Ultrastructure of the Initial Interaction ofPuccinia arachidisandCercosporidium personatumwith Leaves ofArachis hypogaeaandArachis stenosperma

Cultivated peanut,Arachis hypogaeaL., is an economically important species. It is very susceptible to different stresses to which wild species are mostly resistant. Foliar diseases, such as late leaf spot (LLS) caused by the fungusCercosporidium personatum, and rust caused by the fungusPuccinia arachidis, are responsible for decrease in plant growth and productivity. The peanut wild relativeArachis stenospermaaccession V10309 was identified as resistant to a number of pests and diseases, including LLS and rust. Aiming to better understand the mechanisms of resistance ofA. stenospermatoC. personatumandP. arachidis, determine initial key steps of the plant–pathogen interaction and to contribute for studies on genes involved in this interaction, ultrastructural analysis was performed on leaves ofA. stenospermaV10309 (wild, resistant) andA. hypogaeacv. IAC‐Tatu (cultivated, susceptible) inoculated withC. personatumorP. arachidis. For both fungal species, adhesion, germination of spores and hyphal proliferation occurred in both species but was more limited and later inA. stenospermathan inA. hypogaea, and no successful penetration was observed in the former. These data suggest that inA. stenosperma, infection is hampered at the stage of penetration. This is the first morphological description of the first hours of the interaction of plant pathogenic fungi and the resistant wild speciesA. stenosperma.