Abstract
A preliminary survey of genetic diversity among 34 commercially popular Carica papaya cultivars from India and abroad, 6 accessions of Vasconcellea species and 1 accession of Jacaratia spinosa, was done using 20 simple sequence repeat (SSR) markers. The SSR profiles were used to find out total number of alleles, null and rare alleles, Polymorphism Information Content (PIC) values and to calculate similarity matrix using Jaccard’s coefficient. The subsequent dendrogram was made by unweighted pair-group method of arithmetic average (UPGMA) and neighbor-joining method. Based on these parameters a comparison was made between the Indian papaya cultivars and the rest of the accessions. All the markers showed polymorphism and a total of 140 alleles were identified. The average number of alleles was 7 alleles/locus. Categorically the Vasconcellea and Jacaratia species had 54 alleles, the 7 non-Indian Carica papaya accessions had 70 and the 27 Indian accessions had 102 alleles. The average PIC value was 0.735 per marker. A total of 37 rare alleles were identified. Jacaratia spinosa had 17 rare alleles. Nineteen null alleles were detected among the Carica papaya accessions. A Carica papaya accession from South Africa, Hortus Gold had 5 null alleles. The genetic similarity among the accessions ranged from 7% to 67%. In the dendrogram, the Vasconcellea and Jacaratia spinosa accessions separated as a distinct cluster from the rest of the Carica papaya accessions. The study indicated that the accessions of Indian Carica papaya cultivars included in this survey are genetically more diverse than the non-Indian Carica papaya cultivars.
Highlights
The family Caricaceae consists of six genera of herbaceous, shrubby or arborescent dicotyledonous plants having a common phylogenetic origin with Brassicaceae, and with the completely sequenced model plant Arabidopsis (Bremer et al 1998, Rodman et al 1996)
The minimum and maximum molecular weight among the alleles, number of rare alleles, number of null alleles, total number of alleles and Polymorphism Information Content (PIC) values for each marker are given in table
All the markers showed polymorphism and a total of 140 alleles were identified from the experimental set of Caricaceae accessions
Summary
The family Caricaceae consists of six genera of herbaceous, shrubby or arborescent dicotyledonous plants having a common phylogenetic origin with Brassicaceae, and with the completely sequenced model plant Arabidopsis (Bremer et al 1998, Rodman et al 1996). From the perspective of human consumption Carica and Vasconcellea are the two most important genera within Caricaceae (Badillo 1993 and 2000). Vasconcellea grows at a height of 1000 m and higher, above sea level, mostly in wild humid forests, but are semi-domesticated or tolerated in local gardens in the highlands of South America. Ram et al (1985) classified the popular Indian papaya cultivars like Coorg Honey Dew, Washington, CO1, CO2, PusaDwarf, Surya etc. Into various groups like primitive genotypes, traditional genotypes, minor genotypes, local adaptive genotypes and principal genotypes. India has a vast array of indigenous papaya cultivars (Ram 2005), reports of systematic collection, conservation, documentation and evaluation of different germplasms and study of their inherent genetic diversity are limited
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