Influence of inoculum concentration on production of spermogonia and aeciaon pine seedlings infected by basidiospores of Cronartium quercuum f. sp. fusiforme

Seedlings of stash pine and loblolly pine inoculated with four concentratio ns Of basidiospores of Cronartium quercuum f. sp. fusiforme and exhibiting large galls (greater than or equal to 25 mm long) were observed for spermog onial and aecial sporulation. Basidiospores from a genetically heterogeneou s source at 50, 100, 1,000 and 5,000 spores/5-mu l droplet were applied to the severed, succulent terminal of 6-week-old seedlings. Incidence of sporu lation showing (i) spermatia (pycniospores) only, (ii) aeciospores only, (i ii) spermatia and aeciospores, and (iv) absence of sporulation was recorded for 3 years. On slash pine, the percentage of seedlings showing only sperm atia varied significantly and inversely with inoculum concentration. In con trast, the percentage of seedlings showing only aeciospores or aeciospores and spermatia varied directly with inoculum concentration. Results on loblo lly pine were similar. It is suggested that, at low inoculum concentrations , hyphal anastomoses are limited by fewer haploid mycelia in infected tissu es or fewer mating types resulting from incompatible host-parasite interact ions.