Variation in growth, nutrition and phytochemicals of sequentially harvested shoots and fruits, and genetic studies of Lagenaria siceraria landraces in South Africa
Lagenaria siceraria (Molina) Standley, a member of the Cucurbitaceae family, is valued for its many uses, serving as a crucial food source with edible plant parts such as leaves, shoots, fruit pulp, and seeds. However, studies on L. siceraria regarding the relationship between shoot, peduncle and fruit traits during growth; nutritional and phytochemical composition of sequentially harvested shoots and fruits; as well as genetic diversity among landraces using single nucleotide polymorphism (SNP) markers, are limited. These studies are crucial for enhancing plant physiological understanding, optimizing crop yields, improving nutritional value, and preserving genetic diversity in L. siceraria. Therefore, the objectives of this study were to correlate shoot, peduncle, and fruits’ traits during growth; compare the nutritional composition of shoots and fruits, and phytochemical profile of fruits harvested at different maturity stages; and assess the genetic variability using SNP markers in L. siceraria landraces sourced from northern KwaZulu-Natal and Limpopo, South Africa. Multivariate analyses were conducted along with the estimations of heritability. Harvested shoot, peduncle, and fruit traits showed significant variation (p < 0.05) within each growth period and at different growth stages. Peduncles of all landraces became shorter and thicker when fruits were elongating and widening, from 0–5 days after anthesis (DAA). Positive correlations were notable among all shoot traits (shoot length, shoot width, shoot fresh mass, shoot dry mass, and shoot moisture content), and peduncle width correlating with fruit length and width. The first three principal components explained 85% of the total variability. Clustering identified three main groups, with singlets for landraces KRI and NSRC. Landraces were clustered according to peduncle and fruit sizes, as well as availability of harvestable shoots. High heritability estimates were recorded for peduncle length (55.2%) and shoot width (60.2%). Differences in nutrient attributes were significant within and among landraces where shoots and fruits were harvested at various growth stages. Nutritional traits correlated either positively or negatively with each other based on their translocation modes and similar chemical properties. The first five principal components explained 90.218% and 89.918% total variability in shoots and fruits, respectively. Micronutrients Ca, Mg, K, P, and N in shoots and macronutrients Fe, Zn, Cu, and Al in fruits, were the primary contributors of variability. Shoot nutrient content associated landraces into three major clusters, based on landraces with superior and inferior levels of specific nutrients at different growth stages, as well as those with distinctive nutrient profiles. Fruit nutrient status also grouped landraces into two major clusters, reflecting variations in nutrient content at different growth stages. Phytochemical analysis identified five isoprenoids in fruits harvested at 7 DAA across all landraces, namely 1-Dodecene, 2,3-Dimethyldodecane, E-15-Heptadecenal, Eicosane, and Tridecane, 6-propyl. Lighter metabolites in molecular mass displayed shorter retention rates (9.08-16.29 min) with lower relative peak areas (1.09-6.97%), while heavier compounds exhibited longer retention rates (13.42-18.00 mins) with higher relative peak areas (2.25-11.41%). Landraces were grouped into five clusters based on fruit and seed attributes and significant isoprenoid units. Terpenoids were the predominant phytochemicals commonly identified among landraces’ fruits at different stages of growth, where 1-Dodecene; Decane,3,7-dimethyl-; 1-Octadecane; 1-Pentadecene; E-14-Hexadecenal; E-15-Heptadecenal; Eicosane; Tetradecane, 4-methyl; and Tridecane, 6-propyl-, were the highest contributors to variation. Correlation in phytochemicals was predominantly based on their availability at different fruit growth stages. Three distinct clusters grouped landraces according to the unique presence of phytochemicals at different stages of growth, as well as landraces with similar fruit traits and phytochemical availability at different growth stages. Genetic variation at a single nucleotide base was identified among studied landraces, where the sequencing of 16 landraces revealed variations in the target genes ACS27 and CmFIS8. Molecular variance analysis and phylogenetic tree construction indicated variations among landraces. Sequenced landraces showed an average of 1.75 alleles, effective alleles at 0.419, Shannon’s information index at 0.403, expected heterozygosity at 0.265, gene flow at 6.80, and genetic differentiation at 0.082. Sequence variations were observed, and landraces were clustered based on genetic differences. Analysis of Molecular Variance (AMOVA) indicated 100% variation among landraces of different origins.
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