Ultrastructure of the Initial Interaction of Puccinia arachidis and Cercosporidium personatum with Leaves of Arachis hypogaea and Arachis stenosperma

Cultivated peanut, Arachis hypogaea L., 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 fungus Cercosporidium personatum, and rust caused by the fungus Puccinia arachidis, are responsible for decrease in plant growth and productivity. The peanut wild relative Arachis stenosperma accession V10309 was identified as resistant to a number of pests and diseases, including LLS and rust. Aiming to better understand the mechanisms of resistance of A. stenosperma to C. personatum and P. 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 of A. stenosperma V10309 (wild, resistant) and A. hypogaea cv. IAC-Tatu (cultivated, susceptible) inoculated with C. personatum or P. arachidis. For both fungal species, adhesion, germination of spores and hyphal proliferation occurred in both species but was more limited and later in A. stenosperma than in A. hypogaea, and no successful penetration was observed in the former. These data suggest that in A. 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 species A. stenosperma.