First report of rice bacterial leaf blight disease caused by Pantoea ananatis in the United States

Authors: LUNA, EMILY - Colorado State University; LANG, JILIAN - Colorado State University; McClung, Anna; WAMISHE, YESHI - University Of Arkansas; Jia, Yulin; LEACH, JAN - Colorado State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2023
Publication Date: 1/6/2023
Citation: Luna, E., Lang, J., McClung, A.M., Wamishe, Y., Jia, Y., Leach, J. 2023. First report of rice bacterial leaf blight disease caused by Pantoea ananatis in the United States. Plant Disease. https://doi.org/10.1094/PDIS-08-22-2014-PDN.
DOI: https://doi.org/10.1094/PDIS-08-22-2014-PDN

Interpretive Summary: Detection of diseases that are uncommon to the USA rice producing area is important for sustaining the rice industry and production of this globally important cereal grain. Here we report the first identification of bacteria leaf blight disease in rice plants of global rice cultivars grown under field conditions in Arkansas. Subsequent studies determined that this was caused by Pantoea ananatis which is a bacterial organism commonly found in nature, but which has only rarely been associated with disease symptoms in rice. In addition to the observed leaf symptoms, the disease caused reduced grain production in rice plants that were very susceptible. Symptomatic leaves were cultured under laboratory conditions to isolate the causal organism which yielded uniform, yellow-colored bacterial colonies. DNA analysis of the bacterium from the cultures and the leaves was performed using primers that are specific to the gyrB gene region and this was used to verify that the organism was P. ananatis. To determine pathogenicity, two to three seedling leaves of a rice cultivar grown in a quarantine greenhouse were inoculated with the bacterium purified from the symptomatic rice plants. After 7 days, yellow bacterial cultures were recovered from the inoculated leaves which were confirmed to be P. ananatis by using DNA specific primers. Based on colony morphology, repeated pathogenicity tests, and DNA analysis, the causal bacterium for the leaf blight-like symptoms was determined to be P. ananatis. Knowledge that P. ananatis causes bacterial leaf blight symptoms in susceptible varieties of rice grown under environmental condition found in the southern USA is important to develop effective disease management strategies.

Technical Abstract: In August, 2021, bacterial leaf blight-like symptoms were observed on rice plants (Oryza sativa) in research field plots of global rice germplasm grown in Arkansas. The disease caused leaf streaking symptoms, panicle sterility and reduced yield in highly susceptible rice germplasm. The organism isolated from symptomatic leaves formed uniform, yellow-colored colonies on nutrient agar indicating it was a bacterium. PCR-based diagnostics were used to screen for the presence of common rice bacterial pathogens. DNA was isolated directly from extracts of symptomatic field tissue and from the isolated bacterial colonies. Primers specific for Xanthomonas oryzae pvs. oryzae and oryzicola, Burkholderia glumae, and Pseudomonas fuscovaginae did not amplify indicating these were not the causal agents. Sequencing of 16S rRNA gene amplicons suggested the bacterium to be in the genus Pantoea. Amplification with primers specific to the gyrB gene region of P. ananatis, amplicon sequencing, and BLAST analysis confirmed that the bacterium was P. ananatis. Finally, to confirm pathogenicity, leaves of 7-day old seedlings of the cultivar Kitaake were inoculated with a bacterial suspension isolated from the infected field tissue using a scissor-clip inoculation technique and were compared with control seedling leaves inoculated with sterile water. Lesions similar to those observed in the field grown rice were detected on the inoculated leaves 7-days post-inoculation whereas control seedlings did not show lesions. Bacteria recovered from the lesions of the artificially inoculated seedlings were determined to be P. ananatis based on colony morphology, amplification of 16s rRNA, and gyrB sequencing data. Thus, we conclude that P. ananatis is the causal pathogen for leaf blight-like symptoms observed in global rice cultivars grown in Arkansas.