Studies on control of french bean rust (uromyces appendiculatus (pers.) unger var. Appendiculatus) using fungal and bacterial metabolites.

Abstract

Two isolates of Streptomyces spp. and one each of Bacillus subtilis, Trichoderma viride, Aspergilus niger were effective both in vitro and in the greenhouse in controlling rust of French beans. Their inhibitory effects on rust development appeared to be due to production of antibiotic metabolites that inhibited spore germination and formation of rust pustules. Compared with the control, significant decreases in spore germination (P=O.05) were observed with the use of antibiotic culture filtrates. The culture filtrates from these isolates gave greater than 89% reduction in the subsequent number of rust pustules when they were applied as a foliar spray at normal strength concentrations. The culture filtrates were applied to bean plants in the greenhouse 2 hrs prior to inoculation with urediospores of Uromyces appendiculatus. The highest inhibitory effect to rust development was given by Bacillus subtilts CA5 at normal strength concentration, which reduced the number of pustule development by 98% compared to the non-treated plants. No significant differences (P=0.05) were observed between the antibiotic culture filtrates and the standard check Dithane M45 in the control of bean rust in the greenhouse. All the antibiotic culture filtrates screened at both normal, half, and quarter strength concentration levels gave greater than 49.7% reduction in the number of rust pustules. Dilution of the culture filtrates slightly reduced their efficacy in controlling the disease. The antibiotic culture filtrates from the two isolates of Streptomyces spp. coded as 28P and CS35 and one isolate of Bacillus subtilis CAS were effective in controlling rust of French beans in the field. Compared with the control, significant decreases in disease severity (P=0.05) were obtained on plants pre-treated with culture filtrates of isolate 28P, CS35 and CAS. Compared with Dithane M45 80% WP applied at the rate of 2.Sgll, the culture filtrates were comparably effective over the whole period of assessment. The culture filtrates were insignificantly different (P=O.OS) from each other and from Dithane M45. Temperature was found to have an effect on the activity of the culture filtrates from Bacillus subtilis CA5, Trichoderma viride T 1 and Aspergillus niger A 1 in the inhibition of uredial pustule development in the greenhouse. At high greenhouse temperatures of 23-27 C, the antibiotic culture filtrates were more effective and stabler and gave better control of the disease than at lower greenhouse temperatures of 18-20 C. The results were also variable. The chemical Dithane M45 did not show any variations in efficacy at the different temperatures. On the 'Overall the culture filtrates of CA5, Tl and Al were effective only when the weather conditions were less favourable for rust pustule development in the greenhouse