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  • Author or Editor: Avinoam Nerd x
  • Journal of the American Society for Horticultural Science x
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Changes occurring during fruit ripening and duration of fruit development were studied in Selenicereus megalanthus (Scum. ex Vaupel) Moran (yellow pitaya), a climbing cactus grown in protected structures at three sites in the Israeli Negev desert. During ripening, peel color turned from green to yellow, fruit dimensions slightly changed, and pulp content markedly increased. Total soluble solids and soluble sugars in the pulp increased, while starch content decreased. Acidity decreased at the last stage of ripening. Fruit in which most of the peel area had turned yellow (stage 4) were given the highest taste grade by a panel of tasters. Measurements of ethylene and CO2 evolution indicated that fruit was nonclimacteric. The mean number of days from anthesis to fruit of stage 4 was negatively correlated with the mean of the maximum and the minimum temperatures during the growth period. Daily accumulation of heat units (HUs) was calculated as the difference between daily mean temperature and a base temperature of 7 °C. Sum of HUs for the period from anthesis to ripening was 1558±12 HUs.

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Hylocereus undatus [(Haworth) Britton and Rose] is a vine cactus from central America that has been established as a new fruit crop (pitaya) in many tropical and subtropical countries. In order to develop improved irrigation practices, the relationships between water parameters and growth were studied in rooted stem cuttings growing in pots with sandy soil under well-watered and drought-stressed conditions, in a controlled environment. Soil water potential rapidly decreased from -0.02 to -1.5 MPa during the first 5 days of drought. However, growth of new stems emerging from the succulent mature stems only decreased significantly after 3 weeks of drought. After 3 weeks of drought, the water content of growing stems decreased by 2% (P < 0.05) and their water potentials by 0.05 MPa (P > 0.05), as compared with the irrigated controls. At the same time, water content in drought-treated mature stems decreased by 4% (P < 0.05) and water potentials by 0.25 MPa (P < 0.05). Several lines of evidence indicated that active phloem supply of assimilates and associated water reserves from mature stems was the mechanism that allowed developing stems of H. undatus to maintain growth under well-watered and drought conditions: 1) Girdling the phloem of growing stems rapidly inhibited stem elongation. 2) Secretion of sucrose-containing nectar by growing stems was maintained during drought. 3) The water potential gradient was in the wrong direction for xylem transport from mature to young growing stems and axial hydraulic conductivity in young stems was either zero or comparatively low.

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Water relations and fruit development were studied for up to 100 days after anthesis for potted plants of Opuntia ficus-indica (L.) Mill. (a prickly pear) that were either well-watered or water-stressed, each plant consisting of a medium-sized cladode bearing two or three fruit. Even though cladodes of water-stressed plants lost up to 50% of their thickness, their fruit continued to gain water and to develop; at ripening such fruit had only 16% less water than fruit of watered plants. Maturation indicated by the decrease in fractional peel content and increases in pulp weight and in pulp soluble sugar content was hastened by water stress, leading to ripening ≈88 days after anthesis for water-stressed plants, which was 10 days earlier than for watered plants. Fruit had a lower stomatal frequency than the cladodes but both exhibited Crassulacean acid metabolism behavior. Transpiration occurred mainly at night, and the daily amount of water transpired per unit fruit surface area decreased with time, especially for fruit of water-stressed plants. This decrease was related to fruit expansion (leading to decreased stomatal frequency) for watered plants and to both fruit expansion and water stress for water-stressed plants. At 75 days after anthesis, daily diameter changes of fruit were correlated with transpiration, contraction occurring at night and expansion during the daytime, and changes were greater for watered plants for which daily transpiration was higher.

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