Assessment of the genetic diversity of dessert watermelon (Citrullus lanatus var. lanatus) landrace collections of South Africa using SSR markers

Abstract

Dessert watermelon landraces could provide useful germplasm sources for commercial watermelon breeding and/or conservation. This study assessed the genetic diversity present among dessert watermelon landrace collections of South Africa using simple sequence repeat (SSR) markers. Thirty one diverse dessert watermelon landraces were genotyped using 10 polymorphic SSR markers. A total of 94 alleles were amplified among the sampled population. The number of alleles ranged from 2 to 19 with a mean of 9.4 per locus. The number of effective alleles ranged from 1.07 to 9.94 with a mean of 4.61. Observed heterozygosity values ranged from 0.07 to 1.00 with a mean of 0.53. Expected heterozygosity, which measures gene diversity, was 0.66; which partitioned 75, 25 and 0% of the variation within individuals, among individuals and between populations, respectively. The mean gene fixation was 0.18 suggesting high levels of heterozygosity among the collections. The mean polymorphic information content (PIC) of the SSR loci was 0.65 suggesting their value in genetic diversity analysis of watermelon. The collections were allocated into three genetic groups using cluster analysis. The results revealed the presence of genetic diversity among South African dessert watermelon collections. Genetically unique landraces such as SWM-39, SWM-01, SWM-04, SWM-27, SWM-24, SWM-10 and SWM-36 from cluster I; SWM-35, SWM-21, SWM-02, SWM-34, SWM-07 and SWM-31 from cluster II; and SWM-22 and SWM-18 from cluster III were selected based on their high dissimilarity index. These are recommended for further phenotyping using horticultural attributes for effective breeding and strategic conservation.

Genetic Diversity Assessed by Genotyping by Sequencing (GBS) in Watermelon Germplasm

“…In this study, gene flow (Nm) among 68 watermelon accessions was 4.43, suggesting a high genetic introgression. Previous studies reported similar results with a low genetic differentiation value and high gene flow among watermelon [39,40]. Gene flow <1 is considered to be low whereas Nm = 1 is considered to be moderate [41].…”

Morphological and molecular characterization of some pumpkin (Cucurbita pepo L.) genotypes collected from Erzincan province of Turkey

“…SSR markers can be used effectively in population genetics and gene mapping studies because of their advantages as an informative marker system including requiring small amounts of DNA, being codominant and stable, being abundant and scattered throughout the genome, being reproducible and suitable for automation, and having a high level of polymorphism 18 . The SSR technique has successfully been used in the assessment of genetic diversity in cucurbit species such as pumpkin/squash 19 – 22 , bowler 23 , snake melon 24 watermelon 25 , 26 , bitter melon 27 , cucumber 28 . The rate of foreign fertilization in pumpkin is very high.…”

Phenotypic Variability of Root System Architecture Traits for Drought Tolerance among Accessions of Citron Watermelon (Citrullus lanatus var. citroides (L.H. Bailey)

“…The citron watermelon root architecture has a primary taproot and several lateral roots [ 6 ]. Genetic variability has been reported in the species for morphological traits, including RSA traits [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Using a genetically diverse population of citron watermelon accessions collected and grown in the drier parts of South Africa by small-holder farmers, Mandizvo et al [ 26 ] observed variability in the estimated root percentage, taproot length and root dry mass among the accessions after exposure to drought stress.…”