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On-farm and on-station field experiments were carried out to determine the potential of combining Bacillus subtilis with soil fertility management practices on plant parasitic nematodes and growth of common bean (Phaseolus vulgaris). The treatments were Bacillus subtilis (isolate K194), B. subtilis plus cow manure, B. subtilis plus mavuno, Bacillus subtilis plus farmer practice, manure alone ,mavuno alone with farmer practice as the control. The farmers’ practice entailed application of tripple super phosphate and calcium ammoniun nitrate at the rate of 1000 and 890 kg/ha, respectively. Manure and mavuno were applied at the rate of 10 tons and 890 kg/ha, respectively. The on-farm trial was carried out in 12 different farms. The combination of Bacillus subtilis and cow manure led to a 54% reduction in numbers of plant parasitic nematodes, compared to the untreated control. Consequently, damage by root-knot nematodes was 1.6 and 4.5 in plots treated with the combination (B. subtilis and cow manure) and the untreated control, respectively. Compared to the other treatments, combining B. subtilis and organic amendments resulted in the highest nematode evenness diversity. It can be therefore be concluded that the plant parasitic nematodes associated with common bean can be maintained at levels below economic threshold using B. subtilis combined with cow manure, an integration which also demonstrated conservation of the nematode diversity.

Natural entomopathogenic nematodes (EPNs) are considered as potential biological control agents against soil-borne insect pests. This study was conducted to determine the impact of land use on the distribution, occurrence and diversity of entomopathogenic nematode community. Isolation of EPNs was done using the baiting technique and application of morphological identification methods revealed presence of the genus Steinernema. Land use intensification negatively affected the occurrence and recovery frequency in soils of Embu and Taita districts. The occurrence of EPNs was high in soils from coffee than maize and beans which had more nematodes than planted forest and napier grass followed by natural forest and tea respectively. PCR-RFLP of the internal transcribed spacer region on the ribosomal(r) DNA of the EPN isolates and digestion of the products by Alu I enzyme showed molecular variations among the isolates. The study has demonstrated that the frequency of occurrence and species variation of EPNs is different in various land uses.

The effect of soil fertility management practices on nematode destroying fungi was investigated for three seasons in Taita, Kenya. The study aimed at identifying soil fertility practice that promoted nematode destroying fungi in the soil. Field experiments were established in Taita district, the treatments comprised of Mavuno fertilizer, Triple super- phosphate and calcium ammonium nitrate (TSP+CAN), cow manure and a control where no amendments were applied. This experiment was replicated in ten farms and repeated in three planting seasons. Isolation of nematode destroying fungi carried out was using the soil sprinkle technique and the isolates were identified using the key described by Cooke and Godfrey (1964). There were significant difference (P= 1.705 x 10-06) in occurrence of the nematode destroying fungi between soil fertility treatments. The highest mean (1.6) occurrence of nematode destroying fungi was recorded in soils amended with cow manure and the least (0.7) was recorded in soils from the control plots. A mean of 0.78 was recorded in soils from both TSP+CAN and Mavuno fertilizers. Plots amended with cow manure presented the highest diversity of nematodes followed by the control, then TSP+CAN and least in Mavuno with shannon indices of 0.34, 0.15, 0.13 and 0.11 respectively. Sixty percent of all the isolated nematode destroying fungi genera were from plots treated with cow manure and only twenty percent were from plots amended with the inorganic fertilizer. The control plots recorded higher number of nematode destroying fungi compared to the soils that received inorganic fertilizers.

This study was conducted to determine the effect of land use and intensity of land cultivation on the nematode community structure. The land use types represented in the study sites were natural forest, plantation forest, tea, coffee, napier grass, agroforestry, fallow and annual crop cultivation dominated by maize intercropped with beans. Nematode diversity and abundance decreased with intensity of land cultivation, with the natural forest being regarded as the benchmark. The decrease in nematode diversity was assessed using Shannon, Simpson and species richness indices and was used to reflect the underlying changes in physical, chemical and biological properties of soil environment. The highest maturity indices for free-living and plant parasitic index were recorded in the natural forest and intensively cultivated land under annual crops (maize/beans), respectively. Plant parasitic nematodes were predominant in soils that were under agricultural production while saprofagic nematodes dominated the forested land as exemplified by the ratios of free-living to plant parasitic which were, 5.18 and 0.54 in the natural forest and annual crop production systems respectively. Changes in the nematode community structure, as exhibited by diversity indices, may be a reflection of real differences in the soil characteristics and changes in ecosystem functions.

Due to the increased concerns about the effect of agro-chemicals on soil health and soil biodiversity, use of biological methods has become most acceptable alternative methods for farmers to control soil pathogens during crop production. A study was therefore undertaken to determine the occurrence of nematode destroying fungi in Taita Taveta with the aim of isolating and characterizing them for biological control of plant parasitic nematodes. Twenty eight fungal isolates, distributed in three genera, were identified as nematode destroying fungi from all the positive soil samples. Out of the isolates that were identified, 71, 25 and 4 % were in the genera Arthrobotrys, Monacrosporium and Nematoctonus respectively. Arthrobotrys oligospora had an occurrence frequency of 42.9% which was the highest followed by A. dactyloides, M.cionopagum, Monacrosporium sp and Nematoctonus sp with frequencies of 28.6, 17.9 and 7.1and 3.6% respectively. The occurrence of nematode destroying fungi was affected by land use and organic inputs (P ≤ 0.05) while it was not affected by crop rotation (P ≥ 0.05). Napier land use was more diverse than the other land uses with a mean shannon diversity index of 0.717 followed by horticulture (index 0.497). Maize /bean, coffee/beans, fallow and shrub land uses had a mean shannon index of 0. The same trend was observed on richness where napier had a mean richness of 2.2, horticulture 1.8, maize bean 1 while shrub, fallow and coffee/ beans all had mean richness of 0.2. A.oligospora was the most frequently isolated fungi (42.9 %) and showed high potential in biocontrol of plant-parasitic nematodes and was recommended for further studies and development as a biological control agent.