توانایی باکتری‏های محرک رشد در القای آنزیم‏های مرتبط با مقاومت در گیاه برنج علیه Pyricularia oryzae

Rice blast disease caused by Pyricularia oryzae (PO) is one of the important rice diseases worldwide. Plant growth promoting rhizobacteria (PGPR) by colonization of the plant roots and rhizosphere play an important role in the induction of systemic resistance against pathogens. This study aimed to investigate the effect of two PGPR isolates, Alcaligenes faecalis strain O1R4 and Bacillus idriensis strain MR2, on the induction of resistance-related enzymes such as peroxidase and catalase and disease severity in rice plant inoculated with PO. For this purpose, the roots of the seedlings of Hashemi and Hassan Sarai cultivars were inoculated with a suspension of isolates (106-107 CFU/ml) for one hour. Spores of PO were obtained by immersing of infected leaves collected from fields in distilled water. Then, plants in the four-leaf stage were inoculated with the PO suspension (2 × 105 spore/ml). Catalase and peroxidase level were measured one, three, five, and seven days after inoculation using a spectrophotometer. Experiment was performed in a completely randomized block design with eight treatments and four replications. According to the analyses of variance, there was a significant influence of bacterial inoculation on the activity of peroxidase enzyme in the third, fifth and seventh day and on the activity of catalase enzyme from first day to seventh day at the 1% probability level. Comparison of the mean showed that the level of peroxidase and catalase enzymes were increased in the treatments consist of pathogen and A. faecalis 97 and 43 percent in Hashemi and, 174 and 125 percent in Hassan-Sarai cultivars, respectively compared to the positive control. Also, the amount of peroxidase and catalase enzymes were increased in the treatments inoculated with pathogen and B. idriensis 69 and 33 percent in Hashemi and, 195 and 121 percent in Hassan-Sarai cultivars, respectively compared to the positive control. Also, in the simultaneous use of two bacterial isolates, the amount of catalase enzyme increased in Hashemi and Hassan-Sarai cultivars 73 and 166 percent and the amount of peroxidase enzyme became 174 percent in Hashemi and 319 percent in Hassan-Sarai cultivars, respectively compared to the positive control. Also mean of diesese severity in two cultivars was reduced in the treatments consist of pathogen and A. faecalis 37 percent and treatments inoculated with pathogen and B. idriensis 20 persent. This study showed that bacterial isolates reduced the disease severity by inducing systemic resistance to the rice blast disease.