Epidemiological studies on the anthracnose diseases of Stylosanthes spp. caused by Colletotrichum gloeosporioides in North Queensland and pathogenic specialization within the natural fungal populations

Abstract

Field experiments were conducted during three wet seasons (1982-84) on two sites in north Queensland to examine the natural occurrence of anthracnose caused by Collectotrichum gloeosporioides on six Stylosanthes spp. The disease incidence varied from moderate to high in a number of accessions, while others showed good field resistance for the duration of the experiment. Anthracnose severity was similar at both sites, although total rainfall each season was c. four times higher at one site than at the other. In some cases disease severity was higher at the drier site. It was difficult to determine a relationship between the environmental parameters measured (rainfall, temperature and relative humidity) and disease incidence and severity. Disease severity patterns varied between accessions at the same site, indicating a response to a factor or factors not associated with the measured weather parameters. There were seven pathogenicity groups, based on host specificities in glasshouse studies, identified within the Type A fungal population and a further seven groups within the Type B population. This indicates an increase in the number of fungal groups reported in Australia, and suggests that a stepwise increase in specificity may be occurring within the fungal population.