Abstract

This paper aimed to evaluate the transmission of Fusarium oxysporum f. sp. vasinfectum (FOV) and the effects of this pathogen on the initial development of cotton plants following inoculation of seeds. Two cultivars (susceptible and resistant) and two strains (most and least aggressive) of the pathogen were used in this study. The inoculation method was based on the contact between seeds and fungal colonies on substrates containing mannitol. Percentage of FOV in seeds and the percentage of seed germination were evaluated by blother test and germination test, after inoculation. Emergence of seedlings and speed index, initial and final stands, size and dry weight of the plants were verified in trays containing soil substrate. Disease severity, pathogen transmission and plant infection, from seed to plant, were determined in separate trial on plants. Occurrence of the pathogen was higher when inoculum potential was increased for all variables analyzed. The number of normal seedlings, determined by seed germination test, decreased when the incidence of the pathogen in the seed was increased. The same occurred to other variables, in which there was difference between cultivars where IAC 20-233 presented the best performance. No significant differences were found between strains for emergence speed index, initial and final stands variables. Transmission and infection rates were increased according to the inoculum potentials increasing and the maximum pathogen transmission rate, from seed to plant was around 50%.

Key words: Transmissibility, pathogenicity, fusarium wilt disease, cotton.