Location: Sunflower and Plant Biology Research2012 Annual Report
1a. Objectives (from AD-416):
The long term goals of this project are to develop pinto beans with enhanced levels of resistance to white mold.
1b. Approach (from AD-416):
The project is to phenotype a pinto bean RIL population for reaction to white mold over a multi-year period in field trials and greenhouse. The RIL population will be grown and evaluated in a 4-replicate white mold field nursery. The nursery, located at the Montcalm Research Farm in Entrican, Michigan, is naturally infested with high levels of Sclerotinia sclerotiorum, and is irrigated during and after flowering to further encourage disease development. The RILs will be planted in two row plots and will be flanked by two rows of a highly susceptible variety that serves as a spreader of the disease to further promote uniform white mold development. Resistance to white mold will be evaluated, along with yield under disease pressure, architecture, and agronomic desirability. Additionally, the RILs will be evaluated in the greenhouse for genetic resistance to white mold using the straw and oxalate tests. The QTL study will be to genotype the individual lines in the mapping populations and develop a molecular linkage map. The individual RILs of each population will be genotyped using available SSR, TRAP and SRAP markers. Upon completion of this genotyping step, mapping software will be employed to develop a linkage map for each population. Once a linkage map is obtained, QTL analysis software will be used to determine the location of QTL for white mold resistance in the mapping population, and the parent from which each QTL originated. In order to validate the potential of resistance QTL identified in this study a MAS study based on the same resistance QTL will be conducted under severe white mold pressure in a second pinto population during the final growing season. We will investigate the role of specific defense genes in conferring resistance to white mold in pinto bean and explore synteny of Phaseolus QTL with other legumes.
3. Progress Report:
This project was initiated on July 1, 2010, research is ongoing, and the overall objective is to identify resistance genes important in plant defense responses of dry beans to Sclerotinia. QTLs controlling disease incidence in the field and greenhouse and yield were identified in a 94-entry pinto bean RIL population (AP630) generated from cross between AN-37 and P02630 pinto bean breeding lines. Heritability estimates were low for traits like lodging (0.23), days to maturity (0.21), plant canopy height (0.25) and field disease incidence (0.23), whereas traits like yield, seed weight and the straw test had moderately high heritability estimates of 0.53, 0.74 and 0.46 respectively. A linkage map was developed using 107 SSR markers, covering 399 cM across six bean chromosomes. Interval mapping analysis detected four QTLs. A QTL for resistance to white mold in the field in 2007 and 2009 was identified near markers BM157 and IAC90 respectively on bean chromosome Pv01. In 2010 the marker IAC 90 was significantly associated with field resistance in single marker analysis. In 2008 QTL for resistance were detected on Pv03 and Pv07. Yield QTL were detected on Pv02 and Pv05 accounting for up to 39% of observed variation in yield. These QTL were contributed by alleles from the adapted parent P02630, whereas the QTL for the straw test on Pv02, Pv03 and Pv08 came from the resistant parent AN-37. The QTL on Pv02 was consistent in three separate evaluations while the QTL on Pv03 overlapped with that for field disease resistance in 2008 which could imply that the disease score in 2008 were not severely confounded by environmental conditions. Microsatellite marker screening revealed that 43 polymorphic markers associated with resistance from the first population (AP630) were also segregating in AN-37/P02647 half-sib population (AP647). These 34 SSR’s represented 31% polymorphism rate. Single marker analysis with significant markers in the population showed that the AN-37 allele of BMd-34 which was previously unlinked but now mapped near markers on Pv02 increased field resistance by 15%. The QTL on Pv02 is likely the same QTL as was previously mapped by other authors. The favorable alleles of marker BMd-1 in the QTL interval on Pv03 were from the AN-37 parent and contributed to an average of 10% increase in resistance in the greenhouse straw test in three separate tests. The QTL on Pv03 could be the same one that was mapped in the Aztec/ND population from which AN-37 parent was originally selected. In addition a new pinto bean line P07863 identified in the AP630 population was officially released by as the variety ‘Eldorado’ based on superior yield performance under white mold pressure. Eldorado (Reg. No. CV-302, PI 665012) pinto bean, which was developed by Michigan State University AgBioResearch, was released in 2012 as an upright, full-season, disease-resistant cultivar. Eldorado, tested as MSU breeding line P07863, was developed using the single-seed-descent breeding method to the F4 generation followed by pedigree selection for disease, agronomic, and quality traits. In 5 yr of field trials, Eldorado yielded 3364 kg ha-1, flowered in 42 d, and matured in 98 d. Plants averaged 53 cm in height, with a lodging-resistance score of 1.9 and a seed size of 43 g 100 seed-1. Eldorado combines exceptional yield potential and erect architecture with full-season maturity in the pinto seed type. Eldorado has resistance to lodging and high pod placement within the plant structure, making it suitable for direct harvest under narrow-row production systems. The upright architecture also contributes to avoidance of white mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary], a disease intensified by narrow-row production systems. In irrigated trials designed to promote the development of white mold disease, Eldorado had 30% incidence over 5 yr compared with other pinto cultivars that had from 42 to 72% white mold incidence. Eldorado possesses resistance to specific races of rust, virus, and anthracnose. Eldorado has a large, mottled, dry-bean seed that meets industry standards for packaging and canning quality in the pinto bean seed class. Over the past four years (2007-10) of testing under white mold pressure, this line exceeded the test mean by 21% and its performance and white mold resistance level is being confirmed in 2011 trials prior to release.