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  • Author or Editor: G. Yelenosky x
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Aqueous suspensions of ice nucleation active (INA) bacteria [Pseudomonas syringae van Hall and Erwinia herbicola (Löhnis) Dye] and suspensions of nonbacterial agents, silver iodide, phenazine, and flurophlogopite, were used to induce freezing in young citrus trees, ‘Valencia’ orange [Citrus sinensis (L.) Osbeck] on sour orange (C. aurantium L.) rootstock. Trees sprayed with INA agents froze at higher temperatures than unsprayed trees. INA bacteria-induced freezing was significant only when leaf surfaces were allowed to dry prior to freeze tests. Leaves with dry surfaces supercooled 1° to 3°C more than wet leaves, which started to freeze, and about 1° sooner with than without INA agents. Differences between INA bacteria and nonbacterial agents were not significant in the moment of freeze of wet leaves. INA agents induced freezing in citrus leaves usually before −5°, and in water drops, before −4°. Freezing was easier to induce on the underside (abaxial) than top (adaxial) surfaces of leaves. Sucrose, proline, and expressed sap were nonINA on citrus leaves and in drops of water.

Open Access
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Ancymidol (α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol) in soil mix retarded growth of potted citrus plants. Three-month-old ‘Valencia’ orange trees (Citrus sinensis (L.) Osb.) on one-year-old sour orange rootstock (C aurantium L.) grew 92% less in height than control plants in 5 months under greenhouse conditions with 0.10% active ingredient (ai) (by weight) concentration of ancymidol in the soil mix. Concentrations of 0.4% ai resulted in marked growth reduction of 3-month-old ‘Duncan’ grapefruit seedlings (C. Paradisi Macfad.). Other tests showed that neither ancymidol nor the reduced growth following its use increased cold hardening of ‘Valencia’ trees.

Open Access
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Abstract

‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] flowers readily supercooled on young trees tested in a controlled-temperature room. Differential thermal analysis (DTA) determinations with thermocouples inserted into different flower parts indicated ice nucleation occurred from –3.8° to –6.1°C when flowers were attached to trees and from -8.1° to — 11.9°C when flowers were detached. Similar supercooling levels also were noted in ovaries and young leaves. Ice-nucleation-active (INA) bacteria apparently were not involved based on total bacteria counts and flower wash extracts sprayed on flowers. Supercooling of citrus flowers was comparable to flowers of deciduous fruit trees in temperate climate zones. Data indicate a degree of freeze avoidance not previously recognized in citrus reproduction organs.

Open Access
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Abstract

Potted citrus trees, 1-yr-old ‘Valencia’ orange (Citrus sinensis (L.) Osbeck) on 1.5-yr-old Rusk citrange (C. sinensis (L.) Osbeck × Poncirus trifoliata) rootstocks were maintained for 6 consecutive 7-day periods in a controlled environment to induce cold hardiness with cold-hardening temperatures 10 ± 1°C, illumination 500 μeinsteins/m2 per sec (photosynthetically active radiation = PAR), relative humidity, 60 ± 5%. Trees progressively cold hardened as a result of the above conditions and, after 5 weeks, would tolerate −6.7° for 4 hours without apparent injury. Leaves sustained injury up to 5 weeks and stems up to 3 weeks of cold hardening. Solutes increased most rapidly in leaves during the first week as a result of carbohydrate accumulation.

Proline, glutamic acid and valine increased, whereas other amino acids decreased. Water potentials in the leaves of hardened trees averaged −19.5 bars after 6 weeks of cold hardening compared to −5 bars in leaves of unhardened trees.

Open Access
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Abstract

Amo-1618 at 500 to 10,000 ppm reduced plant growth when sprayed on seedlings of 3 species of citrus. The growth retardant affected rate of stem elongation, length of stem internode, and leaf shape, color, and texture. Objectionable tissue abnormalities did not develop.

Open Access
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Abstract

2,3,5-Triphenyltetrazolium chloride (TTC) reduction measures glucose equivalents of substances diffusing from plant tissues. Amounts of diffusing substances are greater from cold-hardened than unhardened citrus. These differences are colorimetrically distinguishable and identify citrus plants exposed to low temp in controlled environment studies.

Open Access

Abstract

Different concentrations and methods of applying paclobutrazol on citrus plants [Citrus limon (L.) Burm. f.] under greenhouse conditions suggest 102 ppm (a.i.) foliar sprays or 20 mg per 2.5 liter pot are threshold concentrations for visible change in growth and development. Most apparent was reduced shoot extension, largely the result of shortened internodes. The leaves were smaller than those on untreated plants but little changed in length/width ratios. Loss of mass (weight) was mostly in the main stem and primary root. The most effective application method was as a soil drench which induced changes in the root as well as the tops of plants. As a stem-sprout inhibitor, paclobutrazol was less effective than “Tre-Hold.” Chemical names used: β-[(4-chlorophenyl)methyl-α-(l,l-dimethylethyl)-1H,2,4-triazole-l-ethanol (paclobutrazol); 1.15% ethyl 1-naphthalene acetate (“Tre-Hold”).

Open Access
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Abstract

Studies show electrical potential (Millivoltage output) generated by citrus seedlings is useful as an indication of freezing in hardened seedlings or where freeze rates are 1° hr-1 or less. Needle-sharp probes of a gold-amalgam wire attached to a strip chart recorder with a variable millivolt supply were used to detect mv changes in seedlings exposed to freeze conditions in an artificial environment room. An abrupt increase of 2 to 6 mv in the mv signal indicated the onset of freezing in the seedlings as checked by the heat of crystallization measured with thermocouples, visual signs of freezing, and subsequent physical damage studies.

Open Access
Authors: and

Abstract

Liquid crystals are a part of a large number of organic compounds which, upon heating, change from a viscous liquid to a clear isotropic liquid. Many liquid crystals are derivatives of cholesterol. In the transition stage between solid and isotropic liquid, liquid crystals possess light scattering properties which result in changes of color in response to changes in temperature (1).

Open Access

Abstract

In the article “Growth Capacity of ‘Valencia’ Orange Buds on Different Rootstocks during Cold-hardening Temperatures” by G. Yelenosky and H.K. Wutscher [J. Amer. Soc. Hort. Sci. 110(1):78–83. 1985.], the figure captions for Figures 2 and 3 were reversed.

Open Access