Genetics of Karnal bunt resistance in wheat: Role of genetically homogenous Tilletia indica inoculum

Abstract

Use of heterogeneous inoculum for Karnal bunt screening in wheat is often considered to decrease precision of genetic analysis of resistance. In the present study, genetic analysis of KB resistance was carried out based on two inoculum systems. First system was based on mixture of 16 isolates of Tilletia indica representing high level of genetic heterogeneity and second consisted of a single compatible monosporidial pair, a specially generated homogeneous inoculum with no within population heterogeneity. Initial attempts at using compatible monosporidial pair by mixing them just before inoculations resulted in markedly poor disease development, thwarting the genetic analysis. Co-culturing of compatible monosporidial pair for 20 days was found to be essential for obtaining adequate level of infection. The two inoculum systems were used on 2 RIL (Recombinant Inbred Line) populations derived from crosses of two established KB resistance donors, HD 29 and W 485 with WH 542, a KB susceptible cultivar. Screening with mixture of isolates indicated two additive genes providing KB resistance in both HD 29 and W 485 whereas three additive genes were found operative against compatible monosporidial pair in both the populations. The additional gene identified with compatible monosporidial pair, is proposed to be overcome by some of the more virulent constituents of mixture of isolates. Mixture of most virulent isolates is, therefore, more useful to identify the KB resistance genes effective against the entire pathogen population in a region.