The germplasm with heat-tolerant traits is one of the crucial targets effective in rice (Oryza sativa L.) breeding for climate change. Hence, the presented research aimed to improve heat-tolerant cultivars through traditional breeding and molecular markers for climate change adaptability. The results showed most of the studied rice genotypes had a wide range of variability for various traits, with this range also reflected among the tested crosses. The best crosses with the highest mean values for all traits were Giza178 × Giza179, Giza178 × IET 1444, Sakha104 × IET 1444, and Giza179 × IET 1444. The general combining ability (GCA) effects revealed cultivars IET 1444, Giza179, Giza178, and Sakha104 with significant positive GCA influences for tillers and panicles plant-1, filled grains panicle-1, and grain yield per plant. The best identified crosses for almost all traits were Giza177 × Giza178, Giza177 × Giza179, Giza177 × Sakha104, Giza178 × IET 1444, and Sakha105 × IET 1444. The principal component analysis (PCA) divided the seven rice genotypes into two groups. The first one included the sensitive rice cultivars, namely, Giza177, Sakha105, and Sakha101, and the second group comprised tolerant genotypes, i.e., Giza178, Giza179, IET144, and Sakha104. Using 18 SSR markers helped assess the genetic diversity in rice genotypes. The studied markers produced 204 alleles, with a mean of 11.33 per locus. A higher number of alleles per locus resulted from primers RM493, RM341, RM3297, and RM3330. The polymorphic information content (PIC), a reflection of allele diversity and frequency, was moderate and ranged between 0.157 for RM504 and 0.872 for RM3330, with an average of 0.756. Based on the SSR cluster analysis, rice genotypes formed two groups; the first group included the sensitive rice genotypes, while the second was the tolerant genotypes.
Rice (Oryza sativa L.), germplasm, breeding, heat tolerance, genetic diversity, GCA and SCA, SSR markers, yield-related traits
In the presented study, the four rice (Oryza sativa L.) parental genotypes, Giza178, Sakha104, IET 1444, and Giza179, were heat-tolerant, while three genotypes, Giza2177, Sakha 101, and Sakha105, were heat-sensitive. The crosses Giza177 × Giza178, Giza177 × Giza179, Giza177 × Sakha104, Giza178 × IET 1444, and Sakha105 × IET 1444 were notably high-yield crosses. Based on genetic diversity, Giza177, Sakha101, and Sakha105 genotypes were sensitive, and Giza178, Giza179, IET144, and Sakha104 were tolerant. The SSR markers RM493, RM341, RM3297, and RM3330 showed the highest alleles. The promising parental genotypes and their hybrids could be beneficial for developing heat-tolerant rice genotypes.