Inhibitory Activities of Ethanol Extracts from 75 Plants Against Two Soil-Borne Pathogens

Soil-borne disease has become a prevalent and intractable issue in current agricultural production, while the existing chemical control agents often lead to pesticide residues and phytotoxicity to crops. In contrast, botanical fungicides possess distinct advantages, including broad-spectrum inhibitory activity, environmental friendliness, as well as easy metabolism and degradation in the ecosystem. This study aimed to target two typical soil-borne pathogens (Phytophthora capsici and Fusarium oxysporum f. sp. niveum), determine the inhibitory activities of extracts from 75 tested plants, and to screen out plant resources with high activity, thereby laying a foundation for the development of novel botanical fungicides.

The growth rate method was employed to determine the inhibitory activities of ethanol extracts of 75 kinds of plants against P. capsici and F. oxysporum f. sp. niveum. The pot efficacy of the screened high-activity extracts against pepper phytophthora disease and watermelon fusarium wilt was determined by means of the root irrigation and the root injury method.

The mycelial inhibition rates of five ethanol extracts of Magnolia officinalis, Notopterygium incisum, Syringa pinnatifolia, Platycladus orientalis and Ilex chinensis against P. capsici were over 60% at the concentration of 1 mg·mL^-1. The inhibition rates of 11 other ethanol extracts, including Rubia cordifolia and Lindera aggregata, ranged from 30% to 60%, while the remaining 59 extracts showed no significant inhibitory activity. Among them, the ethanol extract of M. officinalis had the highest toxicity against P. capsici, with EC₅₀ of 0.023 mg·mL^-1. The mycelial inhibition rates of three ethanol extracts of M. officinalis, Ligusticum chuanxiong and Curcuma longa against F. oxysporum f. sp. niveum were over 60% at the concentration of 1 mg·mL^-1. The inhibition rates of 12 other ethanol extracts, such as Alpinia officinarum and S. pinnatifolia, were between 30% and 60%, and the remaining 60 extracts displayed no significant inhibitory activity. Among them, the ethanol extract of C. longa had the highest toxicity against F. oxysporum f. sp. niveum, with EC₅₀ of 0.606 mg·mL^-1. Pot efficacy results showed that the ethanol extract of M. officinalis exhibited high protective and curative efficacy against pepper phytophthora disease at the concentration of 8 mg·mL^-1, with efficacy rates of 64.74% and 63.25%, respectively. The ethanol extract of S. pinnatifolia showed high curative efficacy against pepper phytophthora disease at the concentration of 8 mg·mL^-1, with efficacy rate of 63.14%. However, the efficacy of both extracts was lower than the control fungicide shenqinmycin (protective efficacy: 81.05%; curative efficacy: 73.72%). The ethanol extract of C. longa showed high protective efficacy against watermelon fusarium wilt at the concentration of 8 mg·mL^-1, with efficacy rate of 69.94%, which was comparable to the control fungicide carbendazim (66.65%). When applied at 2 mg·mL^-1, this extract demonstrated a high curative efficacy against watermelon fusarium wilt, with efficacy rate of 78.08%, which was better than the control fungicide carbendazim (62.42%). In contrast, the efficacy of A. officinarum ethanol extract against watermelon fusarium wilt was less than 50% at all tested concentrations.

Ethanol extracts from S. pinnatifolia, C. longa, and M. officinalis exhibit potent inhibitory activities against soil-borne pathogens, which provides a scientific basis for the subsequent development of new botanical fungicides.