From seed to savior: understanding the biocontrol abilities of seed-derived streptomyces strains against seed borne bean bacterial diseases

Abstract

Phaseolus vulgaris L. (Common bean) is the most important legume for direct consumption worldwide and a leading food used to fight global hunger. The seed-borne bacterial pathogens, Xanthomonas phaseoli pv. phaseoli (Xpp) and Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) are considered an important constraint in crop production. Certain strains of Streptomyces have the ability to inhibit pathogenic bacteria, attributed to their production of various antimicrobial compounds. The Streptomyces FS2 and FS123 strains that exhibited high similarity with Streptomyces murinus and Streptomyces collinus based on 16S rRNA gene sequences were isolated from bean seeds, and antibacterial activities against the Xpp and Cff as well as also their effects on seedling growth were investigated. Both the FS2 and FS123 strains successfully inhibit the growth of the Xpp and Cff in the zone of inhibition test. The FS123 was found to be the promising strain in suppression of bacterial wilt (BW) disease but in a contradictory behavior significantly increase disease severity and the area under the disease progress curve (AUDPC) of common bacterial blight disease (CBB) under greenhouse conditions. Our experiments showed that treating bean seeds with the FS2 strain protects against both seed-borne diseases. We found that the pathogens population is affected when plants are treated with the Streptomyces strains, especially in leaf tissues and endophytic situations. The FS2 strain reduced plant growth despite the disease suppression. The total length of plantlets decreased by 65.7% and 17.89%, and total weights decreased by 44.79% and 9.06%, respectively, in the FS2 + Xpp and FS2 + Cff treatment. Our results demonstrate the biocontrol potential of the Streptomyces strains in the protection of bean against Xpp and Cff with a possible perspective to control these seed-borne diseases. However, attention to the damaging effect of the Streptomyces strains towards plant growth is crucial before introducing biocontrol materials.