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Morphometric Traits and DNA Profiles of Three Generation of Selected Coconut (Cocos nucifera L.) Genotypes
Thesis Abstract:
The genetic variability and relationship of seven coconut genotypes from the original collection site and their representatives in two field gene banks were determined using morphological and molecular marker analyses. The coconut populations consisted of four tall (LAGT, SNRT, BAYT, and WAT) and three dwarf (CATD, TACD, and MRD) varieties. Thirty sample palms per population were assessed morphologically based on the 39 characters listed in the Stantech Manual.
Genetic diversity was also assessed using five Simple Sequence Repeats (SSRs) of microsatellite pairs previously developed for coconut. Morphological characterization revealed that there was substantial variation in almost all the quantitative vegetative and reproductive characters among the seven populations in every site, except in the dwarf and WAT populations. Environmental factors (soil and climate) and age of palms could have contributed to the morphological variations within varieties among sites or replicates. Homogeneity of characters was noted mostly among dwarf populations, which is attributed to their self-pollinating characteristic.
Likewise, qualitative characters (shape of bole, fruit, and nut) revealed homogeneity in each variety across sites which implied that each variety retained its characteristic shapes across location. Diversity indices between sites of each population were all considered moderate ranging from 0.52 to 0.56 H’. Principal component analysis revealed that all the quantitative characters except 11 SCAR, PEDIA and SPWOF had high contributions to variations.
Molecular characterization using five selected microsatellite or simple sequence repeat (SSR) primers revealed a better assessment of genetic variability and relationship of the various coconut genotypes from the original site and their duplicate collections. The heterozygosity and heterogeneity of the tall populations were evident based on the presence of highly polymorphic allele (3-5 alleles per primer or SSR locus). In contrast, the dwarf genotypes clearly showed homozygosity and homogeneity and low genetic diversity because they had few alleles (2 alleles per locus), which were monomorphic.
The molecular dendrogram based on the five microsatellite loci resulted to better clustering of genotypes compared to the dendrogram based on morphological characters. The original populations and its progenies were good enough to replicate the gene bank in another location. Furthermore, the SSRs were effective in separating the seven populations with three primers (CNZ 51, CNI C6, and CN2 A4) and were found to produce specific bands for three distinct dwarf populations, namely: MRD, TACD, and CATD, respectively.
