Genetic diversity and differentiation in citron watermelon [Citrullus lanatus var. citroides] landraces assessed by simple sequence repeat markers

Abstract

Citron watermelon genetic resources are useful for dessert watermelon breeding. The objective of the present study was to assess the genetic diversity present among citron watermelon landrace collections of South Africa using simple sequence repeat (SSR) markers. Thirty four diverse citron watermelon landraces were genotyped using 10 SSR markers. The markers amplified a total of 72 alleles from the sampled populations. Number of alleles ranged from 2 to 17 with a mean of 7.2 per locus. Number of effective alleles ranged from 1.03 to 6.74 with a mean of 3.54. The mean observed and expected heterozygosity were 0.48 and 0.60, respectively. The mean inbreeding coefficient was 0.18 suggesting high levels of heterozygosity among the collections. The mean polymorphic information content (PIC) of the SSR loci was 0.60 suggesting their value in genetic diversity analysis of watermelon. Analysis of molecular variance revealed highly significant difference (P<0.001) among and within individuals. Among and within individuals variance contributed 21 and 78% of the total genetic variance. Cluster analysis separated the genotypes into three distinct genetic groups revealing the presence of wide genetic variation among the citron watermelon genotypes studied. The study identified 5 distinct genotypes from cluster I, 7 from cluster II and 5 from cluster III. These are recommended for further phenotyping using horticultural attributes for effective breeding and strategic conservation.