Search

Moltzan, B. D., Blenis, P. V., and Hiratsuka, Y. 2001. Effects of spore availability, spore germinability, and shoot susceptibility on gall rust infection of pine. Plant Dis. 85:1193-1199. Temporal changes in three factors (shoot susceptibility, spore availability, and spore germinability) were evaluated to estimate their effects on the infection of lodgepole pine (Pinus contorta var. latifolia) by Endocronartium harknessii. Germinability of rust spores from sori free of hyperparasites remained above 80% during the growing season and thus would not have significantly limited infection. In contrast, there was a slight, but statistically insignificant, increase in estimated susceptibility as infection increased from 94% of maximum at 45% shoot elongation to maximum susceptibility at 90% shoot elongation. This was followed by a precipitous decline in estimated susceptibility to 57% of maximum when shoots were 95% elongated. Spore availability was 24% of maximum when shoots were 45% elongated, and thus may have been limiting at the beginning of the growing season. At the end of the growing season, spore availability declined prior to, or simultaneous with, the decline in susceptibility. The combined effect of both factors drastically reduced the number of infections estimated to occur once shoots are more than 95% elongated. As shoots elongated, relatively more infections formed higher on the shoot, supporting the hypothesis that periderm is important in limiting infection.

The effects of Endocronartium harknessii on provenances of Pinus ponderosa planted in 1969 on a coal strip-mine spoil bank in central Pennsylvania were reassessed. In 1982 infection levels among seed sources ranged from 4.9 to 52.5%. In 1991 infection levels ranged from 29 to 95%, and mortality due to rust infection ranged from 9 to 58% among these seed sources. Levels of infection, mortality due to rust infection, and mortality unrelated to rust infection differed significantly among seed sources (P < 0.001, < 0.001, and = 0.023, respectively). Among geographic ecotypes, there were no significant differences among percentages of trees infected (P = 0.094), but there were significant differences among trees surviving outplanting (P = 0.007), mortality due to rust (P = 0.004), and mortality unrelated to rust (P < 0.001). Only one provenance incurred less than 40% infection, indicating that virtually none of these types of provenances are suitable for reforestation in areas of eastern North America where E. harknessii occurs.

Isozyme analyses were made on aeciospore collections from several species of the genus Cronartium and from several formae speciales of C. quercuum. Aeciospores from closely related Endocronartium harknessii also were tested. Esterase isozyme patterns provided the best differentiation. Patterns for Cronartium spp. differed markedly from those for E. harknessii. C.q.f.sp. banksianae, C.q.f.sp. virginianae, C.q.f.sp. echinatae, and C.q.f.sp. fusiforme were easily distinguished