A Rapid Bioassay for the Assessment of Pathogenic Variation in Colletotrichum gloeosporioides infecting Stylosanthes scabra. Sukumar Chakraborty, Division of Tropical Crops and Pastures and Institute of Plant Production and Processing Biometrics Unit, CSIRO, 306 Carmody Road, St Lucia, Queensland 4067, Australia. Peter N. Jones, Division of Tropical Crops and Pastures and Institute of Plant Production and Processing Biometrics Unit, CSIRO, 306 Carmody Road, St Lucia, Queensland 4067, Australia. Plant Dis. 77:1016-1020. Accepted for publication 31 May 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-1016.

Pathogenic variation in Colletotrichum gloeosporioides, causing anthracnose disease of the tropical pasture legume Stylosanthes scabra, was studied using 3-day-old germlings and 6-wk-old seedlings of six host differentials. Disease expression of the host differentials in germling stage was optimized by standardizing pre- and postinoculation temperatures. To test the effectiveness of the germling assay, 10 field isolates were assayed with both germling and seedling assays. There was a significant correlation (r = 0.77) between the two assays. Despite significant variation among runs in both assays, the germling assay correctly assigned 11 of the 12 isolates to the same races as did the traditional seedling assay. Compared to the seedling assay, the germling assay is rapid, uses less inoculum and space, and can be carried out under controlled environmental conditions.