Responses of wound-inoculated seedlings of Pinus ellioitii var. elliottii and Pinus faeda to mycelial cultures derived from multiple and single basidiospores of Cronarfium quercuum f. sp. fusiforme

In 1991, a series of experiments was initiated to examine the effectiveness and research value of inoculating 6-week-old seedlings of slash (Pinus ellionii var. ellionii) and loblolly pine (I’. raeda) with suspensions of basidiospores of Cronartium quercuum f. sp. fusiforme onto wounds made by severing the upper approximately 1 cm of the stems. These experiments were to evaluate the wound technique as an alternative to the standard spray inoculations with basidiospore suspensions, particularly as a means of identifying potential mechanisms of resistance and to facilitate single-spore inoculations. The success of the wound inoculation technique led to experiments in which seedlings of slash pine were wound-inoculated with mycelia from cultures derived from multiplespace and single-basidiospore isolates. These experiments produced what is believed to be the first in vivo infection of pine seedlings by single-basidiospore isolates of C. q. fiiforme. In the most successful inoculation test, galls were produced on 11 of 58 slash pine seedlings inoculated with six different single-spore isolates. Evaluation of single-spore inoculations was continued with mycelium grown from virulent and avirulent cultures of C. q. fusz~onne. Fifty seedlings of a half-sib family of loblolly pine were inoculated with each of five single-spore isolates. One V single-spore isolate resulted in galls (8150). Twelve months after inoculation a cube of tissue was removed from the upper portion of each gall, embedded, sectioned, stained and examined microscopically to evaluate the patterns of colonization and host reactions to the one virulent isolate. Overall, the pattern of colonization was similar to seedlings inoculated with the standard spray technique. However, differences were noted in intensity of colonization and characteristics of spermogonial development.