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  • Author or Editor: George Yelenosky x
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Potted greenhouse-grown, l-year-old `Hamlin' orange [Citrus sinensis (L.) Osbeck] trees on 1.5-year-old rough lemon (C. jambhiri Lush.) rootstock were temperature-conditioned for 6 consecutive weeks in a controlled-environment room to test cold-hardening ability. Holding at 15.6 ± 0.6C during 12-hr days [425 μmol·s-1·m-2 photosynthetic photon flux (PPF) at top of trees] and 4.4C during nights resulted in 100% tree survival and no leaf loss “after 4 hr of – 6.7C in a dark freeze test room. Unhardened greenhouse trees were killed to rootstock. Solute efflux (dS·m-1) from unhardened frozen leaves was > 20-fold that from frozen leaves on hardened trees and nonfrozen leaves on unhardened trees. Oxygen uptake was not significantly impaired in frozen hardened leaves. No 02 uptake was evident for frozen unhardened leaves.

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One- to 4-year-old sweet orange trees, Citrus sinensis (L.) Osbeck cv. Valencia on rough lemon (C. jambhiri Lush.) rootstock, were used in a series of tests on the depth and stability of supercooling in various parts of greenhouse-grown trees held in pots during controlled freezes. Thermocouples were attached to flowers, fruit, leaves, and wood. Supercooling levels were inconsistent, ranging from – 3C to – 7C. Nucleation was spontaneous and well defined by sharp exotherms. Rapid progression of crystallization (≈ 60 cm·min–1) indicated no major obstacles to ice propagation throughout the tree above soil level. The site of initial freezing was variable, with a tendency for trees to freeze from the base of the stem toward the top. The location of tissue damage did not necessarily correspond to the location of initial freeze event. Freezing in the wood often preceded freezing of flowers.

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Abstract

A low-density, semirigid insulating wrap of L-shaped Styrofoam halves with plastic bag inner liners partially filled with water protected young citrus trees adequately in controlled freezes and showed no physical deterioration after 2 continuous years in field trials. Protection was provided by a lag in temperature decrease under the wraps relative to that of ambient air and by the release of heat as water froze in the plastic bags which pressed against the tree trunk. Crystals of either phenazine or silver iodide prevented supercooling of the water below −2.8°C. Citrus plants small enough to fit entirely within the wrap, even succulent new growth, remained uninjured during −6.7°C freezes.

Open Access

Abstract

Leaves of different citrus selections (Citrus sp.) developed visible bleaching (low chlorophyll content) within 14 days during constant 1.7°C and less than 500 μE/m2per sec (PAR) continuous light regimes in controlled temperature facilities. Leaves did not bleach at 21.1° and 10° in continuous light and/or in the dark at 1.7°. Larger amounts of amino acids leaked from bleached than nonbleached leaves and leaf disks from bleached leaves had lower rates of O2 uptake during respirometry at 30°. Plants at 1.7° for 14 days in continuous light were injured more than plants conditioned at 10° during 4-hr freeze tests at −6.7°.

Open Access

Abstract

Shoot organogenesis from detached leaves is not characteristic of all plants, but, when found, the phenomenon is a valuable tool for research and plant propagation. Some of the recent observations of whole-plant development from leaf cuttings include lily (Lilium longiflorum Thunb.) (3) and sweet potato [Ipomoea batatas (L.) Lam] (1).

Open Access

Abstract

Cultivars of citrus, having a wide range in cold tolerance, were conditioned in controlled-environment rooms with and without light: Plants conditioned in the light were injured less than plants conditioned in the dark during subsequent freeze tests. The effect of light was more pronounced at a conditioning temperature of 15°C than at 5°C.

Open Access

Abstract

Colorimetric determination of hydroxyproline in acid hydrolysates of ‘Valencia’ orange (Citrus sinensis [L.] Osbeck), ‘Carrizo’ citrange (C. sinensis × Poncirus trifoliata [L.] Raf.), ‘Cleopatra’ mandarin (C. reticulata Blanco), and rough lemon (C limon [L.] Burm. f.) indicated 14 to 71 μg of hydroxyproline per g of oven-dried leaf tissue. Cold-hardening and growth regulator treatments of different citrus cultivars changed the concentration of hydroxyproline in the leaves. Cultivars with greater concentrations of hydroxyproline before cold-hardening were also more tolerant of freeze conditions after cold-hardening.

Open Access

Abstract

Polyclonal antibodies against the major soluble glycoprotein of trifoliate orange [Poncirus trìfoliata (L.) Raf.] were produced in rabbits. The antisera were used to detect the glycoprotein in foliar protein extracts from a hybrid of Poncirus and Citrus genotypes by immunoblotting. One of the sera was found to be highly specific and was suited to indicate trifoliate gene expression. Cross-reacting bands in protein extracts from citrus callus tissue and in the medium of suspension cell cultures suggest that tissue culture systems can be used for biochemical studies of glycoproteins, but not for genotype characterization.

Open Access

Several stages of citrus (Citrus sinensis L. Osbeck. cv. Valencia) flowers, from very small bud (stage 1) to anthesis (stage 6), were evaluated for free and conjugated polyamines. The concentration of putrescine and spermidine synthesis increased markedly during the early stages, and then declined as the flower buds grew. At anthesis, putrescine and spermidine concentrations had increased significantly. Spermine concentration was very low and showed no significant change during the first three floral developmental stages; however, by stages 5 and 6, spermine concentration showed a slight but significant increase. Eighty percent of the total polyamine content in fully developed flowers is localized in the reproductive organs and only 20% is localized in the petals and the calyx. This study relates changes in conjugated and free polyamines to citrus flower growth.

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Handwarmers placed inside conventional insulating tree wraps increased trunk temperatures and improved tree survival under freeze conditions. Handwarmers generate heat by oxidation of Fe powder. In freeze-chamber tests with air temperature as low as –7.1C for 4 hours, wraps plus handwarmers kept trunk temperatures above freezing. Handwarmers increased minimum temperatures by 7C during a one-night freeze. Benefit of the handwarmer decreased the second night of a simulated two-night freeze but still increased minimum temperature by 1.3C. Tree survival was significantly improved by handwarmers in the freeze-chamber tests. In a field test during a mild freeze, handwarmers increased the minimum temperature by 3.5C the first night but provided no benefit the second night.

Free access