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 <em>Lasioderma theobromae</em> <em>in vitro</em>. Three trials were set up using a completely randomized design with three replications. The first experiment used four isolates of <em>Trichoderma harzianum</em> (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 <em>Ixora, Guieria</em>, and <em>Bauhinia</em>, as well as <em>Eucalyptus</em> resin and <em>Ricinus </em>soap. The four isolates of <em>T. harzianum</em> inhibited the mycelia growth of <em>L. theobromae</em> 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%. <em>Ricinus</em> soap (50%, 100%), <em>Eucalyptus</em> (100%), and <em>Guieria</em> (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 <em>T. harziaum</em>, plant extracts, and mancozeb could be developed as a fungicide to control the soft rot fungus <em>L. theobromae</em> of sweet potato tubers