Parallel Strategies to Control Bacterial Panicle Blight of Rice

Bacterial Panicle Blight (BPB) of rice is a seed-borne disease caused by the bacterium Burkholderia glumae. This disease has affected rice production worldwide and its effects are likely to become more devastating with the continuous increase in global temperatures especially during the growing season. Field data has shown that the disease has been more prevalent in years when the temperatures have been unusually high especially at night possibly due to the bacterial adaptation to grow at temperatures higher than 40oC. With the continuous rise in global temperatures, it is likely that this disease will be more problematic. The bacterium can cause disease symptoms in different tissues and at different developmental stages. In reproductive stages, the bacterium interferes with grain development in the panicles and, as a result, directly affects rice yield. Currently, there are no methods to control the disease as chemical control is not effective and completely resistant cultivars are not available. This work seeks to advance approaches to control the disease. Chapter 2 investigates methods of inoculation to efficiently screen rice cultivars with enhanced resistance to BPB even under conditions of heat stress. Cultivars 311206 and 310802 were identified as resilient to the pathogen and heat stress combination. Overall, the results revealed mostly cultivar-specific responses. Chapter 3 investigates two bacterial strains previously identified having antagonistic activity against B. glumae: Pseudomonas protegens PBL3 and Burkholderia cepacia PBL18. In this work, the biopesticide effect of P. protegens PBL3 and B. cepacia PBL18 was tested, the chemical category of compounds with antimicrobial activity of P. protegens PBL3 was investigated, and conditions favorable for chemical analysis of P. protegens PBL3 were identified. The secreted fraction of P. protegens PBL3 that reduced disease symptoms caused by B. glumae and reduced disease in seedlings, contains a complex mixture of potentially bioactive molecules that have differential activity against B. glumae, and preserves its antimicrobial activity over B. glumae when grown on minimal media