In vitro-induced tetraploids of Plectranthus esculentus are nematode-tolerant and have enhanced nutritional value

Plectranthus esculentus (Family: Lamiaceae), or Livingstone potato, is an edible tuberous vegetable which originated in Africa, with central Africa being the centre of origin. P. esculentus is found throughout the continent, including the north-eastern regions of South Africa. Although the tubers are edible, limited crop improvement has been achieved; therefore, a study comprising in vitro polyploidisation was carried out with subsequent evaluation of plant nutritional value and nematode tolerance of the induced tetraploids compared with the diploid controls. Tetraploid tubers had a higher starch content compared with the diploids, however there was no significant difference in mineral element content for either the leaves or the tubers when induced tetraploids were compared with the diploid control. Further, induced tetraploids appeared to be significantly more tolerant to rootknot nematode, Meloidogyne spp., than the diploids. A significantly higher number of egg masses per root system and number of eggs and J2 (juvenile stage 2) individuals per root system were detected in control plants, compared with tetraploid plants. Induced tetraploidy resulted in plants with a higher nutritional starch concentration and tolerance to rootknot nematode, characteristics which will improve the cultivation and utilisation of the crop. Morphologically, tetraploid plants had fewer, thicker stems per plant compared with diploid plants.