Genetic analysis of resistance to Cercospora Arachidicola Hori in groundnut (ARACHIS HYPOGAEA L.) using simple sequence repeat markers MARKERS

Abstract

Groundnut (Arachis hypogaea L.) is an important global oilseed crop and a major source of protein and vitamins in many rural areas of Africa. In Zambia, the production of groundnut is limited by several factors, among which Early Leaf Spot (ELS) caused by Cercospora arachidicola Hori, is a major destructive disease. Development of resistant varieties to ELS remains the most viable disease management strategy. The objectives of this study were to investigate the type of gene action conditioning resistance and to map quantitative trait loci (QTL) associated with resistance to C. arachidicola as the first step towards the deployment of marker-assisted breeding for groundnut in Zambia. The laboratory work of the study was conducted at ICRISAT laboratories in Nairobi, Kenya while the field work was conducted at Chitedze Research Station in Malawi. The study was conducted between 2013 and 2014. Parental genotypes (Robut 33-1, susceptible and ICGV-SM 95714, resistant) were screened using 394 Simple Sequence Repeat (SSR) markers. All polymorphic markers (82) were used to screen 113 F8 recombinant inbred line (RIL) population alongside their parents. Phenotyping of the RIL population was carried out under field conditions supplemented by irrigation and utilizing diseased debris as primary inoculum. The nature of gene action was determined by using a Chi-square test, performed using the area under disease progress curves (AUDPCs) and the result suggested additive gene action. Inclusive composite interval mapping (ICIM) analysis identified two major and one minor QTL associated with resistance to ELS. Two QTLs were mapped on linkage group 2 with phenotypic variation explained (PVE) by the marker values of 37.91% (LOD 15.73) and 7.98% (LOD 3.5) and additive effects of 25.64 and -11.14 respectively. The third QTL was mapped on linkage group 9 with a PVE value of 12.31% (LOD 5.5) and additive effect of 12.92. The two major mapped QTLs were less than 5 cM from the nearest molecular marker. The study thus concluded that the gene action conditioning resistance to ELS was additive and the molecular markers associated with the two QTLs that were identified could possibly be used in marker-assisted breeding for groundnut. There is however, need to validate the detected QTLs in other locations and over seasons.