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  • Author or Editor: Alexander Lang x
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The effects of spur leaf removal on xylem sap flows and calcium accumulation in fruit of apple (Malus ×domestica Borkh. `Royal Gala') were determined 56 to 61 days after full bloom. Fruit calcium concentrations were reduced but fruit size was not influenced by partial spur defoliation at bloom. Apples exchanged xylem sap with the tree in daily cycles of flow reversal. The presence of local spur leaves promoted this exchange by accentuating the xylem sap drawn out of the fruit during the day, requiring more to flow back into the fruit at night to replace it. Calcium concentrations were lower in the xylem sap leaving the fruit than in that entering it. The reduced calcium accumulation in the fruit borne on defoliated spurs can therefore be attributed to the reduced volume of xylem sap exchanged between tree and fruit.

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Susceptibility of sweet cherry (Prunus avium L.) fruit to rain cracking increases toward maturity and is thought to be related to increases in both tissue pressure ( ) and cell pressure ( ). Furthermore, at a given water potential ( ), one might expect the increase in and the to balance the decrease in osmotic potential ( ). The objectives of our study were to quantify and in developing sweet cherry using vapor pressure osmometry (VPO), compression plate (CP), and the cell pressure probe (CPP). In addition, the tissue water potential was determined by quantifying the bending of strips of fruit skin and the change in projected area of discs excised from the flesh when incubated in a range of sucrose solutions of varying osmotic potentials ( ). Fruit growth followed a sigmoid pattern with time with the Stage II/Stage III transition occurring at ≈55 days after full bloom (DAFB). The and the were constant up to ≈55 DAFB but decreased to –2.8 MPa at maturity. The calculated by subtracting the from averaged ≈350 kPa up to 48 DAFB and then decreased at a decreasing rate to ≈21 kPa toward maturity. The determined from bending assays using excised skin strips or from water uptake of excised flesh discs was essentially constant up to ≈48 DAFB, then decreased until ≈75 DAFB and remained constant thereafter. These values were in good agreement with those determined by VPO. The as determined by CP passed through a transient peak at ≈41 DAFB, then decreased until ≈63 DAFB and remained constant and low until maturity. Similarly, by CPP increased from 27 to 48 DAFB, remained constant until ≈55 DAFB, and then decreased until maturity. Our data demonstrate a consistent decrease in and that coincides with a decrease in of sweet cherry during Stage III. Because and are low relative to , the change in parallels that in . The reason for the low turgor most likely lies in the accumulation of apoplastic solutes. These prevent a catastrophic increase in pressure that would otherwise lead to the bursting of individual cells and the cracking of entire fruit.

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The new apple (Malus ×domestica Borkh.) cultivar Sciros™, resulting from a cross of 'Gala' with 'Splendour', is marketed internationally from New Zealand. A characteristic of this cultivar is the presence of dense, dark green or black nodules in the fruit cortex, located in close proximity to the five sepal vascular bundles. Nodules are visible as green spots beginning about 40 days after bloom and they continue to develop, reaching a length of up to 8 mm at fruit maturity, although there is considerable variation in their size. Large vascular nodules often develop dark brown centers and reduce the visual quality of the fruit flesh. The frequencies of vascular nodules in 61 'Gala' × 'Splendour' hybrids from New Zealand and British Columbia, Canada, were examined. These ranged from a mean of 0 to 12.1, depending on the hybrid. Thirteen hybrids were in the high frequency class (2.76-12.1), 28 in the low frequency (0.04-1.86), and 20 were without nodules. The mean nodule frequency in Sciros™ was 12.1 nodules per fruit, the highest of all hybrids examined. Our survey of 44 other cultivars confirmed the occurrence of vascular nodules in 'Gala' and 'Splendour', with mean vascular nodule frequency of 1.9 and 0.5 nodules per fruit, respectively. Nodules were also found in 'Newtown Pippin' (frequency 0.8), and in a 'Newtown Pippin' × 'Granny Smith' hybrid (frequency 0.1).

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The use of tomato (Solanum lycopersicum) grafting is gaining traction across the United States, but small-scale growers face the challenge of creating optimum postgrafting healing conditions. The practice of blocking light for a period of 2 to 4 days while maintaining high humidity is commonly recommended for healing grafted tomato transplants; however, research is exploring alternatives to this practice. The present study investigated a low-input healing method for grafted tomato transplants with a specific focus on light and the use of propagation heat mats to regulate substrate and healing chamber air temperatures during the 7-day healing process. We hypothesized that 4 days of light exclusion and the use of propagation heat mats would improve grafted tomato transplant survival and growth. ‘Cherokee Purple’ was used as the scion and ‘RST-04-106-T’ was used as the rootstock. The whole plot factor was heat [propagation mats set at 80 °F (heat) or no propagation mat (no heat)] and the subplot factor was light exclusion (0, 4, or 6 days of dark). The highest survival rate among treatments was 97% in 0 days of dark with no heat treatment; survival decreased to 84% in 4 and 6 days of dark with no heat treatments. The plant survival rate was 96% with 0 days of dark and heat treatment; however, the survival rates were 63% and 45% for the 4- and 6-day dark treatments, respectively. The scion stem diameter was largest for transplants grown in 0 days of dark, but there was no difference in stem diameter due to heat treatments. There were no differences among scion or rootstock biomasses due to heat or light treatments. These results demonstrate that propagation mats set at 80 °F to regulate the substrate temperature were detrimental to grafted transplant survival under extended periods of light exclusion. However, this finding creates the basis to explore lower levels of substrate temperature modification. Our work also indicates that light exclusion may not be necessary for healing grafted tomato plants regardless of root-zone temperature treatments. Future work should examine the interactions of various substrate and air temperatures under full light conditions and their effects on grafted tomato transplant survival and growth. This work contributes to the ongoing research of how to optimize low-input healing methods that may be readily adopted by small-scale tomato growers.

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Quality and storability of ‘Pacific Rose™’ apple grown under partial rootzone drying (PRD) were studied over 2 years. The treatments were commercial irrigation (CI) and PRD, which were applied by watering one side of the tree row throughout the season (Expt. 1) or by alternating irrigation between two sides of the tree row when volumetric soil water content ranged between 0.18 and 0.22 m3·m−3 (Expt. 2). The PRD and CI fruit had similar quality attributes at harvest and after storage except that the former had lower weight loss during storage in Exp. 1 and a lower firmness after storage in Exp. 2. Compared with CI, PRD saved water by 0.15 mega liters per hectare in Exp. 1 and by 0.14 mega liters per hectare in Exp. 2. We recommend PRD for humid environments similar to ours.

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Research quantified contributions to total variation in water vapor permeance from sources such as cultivar and harvest date in `Braeburn', `Pacific Rose', `Granny Smith', and `Cripps Pink' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. In a study on `Braeburn' fruit from eight orchards in Central Otago, New Zealand, >50% of the total variation in permeance was associated with harvest date. This variation was the result of a large increase in water vapor permeance from 16.6 to 30.2 (se = 0.88, df = 192) nmol·s-1·m-2·Pa-1 over the 8 week experimental harvest period. Fruit to fruit differences accounted for 22% of total variation in permeance. Interaction between harvest date and orchard effects explained 7% of the total variation, indicating that fruit from the different orchards responded in differing ways to advancing harvest date. Tree effects accounted for only 1% of the total variation. Weight loss from respiration [at 20 °C and ≈60% relative humidity (RH)] comprised 3.04±0.11% of total weight loss, averaged across all harvest dates. In a second study of fruit of four apple cultivars, almost 30% of the total variation in water vapor permeance was associated with cultivar differences. Mean water vapor permeance for `Braeburn', `Pacific Rose', `Granny Smith', and `Cripps Pink' fruit was 44, 35, 17, and 20 (se = 4.3, df = 300) nmol·s-1·m-2·Pa-1 respectively. Over 20% of the total variation was associated with harvest date and arose from a large increase in water vapor permeance from 21 nmol·s-1·m-2·Pa-1 at first harvest to 46 nmol·s-1·m-2·Pa-1 (se = 5.3, df = 200) at final harvest, 10 weeks later, on average across all four cultivars. There was large fruit to fruit variation in water vapor permeance accounting for 25% of the total variation in permeance values. Tree effects only accounted for 4% of the total variation. Water vapor permeance in `Pacific Rose'` and `Braeburn' increased substantially with later harvest but values remained relatively constant for `Granny Smith' and `Cripps Pink'. A simple mathematical model was developed to predict weight loss from `Braeburn' fruit. Based on these findings, it appears worthwhile to increase the stringency of measures to control weight loss in `Braeburn' and `Pacific Rose'` apples, particularly those harvested late in the season.

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Previous research has shown that maple (Acer spp.) leaf litter resulted in fewer common dandelions (Taraxacum officinale) when mulched into established turfgrass. However, the leaves used in that research may have contained herbicide residues and were separated by genus, not species. Our research compared the effects of pesticide-free mulched maple and oak (Quercus spp.) leaves on dandelion populations in an established kentucky bluegrass (Poa pratensis) stand maintained as a residential lawn on sandy loam soil. The objectives of this study were to quantify the effectiveness of maple or oak leaf mulches as an organic common dandelion control method and to identify which maple species and rates (particle size and rate per unit area) provided the most effective control. The experimental design was a randomized complete block with treatments arranged as a 5 × 2 × 2 + 1 factorial, with tree leaf species, leaf particle size, leaf application rate, and control as main factors. Leaf species were red maple (Acer rubrum), silver maple (A. saccharinum), sugar maple (A. saccharum), high sugar content sugar maple, and red oak (Quercus rubra). Particle sizes were coarse (0.4–1.0 inch2) and fine (≤0.2 inch2), and application rates were low (0.5 kg·m−2) and high (1.5 kg·m−2). Mulch applications were made in Fall 2003 and 2004 and data were collected beginning in Spring 2004 on kentucky bluegrass spring green-up, and common dandelion plant counts. The high application rate, regardless of tree genus or species, resulted in the highest green-up ratings. Common dandelion plant counts after one (2003) and two (2003 and 2004) mulch applications at the high rate showed that up to 80% and 53% reduction was achieved, respectively. Results indicate that mulching leaves regardless of genus (oak or maple) or maple species into established turfgrass as a leaf litter disposal method will increase spring green-up and contribute to a reduction in common dandelion population.

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