Background
Fusarium wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici (FOL) is a serious disease that causes significant economic losses in tomato production. Seventeen endophytic Bacillus isolates from tomato roots of Meghalaya were tested for antagonistic and plant growth promotion activities. Dominating arbuscular mycorrhiza fungi (AMF) spores were isolated from the rhizosphere soils of tomato grown in Meghalaya. The effect of different combinations of AMF and endophytic Bacillus on Fusarium wilt severity and growth of tomato plant under pot and field conditions was studied.
Results
The endophytic Bacillus isolates ERBS51 and ERBS10 showed a maximum inhibition against FOL, with 58.43 and 55.68%, respectively, in a dual culture experiment. ERBS51 and ERBS10 were identified as Bacillus velezensis and Bacillus sp., respectively, based on 16s rRNA sequencing. Both isolates were found positive for iturin A, surfactin, bacillomycin D, protease, cellulase, pectinase, alpha-amylase, siderophore, ammonia production and ZnCO3 solubilization. Funneliformis mosseae and Glomus fasciculatum were the dominating AMF species in tomato rhizosphere of Meghalaya. The result of pot and field experiments revealed that out of all the treatments, combination of Funneliformis mosseae + Glomus fasciculatum + Bacillus velezensis + Bacillus sp. was shown to be the best in reducing the severity of Fusarium wilt to 77.44 and 66.74%, respectively. F. mosseae + G. fasciculatum + B. velezensis + Bacillus sp. also recorded the highest in most growth attributes and yield.
Conclusions
Endophytic Bacillus (B. velezensis and Bacillus sp.) and AMF (F. mosseae and G. fasciculatum) were safe and effective biocontrol agents against Fusarium wilt of tomato.
The yield potential of Brassica juncea is constrained by many fungal diseases among which Alternaria blight poses a major challenge worldwide. Endophytic bacteria are increasingly recognized as a promising source of novel organic natural metabolites for a variety of biological activities. However endophytic bacteria belonging to the group Bacillus and fluorescent Pseudomonads are being reported as superior groups exploited for their role in combating phytopathogens. Therefore, the bacteria belonging to the above groups were primarily targeted for this study. In this study, fifty six endophytic bacteria were selectively isolated from seeds, roots and leaves of 20 different cultivars of Brassica juncea growing in various parts of North Eastern Region of India. Out of all isolates tested BS8, BS15, BS21 and FP13 show inhibition of 59.63%, 65.93%, 58.52% and 63.33 % respectively. When tested for functional properties, BS21 produced IAA as well as ammonia, BS15 and FP13 produced only Ammonia whereas BS8 solubilised Phosphate. BS8(Bacillus cereus), BS15(Bacillus subtilis), BS21 (Bacillus subtilis) and FP13 (Pseudomonas fluorescens) were selected on the basis of antagonistic as well as plant growth promoting properties for formulating a microbial consortium and subsequent evaluation in the field.
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