Effect of Tagetes minuta and Capsicum frutescens extracts on Pectobacterium carotovorum, growth, yield and quality of potatoes (Solanum tuberosum)

Abstract

Potato production is hindered by pathogens like Pectobacterium carotovorum that cause blackleg in the field and soft rot after harvest. The purpose of this study was to determine thepossibility of integrating Tagetes minuta and Capsicum frutescens extracts in the management of soft rot and blackleg in potatoes. The research was conducted at the horticulture research and teaching laboratory and field of Egerton University, Njoro. In vitro and in vivo experiments were set up in a Completely Randomized Design and Randomized Complete Block Design with three replications using aqueous extracts of T. minuta and C. frutescens each at 40%, 30% and 20% concentrations. Water and streptomycin sulphate/Copper oxychloride were negative and positive controls respectively. Data collected was analyzed using Genstat edition 4 and significantly different means were separated using Tukey’s HSD test. The treatments were applied on nutrient agar (using a modified disc diffusion method) and on potato chips to test for bacterial growth inhibition and their effect on potato tissue maceration. T. minuta (40%, 30% and 20%) showed zones of inhibition of 7.17 mm, 6.67 mm and 6.10 mm; streptomycin sulphate 8.83 mm which were significantly different from C. frutescens and distilled water that recorded 0.00 mm zones of inhibition. T. minuta and streptomycin sulphate showed a significant difference in the number of days (9 days) to total tissue maceration and percent weight loss from C. frutescens and water that took only 5 days for the potato chips to be completely macerated. For in vivo experiments, the treatments were applied on seed potato before sprouting, sprouted potato before planting and ware potato before storage. The plant extracts showed significant differences on disease incidence and severity on the plants and tubers in the field but showed no significant difference on growth parameters. The potato plants treated with 40% and 30% T. minuta; and copper oxychloride recorded low disease incidents (2 plants/plot) and low severity (40-54%) while those treated with water and C. frutescens showed high disease incidents (4 plants/plot) and high severity (57-93%). Copper oxychloride and T. minuta recorded low percent postharvest infections (6.5-12.11%) while C. frutescens had high infections (40- 95%). The extracts had no significant effects in the dry matter content and total soluble solids of the potatoes. It was found that T. minuta is effective against Pectobacterium both in vitro and in vivo and therefore it can be incorporated in the integrated disease management systems as an affordable bio-control component to manage blackleg and soft rot in potatoes.