Breeding and population genetics studies on coconut (Cocos nucifera L.) composite variety using morphological and microsatellite markers

Results of the study indicate that CCV 0 was predominantly cross-pollinated with outcrossing rates of 91.1% to 91.4%, and selfing rates 8.6% to 8.9%. A large proportion of the cross-pollination events were due to full-sib mating. The biparental inbreeding or crossing between closely related individual occured at the rate of 6.9% to 10.3%. CCV 1 did not attain equilibrium at the single and multilocus levels. Hence, "balanced heterozygosity" was not attained after one generation of random mating. Assessment of inbreeding depression and heterosis was also performed. The effect of inbreeding depression on the economic yield was indirectly studied by using selfing generations of three tall coconut varieties (Laguna Tall and Bago - Oshiro Tall, Mapanget Tall). Inbreeding depression in CCV 1 was also assessed by molecular approach, in which inbreeding depression was measured as reduced level of heterozygosity. Selfing on tall coconut populations resulted in inbreeding depression and increased homozygosity in LAGT, BAOT and MTT populations. Inbreeding depression that was measured as reduced fitness based on the changes in fixation index at SSR loci was high in S3 MTT and S4 MTT. Selfing, full sib mating and biparental inbreeding in CCV 0 resulted in CCV 1 with lower level of heterozygosity. Mid-parent heterosis was present in the intervarietal F1 Tall x Tall coconut hybrids that constituted the CCV 0 for whole nut weight, meat weight and copra weight. The predicted copra weight per nut of CCV 1 was higher than the copra weight per nut of the parental Tall populations; however, it was lower than that of F1 Tall x Tall hybrids. The relationship between heterosis in fruit component traits and genetic distances of the F1 tall x Tall hybrids was also determined. Data indicated that only mid-parent heterosis in copra weight could be correlated with genetic distance. The assessment of population genetic structure was studied in terms of genetic variability and population differentiation of CCV 0 and CCV 1. The genetic diversity was characterized in terms of number of alleles, observed and expected heterozygosity, and fixation index. Wright's Fsub ST and Rho values of unbiased estimator of Slatkin's RST distance was computed as an indicator of population differentiation. Genetic distances between components that were made up of CCV 0 and CCV 1 were computed based on morphological traits, i.e. fruit components in CCV 0 and seedling vigor in CCV 1, and SSR markers. The results showed that CCV 1 was less diverse compared to CCVO population. The CCV 1 had less number of alleles and was deficient in heterozygous genotypes. Genetic differentiation within populations was higher in CCV 1 than in CCV 0 indicating that CCV 1 was more fragmented. The implications of the results of this research to coconut breeding and germplasm management were discussed extensively