ASSESSMENT OF SUSCEPTIBILITY OF GARDEN PEA (Pisum sativum L.) VARIETIES TO ASCOCHYTA BLIGHT AND EVALUATION OF EFFICACY OF CHEMICAL AND BIOLOGICAL (Trichoderma spp.) FUNGICIDES IN NAKURU COUNTY, KENYA

Abstract

Garden pea (Pisum sativum L.) is a nutritionally and economically important legume widely cultivated for its high protein content and nitrogen-fixing capability. However, its productivity is significantly constrained by Ascochyta blight, a fungal disease favoured by cool and moist conditions. This study aimed to evaluate the susceptibility of four garden pea varieties; Nano Progress 9 (Grano), Peas Plum, Peas Kelvedon, and Peas Greenfeast to Ascochyta blight, and to assess the efficacy of selected chemical fungicides (mancozeb, chlorothalonil, benomyl, and carbendazim) and the biocontrol agent Trichoderma harzianum in disease management under field and laboratory conditions in Nakuru County, Kenya. Field trials were conducted in Molo Sub-county using a Randomized Complete Block Design (RCBD) with ten replicates, where soil fertility served as the blocking factor. Laboratory experiments followed a Completely Randomized Design (CRD). Data were analysed using two-way ANOVA for field data, and one-way ANOVA for laboratory data. Means were separated using Fisher’s Least Significant Difference (LSD) test. Although varietal differences in disease severity were observed, they were not statistically significant (p = 0.107), with Peas Nano Progress 9 exhibiting marginally lower severity compared to Peas Plum, Peas Kelvedon, and Peas Greenfeast. All tested fungicides significantly reduced disease severity compared to untreated controls (p < 0.001), with chlorothalonil showing slightly higher efficacy. In vitro dual culture assays demonstrated that Trichoderma harzianum significantly inhibited the growth of Ascochyta pisi, achieving a 90.9% reduction in radial colony diameter (p = 0.001). These results highlight the effectiveness of chemical fungicides and the potential of T. harzianum as a biocontrol agent. However, the limited resistance among varieties underscores the need for breeding programs targeting disease-resistant cultivars. Further research is recommended to validate the efficacy of T. harzianum under field conditions and to explore broader genetic resources for resistance breeding in garden pea varieties. Determination of resistant garden pea varieties coupled with synthetic fungicides and T. harzianum warrants further research, as it presents a promising approach for the sustainable management of Ascochyta blight disease in garden pea.