Jen Tzeng

Plant-parasitic nematodes, particularly the root-knot nematode Meloidogyne incognita, severely threaten agricultural production in tropical and subtropical regions. Although nematode-trapping fungi have been considered environmentally friendly alternatives to chemical nematicides, their field performance often remains inconsistent due to limited ecological adaptation. This study combined a field survey of crop-associated nematode communities with laboratory and greenhouse evaluation of selected nematode-trapping fungal isolates under subtropical conditions. Field surveys across multiple crops identified M. incognita as the dominant plant-parasitic nematode species. Five fungal isolates with different trapping mechanisms were compared for growth under contrasting nutrient conditions and nematode-trapping efficiency. Among them, Drechslerella brochopaga (NTF2), which forms constricting rings, showed superior growth stability under nutrient-limited conditions and the highest nematode mortality in vitro. In greenhouse experiments, NTF2 reduced root gall formation in two of three independent trials, indicating potential but variable suppression of M. incognita on pumpkin. These findings highlight the importance of ecological adaptation and trapping strategy in determining the effectiveness of nematode-trapping fungi for sustainable nematode management.

Cylas formicarius (Fabricius) is a major pest of sweet potato in Taiwan, where no microbial control agents are currently available. This study aimed to identify Beauveria bassiana strains with both high virulence and high spore productivity using a rice-based solid-state fermentation (SSF) system. Eleven field isolates were characterized using morphological traits and multilocus sequence analyses (Bloc, RPB1, RPB2, and TEF). Laboratory assays compared conidial production on 1/2 potato dextrose agar (PDA) and rice substrates and evaluated pathogenicity against adult C. formicarius by estimating median lethal time (LT₅₀) and the onset of mortality (t₀) based on cumulative mortality data. Substantial variation was observed among isolates in growth performance, sporulation, and virulence. Strain TyEf0054 consistently exhibited high pathogenicity, causing more than 80% mortality with conidia produced from both 1/2 PDA and rice, and showed rapid killing activity, with LT₅₀ values of approximately 5.5–5.9 days and t₀ values ranging from 3.55 to 3.99 days. In contrast, some strains exhibited high sporulation and virulence on 1/2 PDA but failed to produce conidia or showed severe clumping during rice-based solid-state fermentation, indicating poor suitability for large-scale production. These results demonstrate that high laboratory virulence alone is insufficient for strain selection and highlight the importance of integrating killing speed, final mortality, and SSF compatibility as joint selection criteria. Overall, TyEf0054 represents a promising locally adapted candidate for the development of commercial mycoinsecticides for sustainable management of sweet potato weevil in Taiwan.