Seasonal variation in the biocontrol efficiency of bacterial wilt is driven by temperature‐mediated changes in bacterial competitive interactions

Abstract

Summary Microbe‐based biocontrol applications hold the potential to become an efficient way to control plant pathogen disease outbreaks in the future. However, their efficiency is still very variable, which could be due to their sensitivity to the abiotic environmental conditions.Here, we assessed how environmental temperature variation correlates with ability of Ralstonia pickettii, an endophytic bacterial biocontrol agent, to suppress the Ralstonia solanacearum pathogen during different tomato crop seasons in China.We found that suppression of the pathogen was highest when the seasonal mean temperatures were around 20 °C and rapidly decreased with increasing mean crop season temperatures. Interestingly, low levels of disease incidence did not correlate with low pathogen or high biocontrol agent absolute densities. Instead, the biocontrol to pathogen density ratio was a more important predictor of disease incidence levels between different crop seasons. To understand this mechanistically, we measured the growth and strength of competition between the biocontrol agent and the pathogen over a naturally occurring temperature gradient in vitro. We found that the biocontrol strain grew relatively faster at low temperature ranges, and the pathogen at high temperature ranges, and that similar to field experiments, pathogen suppression peaked at 20 °C.Together, our results suggest that temperature‐mediated changes in the strength of bacterial competition could potentially explain the variable R. solanacearum biocontrol outcomes between different crop seasons in China. Synthesis and applications. Our results suggest that abiotic environmental conditions, such as temperature, can affect the efficacy of biocontrol applications. Thus, in order to develop more consistent biocontrol applications in the future, we might need to find and isolate bacterial strains that can retain their functionality regardless of the changing environmental conditions.

Bacillus amyloliquefaciens strain QST713 may contribute to the management of SDHI resistance in Botrytis cinerea

“…Furthermore, at the lower tested temperature of 10 °C, fungal spore germination and germ tube growth were delayed, allowing a longer contact of the fungus with the BCA that results in a higher control efficacy. This finding agrees with findings of previous reports suggesting that B. amylolιquefaciens failed to provide high biocontrol efficiency against Ralstonia solanacearum under warm conditions, while it was more effective under cool conditions 39,40 . The higher control efficacy achieved by Ba QST713 treatments at 10 °C compared to that observed at 20 °C is of particular importance taking into account that the most severe grey mould attacks in greenhouse‐grown vegetable crops occur during the winter period, when lower temperatures prevail, and provides evidence for successful disease management when environmental conditions favor the development of grey mould.…”

“…This finding agrees with findings of previous reports suggesting that B. amylolιquefaciens failed to provide high biocontrol efficiency against Ralstonia solanacearum under warm conditions, while it was more effective under cool conditions. 39,40 The higher control efficacy achieved by Ba QST713 treatments at 10°C compared to that observed at 20°C is of particular importance taking into account that the most severe grey mould attacks in greenhouse-grown vegetable crops occur during the winter period, when lower temperatures prevail, and provides evidence for successful disease management when environmental conditions favor the development of grey mould. Furthermore, the observed control efficacy for most of the sdhB mutants achieved by the protective applications of Ba QST713 at 10°C was higher than that observed for the wild-type isolates, providing evidence for the possible role of these treatments in the reduction of SDHI resistance frequency.…”

Molecular Identification and Evaluation of Indigenous Bacterial Isolates for Their Plant Growth Promoting and Biological Control Activities against Fusarium Wilt Pathogen of Tomato

“…This may be due to increased fitness of the isolate B. olei Prd2 to the biotic and abiotic factors of the experimental field. Wei et al (2017) stated that microbe–microbe interactions are very sensitive to several abiotic and biotic factors such as environmental temperature, productivity and microbial community composition, which could affect biocontrol outcomes by changing the strength of species interactions. In the experiment, application of B. olei reduced 44.99 and 41.91% of disease incidence of two tomato cultivar Pusa Rubi and Ratan, respectively as compared to infected untreated control.…”

Bacterial Wilt in China: History, Current Status, and Future Perspectives

“…Therefore, the level of damage is commonly expressed on a crop-by-crop basis and can range from minimal crop loss to a very high economic damage. For instance, bacterial wilt of tomato is a severe problem in the southern provinces of the Yangtze River, ranging from 10% to 80% disease incidence depending on the crop seasons ( Wei et al, 2011 , 2015 , 2017 ). In the case of potato, more than 10 provinces are infested by bacterial wilt disease with estimated yield losses ranging from 10–15% to even 80 or 100% in some hot-spot fields ( Hua et al, 1985 ; Chen et al, 2005 ).…”

“…mutants ( Chen et al, 2004 ; Yang et al, 2008 ), phage ( Wang X. et al, 2017 ) and other microbes ( Guo et al, 2004 ; Xue et al, 2009 ; Yang et al, 2012 ; Huang et al, 2013 ). Due to the unstable performance of application of single biocontrol agent under field conditions ( Wei et al, 2011 , 2015 , 2017 ), beneficial microbial consortia that could better utilize available resources and produce antibiotics may help to improve the consistency and efficacy of bacterial wilt biocontrol ( Wei et al, 2015 ; Hu et al, 2016 ; Yang et al, 2017 ). Novel strategies are also being developed to enhance disease suppression.…”