ABSTRACT: Factors influencing Fusarium head blight (FHB) occurrence and yield losses in winter wheat have extensively been studied through the years; however, reports on the relationship between FHB traits and yield are conflicting. In addition, studies neglected the relationship between FHB traits and thousand-kernel weight (TKW). This study evaluated the variability in the relationship between FHB traits, TKW, and yield under field conditions, using 40 commercial winter wheat cultivars differing in resistance/susceptibility to FHB. In general, the FHB index had greater relation to yield, while Fusarium-damaged kernels (FDK) was more related to TKW. The relationship between yield, TKW, FHB index, and FDK was also determined by resistance/susceptibility of winter wheat cultivars. Fusarium-damaged kernels influenced yield more in moderately resistant (R2 = 43 %) than in susceptible/moderately susceptible cultivars (R2 = 27 %). The influence of the FHB index on TKW was weak (R2 = 9 %) in susceptible/moderately susceptible cultivars and in moderately resistant ones (R2 = 1 %). The potential to predict TKW from yield under pathogen pressure was limited due to the moderate-to-positive correlation between yield and TKW (r = 0.349, p < 0.001). This study provides insights into factors that influence TKW under FHB pathogen pressure and gives direction to more efficient and reliable investigations on grain resistance toward FHB.

O objetivo deste trabalho foi avaliar a variação genética do inibidor de tripsina em variedades cultivadas (Glycine max) e silvestres (Glycine soja) de soja. Foram avaliadas as variações genéticas do inibidor de tripsina Kunitz, representado pela proteína 21-kDa (KTI), e do inibidor de tripsina-quimotripsina Bowman-Birk (BBI), em variedades de soja cultivadas (G. max) e selvagens (G. soja). Ensaios de clivagem foram feitos com endonuclease de incompatibilidade heteroduplex, para a detectar mutações no gene de KTI, com uma única nuclease específica de cadeia simples, obtida a partir de extractos de aipo (CEL I). As variedades de soja estudadas apresentaram baixo nível de variação genética em KTI e BBI. A análise por PCR -RFLP dividiu o BBI-A em A1 e A2 e mostrou que o Tib do KTI é o tipo dominante. A digestão com enzimas de restrição não foi capaz de detectar diferenças entre os tipos de ti-null e outros alelos Ti, enquanto o ensaio com endonucleases com incompatibilidade heteroduplex com CEL I pôde detectar o tipo ti-null. O método de digestão com CEL I fornece uma ferramenta genética simples e útil para a análise de SNP. O método apresentado pode ser utilizado como ferramenta para a triagem rápida e útil de genótipos desejáveis em futuros programas de melhoramento de soja.

The objective of this work was to evaluate the genetic variation of trypsin inhibitor in cultivated (Glycine maxL.) and wild (Glycine sojaSiebold & Zucc.) soybean varieties. Genetic variations of the Kunitz trypsin inhibitor, represented by a 21-kD protein (KTI), and of the Bowman-Birk trypsin-chymotrypsin inhibitor (BBI) were evaluated in cultivated (G. max) and wild (G. soja) soybean varieties. Endonuclease heteroduplex mismatch cleavage assays were performed to detect mutations in the KTI gene, with a single-stranded specific nuclease obtained from celery extracts (CEL I). The investigated soybean varieties showed low level of genetic variation in KTI and BBI. PCR-RFLP analysis divided the BBI-A type into subtypes A1 and A2, and showed that Tib type of KTI is the dominant type. Digestion with restriction enzymes was not able to detect differences between ti-null and other types of Ti alleles, while the endonuclease heteroduplex mismatch cleavage assay with CEL I could detect ti-null type. The digestion method with CEL I provides a simple and useful genetic tool for SNP analysis. The presented method can be used as a tool for fast and useful screening of desired genotypes in future breeding programs of soybean.