Infection process of Puccinia psidii in Eucalyptus grandis leaves of different ages

Rust caused by Puccinia psidii is a serious disease of Eucalyptus and other Myrtaceae. Here we evaluated the pre-penetration processes in leaves at different phenological stages of a susceptible clone (3918) of Eucalyptus grandis. The first ten leaves, from the tip to the base, on the apical branch were detached and inoculated with urediniospores. We found a gradual reduction in fungal germination (88 to 39 %), apressorium formation (78 to 18 %), penetration (69 to 0 %) and sporulation (90 to 0 number of sorus /cm2) with the increase in leaf age. In addition, thickness and amount of wax was higher in the older leaves. The results of this study suggest that resistance to P. psidii infection in older Eucalyptus leaves occurs at the pre-penetration stage.