Prevention of leaf yellowing in Asian soybean rust infected plants is associated with green cotyledon color and the infection index

Abstract

Because the six major known resistance genes to Asian soybean rust (ASR) are pathotype-specific, they rarely offer durable resistance to all ASR pathogens. Thus, other types of resistance such as field resistance or tolerance that confer broad-spectrum resistance to ASR pathogens are required for soybean breeding. The Chinese soybean variety Lu Pi Dou has a green cotyledon color (CC) and a no leaf yellowing (LY) phenotype was previously identified during ASR infection of this strain. This phenotype may reduce yield losses of soybean cultivars infected with ASR infections if it is independent of pathotype-specific major resistance genes and undesirable phenotypes. Thus, to identify associations of LY and CC and other color traits and loci that are linked to the six known ASR resistance genes, recombinant inbred lines (RILs) and backcross (BC) BC2F5 lines were derived from Lu Pi Dou and BRS184 plant strains. Comparisons of LY, CC, and genotypes of simple sequence repeat (SSR) markers revealed that the absence of LY is tightly associated with green CC in accordance with the expression of the genes d1 and d2. However, although variations of LY in RILs with yellow CC predominantly reflected the infection index (IFI), no associations were observed between LY and pubescence color, pod color, seed coat color, or flanking SSR markers for six known ASR resistance loci. An association of LY with CC and IFI was also shown in data from BC populations. Therefore, prevention of LY during ASR infection of Lu Pi Dou was primarily dependent on the double-recessive genotype d1d1d2d2 for CC and secondarily on low IFI.