Host-status and host-sensitivity of wild Cucumis species to Meloidogyne incognita race 4

Abstract

Wild watermelon (Cucumis africanus) and wild cucumber (Cucumis myriocarpus), which are highly resistant to the southern root-knot nematode (Meloidogyne incognita) race 2, have the potential for serving as seedling rootstocks for the highly nematode-susceptible watermelon (Citrullus lanatus) cultivars. In South Africa, due to high labour costs, most cotton farmers are turning to watermelon production. In these regions, there is high incidence of M. incognita race 4. A pot experiment in the greenhouse was, therefore, initiated to investigate the host-status and host-sensitivity of Cucumis africanus and Cucumis myriocarpus to M. incognita race 4, when inoculated with 0, 200, 600, 100, 1400, 1800 and 2200 eggs and second-stage juveniles (J2s). At harvest, 56 days after inoculation, the reproductive factor values at all levels of inoculation were less than one. Penetration indices on both plant species were greater than one, suggesting that the resistance was post-infectional and therefore, introgressible. Sex (male: female) ratios of M. incognita race 4 on the two Cucumis species were greater than one, suggesting that more J2s were converted into males. Infection of Cucumis species by the test nematode had no effect on yield components of the two plant species due to poor feeding sites. The two Cucumis species were, therefore, resistant to M. incognita race 4, with post-infectional resistance, where the sex ratio was skewed towards maleness. Thus, the two Cucumis species have the potential to be used as nematode-resistant rootstocks in watermelon production.