The effect of rice endophyte bacteria on controlling Xanthomonas oryzae pv. Oryzae and expression of phenylalanine ammonia-liase gene in coexistence with Bacillus subtilis

Rice bacterial blight is one of the major factors limiting global rice production. Though the most effective method for controlling this disease is using resistant varieties, they are not stable in farm conditions due to high variability and rapid evolution of pathogenic races. This study was aimed to evaluate rice endophyte bacteria's ability to improving plant growth and biologically controlling Xanthomonas oryzae pv. oryzae.

At the first screening of endophyte isolates was performed to evaluate antagonistic activity against Xanthomonas in tryptic soy agar medium. The stimulation of plant growth by bacterial endophytes was assessed under the growth chamber and greenhouse conditions. The effect of bacterial isolates on disease severity and some rice growth factors under greenhouse conditions were determined, as well. In the final stage, the expression of the Phenylalanine ammonia-lyase gene by endophytic isolate Bacillus subtilis was evaluated using real-time PCR.

In terms of rice seed seedling vigor index, OS40, OS23, OS43, and OS31 isolates had a significant statistical effect as compared to control. Moreover, the use of OS3, OS23, OS31, and OS40 endophytes increased plant growth parameters. OS40 and OS23 bacterial inoculants were more successful in reducing the severity of the disease and the promotion of plant growth. PAL expression level during the experiment period was significantly higher and faster in plants treated with OS40than those treated only with Xanthomonas- isolates.

Rice bacterial endophytes could increase plant growth and reduce disease severity, thus they can be considered as a promising and environmentally- a friendly strategy for sustainable agriculture development.