Screening wild and cultivated cucurbits against root knot nematode to exploit as rootstocks for grafting in cucumber
Yield of mono-cropped cucumber (Cucumis sativus L.) is reduced by root knot nematode (Meloidogyne incognita Kofoid and White). Use of resistant rootstocks in grafting may overcome the problem. Cucurbitaceous species were screened against root knot nematode to evaluate their use as rootstocks in grafting. Inoculation was with nematodes @ 2 J2·g-1 (J2 = second stage juvenile) of soil in pot culture at the 1 to 2 true leaf stage, 45 days after inoculation, plants were uprooted and observations made to calculate Root Knot Nematode Index (RKI). Cucurbita moschata, Cucumis metuliferus, Citrullus colocynthis and Cucumis callosus were resistant having a RKI-2. Cucurbita ficifolia, Cucurbita maxima, Cucumis melo sub sp. agrestis were moderately resistant with a RKI-3. Total phenols content in roots indicates plant resistance to M. incognita. Cucumis metuliferus had the highest mean total phenols content (16.98 mg·g- 1 of root) followed by Citrullus colocynthis (16.08 mg·g-1 of root) and Cucurbita moschata (15.37mg·g-1 of root). Resistant rootstocks possessed higher peroxidase and PPO activity than susceptible ones. Cucumis metuliferus had the highest value of peroxidase and PPO activity (3.83 OD·min-1·g-1 of root and 3.67 OD·min-1·g-1 of root) followed by Citrullus colocynthis (3.26 and 3.63 OD·min-1·g-1 of root), Cucumis callosus (3.02 and 2.98 OD·min-1·g-1 of root) and Cucurbita moschata (2.93 and 2.94 OD·min-1·g-1 of root). Cucumber scions, ‘Green Long’ and ‘NS 408’ had lower peroxidase and PPO activity of 0.64 and 1.42 OD·min-1·g-1 and 0.57 and 1.31 OD·min- 1·g-1 of root, respectively. Resistant and moderately resistant cucurbitaceous species may be used for further studies possibly leading to improved yield.
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