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Resistance

Field Evaluation of Quantitative Resistance to Anthracnose in Stylosanthes scabra. S. Chakraborty, CSIRO Division of Tropical Crops and Pastures, 306 Carmody Road, St. Lucia, Queensland 4067, Australia; A. N. Pettitt(2), R. M. Boland(3), and D. F. Cameron(4). (2)Biometrics Unit, Institute of Plant Production and Processing, CSIRO, St. Lucia, Queensland, Australia; (3)(4)CSIRO Division of Tropical Crops and Pastures, 306 Carmody Road, St. Lucia, Queensland 4067. Phytopathology 80:1147-1154. Accepted for publication 16 April 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1147.

A field study was conducted for two successive growing seasons at the Southedge Research Station, Queensland, Australia, to evaluate and characterize the expression of a quantitative resistance in seven accessions of the tropical pasture legume Stylosanthes scabra to anthracnose caused by Colletotrichum gloeosporioides. These accessions had shown moderate to high levels of resistance to four isolates of the pathogen in earlier glasshouse studies. Five of the seven accessions showed moderate to high levels of resistance in the field. Resistance was generally consistent in the two seasons, despite a high level of initial inoculum in 1989. A ?broken stick? model, fitted using a weighted linear regression, best summarized the disease progress in most accessions. Parameter estimates of the logistic model were not precise enough to be useful in comparing accessions. Two separate rates were used as alternatives to the apparent infection rate. Rate of early anthracnose progress was lower in most accessions than in Fitzroy. Of the eight attributes used, area under the disease progress curve (AUDPC) provided the best measure of resistance in both seasons. A significant rank correlation between AUDPC, spore production in the field, and daily rate of sporulation showed that, in association with other attributes, spore production in the field can be used in evaluating quantitative resistance. Performance of accessions was effectively and simply depicted by combining rankings based on the various attributes in a star plot.