Endophytic Actinomycetes from Wild Rice (Oryza rufipogon Griff.) and Their Biological Activities in Controlling Bacterial Blight and Bacterial Leaf Streak in Rice

Bacterial blight disease caused by Xanthomonas oryzae pv. oryzae and bacterial leaf streak disease caused by X. oryzae pv. oryzicola are the major rice diseases affecting the quality and quantity of rice production. Endophytic actinomycetes are promising biocontrol agents against plant diseases and promote plant growth. This study aimed to isolate endophytic actinomycetes from wild rice (Oryza rufipogon Griff.) collected in Thailand and to evaluated their abilities to control bacterial blight and bacterial leaf streak in rice. A total of 188 actinomycete strains were obtained from wild rice plants. In vitro antagonistic assays showed that 118 strains exhibited inhibitory activity against X. oryzae pv. oryzae and 110 strains against X. oryzae pv. oryzicola. Ten strains that showed strong antagonistic activity against both pathogens were further evaluated for plant growth–promoting traits. Pot experiment conducted on KDML 105 rice showed that all selected strains had positive effects on rice seedlings by increasing root length, shoot length, and seed vigor index. Under greenhouse conditions, strain WRS1.2, which exhibited the highest inhibitory activity against rice fungal pathogens in vitro, reduced the severity of bacterial blight by 73.18 ± 4.31% and bacterial leaf streak by 86.67 ± 10.61%. In addition, strain WRS1.2 was able to colonize KDML 105 rice roots. Based on 16S rRNA gene sequence analysis, strain WRS1.2 was closely related to Streptomyces parvulus NBRC 13193T. In summary, S. parvulus WRS1.2 demonstrated a promising biocontrol agent for both bacterial rice diseases and also promote plant growth. The strain should be further developed and applied to promote sustainable rice production in the future.