene from the University of Wisconsin, developed vectors to transform potato lines, obtained transgenic lines and field tested them at the Muck Soils Research Farm.  These lines show a level of foliar late blight resistance that would have value in commercial potato production.  The RB gene belongs to a class of characterized resistance genes that encode proteins with nucleotide binding and leucine-rich repeat domains (Song et al. 2003).  Recently other late blight resistance genes have been mapped and cloned from S. bulbocastanum (van der Vossen et al. 2003), S. mochiquense (Smilde et al. 2004), and a complex genomic hybrid (Park et al. 2005).  The resistance genes from these Solanum species offers race non-specific resistance unlike those previously utilized from S. demissum.  The ability to transform major late blight resistance genes into potato provides a unique opportunity to pyramid late blight resistance genes in an analytic manner.  In this way we could study the interaction of P. infestans and single and combined gene-based host plant resistance.  Moreover, the pyramided resistance genes in a single genotype should be a better strategy to deploy late blight resistant potato varieties (Dangl and Jones 2001).

     Of the bacterial diseases, Streptomyces scabies is one of the major pathogens that infect potato and cause scab.  The pathogen produces necrotic, corky-textured lesions on the outer surface of the potato.  The lesions can vary in their appearance as being raised, surface or pitted.  Chip processors consider pitted lesions a chip defect because the pit will be apparent in the chip. Surface and raised lesions present less of a problem as potatoes are peeled before they are chipped, thereby removing the lesions.  Even so, since the marketplace for potatoes is quality driven, the presence of scab lesions, especially those which are pitted, on the outer surface of the potato for both table and chipping varieties significantly lessen their marketability. Scab has re-emerged as a problem across the state of Michigan.  The pathogen can survive in the soil for many years and the development of the disease is favored by dry conditions during tuber initiation (Loria et al, 1997).  These two factors are probably a major reason why scab has re-emerged, but this also illustrates the importance of additional study of this disease to formulate a long-term solution..  The best and most reliable solution to scab is through the use of host resistance (Loria et al, 1997, Ross 1986).  Pathogenicity of S. scabies is correlated with production of toxins called thaxtomins (Loria et al, 1997).  These toxins cause tuber tissue browning and induce formation of scab-like lesions on immature tubers (Lawrence et al., 1990).     

     Breeding for resistance to common potato scab is probably the very best way to combat the disease (McKee, 1958).  Genetic improvement from diploid species may be done for a variety of agronomically important traits including yield, chipping quality and disease and insect resistance (Spooner and Bamberg 1994).  Reddick (1953) stated that there are plants resistant to scab and the resistance is heritable.
 
     Once resistance has been characterized it may be crossed to the tetraploid level. Studies have examined the transmission of resistance by using diploid interspecific hybrids (Tai et al., 1996; Murphy et al., 1995).  Material was selected based on their resistance to scab as well as their ability to produce 2n gametes, allowing the resistance to be brought up to the tetraploid level.  Jansky and Rouse (2003) reported similar results with transmission of scab resistance while broadening the resistance to two other diseases, early die (Verticillium dahliae) and early blight (Alternaria solani).  By combining genetically diverse backgrounds of wild material (S. berthaultii, S. tarijense and S. chacoense) and crossing back to the tetraploid level, they were able to produce disease resistant progeny.  Dionne and Lawrence (1961) looked at incorporating scab resistance into the susceptible diploid S. phureja.  They took a scab resistant clone of S. chacoense and crossed it with S. phureja.  The most resistant F1 individuals were crossed to produce the F2 generation.  The F2 was back-crossed (BC) to S. phureja, the recurrent parent.  The resistant BC1 individuals were observed for their resistance to scab.  Dionne and Lawrence concluded that resistance to the disease is not inherited in a simple manner, but that many factors are involved. 

     Long term storage of potatoes is an important aspect of marketing potatoes for chip processing.  Maintenance of low levels of reducing sugars in the potato tuber are important for acceptable processing qualities thus, one of the biggest detriments to potato chip quality is the low temperature sweetening potential of many cultivars. A temperature of 4C is required to reduce sprout growth, moisture loss and disease incidence during storage, however, at this temperature reducing sugars accumulate from the degradation of starch and from the conversion of sucrose to glucose and fructose is catalyzed by invertase.  These reducing sugars have an aldehyde group that reacts with the amino groups of amino acids via the Maillard reaction, resulting in brown potato chips upon processing (Duffus and Duffus 1984).  To maintain low reducing sugar levels, potatoes are stored at 10C.  However, at this temperature it is necessary to apply CIPC (Chlorprophan) during storage or maleic hydrazide to the foliage in the field to obtain good sprout inhibition. 

     Plant breeders are increasingly pressured to satisfy consumer needs as well as growers’ needs.  Today, the American public is concerned about health and food safety.  With over 93% of the US potato crop being consumed domestically, these concerns need to be addressed.   Consumer acceptance has become an important driving force in plant breeding, and nutritional improvement is a promising avenue for increasing crop value.  As a high-yielding, easily grown crop, potatoes have a long history as an important staple food.  Compared to other staple foods such as rice, corn, and cereal grains, potatoes have high levels of vitamin C, vitamin K, and potassium, excellent quality protein, and many other micronutrients.  Furthermore, potatoes are typically less processed than other staple foods, and thus retain more of these nutrients in the edible product.  The potato presents an excellent nutritional base upon which to build.

     Recent work to improve potato nutritional quality has focused on modifying carotenoid, anthocyanin, or antioxidant content, as well as exploring the natural variation for important endogenous nutrients such as vitamin C (Brown et al. 2003; Love et al. 2004; Lu et al. 2001; Reyes et al. 2004).  Thus far, nutritional improvement in potato has been limited to designing potatoes for delivery of unique carotenoids shown to reduce the incidence of particular diseases, or increasing general antioxidant levels.  We have identified vitamin E as a particularly important nutrient currently present at very low levels in potato relative to cereal grains.

     Vitamin E consists of eight compounds with varying antioxidant capacity and bioavailability.  Four of these compounds are tocotrienols, derived from geranylgeranyl diphosphate and homogentisate.  The other four are tocopherols, which are derived from phytidyl diphosphate and homogentisate.  In plants, all eight compounds serve as antioxidants that protect plant membranes, but α-tocopherol is the most bioavailable for humans (Traber 2003).

     Since potato tubers have low levels of endogenous tocopherol, they represent an ideal model for studying the effects of genetic modifications in this biosynthetic pathway.  There are no reports in the literature to increase levels of α-tocopherol in potato, although other studies have produced increases of α-tocopherol levels inadvertently (Romer et al. 2004).  Reports on the levels of tocopherols in cultivated potato tubers indicate that natural variation exists among breeding lines (Sypchalla and Desborough 1989).  For example, yellow-flesh potatoes have 2-fold higher α-tocopherol levels than white-flesh (Romer et al. 2004).  Tocopherols have also been observed to increase naturally during cold storage (Kumar and Knowles 1993).  Conventional breeding is not a practical method for increasing tocopherol levels.  However, we intend to identify lines that are naturally higher in tocopherols for transformation experiments.

     Recent research has shown that is now possible to use transgenic approaches to improve abiotic stress tolerance with few traits than originally anticipated (Zhang et al. 2000).  Physiological and molecular studies have shown that drought-stressed plants increase synthesis of abscisic acid (ABA) and a series of ABA-regulated proteins (Bray 1991). ABA is a multifunctional hormone involving stomatal function, seed development and germination as well as stress responses (Zeevaart and Creelmann 1988). A cDNA for an ABA responsive gene, HVA1 was cloned from barley aleurone layers (Xu et al. 1996).  Expression of the HVA1 cDNA under control of the constitutive CaMV 35S promoter in transgenic tobacco plants conferred delayed leaf wilting when drought-stressed. In rice, Xu et al. (1996) reported that plants transformed with HVA1 gene had higher average shoot height and root fresh weight than wild-type plants.
     An alternate strategy is to express heterologous CBF1 (C repeat/ dehydration-responsive element binding factor 1) genes in plants to improve environmental stress resistance (Thomashow 1999).  CBF1 genes are referred to as master switches that activate expression of COR genes, increasing stress tolerance in the absence of cold stimulation.  Arabidopsis CBF genes also can confer increased dehydration stress resistance to other less closely related species (Hseih et al. 2002a; Hseih et al. 2002b; Owens et al. 2002; Kasuga et al. 2004).  Kasuga et al. (2004) used the stress-inducible rd29A promoter to drive the expression of DREB1A/CBF3 gene in tobacco plants. Tobacco plants expressing DREB1A/CBF3 under the dehydration inducible promoter rd29A were more drought tolerant compared to wild type tobacco plants and had higher photosynthetic activity under drought and cold-nonfreezing temperature. Recently, tomato plants over expressing the Arabidopsis CBF1 gene were more dehydration stress tolerant than wild type plants (Hseih et al. 2002b).  We have obtained the CBF1 gene from Thomashow (CSS) at MSU.  [top]

3.  OBJECTIVES

1.  Utilize conventional breeding techniques to generate seedlings for varietal selection and development and also to introgress exotic Solanum germplasm for the purposes of variety development.

2.  Integrate transformation techniques into the breeding program to introduce genes for insect resistance (Bt-cry3A, Bt-cry1Ia1 and avidin), late blight resistance (RB), water stress (CBF1), nutritional enhancement (Vitamin E) potatoes.

3.  Conduct screening procedures to evaluate early generation breeding material and advanced selections for chip-processing, resistance to Colorado potato beetle and diseases such as late blight (foliage and tuber) and scab.

4.  Study the genetics of key traits targeted for potato improvement.

5.  Develop and evaluate lines with multiple resistance genes to delay/prevent Colorado potato beetle adapting to resistant lines.

6.  Initiate procedures to inbreed germplasm at the 4x and 2 x levels and then study the consequences of this process.

7.  Conduct replicated trials that are designed to evaluate the marketable maturity and adaptability of advanced selections and new releases (from Michigan and other states) with emphasis upon yield, chip-processing, general appearance, dry matter, and blackspot bruise resistance, external and internal defects that affect specific markets.

8.  Continue to name, commercially release, and intellectually protect new potato varieties that are of value to the potato industry.  [top]

4.  EXPERIMENTAL PROCEDURES

Objective 1.     Utilize conventional breeding techniques to generate seedlings for varietal selection and development and also to introgress exotic Solanum germplasm for the purposes of variety development.
 
Breeding, Selection and Variety Evaluation:
     The MSU Breeding program continues to test MSU-bred lines in replicated trials (over 170 lines) and on grower farms (20 lines).  We also enter 3-4 lines in the North Central regional trials, 2-3 lines in the SFA trials and send many of the advanced breeding lines to Ohio, Pennsylvania, Florida, California, North Dakota, Nebraska, Minnesota, North Carolina, Maine, Washington, Wisconsin, Ontario and Quebec Canada and various international sites for testing.  Through a cooperative effort of MPIC (Michigan Potato Commission), MSPA (Michigan Seed Potato Association), Chris Long, the MSU breeding program and the processors we are working to help move the best lines towards larger scale commercial testing and have chip-processing lines evaluated in the Commercial Demonstration Storage facility.  At this time, we have many advanced selections that have chipping or tablestock qualities along with scab or late blight resistance, bruise resistance, etc. with commercial potential.

     Each year the MSU breeding program will cross elite germplasm to generate and field evaluate about 50,000 seedlings on a single-hill basis for adaptation to Michigan.  In the subsequent years these selections are then advanced to 8 hill, 20-hill, 30-hill, and 50-hill plots, with increasing selection pressure for agronomic, quality and disease and/or insect resistance parameters.  We now have in place field sites for early generation selection for late blight, scab and Colorado potato beetle.  Early generation evaluation of these key traits increases our effectiveness in identifying commercially valuable advanced selections.  From this 4-year early generation evaluation and selection phase of the breeding program we generate over 200 MSU-bred advanced selections that are then to be tested and evaluated under more intensive replicated trials at the Montcalm Research Farm.  We are also producing the FG1 and FG2 level seed of the most promising selections from the MSU breeding program for in-state grower-cooperator trials, out-of-state trials, North Central Regional trials, national USPB/SFA trials and MSU research farm trials. 

     Elite clones will be tested for at the Montcalm Research Farm for agronomic performance, marketable maturity, chip processing at harvest and in storage, resistance to pitted scab, potato early die and late blight.  We place these advanced selections into tissue culture and initiate virus eradication procedures so that virus free tissue culture plantlets or tuber sources can be made available to the industry.  The most advanced clones will also be evaluated on differing spacing and nitrogen rates in cooperation with Chris Long.

     Currently, the breeding program has in tissue culture about 100 MSU advanced selections 30 transgenic lines and has 30 new candidates that are in process for transfer to tissue culture.  We want to continue to work closely with the commercial growers and seed industry to test and provide seed for more intensive evaluation.  Through this linkage we hope to identify the breeding selections that have merit to achieve varietal status in Michigan. 

On-farm testing of varieties and advanced selections
     On farm variety trials will be conducted with 12-15 grower-cooperators in Michigan.  Growth characteristics, maturity, yield and quality measurements are made at each location.  Chris Long (CSS) and D.S. Douches coordinate these on-farm trials and decision-making revolves around an annual post-harvest meeting involving the cooperating growers, extension agents, MSU researchers and the MPIC (MSU Potato Variety Day).  The group evaluates the individual trials and the summarized results to make recommendations for the following year and target advanced selections for commercialization.  In addition, Michigan is one of 7 national locations for the Snack Food Association Chip Trials.  These trials are designed to evaluate advanced seedlings that have demonstrated characteristics desired by the chip-processing industry.  Entries are obtained from the various potato breeding programs in the U.S.

     The MSU potato breeding program has been conducting chip-processing evaluations each year on potato lines from MSU and from other states.  For 6 years we have been conducting a long-term storage study to evaluate advanced breeding lines with chip-processing potential in the Dr. B. F. (Burt) Cargill Potato Demonstration Storage facility directly adjacent to the MSU Montcalm Research Farm to identify extended storage chippers.  We are positioned to evaluate advanced selections from the breeding program for chip-processing over the whole extended storage season (October-June).  Tuber samples of our elite chip-processing selections are placed in the demonstration storage facility in October and are sampled monthly to determine their ability to chip-process from storage.  In addition, Chris Long evaluates the more advanced selections in the 10 cwt box bins and manages the 500 cwt. storage bins which may have MSU lines.  Potatoes from these bins are sent to regional chip-processing companies in a cooperative arrangement for evaluation.

Distribution of MSU advanced selections for out-of-state testing and cooperative trials
    Advanced selections will be distributed to cooperators in Ohio, Pennsylvania, California, North Carolina, Maine, Wisconsin, Minnesota, North Dakota, Nebraska, Washington, Ontario and Florida for testing in replicated variety trials.  These cooperative trials will give us information on the adaptability of MSU advanced selections to locations within and outside the Great Lakes region. Four advanced selections from MSU will be entered in the North Central Regional Variety Trial that is conducted over 11 different locations.  Data collected from these trials will be returned to Michigan.  The compiled data will be used to make decisions towards cultivar release.

Germplasm Enhancement:
     In an effort to simplify the genetic system in potato (which normally has 4x chromosomes) and exploit more efficient selection of desirable traits, a "diploid" (2x chromosomes) breeding program has been implemented.  In general, diploid breeding utilizes haploids (half the chromosomes) from potato varieties, and diploid wild and cultivated tuber-bearing relatives of the potato.  These represent a large source of valuable germplasm, which can broaden the genetic base of the cultivated potato and also provide specific desirable traits such as tuber dry matter content, cold chipping and dormancy, along with resistance to disease, insects, and virus.  Even though these potatoes have only half the chromosomes of the varieties in the U.S., they can be crossed with cultivated potato by conventional methods via 2n pollen to transfer desirable genes.  Six Solanum species have been included in the diploid breeding program germplasm base at MSU:  S. tuberosum (adaptation, tuber appearance), S. phureja (cold-chipping, specific gravity, PVY immunity), S. tarijense and S. berthaultii (verticillium resistance, tuber appearance, insect resistance), S. microdontum  (late blight resistance) and S. chaconese (specific gravity, low sugars, dormancy, insect resistance).  In general, the germplasm enhancement component of the breeding program is an investment towards future breeding efforts.  The germplasm base of the breeding program will be broadened with this genetic material for the purpose of enhancing the long-term progress in cultivar development.   In 2005 we have made 4x-2x crosses to transfer the late blight resistance to the cultivated level.  We will begin evaluating this material in 2006.

Objective 2.  Integrate transformation techniques into the breeding program to introduce genes for insect resistance (Bt-cry3A, Bt-cry1Ia1 and avidin), late blight resistance (RB), water stress (CBF1), nutritional enhancement (Vitamin E) potatoes.
   
     Genetic engineering offers the opportunity to introduce new genes into our cultivated germplasm that otherwise would not be exploited.  The production of transgenic potato cultivars carrying the Bt-based and avidin-based insect resistance, RB gene-based late blight disease resistance, CBF1-based cold/frost tolerance, and the genes for Vitamin E synthesis represents a valuable source of breeding germplasm.
 
    We have Colorado potato beetle resistance via the Bt-cry3A gene (Lemhi Russet, Yukon Gold, Onaway, MSE018-1, Jacqueline Lee, NY123 and Norwis) and potato tuber moth resistance via the Bt-cry1Ia1 gene (Spunta and Ranger Russet).  We are also conducting transformation experiments to determine the value of avidin in controlling Colorado potato beetle and other potato insects. 

     The RB gene was transformed (late blight resistance) into MSE149-5Y, MSG227-2 and Spunta and now we are selecting progeny from crosses that contain the RB gene is segregating along with other late blight resistance genes (a strategy to combine multiple resistance genes).  This material will be evaluated in detached leaf tests and field trials at the Muck Soils Research Farm.

     MSE149-5Y was transformed to test the CBF1 gene for water (drought) stress response.  The biological activity of the transgenic potato lines will be evaluated initially under growth chamber and greenhouse conditions before testing in the field.  Transgenic and non-transgenic potato lines will be grown under similar conditions in 3.8L pots under 16/8 h light at 24°C  For water deficit treatment the plants will be grown for various time periods (0, 7, 14, 21 and 28 d) without water.  Leaves will be detached from each plant and weighed for fresh weight with multiple sampling and measurements.  Then the leaves will be dried to determine dry weight.  Chlorophyll fluorescence values will be measured using a pulse-activated modulation fluorometer and leaf conductance will be measured using a LI-1600 steady state porometer.
     
     We have recently transformed potato plants with p-hydroxyphenyl-pyruvate dioxygenase (HPPD) and homogentisate phytyltransferase (HPT) genes to determine whether Vitamin E levels can be increased in the foliage and tubers of potato.  The enzymes we have targeted for overexpression in potato were selected based on results obtained in Arabidopsis and selected crop plants.  Tsegaye and colleagues (2002) obtained a 15-37% increase in tocopherols in Arabidopsis leaves through constitutive overexpression of HPPD.  Overexpression of PDH and HPPD in tobacco plants led to accumulation of 350μg/gdw α-tocotrienol in leaves, whereas none was detected in wild-type plants (Rippert et al. 2004).  HPT was shown to be limiting for tocopherol synthesis in Arabidopsis, where 3 to 4.4-fold higher levels were obtained through constitutive overexpression (Collakova and DellaPenna 2003).  Dr. DellaPenna (BCH) has generously made available the Arabidopsis thaliana HPPD, HPT, and other genes involved in Vitamin E synthesis. 

     We regard at this research (combined with conventional breeding) as the most balanced approach to develop improved varieties with long and short-term breeding strategies. These genes will be of value in the breeding program and continue to look for new genes that may have economic and environmental value provided consumers will accept GM varieties.

Objective 3.  Conduct screening procedures to evaluate early generation breeding material and advanced selections for chip-processing, resistance to Colorado potato beetle and diseases such as late blight (foliage and tuber) and scab.

     Chip-processing:  Chip-processing is a key market trait.  (The addition of the Commercial Demonstration Storage facility enhances our ability to characterize advanced breeding lines from our breeding program.)  We screen advanced breeding lines from MRF, the Commercial Demonstration Storage, and on-farm trials for chip-processing out-of-the-field, and 50°F, 45°F  and 40°F storage (about 6-800 samples during the fall and storage season).  We also screen early generation breeding material from the single, 8-, 20-, 30-, and 50-hill stages for chip processing out-of-the-field, and 50°F and 40°F storage.  About 4,000 samples are processed and this data is computerized and used in the selection and decision making process in the breeding program. 

     Potato Scab:  We continue to screen advanced material in the scab nursery and have identified numerous advanced breeding lines with scab resistance (in cooperation with Dr. Ray Hammerschmidt PLP).  These lines have the potential to advance through the evaluation stages towards varietal naming and/or become parent sources for the crossing block.  We are also experimenting with the use of the tuber reaction to thaxtomin (a Streptomyces-specific compound) to categorize the scab reaction in advanced breeding lines.  If the correlation is high, this lab test would help us identify scab resistant germplasm more effectively.  With the new scab nursery at MSU we have additional space will allow us to start screening early generation material from the breeding program.  This earlier screening should help us identify and select more scab resistant advanced selections. 

     Each year a 5-hill plot by 4-replication field trial at the MSU Soils Farm is conducted to assess resistance to common and pitted scab.  The trial location has been dedicated for scab evaluation for over 10 years and periodically inoculated with the DPZ strain of Streptomyces scabies Thaxter.  The cultivars are ranked on a 0-5 scale based upon a combined score for scab coverage and lesion severity.  Usually examining one year's data does not indicate which cultivars are resistant but it should begin to identify ones that can be classified as susceptible to scab.   Our goal is to evaluate important advanced selections and varieties in the study at least three years to obtain a valid estimate of the level of resistance in each line. 

     Foliar Late Blight Resistance:  The trials at the Muck Soils Research Farm (in cooperation with Dr. Willie Kirk PLP) have helped us in the evaluation of late blight resistance for breeding and genetics purposes (over 750 lines in 2005).  Initially we have had a focused breeding effort to combine late blight resistance, chip processing/tablestock and early maturity. Over 50 possible late blight resistant lines were agronomically tested in 2005.  We are moving through phase 1 and we are pyramiding late blight resistance genes in phase 2 along with scab resistance.  Our greatest priority in crossing is to combine late blight resistance with chip-processing quality and scab resistance.

     Advanced breeding lines and cultivars will be planted in a randomized complete block design with three replications in early June.  We can effectively evaluate 200 lines per season.  The 11 late blight differential lines will be included along with known susceptible and resistant cultivars. Each 1.5m plot will contain four plants at 30 cm spacing, with eight plots per row.  Following inoculation in late-July, plants are mist-irrigated daily with a sprinkler system to prevent plants from drying and to promote humidity within the canopy.  Percent foliar infection will be visually assessed weekly following inoculation during August and early September.  The evaluations will conclude when the susceptible lines reach 100% infection. To compare the reactions of the potato lines across years, the Relative Area Under the Disease Progress Curve (RAUDPC) is calculated for each line (Colon et al. 1995; Kirk et al. 1999). 

     The MSU potato breeding and genetics program has developed a series of late blight resistant advanced breeding lines and cultivars that have diverse sources of resistance to late blight.  The goal is to combine these resistance sources through conventional breeding in combination with marker-assisted selection and transgenic approaches to create cultivars that can be commercialized by the Michigan potato industry.  Three DNA-based markers that are closely linked with late blight resistance QTL’s can be monitored in the progeny of crosses by combining late blight resistance sources.  The goal is to select progeny that carry the markers closely linked with two late blight QTL’s.  Concurrently, Agrobacterium-mediated transformation will be used to combine the RB gene, cloned from Solanum bulbocastanum, with current late blight resistant cultivars and advanced breeding lines from the MSU breeding program.  In 2004, we demonstrated the feasibility of this experimental approach by showing that the RB gene conferred foliar late blight resistance when transferred into a susceptible potato line.  Foliar late blight resistance will be evaluated using detached leaf tests and inoculated field trials at the MSU Muck Soils Research Farm.  Tubers from these field trials will be used to assess tuber blight resistance.

     Growth chamber studies will be conducted with isolates of P. infestans representing diverse genotypes and representative of pathogen populations in Michigan and North America.  Combinations of genotypes of US-1, US-6, US-8, US-10, US-11 and US-14 clonal lineages will be used to inoculate the field resistant potato lines and cultivars to characterize the late blight resistance. 

     Tuber evaluation - Briefly, 10 surface sterilized tubers are inoculated with a sub-peridermal injection of a zoosporangia suspension of different virulent biotypes of P. infestans at about 2 x 10-5 ml (delivering about 20 zoosporangia inoculation-1).  Ten control tubers are inoculated with cold (4oC) sterile distilled H2O.  After inoculation, tubers are stored at 10oC and samples taken for destructive sampling at 40 days after inoculation (Kirk et al., 2001). Sample tubers are sectioned transversely in a series from base of tuber to apical end. Infected potato tuber tissue darkens in response to late blight progress through the tuber.  An image analysis-based rating of the tuber symptom levels will be made.  These studies are in collaboration with Dr. Willie Kirk (PLP)

     Colorado potato beetle resistance:  The MSU potato breeding program makes crosses each year between our parents with partial host plant resistance to select for Colorado potato beetle resistant early generation and advanced selections.  Selections are made at the single, eight, 20 and 30-hill stages to identify agronomically strong selections with beetle resistant pedigrees (glycoalkaloid and glandular trichome-based).  These selections are evaluated at the Montcalm Research Farm beetle nursery in replicated 5-hill plots (in collaboration with Drs. Ed Grafius and Walter Pett ENT).  Defoliation is recorded from emergence of over-wintered adult beetles through emergence of the second generation adults.  Transgenic lines derived from Bt-cry3a, Bt-cry1Ia1 and avidin transformation experiments are also evaluated.  The cages (2 m3) offer a no-choice evaluation of defoliation and beetle behavior.  Each line will be evaluated in 10 plant plots and replicated three times.  Lines with high and low Bt-cry3a expression, Bt-cry1Ia1 and glycoalkaloid-based resistance will be evaluated.  The best beetle resistant material will be selected for advanced replicated agronomic trials at the Montcalm Research Farm and for post harvest chip-processing evaluation.

Objective 4.  Study the genetics of key traits targeted for potato improvement.

     Constructing a high resolution map in S. microdontum:  A diploid mapping population, based upon SSRs and AFLPs, was established between a late blight resistant S. microdontum selection (TF75-5) and a susceptible diploid clone (MSA133-57).  SSR marker, STM0020, was identified to be tightly linked to a major QTL affecting late blight resistance (Bisognin et al. 2004).  Sandbrink et al. (2000) has localized a late blight resistance QTL to chromosome IV, while our data suggests STM0020 is either mapped to chromosome IV or X.  We currently have 5 markers (including STM0020) linked to the late blight resistance QTL. 

     With map-based cloning, the first key step is to accurately determine the chromosomal position of the target gene.  A population of about 1200 individuals will be grown for DNA isolation, tuber production and foliar late blight resistance assessment.  DNA will be isolated from leaf tissue using the Qiagen kit (Valencia, CA) according to the manufacturer’s instructions.  AFLP analysis will be performed as described by Vos et al. (1995) and SSR analysis according to Bisognin et al. (2004).  Bulked segregant analysis (BSA) (Michelmore et al. 1991) will be used to fine map the late blight QTL region.  DNA from both parents and 8-progeny based resistant and susceptible bulks (equal amounts of pre-amplified templates) will be used as determined by the late blight resistant assay.  Choice of AFLP primer combinations will be selected according to the results of BSA.  AFLP markers that are present in the resistant in the resistant bulk and parent will be selected as candidate markers with putative linkage to the resistance locus/loci.  We expect that at least 200 primer combinations to be screened for polymorphisms.  Polymorphisms detected in the BSA will be tested on a subset of the mapping population to confirm the use of dominant single-dose restriction fragments (Wu et al. 1992). Only markers inherited from the late blight resistant parent will be scored and used in the data analysis.  Those markers that pass this stringency will be genotyped on all 1200 progeny.  The linkage group containing the resistance locus will be determined by JoinMap 2.0 (Stam 1993).  A high resolution map will be constructed based upon the recombinants observed between two closely linked markers that flank the chromosomal region.

Objective 5.  Develop and evaluate lines with multiple resistance genes to delay/prevent Colorado potato beetle adapting to resistant lines.

     At this time high leptine expression has been combined with high Bt-cry3A expression in a single genotype (Coombs et al. 2002).  This line, along with lines that have either Bt-cry3A or leptine expression alone, allow us to test the effectiveness of combined resistance mechanisms versus individual mechanisms.  The primary effort of the potato breeding program is to combine these two resistance mechanisms into one cultivar. Such breeding efforts have been initiated to develop advanced breeding lines that express leptine-based insect resistance for the chip processing and tablestock industry. These lines have been crossed to our most advanced breeding lines that have good agronomic performance along with either chip processing or tablestock qualities. The superior individuals from each cross were selected for specific gravity, tuber appearance rating, chip processing, leptine/TGA (total glycoalkaloid) content and Colorado potato beetle resistance. HPLC procedures are being used to measure leptine/TGA concentration in the potato foliage (Sinden et al., 1986).  The superior selections from this breeding effort will be candidates for combining with the Bt-cry3A gene via Agrobacterium-mediated transformation (Douches, et al. 1998).  If there are problems with accumulation of glycoalkaloids in the tubers of clones developed from S. chacoense, then antisense TGA technology will be applied (Stapleton, et al. 1991).  This same strategy of combining natural and engineered traits will be applied to the glandular trichome-mediated resistance.  The combination of Bt-cry3A gene and glandular trichomes may provide a broader-based insect resistance providing control of small-bodied insects such as leafhoppers and aphids along with the Colorado potato beetle.  The avidin gene will be tested initially in susceptible backgrounds.  If this gene shows efficacy against Colorado potato beetle, it will be combined with the leptine-based resistance and with the Bt-cry3A gene to develop double gene vector constructs for transformation.  Lines showing promising beetle resistance under field conditions will be further characterized in the laboratory and will also be used as parental material in breeding programs and/or advanced for further agronomic evaluations.

Objective 6.  Initiate procedures to inbreed germplasm at the 4x and 2x levels and then study the consequences of this process.

     The cultivated potato is a heterozygous clone that follows tetrasomic inheritance.  In crosses between two clones or selfing, little if any traits breed true.  The probability of combining an array of desirable traits from a controlled cross is very low.  If certain traits (e.g. tuber shape, size, number, disease resistance, etc.) could be fixed through an inbreeding process, the percentage of desirable clones to select from would increase, hence, improving potato breeding efficiency.  Our goal is to initiate inbreeding through self-pollination, then selection within a series of elite parental lines.  The segregation of targeted traits will be followed in subsequent generations of inbreeding.  These inbred selections will also be evaluated for other desirable agronomic and economic traits.  When the final lines are selected, the parental value of the lines will be studied.

     At the diploid level, the potato behaves as a self-incompatible (SI), outcrossing, heterozygous clone.  R.E. Hanneman (USDA/ARS) discovered a diploid clone that is self-compatible (SC). When crossed to SI lines, the SC trait segregates as a major dominant gene. Our initial goal is to hybridize our elite diploid germplasm with the SC line.  From these crosses we will make selections for desirable agronomic and economic traits along with SC.  With the introgression of the SC gene we will be able to fix desirable traits, which can then be introgressed to the cultivated 4x germplasm.  Again, like the 4x strategy, fixation of desirable traits should increase the efficiency of potato breeding.

Objective 7.  Conduct replicated trials that are designed to evaluate the marketable maturity and adaptability of advanced selections and new releases (from Michigan and other states) with emphasis upon yield, chip-processing, general appearance, dry matter, and blackspot bruise resistance, external and internal defects that affect specific markets.

     Ten field experiments are conducted annually at the Montcalm Research Farm in Entrican, MI.  They are planted as randomized complete block designs with two to four replications.  The plots are 23 feet long and spacing between plants is 12 inches with inter-row spacing at 34 inches.  Supplemental irrigation is applied as needed.  The round white tuber types are divided into chip-processors and tablestock and are harvested at two dates (Date-of-Harvest trial: Early and Late).  The other field experiments are the Russet, North Central White, Red, Adaptation (tablestock and chip-processors), and Preliminary (tablestock and chip-processors) and Transgenic trials.  In each of these trials, the yield is graded into four size classes, incidence of external and internal defects in > 3.25 in. diameter or 10 oz. potatoes are recorded, and samples for specific gravity, chipping, disease tests, bruising, and cooking tests are taken.  Chip quality is assessed on 25-tuber samples, taking two slices from each tuber.  Chips are fried at 365F and color measured visually with the SFA 1-5 color chart.  Tuber samples are also stored at 45F and 50F for chip-processing out of storage in January and March.  Advanced selections are also placed in the Commercial Demonstration Storage for monthly sampling.  The scab nursery at the MSU Soils Farm and the late blight trial at the Muck Soils Research Farm are used for scab and foliar late blight assessment of lines in the agronomic trials. [top]

5.  RESUME OF PREVIOUS INVESTIGATIONS

Breeding/Variety Development
     Dr. Douches re-established the potato breeding program in 1988 at MSU with the major goal of variety development.  The program has the capacity to conduct variety trials of advanced selections, develop new genetic combinations and identify exotic germplasm that will enhance the cultivar breeding efforts.  In addition, the program utilizes and applies genetic mapping and genetic engineering to improve cultivars.  These in-house capacities (both conventional and biotechnological) put the program in a position to respond and focus upon the most promising directions. The breeding team is multi-disciplinary and closely involves collaborative efforts with Drs. Hammerschmidt and Kirk, (Plant Pathology), Grafius, Pett, and Bird (Entomology).

     The breeding goals of the program are based upon current and future needs of the Michigan potato industry. The research priorities have been established through an annual dialog with the Michigan Potato Industry Commission Research Committee.  Traits of critical importance include high yield potential, disease resistance (pitted scab, late blight, and potato early die), resistance to Colorado potato beetle, chip processing (low reducing sugar accumulation) out-of-the-field and from long-term storage, cooking quality, storability, along with shape, internal quality and appearance.

     Since 2001, we have released five varieties to the industry.  A company from California is interested in marketing Jacqueline Lee, the late blight resistant variety, for the tablestock market. Licensed by MPIC, Michigan Purple, the novel purple-skinned tablestock variety, is under seed production with a strong interest to market at the farm market level along with Jacqueline Lee.  Group Gosselin, a Canadian group has licensed Boulder, a multi-purpose round white potato.  MPIC and Maine potato grower groups are currently licensing Beacon Chipper which was released in 2005.  MSJ461-1, a late blight resistant tablestock is being considered for release in 2007.  Other lines in commercial testing are:

MSJ036-A – Scab resistant chipper that is being fast-tracked for seed production
MSJ147-1 – A high yielding storage chipper with excellent sugar profiles in storage
MSE221-1 – A high yielding, scab resistant tablestock line.
MSL211-3 – A early maturing, bright skinned late blight and scab resistant tablestock line.

In addition, a set of 5 advanced breeding lines with scab resistance and chip-processing qualities are being fast-tracked for seed increase and future commercial testing in 2007 and 2008.

     We are presently using genes in vector constructs that confer resistance to Colorado potato beetle (Bt-cry3A and avidin), potato tuber moth (cry1Ia1 and cry1ac), late blight resistance via the RB gene, lowering glycoalkaloids (STG), nutritional enhancement for vitamin E, and drought resistance (CBF1).  Furthermore, we are investing our efforts in developing new vector constructs that use alternative selectable markers and give us the freedom to operate from an intellectual property rights perspective.  In addition, we are exploring transformation techniques that eliminate the need for a selectable marker (antibiotic resistance) from the production of transgenic plants.  Transformations and evaluation with the vitamin E, avidin, RB, cry1ac and CBF1 genes are in process.  There is also a strong interest from international research groups with these transgenic technologies.  Development of these vector constructs in our program point to some new research avenues.  Three manuscripts are in preparation from the avidin, RB and cry1ac transformation experiments.

     We have had extensive field testing for agronomic performance in replicated trials of our most advanced Bt-cry3A transgenic lines.  These Bt-cry3A lines represent a diverse portfolio of lines that could be commercialized if the intellectual property rights and regulatory requirements could be met.  We will maintain these lines in our program.  If the acceptance of transgenic food crops becomes deregulated, we will consider these lines for commercialization. 

     Common scab in potato is an on-going problem for the industry.  Results from the 2005 MSU scab nursery (in collaboration with Hammerschmidt, PLP) indicate that over 40% of the lines evaluated demonstrated zero to moderate levels of infection to common scab.  This is a significant improvement over the previous year’s evaluation.  In 2004, we began early generation evaluation of scab reaction in the breeding program.  This additional effort has lead to more clones with scab resistance.  In 2006 we are submitting 5 lines in the national scab trial with Liberator being one of the most resistant lines previously tested.  We have initiated some collaboration with the new USDA/ARS plant pathologist (Leslie Wanner) to identify and evaluate scab resistance in potato.

     Since the mid-1990’s we have directed efforts to identify sources of late blight resistance and use this resistance to breed late blight resistant varieties. As of 2005, based upon 9 years of inoculated field experiments (in collaboration with Kirk, PLP), we have at least 8 sources of foliar resistance to the US-8 genotype of P. infestans that have different pedigrees from which their resistance is derived.  The resistance in Jacqueline Lee has now exhibited resistance for 9 years of testing.  MSJ461-1, the chip-processing selection, has the same late blight resistance source Jacqueline Lee and is also resistant to a US-17 genotype of P. infestans in New York.  In 2003 year we added an early generation screen which will improve our ability to select late blight resistant lines with good market characteristics.  In 2005 we field tested the RB-transgenic potato lines for foliar resistance for a second year.  Frito Lay is using the MSU germplasm for late blight resistance in their varietal potato breeding program.

     Quantitative trait loci analysis (QTL) of a diploid mapping population identified closely linked markers associated with foliar resistance to late blight that explained about 70% of the disease reaction (Bisognin et al. 2004) and is resistant to all P. infestans isolates.  Based upon the pedigree and resistance reaction of the S. microdontum germplasm, the resistance in this material is a unique source of resistance that needs to be utilized and combined with other late blight resistance genes. We have been adding genetic markers to fine map this QTL and identify the chromosome.  In addition we have made interploidy crosses (4x-2x) to introgress the late blight resistance.  We are now using marker-assisted selection techniques to monitor the resistance transfer in the interploidy crosses.  In 2003 we identified a major QTL associated with late blight resistance in the tetraploid population and multiple QTLs for late blight resistance in the S. berthaultii mapping population. We established a lab-based late blight screen to characterize field based late blight resistance sources.  This additional foliar characterization allows us to differentiate the resistance sources we are using in the breeding program.

     In collaboration with Grafius and Pett (ENT), have been conducting research to examine the combined effects of Bt-based engineered resistance and natural host plant resistance to the Colorado potato beetle and potato tuber moth.  It is believed that these lines with combined host plant resistance may help in the resistance management of Bt-based crops.  We now have advanced breeding lines with moderate host plant resistance to Colorado potato beetle.  We also created transgenic avidin-expressing potato lines for insect resistance. 

     Two transgenic 'Spunta' clones, G2 and G3, have been identified that produced high control levels of mortality in first instars of potato tuber moth in laboratory tuber tests (100% mortality), and field trials in Egypt (99-100% undamaged tubers).  Field trials in the U.S. demonstrated that the agronomic performance of the two transgenic lines was comparable to 'Spunta'.  We are currently working with USAID, Syngenta and South Africa to commercialize the Spunta-G2 line.  We have also transformed two other important South African varieties with the Bt-cry1Ia1 gene.  We have had training of South African scientists in 2005, developed new vector constructs to feed the product pipeline and continue to develop capacity to submit a petition to deregulate Spunta G2 in South African. If successful, we will be the first public institution to deregulate a transgenic crop in a developing country.  USAID is interested in expanding this effort in other developing countries.

     Late blight, scab and Colorado potato beetle resistance along with extended storage of chip-processing potatoes are some of the major issues facing the potato industry.  MSG274-3 (Jacqueline Lee) is currently being released and is the first variety in the US and Canada that is resistant to the US8 genotype of late blight.  Combined with this resistance are the important market traits of cooking quality, attractive appearance and marketable maturity.  MSA091-1 (Liberator) is the second scab resistant chip-processing variety to be released in the US and Canada.  The Bt-transgenic lines that control the Colorado potato beetle are poised for release when public acceptance is more widely acknowledged.  Dr. Douches developed a new potato line that is the first to combine resistance to both the US8 genotype of P. infestans and to Colorado potato beetle (two of the most economically damaging pests of potato in North America and significantly reduce pesticide use).  Dr. Douches along with the MSU potato research team of Drs. Kirk and Hammerschmidt, Grafius and Pett developed this line (MSG274-38.02) through an integration of conventional and biotechnological approaches. [top]

Cooperative Research in the North Central Region

     The North Central Regional Trials provide the initial framework in which to enhance the cooperative research efforts.  Currently the trials center on the agronomic testing and post-harvest chip processing via cooperative efforts from the Red River Valley Potato Lab.  In 2001, the trials will be enhanced through additional testing/characterization of the lines for late blight, scab, early blight, Verticillium wilt, Fusarium dry rot, and black spot bruise resistance.  In addition, the lines will be characterized for their symptom expression to ring rot and viruses.  This additional testing draws upon from the current expertise of the different research programs at Michigan, Wisconsin, Minnesota and North Dakota.  Along with the continued testing of advanced selections, these additional testing/characterization trials will be available to test early generation selections from these four programs. 

     Germplasm exchange between the four programs has been on going.  Advanced selections for use as parents can be seen in the pedigrees of released varieties.  Currently, over 250,000 seedling tubers are evaluated each year in the field in the combined North Central region breeding programs.  A portion of this germplasm is exchanged at the seedling tuber or cross/population stage between the North Central and other state or USDA breeding programs in the US.

      The other area to formalize our cooperative research effort is with the breeding of cold-chipping cultivars for the chip-processing market. We will draw upon the Red River Valley Potato Lab to characterize additional early generation selections from the breeding programs for chip-processing out of 42F and 50F storage at 3 and 7-month periods.  The centralized evaluations will provide standardization for chip-processing evaluation.  We will utilize the Michigan demonstration commercial storage bins for the characterization of advanced lines nearly ready for commercialization.  Breeding and selection will continue at each location since environmental differences (soil type, rainfall and temperature) preclude a central breeding location, however, we will continue to exchange parents and crosses from each program.  Dr. Joe Sowokinos (U. of Minn.) will be involved in molecular characterization of the UGPase types in the advanced germplasm.

North Central Regional Cooperators:
Dr. Christian Thill    University of Minnesota
Dr. Susie Thompson    North Dakota State University
Dr. Jiwan Palta    University of Wisconsin, Madison

Other Out-of-State Cooperators
Dr. Zanaida Ganga    University of Maine
Dr. Rich Novy        USDA/ARS Aberdeen, ID
Dr. Craig Yencho    North Carolina State University
Dr. Bill Lamont    Pennsylvania State University
Dr. Ron Voss         University of California, Davis
Dr. Alex Pavlista    University of Nebraska
Dr. Chad Hutchinson    University of Florida
Dr. Walter DeJong    Cornell University
Dr. Matt Kleinhenz    Ohio State University
Dr. Barb Christ    Penn State University
Dr. Dermot Lynch    Ag Canada, Lethridge
Ms. Vanessa Currie    Univ. of Guelph
Dr. Joe Sowokinos    University of Minnesota
Dr. Shelley Jansky    USDA/ARS, Madison, WI
[top]

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© 2007 Michigan State University Board of Trustees, and Potato Breeding and Genetics Laboratory