No abstract

Cassava (Manihot esculenta Crantz) production in sub-Saharan Africa (SSA) is constrained by the two biotic constraints namely, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). The aim of this study was to evaluate elite cassava genotypes for variation in agronomical traits, correlate them to CMD and CBSD parameters and identify stable genotypes in Alupe, Kakamega and Kibos in Western Kenya. Twenty three (23) elite cassava genotypes that had shown resistance to either one or both of CMD and CBSD in Eastern Africa were evaluated. The trial was conducted using an alpha lattice balanced design with twenty three (23) genotypes, replicated three times at Alupe, Kakamega and Kibos in Western Kenya for an extended cropping cycle between 2016 and 2017. Results showed significant differences (P ≤ 0.05) between genotypes and location (or agro-ecology), but not interaction (P ≥ 0.05), for all the agronomic performance parameters evaluated. All the 23 cassava genotypes evaluated across the three locations had mean cyanide potential levels ranging from of 3.00–6.00 and were therefore, sweet and not bitter. The significant but negative relationship between CMD and CBSD incidence and severity with agronomic performance implied that their relationship was inverse. Confirmation of stability for agronomic performance was achieved through AMMI analysis, using AMMI stability value (ASV). Stable genotypes based on AMMI stability values (ASV) for fresh root yield across Alupe, Kakamega and Kibos were KBH/2002/066, Kibandameno (a local standard check), NASE-18, Kizimbani and NASE-3. These genotypes need to be further evaluated in more environments to assess their wider adaptability and stability.

Common bean anthracnose caused by Colletotrichum lindemuthianum is one of the major biotic constraints to production of French beans (Phaseolus vulgaris L.) in Kenya. This study aimed at screening French bean genotypes in relation to their response to common bean anthracnose in order to identify potential sources of germplasm for breeding. The genotypes were tested in three sites (Kakamega, Mwea and Kutus) where results revealed a significant genotype by environment interaction effect (p ≤ 0.05) which emphasizes the strong influence of the growing conditions on the expression of host resistance. Physiological characterization identified a total of 14 distinct races out of 16 successfully plated isolates, revealing a very high diversity of C. lindemuthianum in Kenya. Six races have not been reported in previous studies in the country and are considered as new races, that is, races 84, 141, 246, 515, 576 and 768. Andean race 401 was the most virulent race with a virulence index of 67% among the genotypes. Molecular analysis using six sequence characterized amplified region (SCAR) markers revealed polymorphism among the genotypes. The SCAR markers SBB-14, SH-18 and SAB-03 have shown to be useful for marker assisted selection (MAS) of the target resistance genes. This study has also identified locally improved breeding lines as potential donors for resistance breeding to C. lindemuthianum in Kenya.

Aims: To investigate AFLPs for suitability as potential markers for identification of sources of Pythium resistance in bean genotypes preferred by poor small holder farmers.

Abstract:Common bean (Phaseolus vulgaris L.) is an important crop in the daily diet of more than 300 million people worldwide. Despite its importance, bean productivity is declining in western Kenya due to diseases and use of low yielding susceptible varieties. Among the diseases, ALS is a major biotic constraint of bean production in western Kenya. It causes an estimated yield loss of about 80% in the farmers' field when severe. There is still limited information on pathogen distribution in western Kenya hindering breeding for ALS resistance. Therefore, a study was conducted to determine the occurrence of ALS disease in bean growing areas of western Kenya. A disease survey was carried out during the long and short rains seasons of 2013 in six agro-ecological zones namely: Low midland zone 1 (LM1) (Rongo and Bumula), low midland zone 2 (LM2) (Busia, Bungoma and Rangwe), low midland zone 3 (LM3) (Siaya and Teso north), low midland zone 4 (LM4) (Bondo), lower highlands (LH1) (Nandi Central) and upper midland zone 1 (UM1) (Sabatia and Nandi south). UM1 recorded the highest disease incidence and severity, whereas LM4 registered the least. Similarly, there was a significant positive correlation between disease incidence and severity (r = 0.711; p<0.0001). The study found the incidence and severity levels of ALS in western Kenya as high as 100% and 3 respectively. Therefore, farmers should be encouraged to use certified seeds to minimise the severity of the disease.