Semester of Graduation

Summer 2019

Degree

Master of Science (MS)

Department

Plant Pathology and Crop Physiology

Document Type

Thesis

Abstract

Sheath blight (ShB - caused by Rhizoctonia solani) and bacterial panicle blight (BPB - caused by Burkholderia glumae) are economically important rice diseases in Louisiana and other rice-growing regions. Fungicides and oxolinic acid are used to manage ShB and BPB, respectively, but these chemical methods are not sustainable economically and ecologically. Besides diseases, plant utilizable nitrogen (N) in the soil is inadequate for optimum crop yield, leading to the use of inorganic fertilizers and making agriculture less sustainable. To develop alternative biological control methods for protecting rice plants from diseases, rice-associated bacteria were screened based on their antagonistic activities against the pathogens by growth inhibition plate assays. Three strains each of Bacillus spp. and Pseudomonas spp. were selected for evaluation of their disease suppression activities against ShB and BPB, respectively. Rice plants were artificially inoculated with R. solani at the tillering stage, while B. glumae was inoculated at 30% heading separately. Selected antagonistic bacteria were applied via spraying on the sheath (for ShB) or panicles (for BPB) of plants 24 h after pathogen inoculation. Efficacy of the Pseudomonas strains for suppression of BPB could not be determined in the field trials because of low disease pressure. Whereas, field trials in 2017 and 2018 revealed that foliar spray of Bacillus strain REB711 significantly reduced ShB development compared to the non-treated control, although it was less effective than the fungicide azoxystrobin. Seed treatment with Bacillus strain REB711 significantly reduced ShB development in the greenhouse environment, which could result from competition, antibiosis, and/or induction of plant defense system. To identify bacterial agents for rice growth promotion, bacteria isolated from the rice rhizosphere were screened based on their nitrogen-fixing activity, and five isolates were selected to test their ability to promote rice growth at an early seedling stage in the laboratory and greenhouse v conditions. Of five selected isolates, seed treatment with the Pseudomonas strains RRB I-6 seemed to be potential in promoting the growth of rice seedlings. Increases in plant height and soil-plant analysis development (SPAD) scores could have resulted from increased uptake of N or other nutrients or production of phytohormones. These results indicate that Bacillus sp. REB711 and Pseudomonas sp. RRB I-6 could be potential biological agents for managing ShB and promoting rice growth, respectively.

Committee Chair

Ham, Jong Hyun

DOI

10.31390/gradschool_theses.4975

Download

Share

COinS