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

Germination of urediniospores, appressorium formation and penetration by Pu ccinia psidii Winter were studied on detached leaves of resistant and susce ptible clones of Eucalyptus grandis Hill ex Maiden. More than 90% of germin ation and appressorium formation were observed 12 and 18 h, respectively, a fter inoculation for both genotypes. Direct penetration by P. psidii betwee n the anticlinal walls of the epidermal cells occurred. In the susceptible genotype, primary mycelia and haustoria were observed 12 and 18 h, respecti vely, and in the resistant 18 and 24 h after inoculation. After the formati on of the first haustoria, dead cells developed and were followed by a hype rsensitive reaction in the resistant genotype.