Development of Hemileia vastatrix in Coffee Plants With Genetic or Induced Resistance

Systemic resistance to coflfee rust (Hemileia vastatrix) was induced in susceptible cv, "Mundo Novoʹ by spraying foliage with a yeast filtrate. The stages of fungal development were compared in leaves of untreated (MN), induced ʹMtindo Novo" (MN-Ij and coffee rust resistant segregants ofthe hybrid ʹSarchimor" (Sch), Development of H. vastatrix was observed at intervals of 228 h after inoculation. The expression of resistance was detected 48-72 h after inoctilation. ln Sch, it occurred at the one haustorial mother cell (HMC) stage, whereas in MN-1, 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 autofiuorescence which was observed in necrotic cells of the host. In MN-1, 80% of the colonies could not be visualized 72 h after inoculation and host cells at the infection sites were not necrotic.