An efficient method for screening rice breeding lines against races of Magnaporthe oryzae

Authors: OLIVEIRA-GARCIA, ELY - Louisiana State University Agcenter; BUDOT, BERNARD ORENSE - Louisiana State University Agcenter; MANANGKIL, JENNIFER - Louisiana State University Agcenter; LANA, FELIPE DALA - Louisiana State University Agcenter; ANGIRA, BRIJESH - Louisiana State University Agcenter; FAMOSO, ADAM - Louisiana State University Agcenter; Jia, Yulin

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Blast disease of rice caused by the fungus Magnaporthe oryzae is one of the most lethal diseases of rice worldwide. Traditionally the 0-5 scale rating has reached limited success to evaluate disease reactions of breeding lines and rice varieties for breeding and genetic studies. In the present study, we developed a 0-6 scale for blast disease that allowed assignment of rice breeding lines and varieties into six resistance levels (highly resistant, resistant, moderate resistant, moderate susceptible, susceptible, and highly susceptible) by using 40 common rice varieties with known disease reactions under field conditions and tested them against four major blast races (IB1, IB17, IB49, and IE1-K) under greenhouse conditions. Disease reactions using 0-6 rating system verified field observations of rice varieties with blast resistance genes. Varieties carrying the Pi-ta gene were either highly resistant, resistant, or moderate resistant to IB17. The IE1-K race was able to break Pi-ta-mediate resistance of the rice varieties. The Piz gene conferred resistance to the IB17 and IE1-K races. The varieties M201, Cheniere, and Frontier were highly susceptible (score 6; 100% disease) to the race IE1-K. Moreover, varieties that were resistant or susceptible to all four blast races also showed similar levels of resistance/susceptibility to blast disease in the field. Taken together, our data proved that the 0-6 blast scale can efficiently determine the resistance levels of rice varieties against major blast races. This new method will assist rice breeding programs to incorporate durable resistance against major and emerging blast races.

Technical Abstract: Rice blast disease, caused by the ascomycete fungus Magnaporthe oryzae, is the most destructive disease of rice worldwide. The 0-5 scale for blast disease has been broadly used to evaluate resistance of rice breeding lines under controlled conditions. However, the 0-5 scale restricts quantitative classification of the varieties into intermediate resistant and susceptible categories. Here we develop a 0-6 scale for blast disease that allows proper assignment of rice breeding lines and varieties into six resistance levels (highly resistant, resistant, moderate resistant, moderate susceptible, susceptible, and highly susceptible). We evaluated approximately 40 common rice varieties against four major blast races (IB1, IB17, IB49, and IE1-K). Varieties carrying the Pi-ta gene were either highly resistant, resistant, or moderate resistant to IB17. The IE1-K race was able to break Pi-ta-mediate resistance of the rice varieties. The Piz gene conferred resistance to the IB17 and IE1-K races. The varieties M201, Cheniere, and Frontier were highly susceptible (score 6; 100% disease) to the race IE1-K. Moreover, varieties that were resistant or susceptible to all four blast races also showed similar levels of resistance/susceptibility to blast disease in the field. Taken together, our data proved that the 0-6 blast scale can efficiently determine the resistance levels of rice varieties against major blast races. This robust method will assist rice breeding programs to incorporate durable resistance against major and emerging blast races.