IN VITRO EFFICACY OF DISPARATE FUNGICIDES AGAINST Lasiodiplodia theobromae ROOT ROTS OF ORANGE-FLESHED SWEET-POTATO VARIETIES

Abstract

Sweet-potato cultivation is limited globally by many storage rots caused mainly by fungi. The study aimed to test the effectiveness of several types of pesticides against Lasioderma theobromae in vitro. Three trials were set up using a completely randomized design with three replications. The first experiment used four isolates of Trichoderma harzianum (AIM16, NSBM, BGMZ4, and AIM3). The second trial was evaluating types of synthetic fungicides, i.e., mancozeb (50%, 100%), mancozeb+carbendazim (50%, 100%), and mancozeb+metalaxyl+Cu (50%, 100%). The third experiment testing botanical pesticides, namely leaf extracts of Ixora, Guieria, and Bauhinia, as well as Eucalyptus resin and Ricinus soap. The four isolates of T. harzianum inhibited the mycelia growth of L. theobromae by 8.0–100%, significantly different from the control, but there was no significant difference between the isolates. Solutions of mancozeb (100%) and mancozeb+carbendazim (50%, 100%) were more effective in suppressing the development of pathogenic mycelia compared to mancozeb+metalaxyl+Cu. Mancozeb treatment inhibited 8.0–100% of pathogen growth and was significantly different compared to other treatments. Plant extracts inhibited the growth of pathogens by 8.0–100%. Ricinus soap (50%, 100%), Eucalyptus (100%), and Guieria (100%) consistently inhibited the growth of pathogenic mycelia by 70%. Plant extracts and mancozeb were effective in suppressing the growth of pathogenic mycelia. The study indicates that T. harziaum, plant extracts, and mancozeb could be developed as a fungicide to control the soft rot fungus L. theobromae of sweet potato tubers