No abstract

The reliability of a leaf-disk assay to assess resistance of Populusdeltoides Bartr. to Melampsoramedusae Thuëm. f.sp. deltoidae, the causal agent of poplar leaf rust, was evaluated. Leaf disks of eight host genotypes were inoculated in a spore settling tower with 11 isolates of the pathogen in all possible combinations, and the latent period, infection probability, sporulation, and progeny/parent ratio were recorded. Correlations were established between these measures and measures derived from field epidemics, namely the relative area under the disease progress curve, the apparent rate of infection, the final disease severity, and the number of days before defoliation. Four genotypes were highly resistant to all 11 isolates tested with the leaf-disk assay and to the local inoculum in field tests. Three genotypes were highly susceptible in inoculation assays and were also susceptible in the field. One genotype was highly resistant in inoculation assays but had intermediate resistance in the field. Significant correlations (p < 0.05) were found between all leaf-disk and all field parameters.

Modified polyphenol metabolism in Pinus sylvestris was correlated with European pine sawfly attack. The unknown compound was not restricted to damaged tissue, indicating a more general response to injury. IntroductionDuring a chemotaxonomic study of the polyphenols in the foliage of Pinus sylvestris L., an altered chromatographic pattern was found to be associated with European pine sawfly (Neodiprion sertifer Geoff.) attack. The foliage samples were collected in June, 1966, from trees growing in a provenance test near Augusta, Michigan. Samples of year-old (1965) foliage were collected from five trees in each of 25 geographic seed sources.In general, the plantation had been rather heavily attacked by the sawfly. To minimize the possibility of introducing an extrinsic source of variation, foliage collection from damaged trees was avoided whenever possible. Several of the provenances had been more heavily attacked than others, however, and it was necessary to collect foliage from 28 trees that had been severely defoliated. In all cases, only intact needles were collected. Individual tree collections were kept separate, and the samples from insectdamaged trees were marked as such.

No abstract

Twelve isolates of the leaf rust pathogen Melampsora medusae Thüm., collected from six locations across the eastern U.S.A., were tested for their reaction on 18 poplar genotypes at two temperatures of incubation (16 and 26 °C). All isolates were recognized as distinct physiologic races, based on the qualitative and quantitative reaction of the isolates on the cultivars. Temperature was an important factor in determining the level and type of disease expression in most cultivar – isolate combinations. The results support the hypothesis that the physical environment may have an important role in the regulation of this "wild" pathosystem. The high degree of race specificity observed in the Populus genotypes and the polymorphism for virulence in the M. medusae population emphasize the importance of maintaining host diversity to manage this disease.