Biological Agent Treatments to Control Bacterial Leaf Blight and to Improve Plant Growth and Production of Rice

Abstract

Healthy rice seed (free of Xanthomonas oryzae pv. oryzae (Xoo)) could be produced by prevention of Xoo infection from the seed source and the plant. Xanthomonas oryzae pv. oryzae causes bacterial leaf blight (BLB) in rice. The objectives of the research were to evaluate biological agent treatments in controlling BLB and increasing plant growth and seed production of rice. The research consisted of two parts. The first part was aim to obtain the rhizosphere and phyllosphere biological agents capable of controlling Xoo. The first experiment in the first part conducted to isolate the virulent Xoo. The second experiment was a retest for antagonism of rhizobacteria collection against the isolated Xoo which would be used in seed treatments. The third experiment was isolation and antagonism test of phyllosphere bacteria against Xoo to be used in spraying the plants. The second part of this study was the evaluation of biological agent treatment (seed treatment and plants spraying) effects in controlling BLB disease and improving plant growth and seed production. The first experiment was conducted in the greenhouse and the second one in the field using the same experimental design (randomized block design with two factors) and three replications. Seed treatments (first factor) consisted of negative control, positive control, streptomycin sulfate 0.2%, Pseudomonas diminuta A6 + Bacillus subtilis 5B, matriconditioning + streptomycin sulphate 0.2%, and matriconditioning + P. diminuta A6 + B. subtilis 5B. Spraying plants (second factor) consisted of untreated control, streptomycin sulphate 0.2%, biological agent F112, biological agent F198, and biological agent F57. The first experiment from the first part of these studies resulted virulent Xoo isolated from ooze. The second experiment confirmed that P. diminuta A6 + B. subtilis 5B indicated high antagonism against the Xoo. The third experiment produced phyllosphere isolates F112, F198, and F57 showing high antagonism against the Xoo. The first experiment in the second part of these studies showed that matriconditioning + P. diminuta A6 + B. subtilis 5B improved seed germination from 93.6% to 96.9%, plant height from 70.9 cm to 76 cm, plant dry weight from 1.35 g to 1.91 g as compared to positive control. Spraying plants using biological agent F112 increased plant dry weight from 1.40 g to 1.78 g as compared untreated control. Meanwhile, matriconditioning + P. diminuta A6 + B. subtilis 5B followed by spraying plants with biological agent F112 reduced the BLB severity. The second experiment showed that matriconditioning + P. diminuta A6 + B. subtilis 5B improved seedling dry weight. Matriconditioning + P. diminuta A6 + B. subtilis 5B and spraying plants with biological agents F112 controlled BLB and increased plant growth. However, all treatments were not able to increase healthy seed production, these may be due to population of the biological agents applied was not optimum yet.