Control of Magnaporthe oryzae Pathotype Lolium on Ryegrass (Lolium multiflorum Lam.) Seeds Using Fungicides

Abstract

Blast, caused by the fungus Magnaporthe oryzae pathotype Lolium (MoL; anamorph Pyricularia oryzae), is a foliar disease capable of inducing severe yield losses and impairing both the sanitary and physiological quality of Italian ryegrass (Lolium multiflorum Lam.) seeds. Although the seed is not considered the primary source of inoculum for epidemic development, MoL can be transmitted to the coleoptile, leading to seedling mortality, compromising pasture establishment, and facilitating pathogen dissemination to new fields and production areas. Information regarding seed-to-coleoptile transmission and the control of this pathogen through seed-applied fungicides in ryegrass remains limited. The objectives of this study were to determine the transmission rate of MoL from seed to coleoptile, assess its impact on seedlings, and evaluate the efficacy of six fungicide seed treatments, as well as their effects on germination and early seedling vigor under laboratory conditions. The experiment was conducted at the Seed Laboratory of INIA La Estanzuela using a seed lot with 27% MoL incidence, as determined by the blotter test according to ISTA rules. In untreated seeds, MoL transmission from seed to coleoptile reached 55.6%, resulting in 11.7% seedling mortality. Treatments T3 (experimental), T4 (sedaxane + difenoconazole + fludioxonil), and T7 (carbendazim + thiram + iprodione) resulted in no detectable MoL infection in coleoptiles under the experimental conditions.  No phytotoxic effects on seed germination or seedling vigor were detected in any treatments.