ARS | Publication request: A Benefit of High Temperature: Increased Effectiveness of a Rice Bacterial Blight Disease Resistance Gene

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 19, 2009
Publication Date: January 1, 2010
Citation: Webb, K.M., Ona, I., Bai, J., Garrett, K.A., Mew, T., Vera Cruz, C.M., Leach, J.E. 2010. A Benefit of High Temperature: Increased Effectiveness of a Rice Bacterial Blight Disease Resistance Gene. New Phytologist. 185: 568-576

Interpretive Summary: A Benefit of High Temperature: Increased Effectiveness of a Rice Bacterial Blight Disease Resistance Gene K. M. Webb1, 2, 4, I. Oña2, J. Bai1,5, K. A. Garrett1, T. Mew2, C. M. Vera Cruz2, and J. E. Leach3 1Department of Plant Pathology, Kansas State University, 4024 Throckmorton Plant Sciences, Manhattan, KS 66506; 2Plant Breeding, Genetics and Biotechnology, The International Rice Research Institute, Los Baños, Philippines; and 3Department of Bioagricultural Sciences and Pest Management, Plant Sciences, Colorado State University, Ft Collins, CO 80537-1177. 4Current address: USDA-ARS Sugarbeet Research Unit, Ft. Collins, CO 80537, 5 Current address: Deptartment of Diagnostic Medicine/Pathobiology, Kansas State University Summary • Continuous planting of crops containing single disease resistance (R) genes imposes a strong selection for virulence in pathogen populations, often rendering the R gene ineffective. High temperatures promote plant disease and may reduce effectiveness of R genes. In many countries, two rice crops are produced per year, with more disease occurring in seasons with higher temperatures. Here, we monitor performance of one bacterial blight (BB) resistance gene Xa7 in field studies, and address the influence of high temperature on its effectiveness. • Disease severity was monitored in field plots over 11 yr (22 cropping seasons). The virulence of Xanthomonas oryzae pv. oryzae (Xoo) field populations to Xa7 was assessed. Performance of several R genes (Xa3, Xa4, xa5, Xa7 and Xa10) was determined at high and low temperature regimes. • We found that, while exposure to Xa7 over 11 yr is selecting for virulence in the Xoo population, the resistance conferred by Xa7 is still effective. Xa7 restricts disease more effectively at high than at low temperatures. In contrast, other R genes are less effective at high temperatures. • We propose that greater effectiveness of Xa7 at high temperatures may contribute to the durability of Xa7.

Technical Abstract: High temperatures promote development of many plant diseases and reduce effectiveness of disease resistance (R) genes. In many rice producing countries, two crops of rice are produced, with more disease occurring in the season with higher day/night temperatures. While studying the factors that influence durability of rice bacterial blight R genes, we discovered that one gene, Xa7, more effectively restricts disease caused by Xanthomonas oryzae pv. oryzae (Xoo) at high day/night temperature regimes (31oC /29oC and 35oC /31oC) than at low temperature regimes (29oC /21oC). In contrast, other rice R genes (Xa3, Xa4, xa5, and Xa10) are less effective at high temperatures, and allow more disease development than at low temperatures. During a complementary 11 year field study (22 cropping seasons) in the Philippines, we measured an increase in the virulence of the Xoo population in the field plots. However, despite the increased potential for disease, a rice cultivar with the Xa7 R gene effectively reduced disease relative to a near-isogenic rice line without Xa7. We propose that the greater effectiveness of Xa7 during higher temperatures positively impacts the durability of Xa7 in the field.