Seed shattering is an important agronomic trait in rice domestication. In this study, using a near-isogenic line (NIL-hs1) from Oryza barthii, we found a hybrid seed shattering phenomenon between the NIL-hs1 and its recurrent parent, a japonica variety Yundao 1. The heterozygotes at hybrid shattering 1 (HS1) exhibited the shattering phenotype, whereas the homozygotes from both parents conferred the non-shattering. The causal HS1 gene for hybrid shattering was located in the region between SSR marker RM17604 and RM8220 on chromosome 4. Sequence verification indicated that HS1 was identical to SH4, and HS1 controlled the hybrid shattering due to harboring the ancestral haplotype, the G allele at G237T site and C allele at C760T site from each parent. Comparative analysis at SH4 showed that all the accessions containing ancestral haplotype, including 78 wild relatives of rice and 8 African cultivated rice, had the shattering phenotype, whereas all the accessions with either of the homozygous domestic haplotypes at one of the two sites, including 17 wild relatives of rice, 111 African cultivated rice and 65 Asian cultivated rice, showed the non-shattering phenotype. Dominant complementation of the G allele at G237T site and the C allele at C760T site in HS1 led to a hybrid shattering phenotype. These results help to shed light on the nature of seed shattering in rice during domestication and improve the moderate shattering varieties adapted to mechanized harvest.
Abstract. This experiment was carried out at the Farm of Rice Research and Training Center, Sakha, Kafrelsheikh, Egypt during three rice grown seasons from 2014-2016. Three cytoplasmic male sterile lines, two wild abortive type (WA); IR69625A, IR70368A and one (K-type) K17A as females were tested with seven rice genotypes Giza 178, Giza 179, Giza 181,Giza 182, Sakha 105, GZ 6296-12-1-2-1-1 and HR195R as testers using line x tester model of hybridization. The parental lines and their resulting (21F 1 crosses) were evaluated in Randomized Complete Block Design (RCBD) experiment having three replications during 2015 and 2016 growing seasons and surrounded by susceptible rice varieties i.e. Giza 171, Giza 177 and Giza 159 as natural infection to brown spot (Helminthosporium oryzae). Three brown spot acceptability traits; disease severity (%), infected leaves (%) and infected grains/panicle (%) were observed during this investigation. The combined data was calculated over both seasons to test the interaction of the different genetic components. According to the results, the male parents Giza178, Giza179, HR195, Giza 181 and Giza 182 could be utilized either for producing new hybrid combinations or for developing new parental lines in brown spot resistance program. The female line K17A was found to have a good combiner to brown spot resistance. Evaluation of hybrids for heterosis breeding based on mean performance, better-parent (BP %) and mid-parent heterosis (MP %) indicated that, out of 21F 1 hybrid rice combinations, one hybrid K17A x Giza182 found significantly desirable values for most brown spot traits and can be utilized as commercial hybrids resistant to brown spot disease.
Summary Line × Tester experiment was carried out at the Experimental Farm of Rice Research and Training Center (RRTC), Sakha, Kafrelsheikh, Egypt during three growing seasons to evaluate the performance of 21 F1 hybrids along with their parents. Three cytoplasmic male sterile lines, two wild abortive (Wild Abortive); IR69625A, IR70368A and one (Kalinga) K17A as female were tested with seven cultivars/lines as testers. The analysis of variance detected that, highly significant variations among genotypes (parental lines with their crosses) for all traits in both seasons and in their combined analysis. Two hybrid combinations; IR69625A×Giza178 and IR69625A×Giza179 were recorded the best values for grain yield under both seasons and their combined. General combining ability (GCA) and specific combining ability (SCA) effects of genotypes for the studied traits were estimated. The results indicated that, K17A (female) and Giza 179 (male) were the best combiner for early heading date and could be useful to breed early maturing rice cultivars. The CMS line IR69625A and Giza178, Giza179 gave highly significant and positive GCA value and so appeared to be good parental lines combiner in hybrid combinations for high grain yield/plant. The positive values of GCA mean increased for grain yield/plant, which could be useful in breeding programs for high yield potential rice cultivars. The hybrid combination IR69625A×Giza179 showed highly significant and positive SCA estimates under both seasons and their combined. In conclusion, it is clear that this hybrid seemed promising hybrid for earliness and high grain yield under Egyptian conditions.
Rice panicle architecture is directly associated with grain yield and is also the key target in high-yield rice breeding program. In this study, three BC6F2 segregation populations derived from the crosses between two accessions of Oryza meridionalis and a O. sativa spp. japonica cultivar Dianjingyou 1, were employed to map QTL for panicle architecture. Three QTL, EP4.2, DEP7 and DEP8 were identified and validated using substitution mapping strategy on chromosome 4, 9 and 8, respectively. The three QTL showed pleiotropic phenotype on panicle length (PL), grain number per panicle (GNPP), number of primary branches (NPB), number of secondary branches (NSB), and grain width. DEP7 and DEP8 showed yield-enhancing potential by increasing GNPP, NPB and NSB, while EP4.2 exhibited wide grain, short stalk and panicle which can improve plant and panicle architecture, too. Moreover, epistatic interaction for PL was detected between EP4.2 and DEP7, and epistatic analysis between DEP7 and DEP8 for GNPP and NPB also revealed significant two QTL interactions. The result would help us understand the molecular basis of panicle architecture and lay the foundation for using these three QTL in rice breeding.
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