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Late season peach cultivars are usually cold stored for a few weeks to extend the marketing season, but physiological disorders related to calcium deficiency are now emerging. To study the absorption of Ca by the peach fruit, mature trees of two late-maturing cultivars: `Miraflores¿ and `Jesca¿ were treated with Ca applied in two different ways: either as foliar sprays of Ca water solutions, or rubbed on the fruit with a Tara gum gel containing the Ca solution. In both cases, the Ca source was CaCl2. Repeated foliar sprays along the growing season, of aqueous solutions of Ca concentrations ranging from 0.25 to 1% Ca did not affect the concentration of Ca in the peach skin or fruit flesh. Similarly, no effects on the fruit quality traits were observed at harvest. In a second experiment, fruits were rubbed with a calcium containing gel. A great increase in Ca concentration was found both on skin and flesh of fruits treated with 1% Ca. However, fruits treated with 1% Ca resulted in lower flesh firmness and were flat-shaped and exhibited an increased rate in fruit drop.

Calcium-related disorders in fruits lead to the collapse of cells, resulting in tissue enzymatic browning, caused by polyphenol oxidase (PPO) and peroxidase enzymes. PPOs are responsible for the enzymatic browning reaction that occurs in damaged fruits or vegetables. It appears that oxidative browning reactions in plants generally decrease quality by changing nutritional and organoleptic properties. In this work, electrophoresis was used for detection and comparison of active PPO isoforms from apple cv. Golden Delicious fruit tissues. Three types of materials were studied: sound apple pulp, bitter pit affected pulp and corky lesions induced by ammonium oxalate subdermal injections. Three main isozyme bands revealed by catechol staining were detected in the pulp of sound apple. In the apple tissue affected by bitter pit, the intensity of the two bands of high molecular weight increased and two new isozymes appeared, one below the second of greater mass and another one in the zone of low molecular weight. However, in oxalate-induced corky tissue, the lowest molecular weight PPO isozyme found in the natural pits, did not appear while the remaining pattern was analogous. Both the natural process of bitter pit development and the chemically induced one finally resulted in cork-like spots. These dehydrated brown tissues accumulate calcium and show greater PPO activity. However, these two processes must follow different metabolic routes or the speed at which the spots appear in the oxalate-induced process, does not allow for the adaptation of the isozymatic system as it occurs in the natural process.

To study the stomatal contribution to total leaf gas exchange in leaves of paclobutrazol-treated peach trees (Prunus persica (L.) Batsch), counts and measurements of stomata were made. Peach trees (cv. Catherine) were treated with different doses of paclobutrazol at bloom, and later in summer, counts of stomata per unit area of leaf showed that the density increased linearly with the doses, while the length of the stomata also decreased linearly.

Paclobutrazol (Pbz) is a triazol that effectively inhibits vegetative growth in peach. Changes in mineral element concentration have been generally found. However, uneven distribution of the elements in the soil may partially account for these differences. To ascertain these effects, an experiment was designed under controlled conditions, in which sugar beet, used as a model plant, was grown hidroponically, treated with Pbz and the results compared to those from unbearing peach trees grown in the open. The beets were treated with 1 M Pbz at the first trifoliate stage, and the peach trees with 2 g Pbz/tree shortly AFB. A reduction of 85 % in leaf area and of 70 % in dry weight were recorded in Pbz-treated beet plants, while in Pbz-treated peach these were of 40 % in leaf area and 29 % in dry weight. Nutrient concentration on dry weight basis varied little (about 8 % in beet and 11 % in peach). However, but global assimilation of nutrients on a leaf basis, when compared with controls, decreased up to the same extend as dry weight in beet (70 %) while in peach it was of 25 %. From these results it can be inferred that the mineral fertilization in Pbz-treated peach trees can be reduced to the same extend as the expected reduction in vegetative growth, consequently reducing production costs and environmental contamination.

Pear trees cv ‘Agua de Aranjuez’ A-840 (VT) clon, budded in the nursery at 15 and 50 cm from the soil were planted with the union at 10 and 50 cm high, and growth and cropping during the first two years recorded. Scion trunk-cross- sectional area was smaller on the high-worked trees from the time of planting, and stock area at soil level was also smaller on the high-budded trees from the first year after planting. Almost all the high-worked trees carried a crop on the second year of growth, while a few (20%) of the low-budded carried some fruits, which were smaller in size. Differences in size of both scion and stock were greater by the end of the second year.