The technology of hybrid rice utilizing heterosis is an essential requirement for achieving food security. The current study was aimed at assessing the genetic parameters and the gene actions of 15 yield-component traits associated with heterosis, in 9 new parental lines of hybrid rice and their generated hybrids. Five cytoplasmic male sterile (CMS) lines were crossed with four restorer (R) lines using twenty generated line × tester designation hybrid combinations. The results revealed that all the traits were controlled by additive and non-additive gene actions. However, the additive variance was the main component of the total genotypic variance. Assessment of the general combining ability (GCA) detected the best combiners among the genotypes. The hybrid combinations that expressed the highest-positive specific combining ability (SCA) for grain-yield were detected. The correlation between the GCA and SCA was evaluated. The hybrid crosses with high-positive heterosis, due to having a better parent for grain yield, were detected. The principal component analysis (PCA) recorded the first four principal axis displayed Eigenvalues >1 and existing variation cumulative of 83.92% in the genotypes for yield component characteristics. Three-dimensional plots corresponding to the studied traits illustrated that the genotypes Guang8A × Giza181, Quan-9311A × Giza179, II-32A × Giza181, and II-32A × Giza179 are classified as possessing superior grain yield.
Drought is the most challenging abiotic stress for rice production in the world. Thus, developing new rice genotype tolerance to water scarcity is one of the best strategies to achieve and maximize high yield potential with water savings. The study aims to characterize 16 rice genotypes for grain and agronomic parameters under normal and drought stress conditions, and genetic differentiation, by determining specific DNA markers related to drought tolerance using Simple Sequence Repeats (SSR) markers and grouping cultivars, establishing their genetic relationship for different traits. The experiment was conducted under irrigated (normal) and water stress conditions. Mean squares due to genotype × environment interactions were highly significant for major traits. For the number of panicles/plants, the genotypes Giza179, IET1444, Hybrid1, and Hybrid2 showed the maximum mean values. The required sterility percentage values were produced by genotypes IET1444, Giza178, Hybrid2, and Giza179, while, Sakha101, Giza179, Hybrid1, and Hybrid2 achieved the highest values of grain yield/plant. The genotypes Giza178, Giza179, Hybrid1, and Hybrid2, produced maximum values for water use efficiency. The effective number of alleles per locus ranged from 1.20 alleles to 3.0 alleles with an average of 1.28 alleles, and the He values for all SSR markers used varied from 0.94 to 1.00 with an average of 0.98. The polymorphic information content (PIC) values for the SSR were varied from 0.83 to 0.99, with an average of 0.95 along with a highly significant correlation between PIC values and the number of amplified alleles detected per locus. The highest similarity coefficient between Giza181 and Giza182 (Indica type) was observed and are susceptible to drought stress. High similarity percentage between the genotypes (japonica type; Sakha104 with Sakha102 and Sakha106 (0.45), Sakha101 with Sakha102 and Sakha106 (0.40), Sakha105 with Hybrid1 (0.40), Hybrid1 with Giza178 (0.40) and GZ1368-S-5-4 with Giza181 (0.40)) was also observed, which are also susceptible to drought stress. All genotypes are grouped into two major clusters in the dendrogram at 66% similarity based on Jaccard’s similarity index. The first cluster (A) was divided into two minor groups A1 and A2, in which A1 had two groups A1-1 and A1-2, containing drought-tolerant genotypes like IET1444, GZ1386-S-5-4 and Hybrid1. On the other hand, the A1-2 cluster divided into A1-2-1 containing Hybrid2 genotype and A1-2-2 containing Giza179 and Giza178 at coefficient 0.91, showing moderate tolerance to drought stress. The genotypes GZ1368-S-5-4, IET1444, Giza 178, and Giza179, could be included as appropriate materials for developing a drought-tolerant variety breeding program. Genetic diversity to grow new rice cultivars that combine drought tolerance with high grain yields is essential to maintaining food security.
Thirteen rice genotypes were grown in the two successive rice seasons 2017 and 2018 to assess the presence of variability for desired traits and estimate genetic parameters and correlations for traits under normal and heat stress conditions. Analysis of variance revealed significant differences due to environments, genotypes and their interaction for all studied characteristics in both seasons. The estimates of genotypic (GCV) and phenotypic (PCV) coefficient of variation were highly significant for all studied traits and generally, the PCV values were higher than GCV values, in both seasons. Leaf rolling and sterility percentage increased under heat stress, while days to heading, plant height, number of tillers and number of panicles / plant, 100-grainweight and grain yield/plant decreased under heat stress in comparison to normal condition. As mean performance Giza 179, Giza 178 and Sakha 101 surpassed other genotypes in grain yield and its important attributes, while WAB56-50/Sakha101-1, WAB56-50/Sakha101-2 and IR65907-206-7-8/Gyehwa71 gave the lowest grain yield in both seasons. Giza178 and WAB56-50/Sakha101-1 recorded the lowest values of geometric mean productivity, stress susceptibility index and yield index which refer to those genotypes highly tolerance to heat stress, while Giza 177 and Sakha 101 gave the highest values to be the most heat susceptible genotypes under study. Highly positive and significant phenotypic correlations were observed between yield index and leaf rolling, sterility percentage, geometric mean productivity and stress susceptibility index, otherwise number of tillers/plant, number of panicles/panicle and panicle weight, as yield attributes had highly significant negative correlation with the yield index. From the results we can conclude that, the genotypes can be scored as heat tolerant, based on days to heading, leaf rolling, tillering productivity and spikelets sterility percentage.
Drought is one of the major limitations to rice productivity worldwide. The present study compared variation in seventeen rice genotypes of Egyptian origin for morpho-physiological traits to identify the best genotypes with combination of adaptive traits under water-limited condition (DS). The DS reduced days to heading (DTH), plant height (PH), flag leaf angle (FLA), flag leaf area (FLAR), chlorophyll content (CHC), relative water content (RWC), grain yield (GY), and its components. Among genotypes, Hybrid 2 expressed the highest GY, panicle length (PL), number of tillers (NT), panicles per plant (NPP), and harvest index (HI) with maximum spikelet sterility (SS) under non-stress condition (NS), while the same genotype expressed ≈ 41% yield reduction under DS. The genotype Giza 179 had earlier DTH, higher and stable GY, FLAR, and yield component traits such as NPP, PW, and HI across the water regimes with least yield reduction (30.5%) under DS. The GY and FLAR, RWC, PL, NT, NPP, PW, and HI were positively correlated under DS. The cluster analysis showed a similarity index of 25% among genotypes. The high yielding genotypes Giza 179, IET 1444, and IRAT 170 had also increased yield components (PL, NT, NPP, PW, TGW and HI) under DS that were attributed to highest FLAR, RWC, and PH, while having reduced LR, FLA, TR, and SS; therefore, these genotypes were categorized as drought-tolerant. The Hybrid 2 and Giza 179 genotypes can perform well under NS; however, the cultivation of Giza 179, Sakha 107, IET 1444, and IRAT 170 would give an advantage in DS-prone areas, hence, these can be used as a donor parental line in future rice breeding programs.
Drought is one of major abiotic stresses that effect rice production. Roots play vital role in absorption of water and nutrients from soil contributing for drought tolerance. The present study quantified the effects of different irrigation intervals on root development and agronomical traits of three Egyptian rice cultivars, Giza177, Giza178, Sakha107, IET1444 as a popular drought tolerant and Moroberekan as control genotype. Irrigation treatments were imposed 15 days after transplanting and applied for every 4, 8 and 12 days during 2018 and 2019 rice growing seasons. The results showed the reduction in root architecture traits with prolonged irrigation intervals. A significant decrease in plant height, number of panicles plant-1, grain yield (t ha-1) and relative water content, while sterility (%) and water use efficiency significantly increased over irrigation intervals. The highly significant and positive correlation was found among grain yield and root:shoot ratio, relative water content and number of panicles plant-1, while the negative correlation was with root xylem vessel number and sterility. It was concluded that, the drought reduced the grain yield and its components due to poor developed root system. Moroberekan and IET1444 genotypes can be used as a donor parent for rice breeding program. Further studies are also required to identify factors that contribute to the high yield potential of both Giza178 and Sakha107 under different water stress condition. © 2021 Friends Science Publishers
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