Glasshouse and field evaluation of quantitative resistance to Colletotrichum gloeosporioides in tetraploid accessions of Stylosanthes hamata

Abstract

A total of 20 field isolates of Collectotrichum gloeosporioides from Stylosanthes hamata was tested for pathogenicity and differential virulence in glasshouse inoculation experiments. No pathogenic specialization towards S. hamata was noted, but all three major races of the pathogen causing Type A disease were detected using the host differential set of one S. viscose and four S. scabra accessions. There was also little evidence of pathogenic specialization to S. hamata when 37 accessions were inoculated with three isolates representing the three main Type A races on S. scabra and a field isolate from S. hamata cv. Verano. The resistance of 38 accessions of S. hamata, including cvv. Verano and Amiga, was evaluated by inoculating field plots with a mixture of four isolates of C. gloeosporioides. Anthracnose progress was monitored by regular disease assessments and accessions were compared using the terminal disease severity, the rate parameter of logistic and linear models of disease progress and the area under the disease progress curve (ADPC). Accessions showed a continuous range from moderate to high resistance, with Verano and Amiga taking intermediate values. Spearman rank correlations among ADPC, terminal severity in the field, apparent infection rate and the severity in glasshouse tests were generally significant. Several resistant accessions were identified with potential for use in a breeding program to improve the anthracnose resistance of cvv. Verano and Amiga.