Infection of resistant and susceptible Eucalyptus grandis genotypes by urediniospores of Puccinia psidii

Germination of urediniospores, appressorium formation and penetration by Puccinia psidii Winter were studied on detached leaves of resistant and susceptible clones of Eucalyptus grandis Hill ex Maiden. More than 90% of germination and appressorium formation were observed 12 and 18 h, respectively, after inoculation for both genotypes. Direct penetration by P. psidii between the anticlinal walls of the epidermal cells occurred. In the susceptible genotype, primary mycelia and haustoria were observed 12 and 18 h, respectively, and in the resistant 18 and 24 h after inoculation. After the formation of the first haustoria, dead cells developed and were followed by a hypersensitive reaction in the resistant genotype.