Agronomic, genetic, and nutritional characterization of Nightshade (Solanum spp.) accessions

Abstract

Nightshades (commonly referred to as African and/or Black nightshade) comprise several species within a section of the genus Solanum. There are 30 species reported in the section in the world, and about 12 species are found in Africa. Nightshade is an indigenous leafy vegetable in Sub-Saharan Africa (including South Africa) valued for its high nutrient content and therefore nutritional security and a potential to generate income especially in subsistence farming. Its use as a food crop needs to be promoted and for this to be achieved there is a need to understand the genetic background and generate knowledge for cultivation through breeding and precision agronomic studies. Therefore, the limited information available on this neglected and utilized family hinders their development as well as sustainable conservation. Existing knowledge on the agronomic and nutrient potential of these plants is limited and the information regarding the morphological and nutritional assessment of Solanum species found in South Africa is scarce. Therefore, the objectives of this study were: (i) to assess and evaluate the genetic variability in 15 nightshade accessions for agronomic, yield and yield components characteristics, (ii) to assess the variability in nightshade accessions for nutrient traits, (iii) to identify potential parents for future use in breeding programs in South Africa. For two consecutive years (2020 and 2021) trials were carried out on the fields of the North-West University research garden on the Mafikeng campus by executing a randomized complete block design (RCBD) with three replications. The raw data were subjected to analysis of variance using SAS software (version 9.4) at a 5% probability level. Shannon-weaver results exhibited the least diversity as evidenced by low diversity indices for all qualitative descriptors ranging from 0.077 to 0.227 with the lowest average diversity index (0.067), thus suggesting low levels of polymorphism. Multivariate analyses were performed to determine patterns of diversity among accessions. Morpho-agronomic characters for the first two PCs accounted for 62.10% of the total variation and identified stem diameter (mm), fruit fresh mass, leaf fresh mass, leaf dry mass, stem fresh mass, stem dry mass, leaf area, days to 50% flowering, leaf yield, stem yield, and total biomass as the major contributors to variability, while the first two components accounted for 74.61% of the total variation in nutritional traits, Ca, Mg, Zn, Fe, Al, N, K, and P contributed more to the variability. The principal component biplots and cluster analysis among accessions revealed a significant level of variability in both morphological and nutrient traits studied. Cluster analysis resulted in 14 clusters based on accession dissimilarity and similarity. Genetic parameters were estimated for agronomic and nutrient characteristics

and showed a considerable amount of variability. The high mean value, high range of variability and genotypic variance was observed for all traits. The phenotypic variance and phenotypic coefficient of variation were more than the genotypic variance and genotypic coefficient of variation under study, thus indicating the role of environmental influence on tested traits. High genotypic coefficient of variation (GCV %), broad-sense heritability (H2), and genetic advance expressed as a percentage of the mean (GAM %) were calculated (82.28%, 70.59%, and 142.40%, respectively) for the smallest leaf area (cm2). On the other hand, the biggest leaf area (cm2) (172.92%, 50.94%, and 254.25%) had high GCV, moderate H2, and high GAM%, while Fe and Al had moderate (32.35%, 34.78%) heritability coupled with high (277.12%, 435.72%) genetic gain at 5% selection intensity, thus suggesting the effects of additive gene action in the inheritance of these characters and selection may be effective. The study revealed sufficient genetic variability for traits among the 15 nightshade accessions studied, which could be exploited for the improvement of the nightshade breeding programme in the country. Furthermore, the study identified accessions Scabrum, Ncampus, Nshad40, N5547, SRetrflx, NigSN18, ManTown, and Nshad9 as superior accessions for high yield and nutrient-dense of the 15 nightshade accessions.