Genetic variation within a natural Stylosanthes guianensis, Colletotrichum gloeosporioides host-pathogen population

Abstract

Sixteen first-generation selfed (S1) progenies from Stylosanthes guianensis plants collected from a natural population were inoculated with each of 16 Colletotrichum gloeosporioides isolates in a replicated glasshouse experiment. Both host and pathogen collections were obtained from a single site in the Department of Valle, Colombia (76¦ 25'W.; 3¦55'N.; altitude 1720 m). Genetic differences among S1 progenies were detected based on differential disease reaction and on phenotypic differences in two morphological characters. No evidence of major resistance gene effects among or within S1 progenies was found. Both quantitative and qualitative differences among C. gloeosporioides isolates were detected: one isolate type was uniformly pathogenic across the S1 progenies, while a second type elicited large differences in resistance among the progenies. Cultural characteristics of the isolates also differed. Segregation within some S1 progenies for stipule hairiness and for disease reaction suggests that at least some natural outcrossing was occurring in the sampled S. guianensis population. The implications of the results with respect to the design of a disease control strategy for S. guianensis cultivars are discussed.