of Plant Breeding and Crop Science

Common bacterial blight (CBB) is the most serious bacterial disease of common bean in Uganda. It causes severe yield losses of up to 62%. Genetic resistance is the most effective option for controlling CBB in smallholder common bean production systems. This study was carried out to determine the inheritance pattern of CBB resistance in leaf and pod of four new resistance sources. The four resistant and four susceptible genotypes were crossed in a half-diallel mating design. F 1 individuals were advanced to F 2 and evaluated with the parents, in a randomized complete block design replicated twice. Combining ability analysis was performed according to Griffing's (1956) method IV and model 1 using Genstat 12th. General combining ability effects were significant whereas specific combining ability was not suggesting that resistance to CBB in leaf and pod was primarily controlled by additive genes effects. The estimated narrow sense coefficient of genetic determination was moderately high (0.65) for the resistance in leaf and high (0.83) for resistance in pod suggesting that early-generation selection would be effective. Baker’s ratio estimates were relatively high for resistance in leaf (0.79) and pod (0.9) suggesting that hybrids’ performance can be predicted based on the parents’ general combining ability (GCA) effects. A total of 21 okra ( Abelmoschus escuentus L. Moench) genotypes were screened for their reactions against okra mosaic disease (OMD) and flea beetles ( Podagrica species) infestations in field trials which were conducted from May to October, 2015 (wet season) and November 2015 to March 2016 (dry season), in order to identify sources of resistance and or tolerance. The trials were laid out in a randomised complete block design (RCBD) with four replications. Field resistance in the genotypes was assessed at 2, 6 and 10 weeks after planting using a 0 to 5 visual scale based on disease symptoms (where 1 denotes no symptom and 5, very severe symptom). Enzyme linked immunosorbent assay (ELISA) was performed to detect the presence of Okra mosaic virus (OkMV) in the okra genotypes. Populations of the flea beetle ( Podagrica spp.), the vector of OkMV, and the associated leaf and fruit damage were also assessed. All the okra genotypes exhibited a varying range of disease symptoms and the flea beetle infestations, and lacked immunity. Genotypes GH2052, GH2063, GH2026, GH3760, GH5302, GH5332, GH5793, GH6105 and UCCC6 exhibited mild symptoms of OMD, and were less susceptible to flea beetle infestation and associated leaf damage during both seasons. Using ELISA, OkMV was detected in all the 21 genotypes. The mean number of fruits per plant and the mean fruit yield (t ha -1 ) differed significantly ( P <0.05) among the okra genotypes. Genotype GH5332 had the highest fruit yield of 11.88 t ha -1 followed by genotype GH6105 (9.34 t ha -1 ). Percentage fruit damage due to the flea beetle infestation differed significantly among the okra genotypes, ranging between 43.7 and 91.2% and from 47 to 84% in both trials respectively. mosaic virus (OkMV) in leaf samples tested in both rainy and dry seasons. where Y i is the disease severity at the i th observation, X i is the time (weeks) at the i th observation, n is the total number of observations. Data on disease incidence and insect counts were transformed with angular and square root transformations, respectively in order to homogenise the variance before subjecting to ANOVA. All other quantitative data were subjected to one-way ANOVA and two-way ANOVA and the means separated by least significance difference method at 5% level of probability using GenStat Discovery version 4 (VSN International). Pearson's correlation coefficients among the parameters (disease incidence and severity, insect counts and associated leaf and fruit damage and yield data) were calculated using GenStat.