Validation of candidate genes associated with leaf spot resistance in cultivated peanut

Abstract

Peanut is an important oil crop that is grown in several parts of the world including the US, Asia and Africa. Early and Late leaf spot caused by Cercospora arachidicola and Cercosporidium personatum respectively are the most destructive peanut diseases. In the southeastern US, they cause up to 50% yield losses without any fungicidal spraying. Fungicides are not a sustainable method of controlling leaf spot diseases because they are expensive and cause environmental pollution. It is therefore important to breed for resistant peanut cultivars. Sources of resistance have been identified however the genes responsible have not. The aim of this research was to check for significant differences in the expression of seven candidate genes : chitinase I and II, Defensin, Nucleotide Binding Site (NBS), Phenylalanine ammonia lyase (PalI and Pal II) and thaumatin. Forty two peanut genotypes belonging to the three categories (susceptible, medium and resistant) were inoculated with leaf spot disease pathogens 80 days after planting. Disease evaluation was done and gene expression was quantified using real time q RT-PCR. All the genes were upregulated and there were significant differences in the expression of five of the genes studied except for chitinase II and thaumatin.