Epsilon Archive for Student Projects

Abstract

Disease management with biocontrol agents (BCAs) is gaining more attention in recent times as pathogens evolve resistances to chemical treatments. For both cucumber and strawberry productions the fungal disease powdery mildew (PM) is a threat where resistances to several fungicides have been reported. Further PM is more severe in greenhouse environments, which are becoming increasingly common in berry productions. In order to examine the current state of bacterial BCAs on the market, as well as promising bacteria for future PM disease management in cucumber and strawberry, this literature review was conducted. Databases were utilized in order to understand which commercial bacterial BCAs are available and being investigated for their suppression as well as their mode of action against PM.
The results found that bacterial BCAs can act antifungal against PM through several mechanisms, including the production of antifungal compounds, iturin, fengycin, surfactin and prumycin; through secretion of enzymes; inducing the plants; promoting plant growth and through competition with the fungus for nutrients and space. Bacteria from the genera: Bacillus, Pseudomonas Streptomyces and Enterobacter show great potential as BCAs as they exhibit such traits.
The commercial products currently on the market have been shown to suppress PM. Among these Bacillus subtilis strain QST 713 (in commercial products Rhapsody and Serenade) gave varying results on PM inhibition, ranging from sufficient to no significant effect. Actinovate (Streptomyces lydicus) showed success in PM suppression on cucumber, whilst Bacillus subtilis var. amyloliquefaciens FZB24 (in products such as Taegro) gave poor results against PM on strawberries. Although some of the bacterial BCAs exhibit good suppression it is currently not viable as a sole treatment for PM in larger scale productions. The reason being that they require more frequent applications and do not provide enough effects against PM. Currently the bacterial BCAs can only give sufficient disease control when used in combination with conventional fungicides, reducing the overall chemical usage. However, in order to replace fungicides completely, more research must be conducted focusing on finding improved bacterial strains for better survivability on the phyllosphere environment as well as increased antagonistic interactions with PM.