Dynamics of potato late blight on tubers and farmers' management of the disease in Kenya highlands.

Author: Nyankanga, Richard Ombui

Awarding University: Cornell University, USA

Level : PhD

Year: 2003

Holding Libraries: University Microfilms International ;

Subject Terms: Crop diseases ; Farming ; Phytophthora infestans ; Pesticides ;

Pages: 0

Advisors: Adviser: Wien, H C


The focus of this dissertation was on understanding the dynamics of field infection of potato tuber infection by Phytophthora infestans. It also examines methods that could be used to manage tuber blight in the field. Factors affecting the relationship between foliage late blight and tuber infection were studied both in New York and in Kenya. The relationship between levels of foliage blight and tuber infection was examined by varying disease on foliage by different fungicide regimes. Fungicide application either in terms of different rates or spray intervals did not have a significant effect on tuber blight incidence. No significant association was found between foliage disease levels and tuber infection. Generally, cultivar characteristics, soil temperature, and precipitation events moderated the relationship between foliage and tuber blight. Development of regression models using tuber resistance and depth, soil temperature, and precipitation had moderate predictive ability in ny (r<super>2</super> = 0.56) but poor prediction in Kenya (r<super>2</super> = 0.34). Evaluation of hill sizes and mulch as barriers or filters of inoculum before reaching the soil was assessed in ny. Hilling suppressed tuber infection moderately under moderate epidemics but was ineffective under high disease pressure. Mulching was ineffective under the epidemics in the two years the experiments were conducted. Potato cultivars and advanced clones were assayed in vitro over two years in Kenya for tolerance to tuber blight. Relative resistances of the genotypes differed significantly among cultivars and advanced clones. Resistance in tubers was marked by high variability and may be due to minor genes. No significant correlation was observed between components of tuber resistance and foliage blight ratings indicating that tuber resistance might be different from the resistance in the foliage. A range of tuber blight resistance was observed from which lines with resistance may be developed. A survey of farmers was conducted in three potato growing areas in Kenya in 2000 and 2001 to evaluate farmers' perception, knowledge and management potato late blight. Results indicated that farmers had a limited understanding of late blight. High cost of fungicide, poor application techniques, incorrect dosage of fungicides, and preference of susceptible cultivars were among the reasons contributing to lack of adequate control of late blight. Farmers' preference for potato cultivars was not based on late blight resistance. Other constraints like lack of markets, prevalence of bacterial wilt and scarcity of quality seed were identified as serious constraints of potato production. Improvement of potato late blight control should include provision of knowledge and addressing these other constraints.