| Artificial inoculation with isolates of Cronartium quercuum f. sp. fusiforme collected from field studies were used to study temporal (yearly) and spatial (geographical) variation in fusiforme rust incidences on progress of resistant and susceptible open-pollinated of slash pine, Pinus elliottii var. ellottii. The temporal study using inoculum from six-gall mixtures of aeciospores from susceptible families showed statistically significant family, family by isolates, and family by year effects, indicating that pathogenic variability in C. quercuum f sp. fusiforme varied among inocula from different time periods. The spatial study using single-gall isolates from families from each of four locations (family- and location-isolates) showed statistically significant effects of isolate, family, family by isolate, and family by family-isolate by location-isolate, indicating that there was pathogenic variability among single-gall isolates.; Observations on spermatial and aecial sporulation showed that statistically significant difference occurred between large and short galls. The pathogen sporulated less frequently on short galls and had fewer spores per gall surface area than on large galls, suggesting that short galls are a component of partial resistance.; Histological examination of smooth, rough and short galls (resistant reactions) demonstrated several patterns of colonization. The common resistant mechanism among the gall types was the presence of a reaction zone. However, the size, rate of development, and intensity of that reaction zone were the distinguishing features among the gall types. The pattern of colonization demonstrates different mechanisms of resistance of slash pine families to C. quercuum f sp. fusiforme. |
