Abstract
White mold caused by the fungus Sclerotinia sclerotiorum is an important disease in relation to soybean. The use of less susceptible genotypes can be a productive strategy in the management of this disease, and the development of an appropriate methodology for soybean inoculation is useful for the differentiation of disease-resistant genotypes. The present study aimed to assess the susceptibility of 77 soybean genotypes based on their reaction to oxalic acid, as well as to determine correlations between three traditional disease assay methods (detached leaf, non-wounded stem and straw tests) and the results of the oxalic acid assay. Oxalic acid susceptibility was assessed by using a wilting score scale. For the other methods, the severity of disease symptoms was assessed. To compare methodologies, the values obtained for the genotypes using each method were categorized into classes, and a severity index was used to represent individuals within each class. All the methods used were efficient for the differentiation of soybean genotypes in terms of susceptibility to S. sclerotiorum ; however, the behavior of the genotypes depended on the inoculation method adopted. Even though no significant relationship was identified between the severities of the damage resulting from the methodologies, the rankings acquired from the methods strongly agreed. The oxalic acid method was the most rapid, the least laborious, and was the cheapest compared with the other methods that were used.
Highlights
Sclerotinia sclerotiorum (Lib.) de Bary is one of the most devastating and widespread fungal pathogens
It would be most ideal to analyze the susceptibility of genotypes under natural conditions, but S. sclerotiorum has an erratic distribution in the field and depends on specific weather conditions (ALEXOPOULOS et al, 1996)
Some susceptibility screening assays are based on the responses of different genotypes to oxalic acid (GONÇALVES;SANTOS, 2010), the authors are not aware of any publications assessing the levels of resistance of soybean to S. sclerotiorum based on the wilting responses of OA, as has been efficiently used for common bean (KOLKMAN; KELLLY, 2000; ANTONIO et al, 2008)
Summary
Sclerotinia sclerotiorum (Lib.) de Bary is one of the most devastating and widespread fungal pathogens. Some susceptibility screening assays are based on the responses of different genotypes to oxalic acid (GONÇALVES;SANTOS, 2010), the authors are not aware of any publications assessing the levels of resistance of soybean to S. sclerotiorum based on the wilting responses of OA, as has been efficiently used for common bean (KOLKMAN; KELLLY, 2000; ANTONIO et al, 2008). The present study aimed to: 1) establish and test a methodology to assess the level of susceptibility of soybean genotypes to white mold based on the response to OA, 2) compare the results of OA sensitivity to three traditional disease screening methods that use agar plugs with actively growing mycelia as inoculum, 3) analyze the correlations between the methodologies to determine the susceptibility of the genotypes to S. sclerotiorum based on ranking
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