Performance Of Bean Genotypes Under Disease Pressure In Different Environments And Planting Dates In Western Kenya

Abstract

The common dry bean (Phaseolus vulgaris L.), plays an important dietary role as the second most important source of human dietary protein and the third most important source of calories of all agricultural commodities produced in eastern and southern Africa. Dry bean farming in Western Kenya faces challenges of diseases attributed to a limited number of released bean varieties with multiple disease resistance. This study assessed the performance of bean genotypes under varying disease pressure over multiple environments and different planting dates. Common bean varieties were planted in upper-midland zone 1 and upper-midland zone 3-4 in Kakamega County and upper-midland zone 2, upper-midland zone 4 and lower-midland zone 2 in Bungoma County over different sowing dates in the short rains of 2016 and the long rains of 2017. Natural infection of the genotypes by diseases was allowed to occur. Disease intensity, yield and yield components data were collected and subjected to combined analysis of variance with differences between treatments compared at p ≤ 0.05. Diseases observed were anthracnose (Colletotrichum lindemuthianum), scab (Elsinoë phaseoli), angular leaf spot (Pseudocercospora griseola), rust (Uromyces appendiculatus), floury leaf spot (Mycovellosiella phaseoli), Cercospora leaf spot, common bacterial blight (Xanthomonas axonopodis pv. phaseoli), halo blight (Pseudomonas savastanoi pv. phaseolicola), bacterial brown spot (Pseudomonas syringae pv. syringae), bean common mosaic virus, bean common mosaic necrosis virus and golden mosaic virus. The environment had an effect on both disease pressure and yield as the agro-ecological zones performed significantly (p ≤ 0.05) different to each other. Upper midland zone 1 was significantly (p ≤ 0.05) the best performing environment with 1.9 t/ha in the long rains and 1.5 t/ha in the short rain season. Upper midland zone 1 and UM 2 also had higher disease pressure compared to lower lying UM 4 and LM 2. Rust and scab had the highest intensity xviii among the diseases with 44.7 and 51.8% respectively in the short rain season. Genotypes reacted variably to disease pressure in the environments with variety Red 16 generally having the least disease pressure and highest yields of 2.2 and 1.3 t/ha in the long and short rains, respectively. There was significantly (p ≤ 0.05) less disease pressure in the early plantings compared to late plantings. Yield significantly (p ≤ 0.05) decreased as disease pressure increased with lateness of sowing therefore late planting had a combination of high disease pressure and low yields compared to early planting. This study shows that at the environment level, abiotic factors such as precipitation outweigh diseases in their influence on the overall performance of the genotypes. However, disease intensity has an important role on the performance of varieties within an environment. The highest yields are achieved through early planting, as this is when overall disease pressure is lowest. Early planting of beans is a strategy that can effectively manage diseases and should be included in integrated pest and disease management (IPDM) strategies. Varieties Red 16, Cal 33 and Cal 194 showed multiple disease resistance, were high yielding and stable and can be recommended to farmers or further improved by incorporating missing resistances