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  • Author or Editor: G. Yelenosky x
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Abstract

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

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
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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
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

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

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

Greenhouse-grown l-year-old sweet orange trees [Citrus sinensis (L.) Osbeck cv. Valencia] on cold-hardy trifoliate orange [Poncirus trifoliata (L.) Raf.] and cold-sensitive citron (C. medica L.) rootstocks were exposed to cold-acclimation conditions and freeze-tested at -6.7C for 4 hours in a temperature-programed walk-in freezer room. Nonhardened trees generally did not survive the freeze, whereas cold-hardened trees survived with no wood kill on either rootstock. Essentially, all leaves died or abscised during the subsequent 5 weeks in the greenhouse. Freeze survival did not separate rootstocks nor did supercooling in separate trials where Yalencia' wood reached –8.8C before apparent nucleation. Increases in concentration of carbohydrates and proline and decreases in water content in Yalencia' leaves during cold hardening were generally associated with increased freeze tolerance. Other tests, that matched 9-month-old seedlings of citron with trifoliate orange rootstock, showed clear differences in the superior cold acclimation of trifoliate orange over citron, which, however, performed better than expected.

Free access

Ten-month-old seedlings, grown from seed extracted from 22 individual pummelo [Citrus grandis (L.) Osbeck] × trifoliate orange [Poncirus trifoliata (L.) Raf.] citrus hybrid trees that survived -15C freezes near Monticello, Fla., were cold-acclimated in controlled-environment rooms and freeze-tested at -6.7C for 4 h. Freeze damage to open-pollinated progeny was ranked by the number of uninjured seedlings and percentage of leaves killed and wood dieback. Morphological segregation was not associated with differences in freeze survival, and the dominant trifoliate gene was readily evident. Progeny from one tree, identified as 98-71, are considered the most likely candidates for further study in developing cold-hardy citrus trees.

Free access

Abstract

Available young hybrid trees of Eremocitrus glauca with ‘Valencia’ orange (Citrus sinensis (L.) Osbeck), Sicilian sour orange (C. aurantium L.), ‘Nagami’ kumquat (Fortunella margarita (Lour.) Swing.), and Koethen sweet orange (C. sinensis) were more cold hardy than the Citrus or kumquat parent in natural and controlled freezes. Eremocitrus may be a useful source of cold hardiness for breeding cold-hardy citrus hybrids.

Open Access