Potency of endophytic actinomycetes in controlling bacterial leaf blight disease in rice Plant (Oryza sativa)

Abstract

Bacterial Leaf Blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is the most damaging disease in lowland rice growing areas in Indonesia. Endophytic actinomycetes provide advantages to the host plant through enhancement of plant physiological activity or through other modes of action and serve as source of agroactive compounds which can be used as biocontrol agent. The objectives of this experiments were to examine the potency of endophytic actinomycetes in controlling BLB using in planta-in vitro approaches, to characterize and identify the selected endophytic actinomycetes as well as to confirm their colonization in rice plant tissue. To obtain the objectives, the study was divided into three steps: (1) to evaluate the ability of endophytic actinomycetes in controlling BLB based on in planta (field and the greenhouse) experiments, (2) to study the biological control characters of endophytic actinomycetes using in vitro approach, (3) to characterize and identify the selected endophytic actinomycetes and their colonization in rice plant tissue. The field experiments were conducted in dry and wet seasons. The results showed that indigenous endophytic actinomycetes PS4-16 applied by seed coating and soaking techniques suppressed natural infection of BLB during dry and wet season experiments.Area under disease progress curve (AUDPC) values of PS4-16 in dry season and wet season were 1458 and 1923 respectively. Those AUDPC values were significantly different to negative control but no significantly different to the application of sinthetic bactericide. The application of endophytic actinomycetes PS4-16 under dry season could increased rice yield by 17% compared to positive control. The results of green house experiment showed that inoculation of endophytic actinomycetes AB131-1 on rice var. IR64 had a better growth than PS4-16 (21,8%). Endophytic actinomycetes AB131-1 inhibited the BLB better than PS4-16. Based on an in vitro mechanism study, all of the actinomycetes examined showed antibiosis activity against Xoo patotype IV and had a broad antimicrobial spectrum against several Gram positive and negative bacteria as well as inhibited fungal pathogens. Based on their different colony morphology observation, which produced aerial myselia and had spiral spore forming observed under both light and Scanning Electron Microscope, the selected endophytic actinomycetes AB131-1, AB131-2, PS4-16 and LBR02 belonged to the genus Streptomyces spp. The 16S rDNA sequence of AB131-1 showed 89% closed relationship with Streptomyces sp. The AB131-1, AB131-2, PS4-16 and LBR02 were able to colonize rice plant tissue which confirming them as endophytes.