Identification of Resistance Sources against Bacterial Pustule Disease Caused by Xanthomonas axonopodis pv. glycines in Soybean using Excised Leaf Technique

Abstract

Bacterial pustule of soybean is a foliar disease caused by Xanthomonas axonopodis pv. glycines. The organism produces pustules which causes premature defoliation and ultimately results in significant reduction in seed yield and quality. Use of resistant cultivars can be a cost effective and eco-friendly approach to address the issue. This study was aimed at development of a rapid and reliable in-vitro screening method and screening of soybean genotypes for the identification of resistance sources to bacterial pustule disease. One hundred thirty-six soybean genotypes including released varieties, indigenous and exotic germplasm were screened by excised leaf technique for their reaction to bacterial pustule disease. An improved in-vitro technique for screening of bacterial pustule disease was developed.  Rooting and survival studies indicated that soybean leaves excised from 25 days old plants could survive up to 30 days at room temperature in plain water. Inoculation with bacterial suspension of 107 to 109 colony forming units (cfu/ml) at 27±1°C under the photoperiod of 12h/day light showed initiation of chlorotic lesions 48 hours after inoculation. Based on the latent period and appearance of the chlorotic lesions, the genotypes were classified as susceptible, moderately resistant and resistant. Four soybean genotypes (TS-3, P-4-2, Hara Soya and Himso 1685) were  resistant while, seventeen genotypes (AMS MB5-19, Bhatt, DSb-12, JS-335, JS93-05, MACS- 1188, MAUS- 71, PK-262, PS- 1241, Pusa-5, RKS- 18, SL-688, SL-744, SL-958, SL97-52, SL-979, and T99-76) were moderately resistant and rest of the genotypes were susceptible to bacterial pustule disease.