Different methods of assessing susceptibility of soybean genotypes to white mold

Abstract

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.

Reaction of brazilian cotton genotypes to white mold depends on pathogen aggressiveness and incubation conditions

“…This hypothesis is supported by the lack of correlation between the results of the straw test with those of the oxalic acid assay. Possibly, solutions that are more concentrated would be required, in contrast to what was recommended for common beans and soybeans (KOLKMAN;KELLY, 2000;ANTÔNIO et al, 2008;HÜLLER et al, 2016;SOUZA et al, 2016). The inconsistency of the oxalic acid method discourages the indirect evaluation of cotton resistance to white mold, be it by need to optimize the technique or by the combination with other physiological mechanisms of resistance in cotton, such as biosynthesis of phytoalexins, shikimic acid, phenolic compounds or oxalate detoxification (BALDINI et al, 2002;CUNHA et al, 2010;DAVIDSON et al, 2016).…”

“…Sclerotinia sclerotiorum lesion extension in the stem was determined with a ruler, seven days post-inoculation (DPI) (PETZOLDT; DICKSON, 1996;TERÁN, 2008). The proportion of lesion extension in relation to total stem length (HÜLLER et al, 2016) calculated disease severity.…”

“…Alternatively, genotypes can be characterized according to their sensitivity to a solution of oxalic acid. This indirect method is faster, cheaper and less labor intensive, and has been successfully used in common beans, soybeans and sunflower (WEGULO;MARTINSON, 1998;KOLKMAN;KELLY, 2000;ANTÔNIO et al, 2008;HÜLLER et al, 2016). The potential of its use in cotton still has to be elucidated.…”

Reação de genótipos de algodoeiro à Sclerotinia sclerotiorum.

“…A severidade da doença foi obtida pela proporção do comprimento da lesão em comparação com o comprimento total do caule, ambas as medições foram efetuadas com auxílio de uma régua (HÜLLER et al, 2016).…”

“…A patogenicidade do fungo está associada com a produção de ácido oxálico, já que esta substância reduz o pH nos tecidos do hospedeiro, diminuindo a defesa da planta e aumentando a atividade das enzimas responsáveis pela degradação da parede celular (LUMSDEN, 1979). Diversos estudos foram conduzidos a fim de correlacionar métodos de avaliação para as culturas de soja e feijão (ANTÔNIO et al, 2008;HÜLLER et al, 2016). Contudo, são escassos os trabalhos relacionados com o algodoeiro.…”