Improving of Rice Blast Resistances in Japonica by Pyramiding Major R Genes.

Ning Xiao,Yuhong Li,Ling Yu,Xiaoxiang Zhang,Cunhong Pan,Zhengyuan Dai,Aihong Li,Yu Chen,Zhiping Wang,Guangqing Liu,Yunyu Wu,Chengzhi Liang

doi:10.3389/fpls.2016.01918

Abstract

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is a major constraint to rice production worldwide. In this study, we developed monogenic near-isogenic lines (NILs) NILPi9, NILPizt, and NILPi54 carrying genes Pi9, Pizt, and Pi54, respectively, by marker assisted backcross breeding using 07GY31 as the japonica genetic background with good agronomic traits. Polygene pyramid lines (PPLs) PPLPi9+Pi54 combining Pi9 with Pi54, and PPLPizt+Pi54 combining Pizt with Pi54 were then developed using corresponding NILs with genetic background recovery rates of more than 97%. Compared to 07GY31, the above NILs and PPLs exhibited significantly enhanced resistance frequencies (RFs) for both leaf and panicle blasts. RFs of both PPLs for leaf blast were somewhat higher than those of their own parental NILs, respectively, and PPLPizt+Pi54 exhibited higher RF for panicle blast than NILPizt and NILPi54 (P < 0.001), hinting an additive effect on the resistance. However, PPLPi9+Pi54 exhibited lower RF for panicle blast than NILPi9 (P < 0.001), failing to realize an additive effect. PPLPizt+Pi54 showed higher resistant level for panicle blast and better additive effects on the resistance than PPLPi9+Pi54. It was suggested that major R genes interacted with each other in a way more complex than additive effect in determining panicle blast resistance levels. Genotyping by sequencing analysis and extreme-phenotype genome-wide association study further confirmed the above results. Moreover, data showed that pyramiding multiple resistance genes did not affect the performance of basic agronomic traits. So the way to enhance levels of leaf and panicle blast resistances for rice breeding in this study is effective and may serve as a reference for breeders.Key Message: Resistant levels of rice blast is resulted from different combinations of major R genes, PPLPizt+Pi54 showed higher resistant level and better additive effects on the panicle blast resistance than PPLPi9+Pi54.

Highlights

Rice (Oryza sativa) is a staple food crop for more than 50% of the world’s population
For pathogen collection for the determination of both leaf and panicle blast resistances, M. oryzae isolates were obtained from diseased panicles by single-spore isolation
resistance frequencies (RFs) meaning proportions of plants showing resistant phenotype, were calculated according to the following formula: RF = R/(R + S) × 100%, where R is the total number of plants showing resistant phenotype, while S is the total number of plants showing sensitive phenotype

Summary

Introduction

Rice (Oryza sativa) is a staple food crop for more than 50% of the world’s population. Due to highly frequent variation in the M. oryzae population (Bonman, 1992), durable resistance of new rice varieties with only a major R gene could be lost quickly, especially when such a variety is grown in large areas (McDonald and Linde, 2002). To acquire a durable and broad-spectrum resistant variety, pyramiding multiple R genes into a current rice variety is an important and practicable breeding strategy on controlling blast disease (Hittalmani et al, 2000; Fukuoka et al, 2012). NILs, PPLs, and 07GY31 were subjected to the phenotyping of the following basic agronomic traits: growth period, 1000-grain weight, effective panicles per plant, grain number per panicle, seed setting rate, and yield.

Methods

Results

Conclusion