Abstract
BackgroundRice blast caused by Magnaporthe oryzae is one of the most widespread biotic constraints that threaten rice production. Using major resistance genes for rice blast resistance improvement is considered to be an efficient and technically feasible approach to achieve optimal grain yield.ResultsWe report here the introgression of the broad-spectrum blast resistance gene Pi2 into the genetic background of an elite PTGMS line, Feng39S, for enhancing it and its derived hybrid blast resistance through marker-assisted backcrossing (MABC) coupled with genomics-based background selection. Two PTGMS lines, designated as DB16206–34 and DB16206–38, stacking homozygous Pi2 were selected, and their genetic background had recurrent parent genome recovery of 99.67% detected by the SNP array RICE6K. DB16206–34 and DB16206–38 had high resistance frequency, with an average of 94.7%, when infected with 57 blast isolates over 2 years, and the resistance frequency of their derived hybrids ranged from 68.2% to 95.5% under inoculation of 22 blast isolates. The evaluation of results under natural blast epidemic field conditions showed that the selected PTGMS lines and their derived hybrids were resistant against leaf and neck blast. The characterizations of the critical temperature point of fertility-sterility alternation of the selected PTGMS lines, yield, main agronomic traits, and rice quality of the selected PTGMS lines and their hybrids were identical to those of the recurrent parent and its hybrids. DB16206–34/9311 or DB16206–38/9311 can be used as a blast-resistant version to replace the popular hybrid Fengliangyou 4. Likewise, DB16206–34/FXH No.1 or DB16206–38/FXH No.1 can also be used as a blast-resistant version to replace another popular hybrid Fengliangyou Xiang 1.ConclusionsOur evaluation is the first successful case to apply MABC with genomics-based background selection to improve the blast resistance of PTGMS lines for two-line hybrid rice breeding.
Highlights
Rice blast caused by Magnaporthe oryzae is one of the most widespread biotic constraints that threaten rice production
Our results provide a successful breeding example through marker-assisted backcrossing (MABC) to carry out the precise foreground and background selection and to recover rapidly the recurrent parent genetic background to enhance resistance to blast for two-line hybrid rice
Background selection based on 39 Simple sequence repeat (SSR) markers of polymorphism between the donor (Hua1201S) and recurrent parent (Feng39S) was carried out for 155 Pi2-positive plants
Summary
Rice blast caused by Magnaporthe oryzae is one of the most widespread biotic constraints that threaten rice production. Application of MAS has significantly improved the rice breeding process; at least two disadvantages have been observed: 1) introgression of target genes had always accompanied linked chromosomal segments, conferring undesired traits, known as linkage drag; 2) favorable genes sometimes exhibited incomplete function due to differences in genetic backgrounds, which led to difficulties for effective and reliable trait selection. High-density markers, such as SSRs and SNPs, were subsequently applied to whole-genome background selection for improving blast resistance by developing a set of NILs with seven major genes in a Basmati variety (Khanna et al 2015). For improving resistance to rice blast, MAS coupled with whole-genome background selection will be a promising approach for targeted improvement of blast resistance without significant changes in other agronomic traits. It offers a better way to develop a panel of NILs to accurately evaluate the effects of blast resistant genes in the same genetic background
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