Abstract:
Common bean is an essential crop for food security, nutrition, and country economy mainly for Sub-Saharan African’s smallholder farmers. However, the production and productivity of common bean is mainly constrained by post-harvest loss induced by Mexican bean beetle. Thus, the objectives of this study were to evaluate the effectiveness of Plant seed powders (neem, Hochst and wild marigold), leaf powders (sweet fennel and broad-leaved croton), plant essential oils (neem and Hochst.) and cooking oil (African cabbage edible oil) against Mexican bean beetle; to screen common bean genotypes for their resistance to Mexican bean beetle. The experiment was conducted at Plant Protection Laboratory during 2021/2022. To this end, twenty adult unsexed 2-3 days old Mexican bean beetles were introduced to a glass jar containing 150 g of Tiniqe seed for botanical powders and oil treatments. Ten adult unsexed 2-3 days old Mexican bean beetles were introduced to each separate glass jar containing 20 g of different genotypes for screening. In the first botanical powders study, leaf and seed powders of each botanical at three rates of 5, 10, and 15 g, primphos-methyl at 0.2 g, and untreated control, were evaluated. In the second botanical oil test, plant essential and edible oils were compared at three rates of 0.5, 1.5, and 3 mL, primphos-methyl at 0.2 g and acetone-treated control. In the common bean genotype screening experiment, thirty-one common bean genotypes were evaluated for their resistance to Mexican bean beetle. In all the experiments, a completely randomized design (CRD) with three replications were used. All parameters at all botanical seed and leaf powder rates showed a significant (P ≤ 0.05) difference over the untreated control, except for seed damage at 5 g leaf powders of sweet fennel and broad-leaved croton. The plant material neem, wild marigold, and Hochst at the rates of 5, 10, 15 g/ 150 g, and sweet fennel at 10 and 15 g/ 150 g and broad-leaved croton at 15 g/150 g resulted in 96 – 100% seed protection, reduced beetle emergence, seed damage, seed weight loss, and were statistically at par with primphos-methyl. All tested botanical powders recorded 87 – 100% germination. The results of the botanical oils and Ethiopian mustard cooking oil indicated significant (P ≤ 0.05) differences over the acetone-treated control. The botanical oils and Ethiopian mustard cooking oil at rates of 0.5, 1.5, and 3 mL per 150 g common bean produced adult beetle mortality in the range of 93 – 100% and seed protection of 99 – 100%, similar to that of positive control- primphos-methyl. However, common beans treated with botanical oils showed a significant reduction in germination compared to primphos-methyl. The genotype screening indicated significant differences in treatment resistance to Mexican bean beetle. A significant level of variation was recorded for all the parameters measured among the genotypes. Complete resistance was recorded from genotypes RAZ – 11, RAZ – 42, 241752, and 215051 with zero indexes of susceptibility value. Moreover, six other resistance genotypes were also identified from the landrace (211340, NC - 8, EGA034, 230525, 244805, and EGZ044) collection based on Dobie’s susceptibility index. Thus, smallholder farmers can use any of the above indicated botanical powders or oils for post-harvest storage depending on their availability, low cost, and ease of application. However, future research is needed to test these essential oils and powders via various formulations to commercial availability for the small-holder farmers. These genotypes can be used as a source of resistance during variety development for future breeding works through backcross breeding techniques. Further research on the botanical powders and oils under farmer’s storage condition is important. Moreover, periodical screening of common bean genotypes, especially from local landraces, is important to have more resistant sources.