Simple Sequence Repeat Markers Reveal Genetic Diversity Within and among Landrace Collections of Citron and Dessert Watermelon from South Africa

Abstract

<jats:p>Genetic diversity analysis is fundamental for effective breeding and genetic conservation. The objective of this study was to determine the genetic diversity present among dessert watermelon (<jats:italic>Citrullus lanatus</jats:italic> var. <jats:italic>lanatus</jats:italic>) and citron watermelon (<jats:italic>C. lanatus</jats:italic> var. <jats:italic>citroides</jats:italic>) landraces widely grown in South Africa and to select genetically diverse and complimentary genotypes for strategic breeding or conservation. Thirty-one dessert watermelon and 34 citron watermelon landraces were genotyped using 10 polymorphic simple sequence repeat markers. The number of alleles detected per marker ranged from 2 to 23 alleles, with a mean of 13.5 alleles. A total of 135 putative alleles were amplified from sampled watermelon populations. Number of effective alleles ranged from 1.99 to 10.88 alleles with a mean of 5.83 alleles. The mean observed and expected heterozygosity were 0.50 and 0.79, respectively. The mean polymorphic information content was 0.79. Cluster and principal coordinate analyses grouped the two watermelon populations into two separate clusters. The two populations were genetically differentiated with low gene flow, suggesting the presence of high genetic differences between the two populations. Overall, the study established the existence of considerable genetic diversity among South African grown dessert and citron watermelon landraces. Unique dessert watermelon landraces such as SWM-39, SWM-24, SWM-01, SWM-40, SWM-18, SWM-36, and SWM-26; and citron watermelon genotypes including WWM-24, WWM-37, WWM-28, WWM-34, WWM-02, WWM-22, WWM-50, and WWM-36 were selected based on their high dissimilarity index. These could be useful for breeding and systematic conservation.</jats:p>

Phenotypic Variability of Root System Architecture Traits for Drought Tolerance among Accessions of Citron Watermelon (<i>Citrullus Lanatus</i> Var. <i>Citroides</i> (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 estimated root percentage, taproot length and root dry mass among the accessions after exposure to drought stress.…”

Estimates of the variance components, heritability and genetic gains of phenotypic traits in citron watermelon (Citrullus lanatus var. citroides)

“…The non‐sweet citron watermelon types with yellow and orange‐flesh are favoured for cooking various traditional dishes in SSA (Mashilo et al, 2016; Nantoumé et al, 2012, 2013; Ngwepe et al, 2019, 2021). Orange‐fleshed sweet dessert watermelon ( C. lanatus var.…”

“…Despite the nutritional, socio‐economic importance and breeding value of citron watermelon, the crop is underutilized and its economic value is not fully realized and exploited for food, medicine and commercial applications in SSA (Mashilo et al, 2016, 2017; Ngwepe et al, 2019). As a result, there are no improved varieties released and commercialized for production, processing or value adding (Ngwepe et al, 2021; Nkoana et al, 2021).…”

“…These studies revealed the presence of high genetic differentiation among and within genotypes of the crop (Dane & Lang, 2004; Dane & Liu, 2007; Hwang et al, 2011; Levi et al, 2001, 2013; Mashilo et al, 2017; Ocal et al, 2014; Solmaz et al, 2010; Zhang et al, 2016). Based on SSR genotyping, Nantoumé et al (2013) and Mashilo et al (2016, 2017) reported wide genetic differences among citron watermelon landrace accessions in Mali and South Africa, respectively. Extensive genetic differences were detected among Zimbabwean citron watermelon accessions revealed through RAPD and SSR markers (Mujaju et al, 2010).…”

“…Also, various reports indicated that citron watermelon exhibits extensive phenotypic variation for economic traits, which can be targeted for variety design and commercialization (Achigan‐Dako et al, 2015; Maggs‐Kölling et al, 2000; Mashilo et al, 2016, 2017). This will allow watermelon breeders to develop best performing varieties that meet customer requirements and market demand.…”