Antagonistic Activities of Indigenous Lactic Acid Bacteria Isolated from Fermenting Cashew Apples against the Fungal Complex Causing Post-harvest Carrot (Daucus carota L.) Rot in the Department of Daloa, Center-West, Côte d'Ivoire

Abstract

Carrots are an essential food crop in Côte d'Ivoire; however, their shelf life is limited by dehydration and fungal decay. Given the health risks associated with chemical preservatives, identifying biological conservation alternatives is crucial. This study evaluated the capacity of lactic acid bacteria (LAB) derived from local agricultural residues to inhibit the growth of fungi responsible for carrot rot. The methodological approach first involved isolating LAB from fermenting cashew apples and identifying fungal strains from both healthy and decaying carrot samples. Subsequently, direct in vitro dual-culture assays (bacteria–fungi) were performed on Petri dishes. Thirty-three LAB isolates were purified, and eight fungal genera were identified: Fusarium, Aspergillus, Rhizopus, Rhizoctonia, Mucor, Neurospora, Sclerotinia, and Trichoderma. The genera Rhizoctonia, Fusarium, and Sclerotinia were consistently present regardless of carrot condition, though they were more prevalent in decayed samples. Aspergillus, Mucor, and Rhizopus were detected more frequently in spoiled carrots, whereas Neurospora and Trichoderma were primarily associated with healthy carrots. Confrontation tests were conducted using three LAB isolates of distinct morphotypes (B16, B21, and B33) against seven fungal isolates actively involved in carrot decay (Fusarium sp., Aspergillus sp1., Aspergillus sp2., Aspergillus sp3., Rhizoctonia sp., Mucor sp., and Sclerotinia sp.). All three LAB isolates demonstrated biocontrol potential against carrot rot agents. However, isolate B21 exhibited the strongest inhibitory activity, achieving total inhibition (100%) of Fusarium sp. growth and a significant reduction (96.18%) in Aspergillus sp1. These results indicate that the use of lactic acid bacteria represents a promising and sustainable biological control alternative for reducing post-harvest carrot losses.