Using relative penetration and maleness indices in Meloidogyne incognita to establish resistance type in Cucumis myriocarpus
Resistance in plant-parasitic nematodes is broadly classified as pre-infectional or post-infectional. Prebreeding establishment of resistance type in plant-parasitic nematodes is essential where germplasm is to be introgressed into the rootstock breeding lines since only post-infectional resistance is introgressible. A study was conducted to determine whether resistance in wild cucumber (<i>Cucumis myriocarpus</i>) rootstocks to the southern root-knot nematode (<i>Meloidogyne incognita</i>) was pre- or postinfectional. Seven treatments: 0, 200, 600, 1000, 1400, 1800 and 2200 eggs and juveniles, were arranged in a randomised complete block design with 10 replicates. At harvest, 56 days after inoculation, the
relative penetration index [RPI = (Pfin root/Pfin soil) – 1] and the relative maleness index [RMI = (Pftotal males/Pftotal females) – 1] were each greater than one, with the reproductive factors of M. incognita also
being less than one at all levels, without any yield loss. The RPI and RMI suggested that resistance in C. myriocarpus to M. incognita was post-infectional. Thus, the resistance germplasm in this plant could
be introgressed into wild watermelons in the development of nematode-resistant rootstock lines for the management of M. incognita race 2 in highly nematode-susceptible watermelon cultivars.
Key words: Citrullus lanatus, nematode resistance, reproductive potential, watermelon.