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  • Author or Editor: Juvenal Luza x
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Development of roots on M.26 apple shoots grown in vitro induced by A. rhizogenes was compared with that of roots induced by NAA. Shoots were inoculated with 4-day colonies of A. rhizogenes strain A4 and were sampled at 1, 2, 4, 8 weeks after inoculation. Roots formed on approximately 30% of inoculated shoots. Roots induced by A. rhizogenes typically were agravitropic and branching. The outer layer of cells on these roots, especially on older roots, often resembled callus and sloughed off easily when the plants were transferred. The internal structure of the roots did not differ between the two treatments. Roots induced by NAA always arose endogenously and clear connections to the vascular system of the shoots were apparent. Many roots induced by A. rhizogenes appeared to develop exogenously, arising from anomalous cellular proliferation in the cortex of the apple stems or in callus at the base of the stem. These roots also showed vascular connections to the shoot.

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Pistachio (Pistacia vera L.) pollen was examined for capacity to germinate in vitro 2 days after anthesis and at intervals of time after storage at ambient laboratory conditions or at − 20°C. In 1986, fresh pollen of each of four clones examined had high germination percentages on a range of sucrose and agar concentrations. After 1 week at room temperature, germination percentages were < 6%. However, when the same week-old pollen was treated to effect gradual hydration at high humidity prior to being placed on the germination medium, germination increased to > 80% for ‘Peters’ pollen and 10.4% to 63.8% for the three other clones. In 1987, similar results were obtained for ‘Peters’ pollen, where pollen hydrated at high humidity had germination rates at least 50% that of fresh pollen when stored up to 18 days at ambient laboratory temperature and humidity. Pollen stored at −20° showed more exacting in vitro germination requirements than fresh pollen, particularly as time in storage increased. ‘Peters’ pollen retained germination levels comparable to fresh pollen after 4 months at −20°, but, by 12 months, germination percentages had fallen sharply.

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Skin discoloration (SD) formation in peach [Prunus persica (L.) Batsch] and nectarine [Prunus persica (L.) Batsch, var. nectarine] was related to physical damage (abrasion) to the fruit during fruit handling (harvest and hauling operations) within the orchard and during transport to the packinghouse. Vibration and rubbing treatments increased SD formation indicating that tissue damage is involved in SD formation. Anatomical studies comparing sound and SD-injured tissues done by scanning electron and light microscopy indicated that very-low-intensity physical damage could induce brown and/or black spots because of cell disruption in the epidermal and hypodermal layers. The fact that injury was specific to the exocarp tissues (cuticle, epidermis, and hypodermis), and that mesocarp tissue located below the exocarp cells remained sound and turgid, indicated that abrasion injury is associated with SD. Similar types of visible and anatomical injury characteristics were induced by a rubbing treatment, demonstrating that physical abrasion damage affecting just exocarp cells was enough to induce SD:

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The effect of irrigation management strategies on the quality and storage performance of `O'Henry' peaches [Prunus persica (L.) Batsch] was studied for two seasons. The deficit irrigation treatment induced a higher fruit soluble solids concentration and lower fruit weight. The excess irrigation treatment, compared to the optimum treatment, increased the rate of fruit water loss without altering fruit quality and storage performance. Scanning electron microscope observations indicated a higher density of trichomes on fruit from the deficit and optimum irrigation treatments than from the excess irrigation treatment. Light microscopy studies indicated that fruit from deficit and optimum irrigation had a continuous and much thicker cuticle than fruit from the excess irrigation treatment. These differences in exodermis structure may explain the high percentage of water loss from fruit from the excess irrigation treatment compared to the deficit and optimum irrigation treatments.

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Peach and nectarine skin discoloration or inking (SD) has become a fruit industry problem in the last decade. Spots on the skin may be black, tan, purple or brown and vary in shape. SD was related with physical abuse of the fruit occurring during handling (harvest and transport operations) within the orchard.

An anatomical study comparing healthy and damaged (black and brown) tissue of different peach and nectarine varieties was done with the Scanning Electron Microscope (SEM) and Light Microscope (LM). This study indicated that only exocarp cell (epiderm and cuticle) damage was associated with SD. The internal compartmentation of the damaged cells was often disrupted with the contents of the cytoplasm and vacuole mixed and expelled. Mesocarp cells were always intact and turgid. The same anatomical and visible tissue injury symptoms were induced on fruit by abrasion treatments.

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Water used for peach irrigation can be reduced by supplying less than full evapotranspiration (ET) during a specific period of fruit growth (RDI). The effect of RDI technique of fruit quality, internal breakdown and storage performance was studied on `O'Henry' during the 1990, 1991 and 1992 seasons. The three irrigation regimes (50, 100 and 150% ET) imposed during the three seasons induced a higher soluble solids content in the fruit without reduction of postharvest life. Scanning and light microscope observations indicated a modification of cuticle and epidermal characteristics by the three irrigation treatments. These differences in exodermis structure may explain the lower percentage of water loss on fruit from the under irrigated (50% ET) compared to well irrigated (100% ET) and over irrigated (150% ET) treatments during the three seasons.

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