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  • Author or Editor: Thomas G. Beckman x
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Differences in chilling and post-rest heat requirements of various stonefruits were investigated through the use of cuttings collected from field grown trees. Materials studied included P. angustifolia Marsh, P. besseyi Bailey, P. maritima Marsh, P. persica (L.) Batsch (`Agua 6-4', `Flordaking', `Pi Tao', `Redhaven', `Redskin', and `Ta Tao'), P. umbellata Ell. and a Japanese type plum (`Byrongold'). Cuttings were collected after natural leaf fall and shortly after the onset of of chill hour accumulation. Cuttings were stored at 4°C. Groups of cuttings were removed from storage after various amounts of chilling and allowed to develop at 16, 21 or 27°C. Cuttings were observed for both vegetative and flower bud break. Magnitude of differences in chilling and post-rest heat requirements and their implications in the breeding of peaches for low and moderate chill areas will be discussed.

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The effects of short-term soil flooding on gas exchange characteristics of containerized sour cherry trees (Prunus cerasus L. cv. Montmorency /P. mahaleb L.) were studied under laboratory conditions. Soil flooding reduced net CO2 assimilation (A) within 24 hours. Net CO2 assimilation and residual conductance to CO2(gr′) declined to ≈30% of control values after 5 days of flooding. Effects on stomatal conductance to CO2 (gS) and intercellular CO2 (Ci) were not significant during the 5 days of treatment. Apparent quantum yield (Φ) gradually declined to 52% that of controls during these 5 days. In a second experiment, CO2 response curves suggested that, initially, stomatal and nonstomatal limitations to A were of about equal importance; however, as flooding continued, nonstomatal limitations became dominant.

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The rootstock is an essential element for orchard management, influencing scion growth, nutrient concentration, and fruit quality. Seasonal variations in leaf nutrients of ‘UFSun’ grafted on five different rootstocks (‘Flordaguard’, ‘Barton’, ‘MP-29’, ‘P-22’, and ‘Okinawa’) were investigated during the 2017–18 growing season in Citra, FL. There was no significant variation in the macronutrient concentrations (N, P, K, Mg, Ca, and S) among different rootstocks; however, ‘UFSun’ on ‘Okinawa’ and ‘Flordaguard’ showed greater concentrations of Ca, K, and Mg concentration than other rootstocks. In contrast, ‘Flordaguard’ showed less potential to accumulate P as compared with other rootstocks. The Ca concentration was lowest in ‘MP-29’ and ‘Barton’ in April and June. The concentration of macronutrients (N, P, K, Mg, Ca, and S) in leaves was greater in April and October than in December and June. With respect to rootstocks, macronutrients in December and June were the highest in ‘Okinawa’ and the lowest in ‘Barton’. In April, the lowest concentration of macronutrient was recorded in ‘Barton’, whereas the highest concentrations were found in ‘P-22’, ‘Okinawa’, and ‘Flordaguard’. The highest leaf micronutrient concentrations were found in ‘MP-29’ and ‘Barton’, and the lowest in ‘Okinawa’ and ‘Flordaguard’ in June and October. For all rootstocks, concentrations of micronutrients increased between leaf growth in April and senescence in October. The micronutrient concentrations of leaves decreased during December. The widest dynamic changes during the vegetative cycle were found on ‘P-22’. Seasonal trends were more consistent for micronutrients than for macronutrients.

Open Access

Preliminary results of a field trial of 49 different scion varieties grafted onto Nemaguard plus `Redhaven'/Lovell suggest that scion influence on incidence of peach tree short life (PTSL) may be comparable to that of rootstock. After 6 growing seasons survival of the various scion treatments ranged from 5 to 85%. Correlation analyses indicated that those scion varieties exhibiting either early bloom or late defoliation survived better and that those varieties exhibiting both characteristics survived the best. Results indicate that final testing of rootstock candidates for PTSL tolerance must be done with grafted materials and that it may be possible to recommend the planting of certain scion varieties on PTSL sites as well as particular rootstocks for maximum longevity.

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Peach fruit set is affected by cumulative chill and spring frost. A spring frost occurred on 29 Mar. 2015 at the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) Byron station after 3 weeks of bloom, reducing fruit set and resulting in many buttons (abnormally small fruit with dead embryos). Fruit set was rated in 2014, 2015, and 2016 and button set rated in 2015 using the same scale (0 = no fruit/button to 9 = 1–2 fruit/button at every node). The overall fruit set rating was substantially different in the 3 years, averaging 5.61 in 2014, 2.61 in 2015, and 6.04 in 2016. Buttons and skin-damaged fruit in 2015 varied among peach genotypes. Comparison of fruit and button set ratings showed that there was no difference between cultivars and selections, but some significant differences in fruit set for four ripening months, among the 3 years, and among the nine chilling classes, respectively. Among the cultivars, the most common button set rating was 0–3. For example, ‘Sunprince’, ‘Loring’, and ‘Carored’ trees had a high button set rating, whereas ‘Flameprince’, ‘Julyprince’, and ‘Contender’ trees were low. As for peach selections, BY04P1690n was among those with the highest button set rating. In the population derived from a cross of button-prone BY04P1690n and button-free BY99P3866w, fruit and button counts from 10 long fruiting shoots ranged from 4 to 53 fruit (21.63 on average) and 2 to 27 buttons (10.39 on average). The peach button rate ranged from 5.36% to 87.10% (30.70% on average). The range, distribution, and percentage of the button counts suggested that, if buttoning was genetically controlled, it appeared quantitative. Further assessment is needed.

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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.

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