Effect of Crop Management Practises, Temperature and Rainfall on Development of Angular Leaf Spot and Anthracnose on Common Beans in Trans Nzoia County, Kenya

Abstract

Plant disease is a major constraint in common bean (Phaseolus vulgaris L.) production in Kenya. Angular bean leaf spot (als) (Pseudocercospora griseola) and anthracnose of bean (Colletotrichum lindemuthianum) are foliar fungal diseases that affect common beans in Trans Nzoia County. Development of plant diseases are influenced by weather parameters including temperature, humidity, rainfall and farm cultural practices such seed selection, planting time, field sanitation practices and disease control methods. The overall objective of the study was to determine how crop management practices, rainfall and temperature affect the temporal development of angular leaf spot and anthracnose on common beans under diverse agro-climatic zones in Trans Nzoia County, Kenya. Farmers’ perception on seed access approaches to disease management practice for angular bean leaf spot and anthracnose of bean was determined through a survey carried out on 100 randomly selected common bean farmers in Trans Nzoia County by administering a semi structured questionnaire. Data was collected on the sources of seeds, preferred bean varieties, disease knowledge and management methods used by the farmers. A survey was done on six major breeding institutions which were KEPHIS, KALRO, CIAT, Egerton University, Simlaw and Seedco Groups of companies to understand bean breeding and availability of certified seeds to farmers. Purposive sampling method was used to select the key breeders for survey using a semi structured questionnaire which was done virtually. Field experiments were conducted in Kitale, Trans Nzoia County over two cropping seasons that was during the short rains in 2020 and during the long rains in 2021. The experimental treatments were in three plots that was KALRO Research centre (UM 4), Kitale Airstrip (UM 3) and Kibomet (LH 1) with a size of 0.5 hectares each and bean variety Rosecoco GLP 2 was planted in a Randomized Complete Block Design (RCBD). Temperature data was collected using a HoboMobile app while the rainfall measurements were recorded using a rain gauge installed 2m away from the plants within the field. Data on phenological stages of crop, plant height, disease incidence and severity collected two times a week during the cropping season. Samples of diseased plant materials were collected and the disease causing fungi isolated for identification. The survey showed that most farmers (82%) sourced their seeds from local markets and their own saved seeds from the previous harvest which they grow for household consumption. The most xv preferred bean variety was Rosecoco (GLP 2) because of its early maturity, high yielding and adaptability characteristics. Information on good agricultural practices was accessed through the extension officers by majority of the farmers (55%) on how to manage pests and diseases which was a major (51%) challenge on bean production. The major diseases observed on 78% of the farms were angular leaf spot and anthracnose of which most farmers used cultural methods to manage the diseases. Majority of breeders (33%) preferred to breed Rosecoco GLP2 since it had high intake in agroshops which they bred against disease tolerance and resistance. Majority (67%) had bred beans for disease resistance against angular leaf spot and anthracnose. The main challenge was pathogen variability among 50% of the breeders which occurred after the crops have been exposed to the environment. Majority of the breeders (60%) knew about common beans diseases in specific regions through the farm visit reports by extension officers. Results from the field experiments showed that increase in temperature and rainfall caused an increase in disease development. The disease severity was highly significantly (p<0.05) affected by increase in temperature. The development of the disease on the three AEZs was attributed to the varying environmental conditions. However, there was no significant difference in the temperature records on UM4, UM3 and LH1 during the long rains as the AEZs bordered each other hence the close climatic condition. During the short rains, there was a positive significant correlation of 0.031 between temperature and anthracnose severity. There was a significant difference (P<0.05) in temperature means between UM4 and UM3 during the short rains however there was no significant difference (P<0.05) in the different AEZs during the long rains. The study showed that farmer’s cultural practices such as choice of bean varieties and weather elements including temperature and rainfall increase disease development in the cropping system which later affects the expected yields. Breeders concentrated more on early maturity characteristics so that their variety could be accepted by farmers. Alternating periods of high and low rainfall with long periods of high humidity caused increase in both diseases across the three AEZs.