Rice bacterial leaf blight and rice blast caused by Xanthomonas oryzae pv. oryzae and Pyricularia oryzae are the major problem for rice production in Thailand. Chemical control was shown to be less effective. Endophytic bacteria are bacteria that have intimate relationship with their host without inducing any pathogenic symptom. Therefore, this study was focused on the biocontrol of rice pathogens and plant growth enhancement by endophytic bacteria from rice. These two rice pathogens were collected from various area in northern part of Thailand, particularly Chiangmai, Chiangrai, Lumpoon, Lumpang, Prae, Nan, Payao and Mae Hong Son. Eight strains of Xanthomonas oryzae pv. oryzae were obtained from Chiang mai and Payao area. Nineteen isolates of rice blast fungi, genus Pyricularia, were obtained from 8 provinces. From the rice pathogenicity test, Xoo and Pyricularia were 5 and 2 in severity, respectively.
Total of 471 endophytic bacteria were isolated from healthy rice stem and rice seed. The identification results show that Gram-negative bacteria were belonged to the group of Proteobacteria and Bacteroide and gram-positive bacteria were in the group of Firmicutes and Actinobacteria. Gram-negative endophytic bacteria were belonged to the genera of Acinetobacter, Agrobacterium, Burkhoderia, Citrobacter, Enterobacter, Klebsiella, Methylobacterium, Pantoea, Pseudomonas, Serratia, Sphingobacterium, Spingomonas and Stenotrophomonas, while gram-positive bacteria were in the genera of Bacillus, Brevibacillus, Curtobacterium Lysinibacillus, Paenibacillus, Streptomyces and Virgibacillus,. These bacteria were evaluated in vitro for inhibition of X. oryzae pv. oryzae by spot on lawn. Among these, it was found that fifty-five isolates comprising of Acinetobacter, Bacillus, Citrobacter, Klebsiella and Pseudomonas exhibited the antagonistic activity against X. oryzae pv. oryzae. Cell free supernatant of these antagonist bacteria were then investigated the antibacterial activity by agar well diffusion method. Only fourteen isolates of Pseudomonas and Bacillus expressed the inhibitory effect on X. oryzae pv. oryzae. The highest diameter of inhibition zone was obtained from Bacillus velezensis SK63-R283. These 471 bacteria were also tested against P. oryzae by dual culture assay. Total of 75 isolates comprising of the genera of Bacillus, Paenibacillus, Pseudomonas, Enterobacter and Klebsiella showed the inhibitory effect on fungal growth. Bacillus pumilus SK63-R260 showed the highest percentage of fungal growth inhibition at 65.57 %.
The plant growth enhancement of rice endophytic bacteria were investigated by their activities of phosphate solubilizing, nitrogen fixation and production of indole acetic acid. The phosphate solubilizing activity of bacteria were tested on National Botanical Research Institute’ phosphate growth medium (NBRIP) agar. It was found that 98 isolates showed the ability to solubilize phosphate according to clear zone around bacterial colony. They belonged to the genera of Acenitobacter, Bacillus, Brevibacillus, Enterobacter, Klebsiella, Paenibacillus and Pseudomonas. These bacteria were then carried out phosphate solubilizing activity in liquid medium. Results showed that Acinetobacter sp. SK63-R222 obtained the highest solubilizing ability of Ca3(PO4)2, about 261.66 ?g/ml. According to the growth in nitrogen free medium, sixty-six isolates belonging to Acinetobacter, Bacillus, Lysinibacillus, Paenibacillus and Staphylococcus, were able to fix nitrogen. All bacterial isolates were also screened indolic compound production by spectrophotometer. The result of quantitative analysis of IAA production from 77 bacterial isolates showed that Klebsiella pneumoniae SK63-R155 produced the highest IAA (237 ?g/ml).
In the study of rice disease control by biological methods, Bacillus velezensis SK63-R283 bacteria were selected for the pot experiment. It was found that Bacillus velezensis SK63-R283 could reduce the severity of bacterial leaf blight in rice and rice blast disease by 55% and 25%, respectively.
The optimized media were carried out to produce antibacterial substance against Xoo. Commercial bacterial culture media, comprising of nutrient broth, trypticase soy broth and potato dextrose broth, were investigated. The suitable medium for production cell mass and antibacterial substance by Bacillus velezensis SK63-R283 was trypticase soy broth.
The formulation of Bacillus velezensis SK63-R283 for controlling bacterial leaf blight were also studied. Bamboo biochar and kaolin were used as carriers in this experiment. These two substances were effective to maintain bacterial survival with 9 log CFU/g after 2-month storage. Pot experiments using seed treatment and foliar spray showed the decrease in bacterial leaf bight by 35%.
These results suggested that rice endophytic bacteria can be used for biological control of rice diseases and they can be potential for enhancing the plant growth. The others bioformulation of will be developed in ours research lab and the safety of this endophytic bacterium must be test before using in the rice field