EndophyticStreptomyces spp. as BiocontrolAgents of Rice Bacterial Leaf Blight Pathogen (Xanthomonas oryzae pv. oryzae)

Abstract

Xanthomonas oryzae pv. oryr.ae (Xoo), a causal agent of bacterial leaf blight (BLB), is one of the most important pathogens of rice. The effectiveness of ten Streptomyces spp. isolates in suppressing Xoo disease was assessed in planta and in vitro. In planta experiments were carried out in a greenhouse and arranged in a randomized completely block design (RCBD) with three replications. Twenty treatments were tested which included plants inoculated with both Streptomyces spp. andXoo, and plai;its inoculated with only Streptomyces spp. Plants inoculated with Xoo and sprayed with a chemical bactericide, and plants inoculated with only Xoo served as positive controls, whereas plants not inoculated with either Streptomyces spp. or Xoo were used as negative controls. The results showed that the effect of endophytic Streptomyces spp. on BLB disease expressed as area under disease progress curve (AUDPC) wu not significantly different to that oq control plants (P > 0.05). However, plants inoculated with endophytic Streptomyces spp. were significantly taller and produced higher tiller number than control plants (P < 0.05). Streptomyces spp. Isolate AB131-1 gave the highest plant height. Jn vitro studies on biocontrol mechanisms of selected Streptomyces spp. isolates showed that isolate LBR02 gave the highest Inhibition activity on Xoo growth, followed by ABlJl-1 and ABIJl-2. Two isolates (AB131-1 a.nd LBR02) were able to produce chitioase, phosphatase, a.nd sideropbore which included biocontrol characteristics. Morphological and colonization studies under SEM and light microscopy confirmed that the three isolates were endophytic Streptomyces spp. from dilJerent species. These studies found that the paddy plant which was inoculated with endophytic Streptomyces spp. AB131- 1 and infected by Xoo could Increase the height of plant and number of tillers.