Ornamental flowering cherry trees (Prunus species) are popular landscape plants that are used in residential and commercial landscapes throughout most temperate regions of the world. Most of the flowering cherry trees planted in the United States represent relatively few species. The U.S. National Arboretum has an ongoing breeding program aimed at broadening this base by developing new cultivars of ornamental cherry with disease and pest resistance, tolerance to environmental stresses, and superior ornamental characteristics. Knowledge of the genetic relationships among species would be useful in breeding and germplasm conservation efforts. However, the taxonomy of flowering cherry species and cultivars is complicated by differences in ploidy levels and intercrossing among species. We have used simple sequence repeat (SSR) markers developed for other Prunus species to screen a diverse collection of over 200 ornamental cherry genotypes representing 70 taxa in order to determine the genetic relationships among species, cultivars, and accessions. Data were generated from 9–12 primer pairs using an automated DNA genetic analyzer (ABI3770), and subjected to UPGMA cluster analysis. Extremely high levels of polymorphism were exhibited among the materials studied, thus indicating that ornamental flowering cherry germplasm has substantial inherent genetic diversity. This information, combined with traditional morphological characteristics, will be useful in determining genetic relationships among accessions in our collection and for predicting crossability of taxa.
The influence of salinity and plant age on nematode reproduction was determined on two susceptible and six root-knot-nematode-resistant Prunus rootstocks inoculated with Meloidogyne incognita (Kofoid and White). Experiments were conducted under greenhouse conditions over 120 (plant age study) and 75 (salinity study) days. Following inoculation with 4000 nematodes per plant, susceptible 2-month-old GF-677 (Prunus persica L. Batsch. × P. dulcis Mill. Webb) and Montclar (P. persica) were affected significantly more than 1-year-old plants. Barrier (P. persica × P. davidiana Carr. Franch.) plantlets showed a partial loss of resistance in relation to older plants, suggesting that a root tissue maturation period is required for expression of full resistance. Nemared (P. persica); G × N No 22 (P. persica × P. dulcis); and the plums GF 8-1 (P. cerasifera Ehrh. × P. munsoniana Wight and Hedrick), PSM 101 (P. insititia L.), and P 2980 (P. cerasifera) maintained their high level of resistance or immunity, regardless of plant age. Nematode reproduction was higher in GF-677 rootstock in saline soil. Nemared and Barrier showed similar low galling and nematode reproduction in nonsaline and saline soil. PSM 101 immunity to M. incognita was not affected by soil condition.
In vitro micrografting was tested as a technique for inoculating peach [Prunus persica (L.) Batsch] shoot cultures with Prunus necrotic ringspot virus (PNRSV). Cultured `Suncrest' shoots derived from a naturally infected tree (as indicated by ELISA testing) maintained virus in vitro, with virus concentrations in growing tips and folded leaves being several times those of fully expanded leaves. Infected shoots served as graft bases and source of the virus. Grafted tips were derived from `Suncrest' trees that had tested negative for the virus. Leaf samples were collected from the tips following grafting and analyzed for the presence of virus by slot-blot hybridization with a (DIG)-labeled cRNA probe derived from PNRSV RNA 3. Rates of successful grafting ranged from 55% to 73% in three trials and PNRSV was found in all tips analyzed. Virus concentrations approximated those found in source shoots, suggesting that in vitro micrografting should be useful for screening transformed peach shoots for coat protein-mediated resistance to PNRSV. Chemical name used: digoxigenin (DIG).
The influence of B and salinity [3 Na2SO4 : 1 CaCl2, (molar ratio)] on B toxicity and the accumulation of B, sodium, and SO4 in six Prunus rootstocks was evaluated. High salinity reduced B uptake, stem B concentrations, and the severity of toxicity symptoms in five of the six rootstocks. Forward and backward stepwise regression analyses suggested that stem death (the major symptom observed) was related solely to the accumulation of B in the stem tissue in all rootstocks. The accumulation of B and the expression of toxicity symptoms increased with time and affected rootstock survival. No symptoms of B toxicity were observed in leaf tissue. The Prunus rootstocks studied differed greatly in stem B accumulation and sensitivity to B. The plum rootstock `Myrobalan' and the peach-almond hybrid `Bright's Hybrid' were the most tolerant of high B and salinity, whereas the peach rootstock `Nemared' was very sensitive to high B and salinity. In all rootstocks, adding B to the growth medium greatly depressed stem SO4 concentrations. In every rootstock except `Nemared' peach, adding salt significantly depressed tissue B concentrations. A strong negative correlation between tissue SO4 and B was observed. Grafting experiments, in which almond was grafted onto `Nemared' peach or `Bright's Hybrid', demonstrated the ability of rootstocks to influence B accumulation and scion survival.
Two F1 hybrid Prunus rootstocks, K62-68 and P101-41, developed from a cross of `Lovell' [susceptible to both Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood] and `Nemared' (resistant to both root-knot nematode species), were selfed to produce two F2 seedling populations. Vegetative propagation by herbaceous stem cuttings was used to produce four or eight self-rooted plants of each F2 seedling for treatment replications. Eggs of M. incognita and M. javanica were inoculated into the potted media where plants were transplanted, and plants were harvested and roots examined for signs and symptoms associated with root-knot nematode infection ≈120 days later. Segregation ratios in both F2 families suggested that resistance to M. incognita in `Nemared' is controlled by two dominant genes (Mi and Mij) and that to M. javanica by a single dominant gene (Mij). Thus, Mij conveys resistance to both M. incognita and M. javanica.
Fruit trees grown in soils contaminated with lead arsenate (PbHAsO4) pesticide residues are subject to arsenic (As) phytotoxicity, a condition that may be exacerbated by use of phosphate fertilizers. A potted soil experiment was conducted to examine the influence of phosphate fertilizer on accumulation of As and lead (Pb) in apricot (Prunus armeniaca) seedlings grown in a lead arsenate-contaminated Burch loam coil. Treatments were fertilizer source (mono-ammonium phosphate [MAP], ammonium hydrogen sulfate [AHS]) and rate (0, 8.7, 17.4, and 26.1 -mmol/liter), and presence/absence of lead, arsenate contamination (231 -mg/kg coil). Plant biomass accumulation was reduced by lead arsenate presence and by high fertilizer rates, the latter due to soil salinization. Phytoaccumulation of As was enhanced by lead arsenate presence and by increasing MAP rate but was not influenced by AHS rate, salinity, or acidity of soil. Phytoaccumulation of Pb was enhanced by lead arsenate presence but was not influenced by fertilizer treatment.
During the 1984 growing season, 156 peach and 40 nectarine cultivars, 49 plant introductions, and 33 Prunus species or species hybrids were evaluated for susceptibility to bacterial spot [Xanthomonas campestris pv. pruni (Smith 1903) Dye 1978] in North Carolina and South Carolina. Fruit and leaf infection and percentage of defoliation were evaluated in North Carolina, while only leaf infection data were evaluated in South Carolina. No cultivar was immune, but susceptibility varied greatly. Based on leaf infection in the 2 locations, it was concluded that disease pressure was greater in North Carolina. Correlation of fruit infection severity with leaf infection severity and percentage of defoliation in North Carolina was r = 0.30 (P = 0.01) and r = 0.54 (P < 0.01), respectively. Correlation between leaf infection severity and percent defoliation was r = 0.51 (P < 0.01) and r = 0.00 (NS) in North and South Carolina, respectively.
Growth and yield of ‘Montmorency’ cherry varied greatly both within and between species of rootstock clones. Trees on FI2/1 mazzard (Prunus avium L.) were very vigorous and less productive than those on other stocks. Some growth control was found within each species or hybrid group but was most pronounced with P. mahaleb L. clones PI 193688, PI 163091 and PI 193693. Yield efficiency was not necessarily related to tree size but tended to be better with smaller trees. The 3 P. mahaleb clones listed above and the vigorous clones OCR-3 (P. mahaleb × P. avium) and PI 194098 (P. mahaleb) had high yield efficiencies. Trees on F12/1 and P. mahaleb PI 193703 had the lowest yield efficiencies. Based upon ideal orchard spacing for tree size, calculated annual yields exceeded 10 metric tons per ha for 6 of the clonal stocks.
Meiosis and pollen viability of Prunus avium L. cv. ‘Lambert’ were investigated to ascertain whether there were annual or regional effects on the incidence of abnormal meiosis or pollen abortion. Studies of meiosis failed to reveal marked variation among the 3 years investigated. Comparisons between 2 similar and 2 dissimilar locations also failed to reveal marked variability in the incidence of abnormal meiosis which was estimated to be 9.62 ± 1.93%. Examination of microspore development showed that pollen abortion occurred prior to the first mitotic division of the microspore nucleus. Studies of mature pollen failed to reveal significant differences in pollen abortion among the 3 years investigated. Differences between the 2 locations and 2 types of blossom sample used also were non-significant. The mean incidence of pollen abortion was 41.6%.
Aqueous and ethanolic extracts of the Prunus endocarp were found to delay germination and subsequent growth of peach, almond, cucumber and plantago embryos. Constituents in the extracts were partially purified by chromatographic separation on paper and thin-layer plates. While there are several components in the inhibitor complex, one has been identified tentatively as abscisic acid by its Rf values in different solvent systems, reactions with chromogenic reagents and absorption of ultraviolet light. Most of the inhibitors in the endocarp were fixed on anion exchange resins but not on nylon or hide powder. Mild acid hydrolysis of the endocarp yielded no HCN which eliminates cyanoglucosides as having a role in the inhibition. The extractives induced a marked reduction in oxygen uptake by germinating pea seedlings and growth inhibition in cucumbers. The latter was reversible with gibberellic acid (GA).