Expression of quantitative resistance to Colletotrichum gloeosporioides in Stylosanthes scabra at different inoculum concentrations and day-night temperatures

Abstract

Expression of quantitative resistance to anthracnose was studied following inoculation of accessions of the tropical pasture legume Stylosanthes scabra with five different concentrations of Colletotrichum gloeosporioides conidia and at five day-night temperatures in separate experiments. According to Kendall's coefficient of concordance for rankings of accessions at the various inoculum concentrations, resistance in all six accessions was expressed consistently at 102,103, 104, 105 and 106 conidia/ml for race 3 but not for race 4a. Anthracnose severity did not increase with an increase in the inoculum concentration from l05 to 106 conidia/ml for either of the two races. Height and number of leaves/plant in the uninoculated control increased significantly at 30-25¦C when glasshouse-grown seedlings were transferred to four controlled environment cabinets maintained at one of the four day-night temperatures of 30-25,32-22,30-15 or 34-14¦C. Accessions were subjected to one of the four day-night temperatures for a 3 week pre- and 2 week post-inoculation exposures was not significant, predisposition of some accessions to anthracnose resulted in a significant accession X exposure interaction.