Evaluation of Trichoderma spp. on Fusarium oxysporum f. sp. asparagi and Fusarium wilt Control in Asparagus Crop

Abstract

Among the key diseases affecting the asparagus crop (<i>Asparagus officinalis</i> L.), vascular wilting of asparagus caused by <i>Fusarium oxysporum</i> f. sp. <i>asparagi</i> stands out worldwide. This disease significantly shortens the longevity of the crop and limits economic production. Traditional control measures have been largely ineffective, and chemical control methods are difficult to apply, making biological control approaches, specifically the use of <i>Trichoderma</i>, an economical, effective, and risk-free alternative. This study aimed to identify the main factors that affect the efficacy of biopesticides studied as Biological Control Agents (BCAs) against Fusarium wilt in asparagus and to assess the efficacy of <i>Trichoderma</i>-based biopesticides under greenhouse and semi-field conditions. We evaluated the response of three <i>Trichoderma</i> spp. (<i>T. atroviride</i>, <i>T. asperellum</i>, and <i>T. saturnisporum</i>) to environmental variables, such as temperature and water activity, and their antagonistic capacity against <i>Fusarium oxysporum</i> f. sp. <i>asparagi</i>. All three <i>Trichoderma</i> species inhibited the growth of the pathogen in vitro. A decrease in water activity led to a greater reduction in the growth rate. The efficacy of the three biological control agents decreased with higher temperatures, resulting in minimal inhibition, particularly under conditions of restricted available water in the environment. The effect of the fungal inoculum density was also analyzed at two different temperatures. A direct correlation between the amount of inoculum and the score on the Disease Severity Index (DSI) was observed. A notable reduction in DSI was evident in treatments with high inoculum density (10⁶ conidium/mL) for all three species of <i>Trichoderma</i> tested at both temperatures. In greenhouse and semi-field tests, we observed less disease control than expected, although <i>T. asperellum</i> and <i>T. atroviride</i> showed lower disease severity indices and increased the dry weight of seedlings and crowns, whereas <i>T. saturnisporum</i> resulted in the highest disease rate and lowest dry weight. This work highlights that the efficacy of <i>Trichoderma</i> as BCAs is influenced by various factors, including the quantity of soil inocula, and environmental conditions. The study findings have strong implications for selecting appropriate <i>Trichoderma</i> species for controlling specific pathogens under specific environmental conditions.