Genetic diversity and population structure of sugarcane introgressed hybrids by SSR markers

One hundred and seventy two introgressed hybrids from four different introgression groups and in three nobilized stages (F₁, BC₁,and BC₂) involving two genera viz., Sugarcane (Saccharum spp) and Erianthusl (E.arundinaceus),and Coimbatore (Commercials) clones were studied for yield and quality traits, and as well with 30 SSR markers (simple sequence repeats) for diversity and population structure. The yield and quality components of the introgressed hybrids from improved S. spontaneum, improved S. robustum, S. barberi (Pathri) and E. arundinaceus (IK-76-76) showed significant variation. The traits viz., cane height, single cane weight and cane yield showed the highest level of phenotypic and genotypic variation. 456 polymorphic alleles in all with values ranging from 6 (SMC 863-GC) to 24 (NKS 43) with an average of 15 alleles per primer were studied. Polymorphism information content (PIC) generated by 30 SSR primers varied from 0.57 (NKS 1) to 0.94 (NKS 34) and the highest average PIC (0.93) was observed in hybrids of S. spontaneum (SSH). The highest number of observed and effective alleles, and Shannon's index were also registered by introgressed hybrids of SSH and the lowest variability was observed with hybrids of Co canes x S. barberi. SSR-based population genetic measures identified three mating groups involving improved S.officinarum, improved S.robustum and Coimbatore canes with maximum variability. Structure analysis identified 51 introgressed hybrids with abundant genetic variation and low gene flow as a new germplasm source for future sugarcane breeding programmes. Fifty-nine rare alleles were detected, and structure analysis revealed a low degree of admixture between the generated hybrids. Low gene flow estimates from group I (Nm: 1.052, where mostly F₁ and BC₁ hybrids were grouped together) explained that the maximum variability from parental clones was inherited until the BC₁ generation, and high values of Nm in group III also indicated that most of the wild alleles were fixed in the BC₁ population. Structure and cluster analysis (PCoA, UPGMA) explained that the grouping of introgressed hybrids is highly correlated to different stages of nobilization. UPGMA and PCoA methods grouped the individuals into three major clusters, with a clear differentiation of F₁ and backcross hybrids grouped under different internal sub-clusters. The occurrence of wide genetic variability in the population and elite hybrids with a unique genetic base can be exploited in breeding programmes to develop trait specific donors for genetic enhancement and to mitigate climate change.