Virulence patterns of Colletotrichum truncatum isolates causing soybean anthracnose disease and identification of resistance sources

Anthracnose disease caused by Colletotrichum truncatum is a major disease in soybean in India. In the current study, a total of sixty isolates of C. truncatum were tested for their virulence against three soybean genotypes viz., EC 18,596, JS 20-34, and JS 95 - 60. Among them, based on AUDPC (Area Under Disease Progress Curve), CT-18 (OP133629) was found to be the most virulent isolate, followed by CT-12 (OR405122), CT-48 (OR975577) and CT-2 (OR975570). Through pooled ANOVA (Analysis of variance), it was found that there were significant Isolate (I) × Genotype (G) interactions (p < 0.001). Further, a total of ninety-five soybean genotypes were screened against CT-18 (OP133629), where no genotype was found highly resistant. However, seven genotypes viz., NRC 130 (DS = 1.80), NB 208 (DS = 1.85), AGS 136 A (DS = 2.00), NRC 202 (DS = 2.00), NRC 152 (DS = 2.00), EC 34,106 (DS = 2.00) and CAT 1504 (DS = 2.00) were found to be resistant. A sub-set of seventy-one agronomically superior genotypes and a high-yielding variety JS 20-98 were used in molecular diversity analysis. Out of them, one soybean genotype EC 572,136 was ungrouped, while the remaining 71 genotypes were grouped into six major clusters. Cluster I contained only three genotypes - EC 572,109, JS 20-20, and JS 20-38. Cluster II includes EC 34,372, EC 39,150, and EC 34,106. Cluster III consists - JS 90 - 41, TGX 854 - 429, JS 20-98. Cluster IV consists of only two genotypes - FASSY COOK and AGS 163 A. Cluster V includes 6 genotypes EC 915,933, NRC 130, PP 6, NB 208, MAUS 795 and CAT 1504. Cluster VI was subdivided into VIa and VIb. Cluster VIIa consists of JS 95 - 60, YP 34, M 43, M 41 and M 21. The remaining 49 genotypes were included in cluster VIIb. Diverse resistant genotypes will further be utilized in breeding for anthracnose resistant varieties.