Potential of sequential cropping in the management of root-knot nematodes in okra
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The response of different crops to a mixed population of root-knot nematodes, Meloidogyne javanica and M. incognita and their potential as suppressants in sequential cropping systems was evaluated in greenhouse and field experiments. Crops rated as resistant were five maize cultivars, four sorghum cultivars, two millet varieties, guwar and two pigeonpea cultivars which had galling indices ranging between 1.4-3.6. cowpea cv. K80 was rated as moderately resistant with a galling index of 4 while greengram and cowpea cv. KKI were rated as susceptible with galling indices ranging from 5.6 to 7.4. Four crops namely sweetcorn, babycorn, maize cv. Pioneer (Ph3253) and guwar were selected after the greenhouse tests for field trials, based on their poor host status to root-knot nematodes as well as relative acceptability to vegetable growers. These crops were then incorporated into a rotation program with okra. Initial and final J2 numbers in the field were determined before planting and at the end of the season, respectively. Okra was then sown in the plots previously grown with the selected nematode suppressive crops and the nematode numbers determined mid and end of the season. A 44 and 21% decline in nematode numbers was recorded in plots under guwar or sweetcorn and babycorn, respectively. In contrast, a 441% increase in nematode numbers was recorded in plots under continuous crop of okra. The galling index on a crop of okra that followed sweetcorn was 3.3 compared to 8.6 in the control which was continuously under okra, resulting in an increase in yield within a range of 60-92%. This underscores the potential of rotating highly susceptible crops with poor hosts in the management of root-knot nematodes.