Quantitatively expressed resistance to anthracnose (Colletotrichum gloeosporioides) in Stylosanthes scabra

Nineteen accessions of Stylosanthes scabra that had low terminal severities of anthracnose in the field were evaluated for their response in the glasshouse using four isolates representing three different races of Colletotrichum gloeosporioides. Accessions could be allocated to one of three groups: one showed a higher disease severity after inoculation with isolate UQ14 compared to the other isolates; the second showed a higher severity after inoculation with isolates WRS32 and/or WRS20 compared to isolates SR4 and UQ14, and the third group showed moderate to low disease severities following inoculation with all four isolates. Based on reduced disease severity and compatible infection types, a set of six accessions was selected from the three groups for further testing, two of which showed no significant difference in their response to the four isolates. Two components of resistance, incubation period and infection efficiency were studied in the selected accessions. Of these, incubation period appeared unrelated to the expression of resistance. Criteria for identifying this form of quantitatively expressed resistance are discussed.