INHERITANCE OF ANTHRACNOSE RESISTANCE IN THE TROPICAL PASTURE LEGUME STYLOSANTHES HAMATA

Eight tetraploid accessions of the tropical pasture legume Stylosanthe s hamata with varying levels of response to the anthracnose pathogen ( Colletotrichum gloeosporioides) were crossed in a half diallel scheme. Based on mean disease severity ratings (MDR), two parents, 55830 and 75164, were grouped as resistant (R), 55828 and 65365 were susceptible (8), and the remaining four, cvv. Verano and Amiga and 65371 and 7516 2 were moderately resistant (MR). Of these, the two resistant parents appear to carry different genes for resistance. The MDR of 20 of the 2 8 F-2 populations was significantly different from their mid-parent MD R and the expression of resistance, in most cases, was recessive. Only a limited number of the Fz distributions for crosses between RxS, RxM R and MRxS parents conformed to a single gene model. The inheritance p atterns observed were considered to be predominantly quantitative. Var iation for general combining ability, was as large as or larger than t hat for specific combining ability suggesting that a large proportion of the genetic differences among the parents was additive. The finding that the resistance is inherited as a quantitative trait is consisten t with results on the epidemiology of anthracnose in tetraploid S. ham ata.