Potential Antagonistic Bacteria against Verticillium dahliae Isolated from Artificially Infested Nursery

Xiaofeng Su,Yi Wang,Guoqing Lu,Haiyang Liu,Siyuan Wu,Huiming Guo,Lu Liu,Xi Jin,Chen Wang,Hongmei Cheng

doi:10.3390/cells10123588

Abstract

As an ecofriendly biocontrol agent, antagonistic bacteria are a crucial class of highly efficient fungicides in the field against Verticillium dahliae, the most virulent pathogen for cotton and other crops. Toward identifying urgently needed bacterial candidates, we screened bacteria isolated from the cotton rhizosphere soil for antagonisitic activity against V. dahliae in an artificially infested nursery. In preliminary tests of antagonistic candidates to characterize the mechanism of action of on culture medium, 88 strains that mainly belonged to Bacillus strongly inhibited the colony diameter of V. dahliae, with inhibiting efficacy up to 50% in 9 strains. Among the most-effective bacterial strains, Bacillus sp. ABLF-18, and ABLF-50 and Paenibacillus sp. ABLF-90 significantly reduced the disease index and fungal biomass of cotton to 40–70% that of the control. In further tests to elucidate the biocontrol mechanism (s), the strains secreted extracellular enzymes cellulase, glucanase, and protease, which can degrade the mycelium, and antimicrobial lipopeptides such as surfactin and iturin homologues. The expression of PAL, MAPK and PR10, genes related to disease resistance, was also elicited in cotton plants. Our results clearly show that three candidate bacterial strains can enhance cotton defense responses against V. dahliae; the secretion of fungal cell-wall-degrading enzymes, synthesis of nonribosomal antimicrobial peptides and induction of systemic resistance shows that the strains have great potential as biocontrol fungicides.

Highlights

Verticillium dahliae, a soil-borne phytopathogenic fungus, is the causal agent of a destructive vascular wilt known as Verticillium wilt
The results reveal that ABLF-18, ABLF-50 and ABLF-90 strains have potential for furdevelopment to improve the the plant resistance against ther development to improve plant resistance against
Mitogen-activated protein kinases (MAPKs) and PR10 exhibited evident increase in ABLF-90, 9- and 7-fold in expression, respectively. These results demonstrated that the antagonistic bacteria could enhance the expression of cotton genes relevant to the systemic resistance

Summary

Introduction

Verticillium dahliae, a soil-borne phytopathogenic fungus, is the causal agent of a destructive vascular wilt known as Verticillium wilt. This fungus was firstly reported in America and rapidly spread throughout the world [1]. Microsclerotia, the main survival structure of V. dahliae in fields, are very difficult to eliminate from soils and responsible for great economical losses annually [5,6]. Their high tolerance to extreme temperature and pH conditions enables them to survive for nearly 20 years [7,8]

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Conclusion