Genetic improvement of resistance to blast and bacterial blight of the elite maintainer line Rongfeng B in hybrid rice (Oryza sativa L.) by using marker-assisted selection

Rice blast caused by the fungus Magnaporthe grisea and bacterial blight (BB) caused by Xanthomonas oryzae pv. Oryzae (Xoo) are two major rice diseases in the world. An elite, early maturing maintainer line of hybrid rice, Rongfeng B hybrid rice is susceptible to both blast and BB. For improving its diseases resistance, BL122 and CBB23 were used as the donors of blast resistance genes Pi1 and Pi2 and BB resistance gene Xa23, respectively. These resistant genes were introgressed into Rongfeng B by using a marker-assisted backcross breeding programs, and two improved lines D521 and D524 with Pi1, Pi2 and Xa23 were developed. The results indicated that both improved lines showed high resistance to leaf and neck blast and BB. The resistance frequencies for the rice blast and the length of lesions resulting from BB ranged from 96.7 to 100% and 0.77 to 1.18 cm, respectively. The two improved lines showed the desired variation in the majority of evaluated agronomic traits, including the number of grains per panicle, the grains weight, plant height, and seed setting rate. A new cytoplasmic male sterile line, Rongfeng 3A, with Pi1, Pi2, and Xa23, was successfully developed through successive backcross breeding.Keywords: Gene pyramiding, marker-assisted backcross breeding, rice blast, bacterial bligh

Bulk segregant analysis coupled with transcriptomics and metabolomics revealed key regulators of bacterial leaf blight resistance in rice

Abstract Background Bacterial leaf blight (BLB) is a highly destructive disease, causing significant yield losses in rice (Oryza sativa). Genetic variation is contemplated as the most effective measure for inducing resistance in plants. The mutant line T1247 derived from R3550 (BLB susceptible) was highly resistant to BLB. Therefore, by utilizing this valuable source, we employed bulk segregant analysis (BSA) and transcriptome profiling to identify the genetic basis of BLB resistance in T1247. Results The differential subtraction method in BSA identified a quantitative trait locus (QTL) on chromosome 11 spanning a 27-27.45 Mb region with 33 genes and 4 differentially expressed genes (DEGs). Four DEGs (P < 0.01) with three putative candidate genes, OsR498G1120557200, OsR498G1120555700, and OsR498G1120563600,0.01 in the QTL region were identified with specific regulation as a response to BLB inoculation. Moreover, transcriptome profiling identified 37 resistance analogs genes displaying differential regulation. Conclusions Our study provides a substantial addition to the available information regarding QTLs associated with BLB, and further functional verification of identified candidate genes can broaden the scope of understanding the BLB resistance mechanism in rice

Breeding and Application of Restorer Guanghui 1002 with Weak Photoperiod Sensitivity and Bacterial Blight Resistance in Hybrid Rice

It is of significance to develop and promote late-maturing rice varieties with weak sensitivity to photoperiod for bringing the potential of light and temperature resources into full play at the late growing stage, and enhancing the yield and the grain quality of rice in the late cropping season in South China. By using both traditional breeding and molecular marker-assisted selection to pyramid Xa7, the dominant and wide-spectrum resistant gene of bacterial blight, LP1(LH1)and LP2 (LH2), the complementary gene inducing photoperiod sensitivity, a late-maturing restorer line Guanghui 1002 (R1002) with bacterial blight resistance and the characteristic of weak sensitivity to photoperiod induced by gene interaction. And seven late-maturing high yielding hybrid rice varieties, such as Jifengyou 1002 and Taiyou 1002 derived from the restorer line R1002, were developed and approved for commercial production at national level or provincial level. Among them, Jifengyou 1002 not only had high and stable yield, but also had strong diseases and lodging resistance and wide adaptability. It was recognized by the Ministry of Agriculture and Rural Affairs as a Super Rice variety and the leading agricultural variety in Guangdong Province, and has been the weakly photoperiod-sensitive variety with the largest annual planting area for 5 consecutive years in South China. Taiyou 1002 had fine grain quality, and won the gold prize in the third national taste evaluation of high-quality rice varieties. It also has been widely grown in South China, and became a leading variety in Guangdong Province. Based on the characteristics of the R1002-derived hybrid rice varieties, the high-yield seed production techniques in Guangdong and Hainan were worked out, and a record of 4.59-4.97 t/hm2 of seed production was created for Jifengyou 1002 in Hainan. Strategies for breeding hybrid rice varieties with bacterial blight resistance and enhancing the efficiency of breeding restorer lines with photoperiod sensitivity and longer growth duration were discussed