Maina mwangiRuth KahuthiaAgong, Steve Ochieng2022-03-252022-03-252021http://ir-library.ku.ac.ke/handle/123456789/23339A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of Master of Science in Crop Protection (Plant Pathology) in the School of Agriculture and Enterprise Development of Kenyatta University, 2021Potato late blight (Phytophthora infestans (Mont.) de Bary) is a major threat to potato production instigating overreliance on synthetic fungicides. Synthetics however, cause human health complications, environmental pollution and resistance development by late blight; this can be substituted with safer biological control options. The study objective was to enhance potato production through sustainable management of potato late blight. In May 2018, a baseline survey was carried out in Nyandarua County to assess the socio-demographic factors, potato production and crop management practices that impact on prevalence of potato late blight. Overall, 105 small scale farmers were interviewed using semi-structured questionnaires. Survey data was analyzed using SPSS v.20. Fungi were isolated from potato rhizosphere using serial dilution method and subsequently screened in vitro via dual culture technique. Crude extracts were prepared from bioactive plants using maceration technique then evaluated in vitro via poison food technique. Data, on P. infestans mycelial growth inhibition and suppression by fungal isolates and crude extracts, respectively, was analyzed using SAS v.9.2 at P≤0.05. Azadirachta indica extract and Trichoderma hamatum isolate caused significant suppressive and inhibitory effects in vitro of up to 59.1 and 50.2%, respectively. Trichoderma harzianum, T. afroharzianum, T. asperellum, A. indica, Pistacia lentiscus and Tithonia diversifolia significantly (P<0.05) suppressed pathogen growth in vitro thus were considered for further screening in the field. Isolates were tested on potato cultivars, Shangi and Tigoni, compared to water and Master® as controls. The trial was an RCBD for three cropping seasons, including two long rains (May to August 2018 and April to July 2019) and one short rain (December 2018 to March 2019). Data on disease incidence, severity and yield was analyzed using SAS v.9.2 at P≤0.05. Findings showed male dominance in potato production at 62%, 43.8% of respondents attained primary education, 74.3% used saved seeds and 65.8% used a single fungicide class. Under field evaluation, T. hamatum significantly (P<0.001) reduced disease incidence and severity on Shangi and Tigoni by up to 92.7±4.3 and 54±6.1%, respectively (May to August 2018). Azadirachta indica and T. hamatum supressed disease up to 89.1±2.3 and 65.2±4.5%, respectively, on Tigoni variety. Fungal antagonists generally caused significantly (P≤0.001) higher yields compared to plant extracts. During May to August 2018 and April to July 2019, T. harzianum and T. diversifolia yielded up to 3.65±1.2t/ha and 5.75±1.3t/ha, respectively. Education is considered important as knowledge level influences decision making and adoption of technologies and practices. Use of farm saved seeds is a potential source of inoculum and use of single fungicide class could lead to resistance development. Therefore, enhancing farmers‟ knowledge and promoting good agricultural practices that include IPM can improve management of potato late blight thus enhancing productivity. These results demonstrate existence of biologically active microorganisms and crude extracts from plants in the local environment that can be exploited towards developing affordable and safer management products for use against P. infestans.enBiocontrolBlight Phytophthora InfestansFungal AntagonistsPlant ExtractsKiambuNyandarua CountiesKenyaThesis