African nightshades: genetic, biochemical and metabolite diversity of an underutilised indigenous leafy vegetable and its potential for plant breeding

ABSTRACT

African nightshades are becoming more important as leafy vegetables in sub-Saharan Africa. Previously considered as food for the poor, their cultivation is now being promoted, and some cultivars are commercialised; however, most farmers use self-produced seeds, leading to low and varying yields. Improvement through conventional breeding depends on the available genetic diversity, the possible breeding systems, and the nutritional value of the accessions. Therefore, we review the information on these topics with the following main outcomes: the most commonly discussed species, S. nigrum, S. scabrum, S. villosum, and S. americanum, could be differentiated using molecular markers, but further sub-clustering was rarely possible, and statistical support often missing. S. nigrum and S. scabrum seem to be most closely related to each other. The mainly self-pollinating African nightshades form a polyploidy series with diploid (2n = 2x = 24) to hexaploid taxa. Interploidy hybridisations between diploids and tetraploids are possible, whereas the hexaploid S. nigrum and S. scabrum could not be crossed to genotypes of lower ploidies. Solanine, solamargine, solasonine, and chaconine are the major steroidal alkaloid glucosides in African nightshades. Amounts are age and environment dependant. Mineral and vitamin contents in leaves are at least as high as in Brassica oleracea or Spinacia oleracea, underlining their relevance as local vegetables.

KEYWORDS:

• Solanum nigrum
• Solanum scabrum
• genetic diversity
• cytology
• glycoalkaloids
• polyploidy

Acknowledgments

The authors gratefully acknowledge funding from the project HORTINLEA by the German Federal Ministry of Education and Research (BMBF) and the German Federal Ministry of Economic Cooperation and Development (BMZ), within the framework of the GlobE (Global Food Security) program.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Bundesministerium für Bildung und Forschung [grant number 031A248E]; and the Bundesministerium für Wirtschaftliche Zusammenarbeit und Entwicklung.