Termoterapia em sementes de cebola para controle de alternaria porri

Abstract

The fungus Alternaria porri is the causal agent of purple blotch in onions, a seed-borne disease that hinders crop development, leading to economic losses in production. Seed heat treatment can be effective in controlling Alternaria porri in onion cultivars susceptible to this pathogen. The objective was to evaluate the reduction of Alternaria porri incidence in onion seeds after thermotherapy. The experiment was conducted at the Federal University of Fronteira Sul - Erechim Campus, in the Phytopathology Laboratory and in a greenhouse, from May 2023 to May 2024. Seeds of the Baia Periforme cultivar (susceptible to purple blotch), without chemical treatment, were used. Pathogen inoculation was performed from an isolate obtained from a chive plant (Allium schoenoprasum L.) showing symptoms of the disease. The experiment was conducted in a completely randomized design with seven treatments: TN: negative control (no inoculation and no treatment), TP: positive control (inoculation and no treatment), T10: inoculation and heat treatment at 50 ºC for 10 minutes, T20: inoculation and heat treatment at 50 ºC for 20 minutes, T30: inoculation and heat treatment at 50 ºC for 30 minutes, T40: inoculation and heat treatment at 50 ºC for 40 minutes, and T50: inoculation and heat treatment at 50 ºC for 50 minutes. Evaluations included: germination (%), pathogen incidence (%), emergence in the greenhouse (%), and seedling length (cm). Treatment T30 achieved good control of pathogen incidence (9.5%) without compromising germination, emergence, and seedling length. The treatment with the longest submersion time, T50, also achieved good control of pathogen incidence (9.5%); however, germination (75.7%) and emergence (39.5%) decreased, making this treatment duration unfeasible. Therefore, thermotherapy of onion seeds infected with Alternaria porri for 30 minutes at 50 ºC ensures the lowest pathogen incidence and the best physiological potential of the seeds.