Agronomic evaluation and genetic studies of Lagenaria siceraria populations derived from landraces collected from KwaZulu-Natal, South Africa

Abstract

Lagenaria siceraria is one of the most important cucurbitaceous vegetables due to its prolific bearing habit, utility as a cooked vegetable and its low cost of cultivation. The fruit is a vital source of minerals, vitamins, cucurbitacins, campesterol, polyphenols and 1.6% choline in sitosterol on dry weight basis. The edible fleshy parts of the vegetable are leaves, shoots, fruit and seeds. The crop is grown under subsistence farming with no genetically improved cultivars. No previous studies have reported the crossing of L. siceraria landraces collected from KwaZulu-Natal, South Africa to generate new populations. Therefore, there was a need to develop F1 populations from L.siceraria landraces with desirable traits and evaluate their agronomic and nutritionalattributes for commercial and subsistence farming. The first objective of the study was to evaluate the morpho-agronomic traits among the selected parental landraces and created F1 progenies, and the second one was to analyse the nutritional variability of the selected parental landraces and created L. siceraria F1 progenies. In the first study, the diversity present among 19 genotypes of (seven parental landraces and twelve F1 offspring) was investigated using morpho-agronomic qualitative and quantitative traits. Significant differences (P < 0.05) were observed among quantitative traits suggesting considerable genetic variability. The genotypes displayed significant variation in most qualitative traits of fruits (colour, texture and shape) and seeds (colour, size and shape). The genotypes evaluated in the present study exhibited a wide range of diversity in quantitative traits including days to emergence, emergence percentage, seedling height, leaf area, main vine length, days to flowering, days to edible harvest maturity, days to drying harvest maturity, fruit neck length, seed width and leaf growth percentage. The first five principal components on quantitative traits among the evaluated 19 genotypes contributed 74.84% of the variability. For quantitative traits, emergence percentage, seedling height, cotyledons size, leaf area, vine length, number of leaves, number of branches, number of seeds per fruit, fruit mass, fruit rind thickness, hundred seed mass, total seed mass, fruit length, fruit width, seed width, fruit yield, yield per plant, leaf chlorophyll content, total fruit mass per plot, fruit neck length and seed length were correlated positively with the first principal component (PC1), which accounted for 34.46% of the total variation. Days to emergence, days to flowering, days to edible harvest maturity, days to drying harvest maturity, shoot growth percentage, cotyledon leaf area, leaf area, vine length, number of leaves, number of branches, fruit mass, fruit rind thickness, hundred seed mass, fruit width, seed length and seed width correlated positively with PC2, which accounted 14.48% of total variability. The biplot and dendrogram clustered genotypes into five clusters according to their vegetative, fruit and seed traits. F1 progenies displayed more heterosis or hybrid vigour than parental landraces in 15 quantitative traits (53.57%) out of the 28 evaluated traits. Hence, the F1 progenies can be used for further Lagenaria siceraria genetic improvement. In the second study, the diversity present among 19 genotypes was investigated using taste (very sweet, sweet, neutral, bitter and very bitter) and mineral nutrients. With a participant’s test, we observed a major difference in taste between the 19 genotypes. A very sweet genotype (RRPxNSC) and sweet genotype (NqSCxNSC) would typically be utilized to make jams and sweets. There were insignificant differences (P > 0.05) among mineral contents of the genotypes, suggesting no considerable mineral composition variability. The first five components among the 19 genotypes evaluated contributed 89.97% of the variability. The following minerals/nutrients, namely, crude protein, calcium, magnesium, zinc, copper, manganese, iron, and phosphorus positively correlated with the first principal component (PC1), which accounted for 42.42% of the total variation. Calcium, magnesium, potassium, sodium, zinc, manganese, iron, and aluminium had a positive correlation with the second principal component (PC2), which accounted for 24.78% of the total variation. The biplot and dendrogram clustered genotypes into five clusters according to the macronutrients and micronutrients. The NSRC genotype was unique because of its characteristics of having high contents of crude protein, phosphorus, magnesium, zinc, manganese and iron but low potassium content, and thus making it suitable to supply minerals for human consumption. The differences in the Lagenaria siceraria genotypes also occur in the taste and in the composition of the various nutrients present in them and not only in the morphological traits. Since we have obtained the variation in mineral content among the genotypes, the analysis of vitamins and phytonutrients is recommended for future studies.