Inter-generic grafting of watermelon on wild Cucumis species: a success story in nematode management

Inter-generic grafting between plant genera within the same family is limited by incompatibility challenges. A locally developed inter-generic grafting procedure between highly nematode-susceptible Citrullus cultivars and highly nematode-resistant indigenous members of the genus Cucumis resulted in 100% survival of the inter-grafts. Subsequent trials were conducted to determine the performance of the inter-grafts with respect to: (1) Cucumis nematode-resistant rootstocks retaining their nematode-resistance status to Meloidogyne incognita and (2) Citrullus cultivars retaining their growth potential under greenhouse conditions. Treatments, namely (i) ungrafted watermelon, (ii) watermelon-on-Cucumis africanus and (iii) watermelon-on-Cucumis myriocarpus, were each inoculated with 1000 eggs and second-stage juveniles of M. incognita race 2. Relative to ungrafted watermelon cultivars, grafting 'Congo' on Cucumis africanus and Cucumis myriocarpus reduced reproductive factor values by 92-93%, while, for 'Charleston Gray', the reduction was 94-96%. Similarly, root galls were reduced by 94-96 and 90-98% for 'Congo' and 'Charleston Gray', respectively. In field validation, inter-grafting improved early flowering and higher fruit yield than the ungrafted controls. In conclusion, nematode-resistant Cucumis seedling rootstocks invariably retained their non-host status capabilities to Meloidogyne species, while inter-generic grafting enhanced the productivity of the two Citrullus cultivars.