Efficacy of Neem, Tithonia And Tephrosia Leaf Extracts in Management of Root-Knot Nematodes in French Beans(Phaseolus Vulgaris L.) in Tharaka Nithi County, Kenya

Abstract

Agricultural production within the smallholder farming sector of East Africa is constrained by numerous factors including parasitic nematodes.Existing control measures involving applications of chemical nematicides are not viable in the medium to long term due to environmental concerns relating to their toxic residues. There is therefore a need to develop alternative control options for integrated parasitic nematode management that will promote soil eco health and reduce parasitic nematode densities. Meloidogyne spp is a major problem in Frenchbeans (Phaseolus vulgaris L.) productionsystems. In the search for alternatives to synthetic control of nematodes, a study was conducted at Chuka University Horticultural Demonstration Farm to determine the phytochemicalconstituents and nematicidal effects of crude extracts of Neem, Tithonia and Tephrosia on the control of root-knot nematodes in Frenchbeans. Crude extracts were subjected to phytochemical screening for the detection of various bioactive constituents. Constituents in Neem were alkaloids and saponins, In the invitro experiment the LC50 value of each extract was determined by assessing the mortality of juveniles and egg hatch (in the range of 5–95%) after 24, 48 and 72 hr for seven days. In a lath house pot and field experiments to determine the efficacy of the crude extract application on Frenchbeans root-knot nematodes, the Fenchbeans were planted on nematode infested soils and data on growth, development and yield components was collected. In the lath-house 5 kg pots were filled with steam-sterilized soil and infested with second stage juveniles of Meloidogyne spp.Similarly in the field experiment the planting holes were inoculated with second stage juveniles of Meloidogyne spp. The data collected was subjected to analysis of variance and significantly different means were separated using Tukey‟s Studentized Range Test at P≤0.05. In the phytochemical analysis Tithonia extracts showed the presence of alkaloids and flavonoids while Tephrosia only showed the presence of flavonoids. In invitro study, comparison between LC50 values of the extracts indicated that Neem and Tithonia at 100ml/l were the most effective on the mortality of juveniles and immobilized more than 80% of the juveniles treated. On egg hatching Neem extracts at 100ml/l were the most effective with over 90% inhibition. Among extracts treatments evaluated, crude leaves extracts obtained from Tephrosia at 100ml/l inhibited the greatest egg hatching at 0.8 eggs. Oxymyl (positive synthetic control) inhibited the greatest hatching among the treatments at 0.2 eggs. From the study the greatest egg hatching was observed in in the untreated controls at 5.5 eggs. Among the extracts evaluated, maximum mortality was recorded with Neem at 100 ml/l at 12.2 juveniles. Oxymyl inhibitory effects was recorded at 9.4 juveniles while the least inhibitory effects were observed in the untreated control at 4.3 juveniles. In both lath-house and field studies crude extract treated plots when compared to the positive control significantly had higher number of pods and pod weight. From the study it was observed that the untreated control treatment attained the least pods weight of 24.9 and 28.0 in Trials I and Trials II respectively. Neem at 50ml/l attained the highest average mean pods weight of 50.9 in both Trials I and Trials II .Oxymyl attained an average weight of 48.7 and 49.3 in Trials I and Trials II respectively. Untreated control recorded the least mean number of pods at 9.4 and 9.5 pods respectively in Trials I and Trials II. Neem at 100 ml/l attained the highest average mean number of pods at 17.4 and 17.6 pods respectively in Trials I and Trials II. (positive control) attained 15.3 and 15.5 pods respectively in Trials I and Trials II.BothLath house and field experiments indicated that the crude extracts tested had varying effects, with the majority of them reducing galling on Frenchbeans. The Neem extracts treatments had the lowest mean galling index followed by Tithonia.There was a significant (P ≤ 0.05) difference ingalling indices and yield between the leaves extract treatments and the control in both field and lath house pot Trialss. Root-knot nematode galling indices were highest in the untreated controlat 10a clear indication that the crude extracts suppressed the root-knot nematodes. There was however no significant difference between galling efficacies of crude extracts and Oxamyl in the lath house pot experiment. Once adopted, this integrated approach will result in increased yields and income to smallholder farmers. The crude extracts are affordable, easy to apply as well as environment friendly and hence sustainable over a long period of lime.