Evaluation of restorer fertility and heterosis rate in some of the rice genotypes

Rice is one of the most valuable nutrients for the food security in the world. Gowing population and changes in diet habits in the world, it is necessary to increase rice production. Using hybrid rice technology to increase grain yield can be an effective step in achieving food security (Shabestari & Mojtahedi, 2008), Therefore, it is important to examine the different characteristics and indices of parents and the resulting hybrids. Yield increase in hybrid rice is due to plant growth period and high harvest index. Increasing of number of grains and panicle weight increases grain yield in hybrid rice. Limitation of suitable cultivars to restorer, low number of effective lines and their genetic basis and cooking quality have always been the main problems of hybrid rice production in the Iran. The purpose of this experiment was identify of restorer lines in crosses with the sterile cytoplasmic line of Neda A to finally identify suitable parent lines and use them for hybrid breeding programs.

This experiment was conducted in two years )2018-2019 (in the Genetics and Agricultural Biotechnology Institute of Tabarestan. Plant materials included 26 restorer lines sent by the International Rice Research Inistitute (IRRI) as the male parent, and the Cytoplasmic male sterile (CMS) lines of Neda A as the female parent with Shirodi and Neda (control varietirs). The traits such as number of days to 50% flowering, number of days to maturity, plant height (cm), number of fertile tillers, length of spikelet (cm), number of floret in spikelet, number of spikelet per panicle, pollen grain sterility percentage, spikelet fertility percentage, grain length (mm), grain width (mm), weight of 1000-grains (gr), and grain yield (gram per square meter) were measured. Finally, crosses with the desired pollen grain fertility, spikelet fertility, and good yield were selected and introduced. The analysis of data was performed using SAS9.1 software. Cluster analysis of data was done with Ward method (using PAST software) and the dendrogram cuts were performed based on the formula proposed by (Darvish Kajouri, 2009).

Among the parental lines of fertility restorer, IR68078-15-2-2-2-2-2 R and R4842-2-3-2-1R lines had the highest number of tillers and the highest percentage of spikelet fertility were observed in the line MILYANG 46. The IRi347 line had a higher yield than all the restorer lines due to its high number of fertile spikelet and low percentage of pollen grains fertility. Cluster analysis of the genotypes placed them in five separate clusters. The mean heterosis of the hybrids for the yield trait as compared to the parents, the superior parent, and the control variety showed a variation from -94.54 to 57.46% for the parent, from -94.73 to 35.45% for superior parent, and from -2.94 to 42.52% for the control.

According to the result of the current research, the hybrids with optimal yield and high percentage of pollen as well as high spikelet fertility included the crosses of Neda A with IR68078-15-2-1-2-2-R, IR 65912-90-1-6-3-2-2R, IR36, MILYANG 54, and IR 56 hybrids which produced yields of 7112, 8708.3, 6340.3, 7253.3, and 6828.8 kg.m2 with standard heterosis values of 16.40, 42.52, 3.77, 18.74 and 8.49 respectively. Among the superior hybrids, NedaA/ MILIANG 54 hybrid had the highest milling and suitable amylose content, and NedaA/IR68078-15-2-1-2-2- R hybrid had a favorable aroma. These hybrids also exhibited good heterosis and were recognized as the best hybrids in terms of agronomic traits, which can be used for yield improvement. Since the lines studied are imported, it is necessary to make attempts to adapt them and also use them in crosses, which can lead to the production and release of promising new rice hybrids (Baloch Zehi et al., 2016).