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Maintenance of genetic resources within the National Plant Germplasm System includes preserving the genetic constituency of accessions as close to the original sample as possible. Genetic changes that can arise during seed regeneration include both an overall loss of genetic diversity within heterogenous accessions and changes in the gene frequencies within accessions. Two germplasm collections are being examined with molecular methods at the Western Regional Plant Introduction Station (WRPIS) for evidence of such genetic change. In the case of pea, gross observation of seed and plant characters indicate that vigorous plant culling during a comprehensive Pea Seedbourne Mosaic Virus eradication program a decade ago resulted in the overall loss of genetic diversity in some heterogenous accessions. Isozyme data has corroborated these observations. Molecular markers are beginning to be used, both to quantify possible genetic changes in accessions as a result of the eradication process, and to document success in reintroducing diversity by repeating the eradication process with additional seed from archival seedlots. In the case of ryegrass, the practice of bulking the seed harvested from regeneration plots may bias the seedlot toward genotypes that are more fruitful. Isozyme analysis after two regeneration cycles showed that balanced sampling (equal seed no./plant) maintained allele frequencies close to the original seed sample. A bulk harvest sample and a sample with an equal number of spikes harvested from each plant showed some significant change in allele frequency, but no significant changes were seen in the allelic richness of accessions, or in the level of an accession's overall heterozygosity. A regeneration sample with an equal number of seed/plant will therefore best preserve gene frequencies within accessions, but loss of an accessions overall diversity will not diminish as a result of less than ideal sampling methods in ryegrass.

The ability of peach leaves to absorbed and translocated foliarly applied ¹⁵N-urea in mature peach (Prunus persica) trees was determined. Urea uptake experiments were conducted in June, October, and November 1995. Peach leaves absorbed ≈80% of the urea within 48 hr of application in all three experiments based on urea rinsed from leaf surfaces. Similarly, leaf ¹⁵N content reached a peak 48 hr after application. Translocation of ¹⁵N out of leaves, however, was more rapid in October then November. In October, 24% of the ¹⁵N remained in the leaves 2 weeks after application, while, in November, 80% stayed in the leaves and fell to the orchard floor. Thus, applying urea in mid November did not allow enough time for the N to be transported out of the leaves before leaf abscission. Timing of foliar urea application is critical to maximize N transport into perennial tissues of peach trees. ¹⁵Nurea resorption out of leaves and into perennial tree parts (roots, trunk, current year wood, etc.) is discussed.

We investigated if salt tolerance can be inferred from observable cues based on a woody species’ native habitat and leaf traits. Such inferences could improve species selection for urban landscapes constrained by soils irrigated with reclaimed water. We studied the C3 tree species Acer grandidentatum Nutt. (canyon maple; xeric-non-saline habitat) that was hypothesized to have some degree of salt tolerance based on its semiarid but non-saline native habitat. We compared it with A. macrophyllum Pursh. (bigleaf maple) from mesic/riparian-non-saline habitats with much larger leaves and Eucalyptus camaldulensis Dehnh. (eucalyptus/red gum) from mesic-saline habitats with schlerophyllous evergreen leaves. Five levels of increasing salt concentrations (non-saline control to 12 dS·m⁻¹) were applied over 5 weeks to container-grown seedling trees in two separate studies, one in summer and the other in fall. We monitored leaf damage, gas exchange, and hydric behavior as measures of tree performance for 3 weeks after target salinity levels were reached. Eucalyptus was the most salt-tolerant among the species. At all elevated salinity levels, eucalyptus excluded salt from its root zone, unlike either maple species. Eucalyptus maintained intact, undamaged leaves with no effect on photosynthesis but with minor reductions in stomatal conductance (g _S). Conversely, bigleaf maple suffered increasing leaf damage, nearly defoliated at the highest levels, with decreasing gas exchange as salt concentration increased. Canyon maple leaves were not damaged and gas exchange was minimally affected at 3 dS·m⁻¹ but showed increasing damage at higher salt concentration. Salt-tolerant eucalyptus and riparian bigleaf maple framed canyon maple’s moderate salt tolerance up to 3 dS·m⁻¹ that appears related to seasonal soil drying in its semiarid native habitat. These results highlight the potential to infer a degree of salt tolerance from either native habitat or known drought tolerance in selecting plant species for urban landscapes limited by soil salinity or brackish irrigation water. Observable cues such as xeri-morphic leaf traits may also provide visual evidence of salt tolerance.

A long-term horticultural experiment was conducted at two geographically distinct sites in southern Missouri in 2011–15 to study the response of American elderberry [Sambucus nigra (L.) subsp. canadensis (L.) Bolli] to various soil nitrogen (N) fertilizer levels. Three commercially available elderberry cultivars (‘Adams II’, ‘Bob Gordon’, and ‘Wyldewood’) were used. The three cultivars were each assigned to 16 of 48 four-plant plots in a completely randomized manner at each site. Four replications of four N fertilizer treatments (0, 56, 112, 169 kg⋅ha⁻¹ N) were randomly assigned to each cultivar’s plots and applied for 4 years (2012–15). Fruit yields, plant growth, phenology, and pest incidence were determined each year. Fruit quality was assessed by analyzing basic juice characteristics as well as organic acids, carbohydrates, anthocyanins, and polyphenols from 2012–14 samples. Leaf tissue analysis determined the plants’ mineral contents in 2012–14. Most factors evaluated were significantly affected by site, year, and cultivar, whereas the effects of N fertilizer treatment were less definitive. Fruit yields and plant growth increased with increasing N levels. For example, plants fertilized with 0, 56, 112, and 169 kg⋅ha⁻¹ N produced 123, 137, 155, and 161 fruiting cymes per plot (5.8 m²), respectively. The eriophyid mite incidence was higher on fertilized plants, but other pests were not influenced by the N treatment. Basic fruit juice characteristics (soluble solids, pH, titratable acidity, polyphenols) were not influenced by the N treatment, whereas total anthocyanins were statistically higher in unfertilized plants. Levels of organic acids and carbohydrates in juice varied statistically among N treatments, but patterns were difficult to discern. Leaf N concentrations were correlated with N fertilizer levels—2.75% N with the highest fertilizer level compared with 2.55% N in unfertilized plants. Leaf levels of most other macronutrients varied, but consistent patterns did not emerge, and none of the micronutrients was different among N treatments. Although elderberry plants responded positively to increased N fertilizer levels in terms of plant growth and fruit yield, genetics (cultivar) and environment (site, year) were more influential on most other experimental factors evaluated.