Systemic resistance to coffee rust (Hemileia vastatrix) was induced in susceptible cv, ‘Mundo Novo’ by spraying foliage with a yeast filtrate. The stages of fungal development were compared in leaves of untreated (MN), induced ‘Mundo Novo’ (MN‐I) and coffee rust resistant segregants of the hybrid ‘Sarchimor’ (Sch). Development of H. vastatrix was observed at intervals of 228 h after inoculation. The expression of resistance was detected 48–72 h after inoculation. In Sch, it occurred at the one haustorial mother cell (HMC) stage, whereas in MN‐I, it occurred at the 2nd HMC stage. In Sch the majority of aborted colonies were associated with necrotic host cells, and the collapsed fungal hyphae exhibited a yellow autofluorescence which was observed in necrotic cells of the host. In MN‐I, 80% of the colonies could not be visualized 72 h after inoculation and host cells at the infection sites were not necrotic.
Susceptible coffee plants (Coffea arabica cv. ‘Mundo Novo’) treated with a suspension of Bacillus thuringiensis or with three of commercial products (Thuricide HD, Bactimos and Bactospeine PM) of B. thurngiensis were protected against a later inoculation with Hemileia vastatrix, the causal agent of coffee leaf rust. Thuricide HD was effective at concentrations from 5 to 20 mg/ml; at this concentration, protection reached 90 %, lasted for at least 5 weeks, and was systemic. Induced resistance was determined by the reduction of the average number of lesions per leaf in treated leaves when compared with non‐treated controls. A decrease in lesion size as well as a delay in sporulation time were also observed in protected plants treated with Thuricide HD.
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