Soybean Resistance to White Mold: Evaluation of Soybean Germplasm Under Different Conditions and Validation of QTL

Abstract

Soybean (Glycine max L. Merr.) white mold (SWM), caused by Sclerotinia sclerotiorum (Lib) de Barry), is a devastating fungal disease in the Upper Midwest of the United States and southern Canada. Various methods exist to evaluate for SWM resistance and many quantitative trait loci (QTL) with minor effect governing SWM resistance have been identified in prior studies. This study aimed to predict field resistance to SWM using low-cost and efficient greenhouse inoculation methods and to confirm the QTL reported in previous studies. Three related but independent studies were conducted in the field, greenhouse, and laboratory to evaluate for SWM resistance. The first study evaluated 66 soybean plant introductions (PIs) with known field resistance to SWM using the greenhouse drop-mycelium inoculation method. These 66 PIs were significantly (P < 0.043) different for resistance to SWM. However, year was highly significant (P < 0.00001), while PI x year interaction was not significant (P < 0.623). The second study compared plant mortality (PM) of 35 soybean breeding lines or varieties in greenhouse inoculation methods with disease severity index (DSI) in field evaluations. Moderate correlation (r) between PM under drop-mycelium method and DSI in field trials (r = 0.65, p < 0.0001) was obtained. The PM under spray-mycelium was also correlated significantly with DSI from field trials (r = 0.51, p < 0.0018). Likewise, significant correlation (r = 0.62, p < 0.0001) was obtained between PM across greenhouse inoculation methods and DSI across field trials. These findings suggest that greenhouse inoculation methods could predict the field resistance to SWM. The third study attempted to validate 33 QTL reported in prior studies using seven populations that comprised a total of 392 F4 : 6 lines derived from crosses involving a partially resistant cultivar “Skylla,” five partially resistant PIs, and a known susceptible cultivar “E00290.” The estimates of broad-sense heritability (h2) ranged from 0.39 to 0.66 in the populations. Of the seven populations, four had h2 estimates that were significantly different from zero (p < 0.05). Single marker analysis across populations and inoculation methods identified 11 significant SSRs (p < 0.05) corresponding to 10 QTL identified by prior studies. Thus, these five new PIs could be used as new sources of resistant alleles to develop SWM resistant commercial cultivars.

The medium‐term impacts of integrated crop–livestock systems on crop yield and economic performance

“…The reason for lower soybean yield in 2018 and 2019 is not clear but could be related to white mold (Sclerotinia sclerotiorum) infestation in 2018 and herbicide failure in 2019. White mold has been shown to be a bigger problem in wet years, typical of 2018 (Kandel et al, 2018;Westphal et al, 2015). The cultivar used in 2018 was earlier maturing (MG 1.9) as compared to the cultivars in other years.…”

Identification of new sources of resistance in Rajmash (Phaseolus vulgaris L.) against powdery mildew (Erysiphe polygoni) and stem rot (Sclerotinia sclerotiorum) diseases

“…Powdery mildew disease scoring was done as described by Gawande and Patil, (2003) using 0-5 rating scale: 0= Highly resistance (no infection); 1= resistance (0.1-10.0% leaf area infection); 2= moderately resistance (10.1-25.0% leaf area infection); 3= moderately susceptible (25.1-50% leaf area infection); 4= susceptible (50.1-75% leaf area infection); and 5=highly susceptible (75.7-100% leaf area infection). Likewise, stem rot disease scoring was done as suggested by Kandel et al, (2018) and accordingly genotypes were rated on 0-4 scale: 0 = no symptoms (Highly resistant); 1 = less than half stem girdled (Resistant); 2 = more than half stem girdled (Moderate resistant); 3 = whole stem girdled (Susceptible); 4 = plant dead (Highly Susceptible).…”

Genome-wide association mapping of Sclerotinia sclerotiorum resistance in soybean using whole-genome resequencing data

“…Partial resistance is controlled by multiple genes or quantitative trait loci (QTL). Numerous mapping studies have been conducted and have identified more than 114 QTL via conventional biparental mapping [1,11,13,16,17,29,34]. Although this method has been widely used for QTL mapping, it is still limited to the genetic diversity present in the two parents.…”