Biocontrol agents promote growth of potato pathogens, depending on environmental conditions

Abstract

SummaryThere is a pressing need to understand and optimize biological control so as to avoid over‐reliance on the synthetic chemical pesticides that can damage environmental and human health. This study focused on interactions between a novel biocontrol‐strain, Bacillus sp. JC12GB43, and potato‐pathogenic Phytophthora and Fusarium species. In assays carried out in vitro and on the potato tuber, the bacterium was capable of near‐complete inhibition of pathogens. This Bacillus was sufficiently xerotolerant (water activity limit for growth = 0.928) to out‐perform Phytophthora infestans (~0.960) and challenge Fusarium coeruleum (~0.847) and Fusarium sambucinum (~0.860) towards the lower limits of their growth windows. Under some conditions, however, strain JC12GB43 stimulated proliferation of the pathogens: for instance, Fusarium coeruleum growth‐rate was increased under chaotropic conditions in vitro (132 mM urea) by >100% and on tubers (2‐M glycerol) by up to 570%. Culture‐based assays involving macromolecule‐stabilizing (kosmotropic) compatible solutes provided proof‐of‐principle that the Bacillus may provide kosmotropic metabolites to the plant pathogen under conditions that destabilize macromolecular systems of the fungal cell. Whilst unprecedented, this finding is consistent with earlier reports that fungi can utilize metabolites derived from bacterial cells. Unless the antimicrobial activities of candidate biocontrol strains are assayed over a full range of field‐relevant parameters, biocontrol agents may promote plant pathogen infections and thereby reduce crop yields. These findings indicate that biocontrol activity, therefore, ought to be regarded as a mode‐of‐behaviour (dependent on prevailing conditions) rather than an inherent property of a bacterial strain.

Understanding and exploiting plant beneficial microbes

“…The definition of large scale, in fact, has changed rapidly from hundreds [16] to tens of thousands [20] of strains. Recent plant-associated bacterial and fungal isolate collections (summarized in Table 1) are derived from sugarcane [20]; grapevine [21–23]; potato [24]; tomato [25]; eucalyptus [25]; rice [26,27]; ancient wheat ancestors [19]; lettuce [28]; Arabidopsis [16, 29]; poplar [29]; and from plants growing in an arsenic-contaminated soils [30]. The increasing volume of isolate collections will tax existing repositories; yet the genomic diversity contained in the bacterial isolates that are being obtained is not nearing saturation [16].…”

Antipathy of <b><i>Trichoderma</i></b> against <b><i>Sclerotium rolfsii </i></b>Sacc.: Evaluation of Cell Wall-Degrading Enzymatic Activities and Molecular Diversity Analysis of Antagonists

“…In contrast, biocontrol agents may promote plant pathogen infections depending on environmental conditions and thereby reduce crop yields. The biocontrol activity ought to be regarded as a mode of behavior (dependent on prevailing conditions) rather than an inherent property of a biocontrol agent [Cray et al, 2016].…”

The Effect of Cell Immobilization by Calcium Alginate on Bacterially Induced Calcium Carbonate Precipitation

“…Each bacterium has a very specific and narrow water activity for optimum metabolism and growth [18]. More recent studies show that Bacilli and closely related bacteria are moderately xerotolerant [19,20]. For near future applications of bio self-healing concrete, it is necessary to design a matrix capable of shielding the cells in a concrete environment.…”