Charactrization and determination of efficacy of local trichoderma isolates as a biocontrol agent (BCA) on fusarium wilt on beans (phaseolus vulgaris l).
Recent studies show Trichoderma species are not only parasites of fungal plant pathogens but also can enhance plant growth and development. Heavy applications of agrochemicals in soils in Embu County due to dependence on inorganic fertilizers and pesticides have potential to cause negative effects on environment leading to decrease of food production in agriculture. A study was conducted to evaluate virulence efficacy of local Trichoderma isolates as Biocontrol Agent (BCA) on soil pathogenic fungi. Isolates of Trichoderma koningii, Trichoderma asperellum, Trichoderma atroviride, Trichoderma reesei, and Trichoderma harzianum from Embu soils were evaluated for their ability to inhibit the mycelial growth of pathogenic fungi Fusarium oxysporum f.sp. phaseoli., in culture. Trichoderma spp. were also evaluated for the suppression of Fusarium oxysporum f.sp. phaseoli., under greenhouse condition. Trichoderma spp. were further investigated for their ability to promote plant growth and development of maize and bean seedlings in Embu County in Kenya. Subsequently, genetic characteristics of the five Trichoderma isolates were analyzed to confirm bioefficacy activities in relation to their molecular similarity. Trichoderma isolates significantly (p < 0.01) reduced the mycelial growth of the pathogen. Growth suppression by Trichoderma reesei against Fusarium oxysporum f. sp. Phaseoli., had the highest effect in inhibition of mycelial growth (60.0%) with p-value 0.018), followed by Trichoderma koningii (55.2%) with (p=0.014) deploying antibiosis and mycoparasitism mechanisms. Differences were observed with treatment of Trichoderma reesei combined Manure recording the highest with seed emergence germination index of 1.88, followed by Trichoderma koningii combined Fusarium oxysporum (1.86). The application of inoculum with Trichoderma koningii combined Fusarium oxysporum (6.7%) and Trichoderma reesei combined Manure (6.7%) gave the highest reduction in disease incidence of Fusarium wilt on bean plants. Treatments with manure increased the shoot height by 36.6 mm followed by inoculation of Trichoderma koningii + Manure (35.2) and Trichoderma koningii (34.7). Effects were highly significant at p < 0,001 with f- value of 4.716. The highest rate of seedling emergence was 84% for maize seeds coated with the Trichoderma inoculum and planted in soil amended with manure. Similarly, differences were observed with Manure + Trichoderma treatment of 74.40% and Manure (74.00%) recording the highest germination rates followed by both Trichoderma treatments with both TSP/CAN and Mavuno (69.60%). This study demonstrated that local isolates of Trichoderma reesei and Trichoderma koningii were identical in their biocontrol characteristics as well as potential for use as biological control agents to protect bean plants from Fusarium oxysporum f.sp. phaseoli.,