Biological control agents (BCAs) of verticillium wilt: influence of application rates and delivery method on plant protection, triggering of host defence mechanisms and rhizosphere populations of BCAs

Abstract

Verticillium dahliae causes severe yield reductions in a variety of important annual crops worldwide. Control of verticillium wilt has relied on soil fumigation; however, the use of the main soil fumigant, methyl bromide, has been banned in the European Union since 2010, creating a demand for novel crop protectants. As such, the use of biocontrol agents (BCAs) is an appealing management strategy. Prerequisites for the development of a successful BCA are an understanding of the modes of action of the antagonist, its ecological fitness and an efficient and economically feasible delivery system. Therefore, two BCAs (Paenibacillus alvei K165 or the nonpathogenic Fusarium oxysporum F2) and two release strategies (seed coating or amendment of the transplant soil plug) were assessed against verticillium wilt of aubergine (eggplant). Mixing the transplant soil plug with K165 or F2, at a rate of 10 and 20% (v/v), respectively, reduced verticillium wilt symptom development. Furthermore, a positive correlation was revealed between the release strategy and the BCA rhizosphere population. Correlation analysis also showed that disease severity was negatively correlated to the rhizosphere size of the BCA population. In addition, qPCR analysis showed that both BCAs induced the expression of the pathogenesis-related (PR) proteins PR1 and PR4 in the stem of aubergines before and after inoculation with V. dahliae in a manner that suggests a link with the rhizosphere size of the BCA population.

Bacillus thuringiensis and Bacillus weihenstephanensis Inhibit the Growth of Phytopathogenic Verticillium Species

“…Other control strategies such as crop rotation, the usage of resistant plant species, and soil solarization have only limited efficiency (Haas and Défago, 2005; Depotter et al, 2016). They are either ineffective, time-consuming, costly, may have a severe environmental impact, or even could affect human health (Angelopoulou et al, 2014). …”

“…Moreover, some of these plant growth-promoting bacteria (PGPB) have been used as biological control agents against plant diseases and pests (Ahemad and Kibret, 2014). However, common fungal antagonistic bacteria such as Pseudomonas species have only limited inhibitory impact on Verticillium due to the long-term persistence of Verticillium microsclerotia in soil (Angelopoulou et al, 2014). Members of the endospore-forming genus Bacillus possess a high potential as new fungal antagonists.…”

Verticillium dahliae-eggplant as the pathosystem model to reveal biocontrol potential of three Trichoderma spp in green house conditions

“…In fact, different research work demonstrated the potential of different antagonists like Thalaromyces flavus, Fusarium oxysporum and phomopsis sp. to control different Verticillium wilt in tomatoes, pistachio, cotton and eggplant (Marois et al, 1982;Tjamos et al, 2004;Zheng et al, 2011;Angelopoulou et al, 2014). Recently Yuan et al (2017) research work on biocontrol efficacy of Penicillium simplicissimum with DI = 41.4%, Acremonium sp with DI = 39.2%, Leptosphaeria sp.…”

Scientific opinion on the pest categorisation of Verticillium dahliae Kleb

“…Effective bacterial antagonists include plant growth-promoting rhizobacteria, such as pseudomonads (Sharma and Novak., 1998) and other genera obtained from plant rhizospheres (Berg et al, 1994;Angelopoulou et al, 2014). Examples of fungi that have some efficacy include Pythium oligandrum (Al-Rawahi and Hancock, 1998), Heteroconium chaetospira (Narisawa et al, 2002), Talaromyces flavus and Trichoderma spp.…”

“…Metam sodium reduced levels of V. dahliae inoculum in potato field experiments by 60-80 %, and shank injection was more effective than chemigation (Overman, 1982). As metam sodium and methyl-bromide have been phased out, no soil fumigants are currently available for the control of Verticillium wilt diseases in the risk assessment area (Subbarao, 2002;Angelopoulou et al, 2014).…”