QTL Conditioning Physiological Resistance and Avoidance to White Mold in Dry Bean

white mold with upright architecture has progressed relatively slowly. Cumbersome screening methods, low Physiological resistance is an important component of integrated heritability, and few available resistance sources have strategies used to control white mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary], a major disease of common bean (Phaseolus contributed to the lack of progress for enhancing physiovulgaris L.) in North America. Information pertaining to inheritance logical resistance. This situation may soon be alleviated, of physiological resistance, as detected by the greenhouse straw test, however, as the recently developed Bean White Mold and its relationship with field resistance is lacking. The objectives of Nursery (Steadman, 1995, 1997; Steadman et al., 1999) this study were to compare physiological resistance as detected by and novel, less cumbersome screening methods (Pettwo separate straw tests with field resistance, evaluate heritability of zoldt and Dickson, 1996; Steadman, 1997; Kolkman and physiological resistance, and to characterize the disease reaction of Kelly, 2000) are helping to identify, characterize, and G 122 by quantitative trait locus (QTL) analysis. This was done in a select for physiological resistance to white mold in comrecombinant inbred population (A 55/G 122) consisting of 67 F8mon bean (Miklas et al., 1998, 1999). The straw test derived lines. The greenhouse tests with five and six replications, (Petzoldt and Dickson, 1996) is a simple procedure for respectively, and the field test with three replications were conducted in randomized complete block designs. Moderate heritability for disevaluating physiological resistance primarily within ease reaction (scored from 1 5 no symptoms to 9 5 severe disease) stem tissue. However, little is known about the inheriwas observed across the straw tests (0.65) and in the field (0.78). tance of this trait. Inheritance of disease reaction was further investigated with a frameThe landrace cultivar G 122, has exhibited field resiswork linkage map composed of 74 markers. Interval mapping detected tance to white mold in the Bean White Mold Nursery a QTL on linkage group B7 near the phaseolin seed protein (Phs ) (Steadman, 1997; Steadman et al., 1999) and elsewhere locus that explained 38% of the phenotypic variation for disease score (Kmiecik and Nienhuis, 1998; Park et al., 1999a). The across the straw tests. The same B7 QTL (26%), and an additional field resistance of G 122 likely results from physiological QTL (18%) on B1 near the fin gene for determinate growth habit, resistance. The breeding line A 55 expresses avoidance conditioned field resistance. A QTL (34%) for canopy porosity, a due to its upright architecture and narrow growth habit. measure of potential disease avoidance, also mapped to the fin locus. Results confirmed that physiological resistance as detected by the Our objectives were to gain a better understanding of straw test was an integral component of field resistance, and that resistance to white mold in G 122 using QTL analysis, both physiological and avoidance mechanisms contributed to field evaluate heritability of physiological resistance as deresistance in the A 55/G 122 population. The landrace G 122 clearly tected by the straw test, and compare physiological resisprovides breeders with a heritable source of physiological resistance tance as detected by the straw test with field reaction. to combat white mold disease. MATERIALS AND METHODS Plant Materials W mold is one of the most important fungal diseases of common bean worldwide. Combining G 122 is an upright determinate bush (Type I, Singh 1982) physiological resistance with avoidance mechanisms bean of Andean origin with elongated, cranberry bean-type seeds. In addition to white mold resistance, G 122, collected (upright plant architecture, open canopy) is the current from India as PI 163120, and also known as ‘Jatu Rong’, breeding strategy for minimizing yield losses due to exhibits heat tolerance (Shonnard and Gepts, 1994). A 55 is white mold in common bean. Upright architecture proan indeterminate, upright short vine (Type IIa), advanced motes air and sunlight penetration into the plant canopy black bean breeding line of Middle American origin developed creating a drier microclimate less conducive to white at CIAT (Center for Tropical Agriculture, Cali, Columbia) mold epidemics (Blad et al., 1978; Coyne et al., 1974, that exhibits field avoidance to white mold under moderate 1977; Fuller et al., 1984a; Park, 1993a; Schwartz et al., disease pressure; however, under heavy disease pressure A 1978, 1987). Avoidance, in the absence of physiological 55 is known to be susceptible to white mold in the field (Park, resistance, can be overcome in the presence of severe 1993b; Steadman, 1995). A population of 67 F8-derived recomdisease. binant-inbred lines (RILs) from a cross between A 55 and G 122 were generated using the single seed descent method. Germplasm lines and cultivars with upright architecThe white mold resistant black bean line I9365-31 (Miklas et ture have become commonplace (Hosfield et al., 1995; al., 1998) and susceptible ‘Othello’ pinto bean were included Kelly et al., 1992a, 1992b), whereas development of as checks in the greenhouse test. cultivars which combine physiological resistance to Genetic Linkage Map P.N. Miklas and R. Delorme, USDA-ARS, 24106 N. Bunn Rd., Prosser, WA 99350; W.C. Johnson, USDA-ARS, Cornell University, GeA linkage map for the A 55/G 122 RIL population was neva, NY 14456; and P. Gepts, Dep. of Agronomy and Range Science, previously developed by Johnson (1997, http://agronomy.uc University of California, 1 Shields Avenue, Davis, CA 95616-8515. davis.edu/gepts/mapdata2.htm#framework; verified October Received 12 Jan. 2000. *Corresponding author ([email protected]. edu). Abbreviations: cM, centimorgan; MAS, marker-assisted selection; QTL, quantitative trait locus or loci; RIL, recombinant inbred line. Published in Crop Sci. 41:309–315 (2001).