Microscopic and molecular studies in the biological control of rice blast caused by Pyricularia oryzae with Bacillus sp. BMH under greenhouse conditions

Abstract

Rice (Oryza sativa L.) feeds around half of humanity mainly in Asia, South America, and Africa. Pyricularia oryzae Cav. (syn. Magnaporthe oryzae Couch) is the causative agent of the most devastating disease of rice worldwide. The purpose of this study was to evaluate the efficiency of the selected Bacillus sp. strain BMH in relation to its antagonistic attributes against P. oryzae as well as rice cultivar BRS.MG Caçula growth promotion, productivity, and its ability to colonize tissues and induce resistance in plants using microscopy, genes expression, and pot assay under greenhouse conditions. The soil and seedlings were inoculated with Bacillus sp. BMH and the seedlings were sprayed with P. oryzae isolate A10965. The severity evaluation and microscopic analysis showed that BMH was able to reduce rice blast severity with 53.12%, 50%, and 37.5% for soil inoculation, preventive control, and the mixture of pathogen-BMH treatments respectively at 28 DAI. Rice plants were higher following the Bacillus sp. BMH inoculation in soil with 25.73 cm compared to the control treatment with 21.93 cm at 63 days after sowing (DAS). Likewise, the number of tillers was higher with 12.6 for BMH against 9.13 for control as well as grain weight with 10.17 g for BMH treatments against 7.14 g for untreated one. BMH enhanced plant growth promotion (PGP) and production, which illustrates its potential use as a biocontrol agent. The Confocal Laser Microscopy (CLM) and Scanning Electron microscopy (SEM) showed the colonization of rice root vascular tissues as well as foliage by Bacillus sp. BMH cells, which indicates its endophytic potential. In the molecular study, the expression of genes responsible for conferring resistance to the blast was studied upon colonization of the plants by beneficial and pathogenic microbe’s invasion, namely ALD1, OsPR1a, OsPR1b, OsGLN1, OsWRKY28. Soil inoculation with BMH or sprayed on the surface of leaves resulted in the stimulation of rice defense mechanisms against blast disease by upregulating the rice β-1,3-glucanases (OsGLN1) and OsPR1a, which are thought to be involved in plant normal growth and development, playing a direct role in defense against fungi, and other stressors. The results obtained in this research demonstrate the beneficial interaction between rice plants and BMH, as well as the blast management strategy, that could help to reduce dependence on fungicides and contribute to the sustainability of rice cropping.