Survival and dispersal of Puccinia psidii spores in eucalypt wood products.
The rust, caused by Puccinia psidii, is one of the most important diseases of Eucalyptus and other Myrtaceae. The disease can be spread by windblown fungal spores, infected rootted cuttings, seedlings, pollen and other host tissues that increase the risk of its introduction to rust free countries as well as of spreading new pathogen lineages. To assess the risk of disease spread by transport of spores on wood products, we evaluated the effect of height of traps installed in different eucalypt timber and wood pulp storage areas on rust spore capture. We also evaluated P. psidii spore dispersal in the field and survival of P. psidii urediniospores and teliospores under different temperatures (15, 25, 30, and 35°C) and relative humidity (35, 55, 70 and 87%) for up to 120 days. Spore viability was evaluated in vivo by germination on leaves of a susceptible hybrid E. urophylla × E. grandis clone and by staining with fluorescein diacetate. The number of P. psidii spores captured in timber and wood pulp storage areas was significantly lower than in eucalypt plantations that contained infected plants. A combination of high temperature and high relative humidity decreased spore survival. Urediniospores and teliospores survived 90 days at 15°C and 35% relative humidity, but only 10 days at 25 to 30°C and 70% relative humidity. The results of this study indicated that although rust spores may reach wood products (timber and pulp) storage areas in very low numbers, the adverse environmental conditions encountered in these areas and during overseas transport do not favor spore survival. Thus, the risk of spread of this pathogen into new areas in the absence of infected host plants is considered extremely low to inexistent.