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Hybrid Rice (hybrid + rice)

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Life Sciences100%

Selected Abstracts

Pyramiding of Xa7 and Xa21 for the improvement of disease resistance to bacterial blight in hybrid rice

PLANT BREEDING, Issue 6 2006
J. Zhang
Abstract ,Minghui 63' is a restorer line widely used in hybrid rice production in China for the last two decades. This line and its derived hybrids, including ,Shanyou 63', are susceptible to bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo). To improve the bacterial blight resistance of hybrid rice, two resistance genes Xa21 and Xa7, have been introgressed into ,Minghui 63' by marker-assisted selection and conventional backcrossing, respectively. The single resistance gene-introgressed lines, Minghui 63 (Xa21) and Minghui 63 (Xa7) had higher levels of resistance to bacterial blight than their derived hybrids, Shanyou 63 (Xa21) or Shanyou 63 (Xa7). Both Xa21 and Xa7 showed incomplete dominance in the heterozygous background of rice hybrids by infection with GX325 and KS-1-21. The improved restorer lines, with the homozygous genotypes, Xa21Xa21 or Xa7Xa7, were more resistant than their hybrids with the heterozygous genotypes Xa21xa21 or Xa7xa7. To further enhance the bacterial blight resistance of ,Minghui 63' and its hybrids, Xa21 and Xa7 were pyramided into the same background using molecular marker-aided selection. The restorer lines developed with the resistance genes Xa21 and Xa7, and their derived hybrids were evaluated for resistance after inoculation with 10 isolates of pathogens from China, Japan and the Philippines, and showed a higher level of resistance to BB than the restorer lines and derived hybrids having only one of the resistance genes. The pyramided double resistance lines and their derived hybrids have the same high level of resistance to BB. These results clearly indicate that pyramiding of dominant genes is a useful approach for improving BB resistance in hybrid rice. [source]

Genetic diversity among parental lines of Indica hybrid rice (Oryza sativa L.) in China based on coefficient of parentage

PLANT BREEDING, Issue 6 2006
S. Wang
Abstract Genetic diversity constitutes the raw material for plant improvement, and provides protection against genetic vulnerability to biotic and abiotic stresses. Diversity of parental lines of indica hybrid rice in China is not well-characterized. The major objective of this study was to quantify genetic diversity of Chinese parental lines of hybrid rice via coefficient of parentage (COP). All 100 parental lines of hybrid rice widely used in hybrid breeding and commercial production during 1976,2003 were studied by COP analysis. The mean COP for the 100 parental lines was low (0.056), indicating a potentially high degree of diversity in Chinese hybrid rice breeding. Forty-nine percent of all pairs of parental lines were completely unrelated by pedigree data. The low mean COP for the parental lines was attributed to a continual incorporation of exotic germplasm (wild rice, japonica and javanica etc.) into the genetic base over time, to the introduction of foreign germplasm from the Philippines (International Rice Research Institute), Korea, the United States, Thailand, and Guyana as breeding stock. The mean COP from 1976 to 1990 was twice as much as that from 1990 to 2003. Cluster analysis was an effective method to discriminate diversity, ten clusters were identified, and maintainer lines, restorer lines and other parental lines with special genetic background were clearly grouped. In addition, restorer lines were further divided into 11 sub-clusters, which basically was in agreement with hybrid rice breeding. Among ten provinces, Hunan, Sichuan and Fujian were outstanding for breeding 54 of 100 parental lines in hybrid rice production, and the genetic diversity of parental lines in Fujian, Sichuan,Guangxi, Hunan and Jiangsu were all narrower than that in Hubei, Guangdong, Zhejiang and Jiangxi. The result of coefficient of parentage analysis for 100 parental lines may promote the management of parental diversity and hybrid rice breeding in China. [source]

QTL analysis of cooked rice grain elongation, volume expansion, and water absorption using a recombinant inbred population

PLANT BREEDING, Issue 2 2005
X. J. Ge
Abstract The traits of elongation, volume expansion, and water absorption are very important in determining the quality of cooked rice grains. In this study, quantitative trait loci (QTL) analysis of these traits was performed using a recombinant inbred population derived from a cross between two indica cultivars, ,Zhenshan 97' and ,Minghui 63,' which are the parents of the most widely grown hybrid rice in China. Using a linkage map based on 221 molecular marker loci covering a total of 1796 cM, a total of 33 QTLs were identified for the nine traits tested. QTLs were detected on chromosomes 1,3, 5,9, and 11, respectively. The QTLs identified included three for cooked rice grain length elongation (chromosomes 2, 6, and 11), six for width expansion (chromosomes 1- 3, 6, 9, and 11) and two for water absorption (chromosomes 2 and 6). Interestingly, a single QTL located near the wx gene on chromosome 6 seemed to influence all the traits tested for the cooked rice quality. [source]

Transgenic rice hybrids that carry the Rf-1 gene at multiple loci show improved fertility at low temperature

PLANT CELL & ENVIRONMENT, Issue 4 2005
TOSHIYUKI KOMORI
ABSTRACT By using a genomic fragment that carries the rice (Oryza sativa L.) fertility restorer gene, Rf-1, rice restorer lines harbouring multiple Rf-1 genes on different chromosomes were developed by genetic engineering and crossing. Hybrid lines that were obtained by crossing the restorer lines having two and three Rf-1 genes with a cytoplasmic male sterile (CMS) line had nearly 75 and 87.5% pollen fertility rates under a normal condition, respectively, whereas a conventional hybrid line showed a 50% pollen fertility rate. Furthermore, the seed set percentage under low temperature conditions was much higher in the hybrid lines with multiple Rf-1 genes than the conventional hybrid line. These results indicate that multiplication of the Rf-1 gene conferred cold tolerance at the booting stage to hybrid rice through increasing the potentially fertile pollen grains. This strategy to improve fertility at low temperature of hybrids could be applied to any grain crops that are developed based on CMS and its gametophytic restorer gene, let alone rice. [source]