Suppressive effects of composts on soil-borne and foliar diseases of French bean in the field in the western Indian Himalayas

Abstract

The high incidence of various soil-borne and foliar diseases is a major production constraint in the profitable cultivation of French bean. Compost and compost teas have been widely explored as an eco-friendly option for controlling plant diseases in container mixes. However, there is limited information regarding their disease suppressive potential under field conditions especially against diseases of French bean. The aim of this study was to investigate the suppressive potential of six composted substrates (farmyard manure, poultry manure, vermicompost, spent mushroom compost, Lantana camara and Urtica sp.), in comparison to a recommended chemical fungicide (carbendazim), against soil-borne and foliar diseases of French bean under the conditions of western Indian Himalayas. The field experiment was conducted over two growing seasons and the composts applied as a soil amendment and later as foliar sprays of their fermented extracts. There was a high level of root rot suppression (>33%) in the poultry manure, Lantana and Urtica compost treatments in both experimental years and these treatments were on par with the chemical seed treatment. All the compost treatments showed a moderate but significant reduction (>20%) in angular leaf spot severity also but none was comparable to that of chemical sprays. There was considerable variability in the suppressiveness of different composts. Overall, poultry manure, composted Urtica sp. and composted Lantana camara treatments were superior to other composts in suppressing both Rhizoctonia root rot ( Rhizoctonia solani Kühn) and angular leaf spot ( Phaeoisariopsis griseola (Sacc.) Ferraris). The different compost treatments exerted a significant effect on the population of Trichoderma spp. and fluorescent pseudomonads in the plant rhizosphere. The highest population of these antagonists was recovered from poultry manure and Urtica compost treatments indicating that it may be a major factor contributing towards the higher disease reduction observed in these treatments. All composts increased yield over the control with maximum yields recorded in poultry manure and Urtica treatments. Although Lantana compost suppressed disease, the yield levels in this treatment were quite low indicating that the compost may be phytotoxic. Our results suggest that application of composts and compost extracts derived from poultry manure and Urtica sp. has the potential to provide effective control of diseases and improve yield in bean under field conditions.