PLANT-PARASITIC NEMATODES ASSOCIATED WITH MAIZE, SORGHUM AND PEARL MILLET AND INTERACTIONS OF Pratylenchus brachyurus WITH MAIZE AND SORGHUM IN THE NIGERIAN SAVANNAS

PLANT-PARASITIC NEMATODES ASSOCIATED WITH MAIZE, SORGHUM AND PEARL MILLET AND INTERACTIONS OF Pratylenchus brachyurus WITH MAIZE AND SORGHUM IN THE NIGERIAN SAVANNAS

Abstract:

This study was undertaken to determine the identity, distribution and economic importance of plant-parasitic nematodes associated with maize, sorghum and pearl millet. Subsequently, the population dynamics of one of the most important nematodes was studied in order to develop management strategies for the nematode. Twenty genera of plant-parasitic nematodes, occurring in varying frequencies and populations in farmers’ fields were found associated with maize, sorghum, and pearl millet. Cluster analysis classified the nematodes into three broad groups. Group I, comprised nematodes that occurred frequently and usually of high population. Group II, consisted of nematodes that were not widely distributed and occurred usually in low numbers while Group III, was made up of nematodes of occasional occurrence and usually in very low numbers. Out of the twenty nematode genera, six genera, viz.; Helicotylenchus, Tylenchus, Pratylenchus, Scutellonema, Aphelenchoid.es and Hoplolaimus appeared to be the most important on account of the frequency of their occurrence, and population densities. Further analysis on the pattern of distribution/and or association of the nematodes in the various fields resulted in eight field groups, the nematode populations of each genera varying from field to field. This suggests a close relationship (interaction) between nematode species and field conditions. The cropping systems in the field were found to influence nematode occurrence and population densities. Maize-based systems were particularly found to favour the distribution and population densities of most nematode species compared to systems dominated by sorghum, millet, and legumes. Out of the six nematode genera rated as important in this study, Pratylenchus brachyurus was selected and some detailed studies conducted on maize and sorghum. P. brachyurus was shown to be pathogenic on both maize and sorghum resulting in significant reduction in plant growth. This reduction was however more for maize than sorghum. Results of the study on effect of different population densities of P. brachyurus on maize showed that all growth parameters were reduced at all populations tested when compared to the check. Nematode invasion reached a maximum at a density of 2000 nematodes and declined thereafter. The reaction of thirteen maize cultivars to P. brachyurus was studied in the screenhouse. None of the cultivars was found to be resistant. Nematode multiplication was highest in improved cultivars especially hybrids. Studies on the population dynamics of the nematode in June sown maize showed that P. brachyurus infected maize as soon as roots emerged. Populations increased rapidly and reached a maximum in roots and soil in early September and late August, respectively. Economic importance of P. brachyurus was determined by treating infested field with furadan 3G at 2.0 kg a.i/ha. Pre-plant (about 300 nematodes/500 ml soil) populations were significantly reduced resulting in a yield increase of about 38%.

PLANT-PARASITIC NEMATODES ASSOCIATED WITH MAIZE, SORGHUM AND PEARL MILLET AND INTERACTIONS OF Pratylenchus brachyurus WITH MAIZE AND SORGHUM IN THE NIGERIAN SAVANNAS

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