Botanical Extracts and Antagonistic Fungi for the Sustainable Management of Wheat Blast Caused by Pyricularia oryzae Triticum Pathotype

Abstract

Wheat blast, caused by Pyricularia oryzae Triticum pathotype (PoT), is a major threat to wheat production and highlights the need for sustainable alternatives to conventional fungicides. This study evaluated the antifungal, growth-related, and disease-suppressive effects of botanical extracts from Lippia alba and Allium sativum and the antagonistic fungi Trichoderma harzianum and Epicoccum nigrum against PoT under in vitro and in vivo conditions. In dual-culture and poisoned-food assays, A. sativum extract (5 mL) and T. harzianum (TH-FCCT-1155-4) strongly inhibited PoT, completely suppressing conidiation and reducing mycelial growth by more than 90% and 58%, respectively. Seed treatments with A. sativum, T. harzianum, and E. nigrum were non-phytotoxic and were associated with higher values for several seedling growth parameters in PoT-infected seedlings, including leaf number, stem thickness, and dry biomass, while reducing seed-to-seedling disease transmission. Foliar applications at the seedling (GS 1.5) and anthesis (GS 6.0) stages reduced disease development in several cultivar–isolate combinations, although treatment responses varied among PoT isolates and wheat cultivars. At anthesis, treatment effects on spike disease severity and thousand-grain weight (TGW) also varied among cultivar–isolate combinations. In contrast, L. alba showed phytotoxic effects at 1000 ppm and did not consistently reduce spike disease severity when applied at anthesis. RT-qPCR analysis showed that garlic seed treatment was associated with higher transcript abundance of the defense-related genes PR5 and APX at specific sampling times between 48 and 72 h post-inoculation. Overall, these results identify A. sativum, T. harzianum, and E. nigrum as candidates for further evaluation in standardized greenhouse and field studies for wheat blast management and provide evidence that their effects may involve direct antifungal activity and, in the case of A. sativum, modulation of host defense responses.