Characterization and Utilization of Rice Defense Associated with Partial Resistance to Bacterial Panicle Blight: An Emerging Rice Disease Problem in the Southeastern United States

Abstract

Rice is a staple food for much of the world’s growing population. Rice production is limited by a number of abiotic and biotic factors. These factors have direct effects on food security because less food is available to growing population. Bacterial panicle blight (BPB), caused by the bacterium Burkholderia glumae, is an emerging disease that causes grain rot, panicle discoloration, and unfilled grains in rice. Up to 70% of yield reduction has been reported in severely infected rice fields. No completely resistant rice cultivars have been identified, however, a medium-grain cultivar, Jupiter, showed a high level of partial resistance to this disease. A research was conducted to characterize and utilize the rice defense system associated with partial resistance to BPB. Various chemical compounds and biological agents were used to enhance the rice defense system and in vitro control of B. glumae, respectively. Microarray studies done by Dr. Nandakuar and Dr. Rush, showed that several defense related genes and transcriptional regulators were highly up-regulated in Jupiter and slightly up-regulated in Trenasse, a susceptible long-grained cultivar, when challenged with B. glumae. Induction of the expression of those genes in Jupiter and Trenasse were verified by reverse-transcription PCR. Genes encoding an NAC-like transcription factor (NTF) and a grain filling protein, prolamin, was highly induced in Jupiter but not in Trenasse under different treatments of B. glumae and its mutant derivatives. These genes may be involved in the partial resistance to BPB, and could be used as a genetic marker and breeding tools to develop BPB resistant rice cultivars. In an attempt to develop control measures for BPB in rice, several chemicals, including jasmonic acid, salicylic acid, ascorbic acid, 2, 6-dichloroisonicotinic acid, and ethylene, known to induce plant defense systems against various plant pathogens were tested for their ability to enhance rice defense systems and reduce BPB development. Results showed that pretreatment of rice with ascorbic acid significantly suppressed BPB development while only minimally reducing yield. In the meantime, several biological agents isolated from rice leaves showed antagonistic effect on B. glumae, and Rhizoctonia solani, the causal agent of sheath blight in rice.