Biocontrol efficacy of Trichoderma isolates in controlling aflatoxinogen fungi (Aspergillus flavus) and growth promoting of maize in Cameroun

Abstract

<title>Abstract</title> Maize is a significant cereal crop, serving as a dietary staple and an indispensable raw material for industrial use in Cameroon. Aflatoxinogen fungi (<italic>Aspergillus</italic> spp), an opportunistic plant microorganism, alter by mycotoxin the biochemical components in maize during processing and storage, causing post-harvest losses and compromising food safety. The use of <italic>Trichoderma</italic> spp as a biological control agent against aflatoxigenic fungi and as a fertilizer has long been proven in agriculture by numerous researchers. This study aimed to isolate and characterize <italic>Trichoderma</italic> spp from maize rhizosphere soil and assess its potential for biological control of <italic>Aspergillus</italic> spp isolated from maize seeds and for promoting the growth of maize. Isolation and sequencing showed that our isolates were <italic>Trichoderma harzianum</italic> for CR-TS1 and <italic>T. ghanense</italic> for CR-TS3, CR-TS4, and CR-TC1. When tested directly against <italic>A. flavus</italic> on a PDA medium, the <italic>Trichoderma</italic> spp inhibited growth with percentages of 78.83%, 77.01%, 75,88%, and 74,95% for CR-TS1, CR-TS3, CR-TC1, and CR-TS4 respectively. Similarly, to verify our isolates' capacity to secrete volatile compounds, a remote confrontation test was carried out by contrasting <italic>Trichoderma</italic> spp and <italic>Aspergillus</italic> spp. The results of this test demonstrated the secretion of volatile compounds by our <italic>Trichoderma</italic> spp with inhibition of 40.94%, 29.48%, 34.36, and 32.19% respectively for CR-ST1, CR-ST3, CR-TC1, and CR-TS4. Our study also showed that isolated <italic>Trichoderma</italic> spp can produce extracellular enzymes such as amylase, protease, and lignase. Similarly, the phosphate solubilization test on Pikovskaya (PVK) medium and the siderophore test on chrome azurol S (CAS) agar medium using our <italic>Trichoderma</italic> spp isolates were all positive, with halo formation around the colony for phosphate solubilization and a color change from blue to yellow for the siderophore. IAA, one of the phytohormones essential not only for the microorganism but also for the plant, tested positive on PDB medium supplemented with L-tryptophan. Similarly, the application of 10⁷ spores/ml of suspension to maize seeds in vitro significantly (p &lt; 0.05) boosted maize germination from 90 to 100% compared with the control, which was at 80%. The results of pot experiments carried out to assess the growth promotion effect of our isolates showed a significant increase in plant size, root length, dry and fresh weight of plants and roots, as well as chlorophyll production. All these results show that our isolates can be used in agriculture as a biocontrol agent for aflatoxinogenic fungi and as a fertilizer.