Abstract:
These studies on evaluation of cassava cultivars and intercropping with legumes as an integrated nematode control strategy in cassava production were carried out as greenhouse/microplot and field experiments. Of the 200 cultivars screened for resistance to Meloidogyne spp., only 76 survived and from this lot only 3 lines 77/227, TMS30572 and 73/222, showed any resistance while 7 others namely NR8082, 75.668, 73/238 (Egbenegbe), 73/295, 73/118, 75740(Panya), 82/00661 and 73295B were tolerant. All the other cultivars tested were susceptible. The second experiment, to determine the economic threshold level of the root-knot nematode M. javanica populations on two cassava varieties, showed that, with the exception of the control plants, the root-knot nematode damage was obtained at all levels of the inoculum used and the root-knot nematode populations had no significant effect on the aerial growth parameters like leaf and stake weights. The two cassava varieties differed significantly in the final nematode population in their roots. The economic threshold level was identified as an initial density of 500eggs/plant. The lower pest values obtained for TMS30572 with increase in inoculum density further confirmed it to be resistant to M. javanica. Intercropping four cassava varieties with four legume types in microplots revealed that nematode at both levels used, (0 and 1,000 eggs/plant) had no significant effect on growth and yield of the cassava but amongst sole and legume-intercropped cassava cultivars, significant differences were obtained. The feeder roots and stake/stem weights of the sole cassava varieties were significantly higher (p>0.05) than their intercropped mixtures with legumes. The highest tuber yield values were observed for NR8083 planted sole (630g/plant) followed by TMS30572 intercropped with bambaranut (537g/plant). Nematode-treated plants were significantly affected when they were destructively sampled for damage symptoms on the cassava. Though no significant effect was observed on yield, the significant nematode damage effects on the cassava indicate that the root-knot nematodes affect the outward appearance, the shelf life and storability of the cassava products. The productivity of the legumes under cassava was significantly different (p<0.05) especially on the aerial plant growth. Generally, the legume leaf, stake and feeder root weights (with a few exceptions) had higher sole values than their intercropped components. The same pattern was evidenced for the number of root nodules, where the sole legume number of nodules was higher than that of the intercrops. Significant legume yield differences (p<0.05) were obtained between NR8082-groundnut (60.62g/plant) and NR8082-bambarranut (17.2g/plant). The observed trend was that the intercropped legumes were lower in seed yield than their corresponding sole components. The number of root nodules had a direct linear relation with legume seed yield. However nematode treatment had no significant effect on the legume growth values. Legumes in intercrop mixtures had lower damage symptoms than their corresponding sole crops and sole groundnut was higher in infection scores right through than its intercropped legume cassava mixture. Notably, significant interaction was obtained in number of nematodes in the roots between the legumes in the mixtures and nematode treatment. The legumes in the mixtures significantly (p<0.05) reduced the damage effect of nematode treatment. The results from the two field sites followed the same trend as those obtained in the microplots. However, for bambaranut its intercrop variety for NR8083, TMS50395 and TMS30572 yielded more than the sole component. NR8083 cassava intercropped groundnut had the highest Land Equivalent Ratio (LER) of 1.811 in Site 1, followed by TMS50395 intercropped groundnut had highest LER (1.626) in Site 2. In line with the goal of Integrated Pest Management (IPM), integrating use of resistant cassava cultivars and intercropping with legumes has been identified as a successful IPM package for our farmers.
