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- Author or Editor: R. P. Marini x
Strawberry plants (Fragaria × ananassa Duch. cv. Catskill) were subjected to several freezing temperatures to study growth and development following various degress of crown injury. The T50 was approximately —l2.5°C, but exposure to nonlethal temperatures resulted in abnormal growth of leaves, early runner production, decreased blossom numbers, and browning of crown tissues. Browning of crown tissues was associated with number of runners, number of blossoms, size of leaves, dry wt of leaves, and test temperatures. Number of blossoms emerging was negatively correlated with low freezing temperature, while early runner emergence was positively correlated with low temperature.
Controlled freezing of everbearing strawberry blossoms (Fragaria × ananassa Duch.) at weekly intervals during the autumn bloom period indicated that the killing temperature decreased about 2°C. During the June bloom period, the killing temperature was similar for June-bearing and everbearing cultivars.
The viability of freeze-stressed Fragaria × ananassa Duch. cv. Catskill strawberry crown tissues was evaluated using triphenyl tetrazolium chloride (TTC) reduction and oxidative browning. Both tests showed the medulla tissue to be the most susceptible to low-temperature injury, while vascular tissue was least susceptible. TTC reduction appears to be negatively related to tissue browning, and both provide similar results pertaining to tissue viability.
Peach trees [Prunus persica (L.) BatSch.] blossom-thinned by hand were overthinned due to poor fruit set of the remaining flowers; however, their yield was equivalent to trees hand-thinned 38 or 68 days after full bloom (AFB). Blossom-thinned trees had three times the number of flower buds per unit length of shoot and had more than two times the percentage of live buds after a March freeze that had occurred at early bud swell the following spring. Blossom-thinned trees were more vigorous; their pruning weight increased 45%. For blossom-thinned trees, the number of flowers per square centimeter limb cross-sectional area (CSA) was two times that of hand-thinned trees and four times that of the control trees for the next season. Fruit set of blossom-thinned trees was increased four times. Flower buds on the bottom half of shoots on blossom-thinned trees were more cold tolerant than when hand-thinned 68 days AFB. Fruit set per square centimeter limb CSA was 400% greater the following year on blossom-thinned trees compared to controls. Removing strong upright shoots on scaffold limbs and at renewal points early in their development decreased dormant pruning time and weight and increased red pigmentation of fruit at the second picking. The number of flower buds per unit shoot length and percent live buds after the spring freeze were negatively related to crop density the previous season for trees that had been hand-thinned to varying crop densities at 48 days AFB. According to these results, blossom thinning and fruit thinning to moderate crop densities can influence the cold tolerance of peach flower buds in late winter.
Procedures are considered which allow the researcher to determine the number of experimental units required to achieve stated experimental objectives. It is proposed that, prior to obtaining estimates of sample sizes, the researcher must obtain estimates of the important factors which influence the experimental variation. Experimental situations considered are those which range from problems in which only one factor influences the experimental variability to a complex example in which several factors must be considered.
Peach [Prunus persica (L.) Batsch cv. Harken] fruit were harvested at the firm-mature stage on 5 different dates. Fruit of uniform size were sampled randomly on each date from each of 4 quadrants per tree and evaluated for color, firmness, and soluble solids using the red and green sides of each fruit. A statistical model was used to identify and separate the sources of within- and among-tree variation in fruit quality indices. All quality indices were affected by harvest date. Fruit- and tree-related interactions accounted for a major part of the total random variation. Variance estimates were used to determine numbers of trees per treatment and fruit per tree needed to detect fruit quality differences of a desired magnitude. In general, 6 trees per treatment and 12 to 16 fruit per tree could be expected to detect meaningful differences in fruit quality in experiments involving 2 treatments.
Net photosynthesis (Pn) rates of greenhouse-grown apple leaves were unaffected for at least 24 hours after shoot detachment. With shoots detached from orchard trees, overnight holding did not affect Pn rates nor stomatal resistance. Use of detached shoots for Pn and dark respiration (Rd) determinations in apple leaves was concluded to be a valid technique.
The objectives of this experiment were to test the efficacy of a mechanical string thinner (Darwin PT-250; Fruit-Tec, Deggenhauserertal, Germany) on apple and to identify an optimal range of thinning severity as influenced by spindle rotation speed. Trials were conducted in 2010 and 2011 at the Pennsylvania State University Fruit Research and Extension Center in Biglerville, PA, on five-year-old ‘Buckeye Gala’/M.9 apple trees that were trained to tall spindle. A preliminary trail on five-year-old ‘Cripps Pink’/M.9 was conducted to determine the relationship between string number and thinning severity. As the number of strings increased, the level of thinning severity increased. A range of spindle speeds (0 to 300 rpm) was applied to the same trees for two consecutive years. As spindle speed increased, blossom density (blossom clusters per limb cross-sectional area) was reduced as was the number of blossoms per spur. In 2010, leaf area per spur was reduced 9% to 45%. In 2011, the fastest spindle speed reduced leaf area per spur 20%. Although increased spindle speed reduced cropload, injury to spur leaves may have inhibited increases in fruit size. The largest gain in fruit weight was 28 g (300 rpm) compared with the control. In both years, the most severe thinning treatments reduced yield by more than 50%. There was no relationship between spindle speed and return bloom. Severe thinning treatments (240 to 300 rpm) caused significant reductions in spur leaf area, yield, and fruit calcium and did not improve fruit size or return bloom. Spindle speeds of 180 and 210 rpm provided the best overall thinning response and minimized injury to spur leaves, but cropload reduction was insufficient in years of heavy fruit set. Therefore, mechanical blossom thinning treatments should be supplemented with other thinning methods. Mechanical string thinning may be a viable treatment in organic apple production, where use of chemical thinners is limited.
In three experiments, diameters of apples representing 7% to 30% of the fruit on a tree were measured at ≈60 days after full bloom. Using previously published regression equations, the early-season fruit diameter values were used to estimate apple fruit weight at harvest (FWH). At harvest, all fruit on sample trees were weighed and the distributions of estimated FWH for fruit measured early in the season were compared with distributions of the actual FWH for whole trees. Actual FWH was normally distributed for only one of the three experiments. Although the estimated mean FWH averaged for the 10 trees was within 9% of the actual mean FWH for all three experiments, the distribution of estimated FWH differed significantly from the actual distribution for all three experiments. All fruit were then assigned to appropriate commercial fruit sizes or box counts (number of fruit/19.05 kg). Fruit size tended to peak on the same four box counts for the estimated and actual populations, but the estimated populations had too few fruits in the small- and large-size box counts. Using early-season estimates of FWH, commercial apple growers and packers can predict fairly accurately the percentage of the crop that will fall into the peak box counts, but a more accurate early-season estimate of the fruit size distribution will likely require measuring 50% of the fruit on a tree.