02546nam a2200181 a 450000100080000000500110000800800410001910000180006024501230007826000980020152019640029965300110226365300200227470000160229470000190231070000170232970000180234618806332011-04-14       2008    bl uuuu     u00u1 u    #d1 aRAMIRO, D. A.  aEarly haustoria development in coffee (Coffea arabica) - rust (hemileia vastatrix) interaction.h[electronic resource]  aIn: INTERNATIONAL CONFERENCE ON COFFEE SCIENCE, 22. 2008, Campinas, São Paulo, Brazil.c2008  aAccording to their lifestyle, plants parasitic fungi may be classified in necrotrophs which obtain nutrients from dead cells or biotrophs which obtain nutrients from living host tissue. A common feature of the biotrophs is the formation of specialized structures called haustoria, which are responsible for uptake of nutrients from the host cells they invaded. Avirulence (Avr) genes and their respective products that are recognized by the resistance proteins inside host cells may be specifically expressed in haustoria, leading to the rapid activation of defense responses against the fungus. The objective of this study was to assess the time-course of the orange rust fungus (Hemileia vastatrix) haustoria differentiation in coffee (Coffea arabica). Histological characterization of H. vastatrix (race II) development in Tupi (immune) and Catuai (sporulation level 4) was assessed by light microscopy examination of cross sections of infected leaf fragments stained with lactophenol blue. In both interactions, careful examination of infection sites made at 600x revealed that haustorial differentiation occurred as soon as the fungus enters stomata, much earlier than previously described in the literature. Haustorium mother cell (HMC) and haustoria (termed “pioneers haustoria”) were found in the guard and adjacent cells of the stomata, before the colonization of parenchyma had occurred. In all interactions, after pioneer haustoria differentiation, the fungus displayed the usual sequence of growth stages: anchor, new HMC and haustoria development in stomatal cells and in the parenchyma. Until 36 hours after inoculation, rust development in the two cultivars did not differ. Examination of host cell death, characteristic of the hypersensitive reaction in resistant varieties, and of defense genes regulation during rust infection are currently being examined to assess the coffee resistance responses linked to pioneers haustoria formation.  aCoffee  aParasitic fungi1 aESCOUTE, J.1 aPETITOT, A.-S.1 aMALUF, M. P.1 aFERNANDEZ, D.