Two-line hybrid rice breeding manual , Two-line hybrid rice breeding manual , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

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Two-line hybrid rice breeding manual.

The genetic basis of heterosis was studied through mid-parent, standard variety and better parent for 11 quantitative traits in 17 parental lines and their 10 selected hybrids in rice (Oryza sativa L.). The characters were plant height, days to flag leaf initiation, days to first panicle initiation, days to 100% flowering, panicle length, flag leaf length, days to maturity, number of fertile spikelet/panicle, number of effective tillers/hill, grain yield/10-hill, and 1000-grain weight. In general the hybrids performed significantly better than the respective parents. Significant heterosis was observed for most of the studied characters. Among the 10 hybrids, four hybrids viz., 17Ax45R, 25Ax37R, 27Ax39R, 31Ax47R, and 35Ax47R showed highest heterosis in 10-hill grain yield/10-hill. Inbreeding depression of F2 progeny was also studied for 11 characters of 10 hybrids. Both positive and negative inbreeding depression were found in many crosses for the studied characters, but none was found significant. Selection of good parents was found to be the most important for developing high yielding hybrid rice varieties.

Genetic basis of heterosis and inbreeding depression in rice (Oryza sativa L.).

Natural variation in seed dormancy is controlled by multiple genes mapped as quantitative trait loci in major crop or model plants. This research aimed to clone and characterize the Seed Dormancy1-2 (qSD1-2) locus associated with endosperm-imposed dormancy and plant height in rice (Oryza sativa). qSD1-2 was delimited to a 20-kb region, which contains OsGA20ox2 and had an additive effect on germination. Naturally occurring or induced loss-of-function mutations of the gibberellin (GA) synthesis gene enhanced seed dormancy and also reduced plant height. Expression of this gene in seeds (including endospermic cells) during early development increased GA accumulation to promote tissue morphogenesis and maturation programs. The mutant allele prevalent in semidwarf cultivars reduced the seed GA content by up to 2-fold at the early stage, which decelerated tissue morphogenesis including endosperm cell differentiation, delayed abscisic acid accumulation by a shift in the temporal distribution pattern, and postponed dehydration, physiological maturity, and germinability development. As the endosperm of developing seeds dominates the moisture equilibrium and desiccation status of the embryo in cereal crops, qSD1-2 is proposed to control primary dormancy by a GA-regulated dehydration mechanism. Allelic distribution of OsGA20ox2, the rice Green Revolution gene, was associated with the indica and japonica subspeciation. However, this research provided no evidence that the primitive indica- and common japonica-specific alleles at the presumably domestication-related locus functionally differentiate in plant height and seed dormancy. Thus, the evolutionary mechanism of this agriculturally important gene remains open for discussion.

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Map-Based Cloning of Seed Dormancy1-2 Identified a Gibberellin Synthesis Gene Regulating the Development of Endosperm-Imposed Dormancy in Rice

Bacterial blight (BB) of rice caused by X oryzae pv oryzae is a major production constraint in commercial hybrid rice production in the Philippines because most of the parental lines used in hybrid production do not carry resistance genes against the pathogen In this study, three bacterial blight resistance genes, Xa4, Xa7 and Xa21, were introgressed to a temperature-sensitive genetic male sterile (TGMS1) line A three-way cross of AR32-19-3-3/TGMS1//IRBB4/7 (PR36944) was made to produce 1,364 F2 plants carrying various combinations of Xa4, Xa7 and Xa21 Individual plants were characterized for reaction to bacterial blight PXO61 (race 1), PXO86 (race 2), PXO99 (race 6) and pollen sterility Of 144 F2 plants demonstrating resistance against PXO61, PXO86 and PXO99, 22 exhibited highly resistant phenotypes with mean lesion lengths ranging from 037–297 cm Analysis of disease reaction identified 20 potential TGMS F2 plants containing Xa4, Xa7 and Xa21 while 78 plants with Xa4 + Xa7 Phenotypic and polymerase chain reaction (PCR) analyses confirmed PR36944-450, PR36944-473 and PR36944-700 as homozygous for Xa7 and Xa21 and highly resistant to all three Xoo races Fertility of PR36944-450 and PR36944-700 was restored at permissive temperature in a growth chamber BB-resistant TGMS lines should facilitate breeding two-line hybrids in the tropics

Introgression of Xa4 , Xa7 and Xa21 for resistance to bacterial blight in thermosensitive genetic male sterile rice ( Oryza sativa L.) for the development of two-line hybrids

The Wild Abortive (WA) system is the major cytoplasmic male sterility (CMS) source for hybrid rice production in indica rice and its fertility restoration is reported to be controlled by two major loci viz. Rf3 on chromosome 1 and Rf4 on chromosome 10. With the availability of the rice genome sequence, an attempt was made to fine map, develop candidate gene based markers for Rf3 and Rf4 and validate the developed marker system in a set of known restorer lines. Using polymorphic markers developed from microsatellite markers and candidate gene based markers from Rf3 and Rf4 loci, local linkage maps were constructed in two mapping populations of ~1,500 F2 progeny from KRH2 (IR58025A/KMR3R) and DRRH2 (IR68897A/DR714-1-2R) hybrids. QTLs and their interactions for fertility restoration in Rf3 and Rf4 loci were identified. The identified QTL in both mapping populations together explained 66–72 % of the phenotypic variance of the trait suggesting their utility in developing a marker system for identification of fertility restorers for WA-CMS. Sequence comparison of the two candidate genes from the Rf3 and Rf4 regions in male sterile (A) and restorer (R) lines showed 2–3 bp indels and a few substitutions in the Rf3 region and indels of 327 and 106 bp in the Rf4 region respectively. The marker system identified in the present study was validated in 212 restorers and 34 maintainers along with earlier reported markers for fertility restoration of WA-CMS. Together DRCG-RF4-14 and DRCG-RF4-8 for the Rf4 locus and DRRM-RF3-5/DRRM-RF3-10 for the Rf3 locus showed a maximum efficiency of 92 % for identification of restorers.

https://krishi.icar.gov.in/jspui/bitstream/123456789/65294/1/balajietal2012.1007_s10681-012-0737-6.pdf

Fine mapping of Rf3 and Rf4 fertility restorer loci of WA-CMS of rice Oryza sativa L and validation of the developed marker system for identification of restorer lines

M. T. Lopez

Papers

Hybrid rice breeding manual.

Nucleus and Breeder Seed Production of Thermosensitive Genic Male Sterile Lines