Morphology and genetic relationships in members of the Solanum nigrum L. complex used for jam production in the Highveld of South Africa

Abstract

The family Solanaceae consists of many important crop species such as tomatoes, potatoes and peppers. The Solanum nigrum complex (black nightshades) also form part of this family and are an emerging, important food source in parts of Africa. Both leaves and ripe fruits are consumed. Additional advantages of the nightshades include several medicinal properties, high nutritional value and natural resistance mechanisms against many disease causing pathogens of the Solanaceae. The objectives of this study were to compare accessions used for “nastergal” jam production in the Highveld of South Africa to reference species of the S. nigrum complex using (i) morphological (ii) ploidy and (iii) molecular information. Twenty-nine morphological traits separated the farm-collected samples into three distinct groups. Flow cytometry indicated the presence of a polyploidy series (diploid, tetraploid and hexaploid entities), and the presence of possible hybridization events within the complex. ITS rRNA and three chloroplast genes (matK, ndhF and rbcL) were sequenced for phylogenetic analysis. ITS yielded 19 informative sites across 600bp, while only six informative sites were identified across 3600bp of chloroplast gene sequences. Chloroplast genes yielded few phylogenetically informative sites, and were not able to distinguish between nightshade accessions. Diversity array technology, a whole genome genotyping approach on microarrays, produced 1145 polymorphic markers between the accessions. ITS rRNA gene sequencing and DArT data produced similar results, with three main groups distinguished, supported by morphological data. Our data suggests that farmers are using fruits of Solanum retroflexum, Solanum chenopodioides and Solanum americanum for jam production. Future work includes measuring levels of vitamin C, proteins, sugars and anthocyanins in the berries, as well as solanine content to shed light on assumptions concerning the toxicity of unripe berries. The results obtained could aid in the identification of germplasm which would be suitable to initiate breeding programs for enhanced physiological or metabolic traits for high quality jam production.