Morphological Variation of Strychnos spinosa Lam. Morphotypes: A Case Study at Bonamanzi Game Reserve, KwaZulu-Natal, South Africa

Abstract

Strychnos spinosa Lam. of the Loganiaceae family is associated with versatility, poverty eradication, and rural economic development. However, the morphological diversity of S. spinosa is not well documented. This limits efforts toward its improvement and commercial exploitation. This study aimed to characterize the variability, vegetative and reproductive traits, and heritability of S. spinosa morphotypes at Bonamanzi Game Reserve. The majority of the morphotypes had green, rough, round immature fruits with dark green, elongated, open fully developed leaves. Fruits varied between roundish and pyriform shape as well as green and purple colour. Positive correlation was mainly seen between fruit and seed traits. Principal component analysis indicated fruit and seed traits as major discriminating factors for morphotypes, followed by leaf size and seed thickness. A dendrogram primarily grouped morphotypes according to fruit texture. Genotypic variance and genotypic coefficient of variation were higher than environmental variance and environmental coefficient variation in reproductive traits of S. spinosa. A rough pericarp texture and purple tinge on the immature leaves of some morphotypes was recorded for the first time. Differences in morphological features across S. spinosa morphotypes indicate a high level of diversity that could be utilized by breeders to generate new cultivars. This first report on variability and heritability among S. spinosa morphotypes forms the basis of available germplasm essential for future breeding programs.

Assessing Genetic Variation among Strychnos spinosa Lam. Morphotypes Using Simple Sequence Repeat Markers

“…The grouping of morphotypes in the dendrogram according to the variation of pericarp texture, using SSR markers (Figure 4) confirms the similar grouping based on the morphological traits [3]. The exceptions where the morphotypes were previously grouped on their own using the morphological traits [3] but are associated with the others in the SSR analysis (Figure 4), would indicate that those morphotypes were expressing different phenotypic traits that were from the same genomic origin. This probably explains the fading of roughness in the pericarp texture for some morphotypes during fruit growth, which requires further investigation.…”

“…The population structure for K = 3 (Figure 2) and the highest delta value that occurred at K = 3 (Figure 1) indicated that the morphotypes can be divided into three subpopulations with admixed morphotypes amongst the subpopulations. This demonstrates a complex history of gene flow and admixtures among the different populations [38], which may have contributed to the observed morphological diversity of Strychnos spinosa [3]. The affinities produced by population structure (Figure 2) generally agreed with the genetic distance (Supplementary Materials) of closely related morphotypes GSR-GRO and GRP-GEO in sub-population K3.2, and closely related morphotypes GRR-GEF and GvRR-dGEO in subpopulation K3.3.…”

“…Although the range is similar, the primers used for these species were different. The fourteen SSR markers detected a lesser total number of alleles (159) and a range of alleles per marker (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) among Strychnos spinosa morphotypes (Table 1) compared with the total number (207) and the range of alleles per marker (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) detected in Passiflora edulis Sims accessions [21]. A range in major allele frequency from 0.24 to 0.85 with an average of 0.51 in this study (Table 1) was similar to the range (0.17-0.94) and average (0.56) among Psidium genotypes [21].…”

“…Domestication of wild plants is complicated by the fact that the plants have high genetic diversity coupled with equally high morphological diversity between and within populations [2]. Studies reported by Mbhele et al [3] have revealed distinct morphotypes based on the following traits: colour of recently sprouted but open leaves (young leaves), colour, shape, and form of fully developed leaves, as well as colour, texture, and shape of the immature fruits. It is therefore logical to conduct genetic analyses of the morphotypes to determine the underlying genetic characteristics of the morphotypes.…”

“…This study aimed to determine genetic diversity among Strychnos spinosa morphotypes using SSR markers, which is one of the prioritised tasks in a germplasm repository for fruit trees [13]. Determining the genetic basis of the morphological diversity among various Strychnos spinosa morphotypes identified by Mbhele et al [3] will help identify genes for future breeding programs.…”