Identification of resistant genotypes considering polygenic systems in host-pathogen interaction

Plant resistance to pathogens is the most efficient form of disease control . However, identification of resistant genotypes is often difficult, especi ally when the genetic basis for the host-pathogen relationship is unknown. This study was carried out to test a methodology capable of providing, in a simple way, information about host vertical and horizontal resistance as w ell as pathogen virulence. A simulation using twenty, ten, and five pathoge n races and twenty hosts was carried out. Host reaction was controlled by t en genes with two alleles each. Eight genes had little effects, one had med ium and the other strong effects. Genetic control of pathogenicity was iden tical to that of the host. Only homozygous genotypes were used for pathogen s and hosts in this simulation, with no epistatic effects. Simulation was b ased on the expected disease severity with the inoculation of twenty hosts with twenty pathogen races, according to additive and interactive models pr oposed by Parlevliet and Zadoks (Euphytica 26. 5-21, 1977). Data were analy zed by model IV of Griffing, using a partial diallel scheme. A high correla tion was found between general reaction ability (GRA) and potential host re sistance, which proved to be an indicator of horizontal resistance. A high correlation between general aggressivity ability (GAA) and potential pathog enicity of the race also proved to be an aggressivity indicator. Specific i nteraction ability (SIA) is an indicator of host Vertical resistance and pa thogen virulence. Simulation with a lower number of races (ten and five) sh owed similar results. SIA was significant in both the interactive and addit ive models.