Evaluating diversity among Kenyan papaya germplasm using simple sequence repeat markers

Abstract

Papaya is an important fruit crop, produced in Kenya for local consumption and export. Despite a history of varietal introductions, no attempts concerned on developing varieties suited to Kenyan conditions have been documented. The objective of this study was to provide information on the diversity of germplasm available in Kenya, as a precursor to systematic plant breeding program. Forty two papaya accessions were collected from farmers' fields located in Coast, Rift Valley, Western, Nyanza, Central and Eastern provinces. Genetic diversity was determined using seven simple sequence repeat (SSR) markers, computing allelic richness and frequency, expected heterozygosity and cluster analysis. Results indicated that the markers were highly polymorphic among the accessions, with polymorphic information content (PIC) varying from 0.75 to 0.852 with an average of 0.81. The genetic similarity among the 42 papaya accessions ranged from 0.764 to 0.932 with an average of 0.844 showing that most papaya accessions used in this study were closely related. About 96.9% of the pair-wise comparisons among papaya accessions exhibited genetic similarity greater than 0.802, while less than 4% (3.1%) showed genetic similarity lower than 0.802. The phylogenetic analysis grouped the 42 accessions into two main clusters A and B. Cluster A had four sub-clusters while cluster B had one cluster. Accessions from Coast, and some from Rift Valley Provinces, presented the highest variation, being scattered throughout the tree, with little or no differentiation from most accessions, whereas some accessions from Coast regrouped in clusters A (iv) and B. The genetic differences among the accessions revealed by the formation of distinct clusters suggest significant genetic variability emanation from varying sources of the papaya germplasm in Kenya. Although the level of genetic diversity revealed by SSR markers in this study is sufficient to distinguish between breeding lines for varietal protection, the rather narrow genetic diversity demonstrated indicates the need to introduce new germplasm or use other techniques such as mutation and genetic engineering to provide breeding materials for the future improvement of papaya in Kenya.

Genetic Diversity of Puerto Rican Farmer-held Papaya (Carica papaya) Using SSR Markers

“…Genetic diversity estimators revealed similar results to other genetic diversity studies using SSR markers (Asudi et al, 2013;Brown et al, 2012;Matos et al, 2013). When evaluating H o for the USDA germplasm samples, we found similar results as Brown et al (2012) which evaluated a total of 20 samples from the USDA germplasm repository and reported an H o of 0.14 (similar to 0.138 in our analysis).…”

“…The genetic diversity of papaya has been studied both morphologically and at a molecular level (Aikpokpodion, 2012;Alonso et al, 2009;Asudi et al, 2013;Brown et al, 2012;Matos et al, 2013;Ocampo Perez et al, 2006a;Sengupta et al, 2013;Sudha et al, 2013). Morphologically, papaya has been shown to possess great diversity (Ocampo Perez et al, 2006a).…”

Informativeness of minisatellite and microsatellite markers for genetic analysis in papaya

“…This average number of alleles was consistent with previous observations made by other authors, who reported averages of 4.02 (Oliveira et al 2010b) and 4.53 alleles per locus (Matos et al 2013) in the analysis of Brazilian papaya genotypes. In contrast, a higher average number of alleles per locus (6.60) was found by Ocampo Pérez et al (2007), who analyzed 72 papaya genotypes with 15 microsatellite markers, and by Asudi et al (2013), who analyzed 42 papaya genotypes from six regions in Kenya, in which 11.93 alleles per locus were observed.…”

“…According to Asudi et al (2013), no rare alleles were found in the first study involving the genetic characterization of papaya germplasm from Kenya using microsatellite markers. These findings reinforce the importance of using molecular markers to identity and further apply strategies to preserve these rare alleles in papaya germplasm from Brazil.…”

Evaluation of the morphological and quality characteristics of new papaya hybrid lines in Kenya

“…These include 'Kapoho solo' (Storey, 1969), 'Waimanalo', '77', '116', '273' from Hawaii, 'Cavite', introduced from the Philippines, '417', '418' and '455' from India, 457 from Indonesia and 'Kiru' from Tanzania. Locally developed papaya cultivars included 'Kitale', 'Malindi' and 'PP1' (Imungi and Wabule, 1990;Asudi et al, 2013). Recent evidence also indicates that various commercial cultivars such as 'US', 'Redlady', 'Sunrise', 'Sunrise-Solo' and 'Honey dew' originating from Asia and America, are regularly imported as seeds by commercial papaya growers in Kenya.…”