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  • Author or Editor: P. C. Andersen x
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The Cohesion Tension Theory, first in 1894 introduced by Dixon and Joly is the theory most often invoked to explain water movement in a transpiring plant. The pressure chamber technique has provided the strongest indirect evidence for this theory. However, controversy remains because 1) the necessary pressure gradients in xylem vessels have never been measured directly; 2) it is uncertain how continuous water columns under great tensions could persist in a metastable state for extended periods of time, and; 3) direct pressure probe measurements on individual xylem vessels have not been indicative of the extreme negative pressures obtained with the pressure chamber. Xylem fluid is an energy-limited resource containing the lowest available carbon (energy content = 2 to 15 J/cm3) of any plant tissue. However, many species of xylophagous leafhoppers subsist entirely on this dilute food source, despite the negative pressures thought to occur in xylem vessels. Carbon limitations of leafhoppers were underscored by 1) high feeding rates; 2) an unprecedented assimilation efficiency of organic compounds (i.e., >99%); 3) ammonotelism, and; 4) synchronization of feeding to optimum host nutrient content both seasonally and diurnally. The maximum tension that can be generated by the cibarial pumping mechanism of an insect based on anatomy and biochemistry is about 0.3 to 0.6 MPa, far below the purported xylem tensions occurring during most daylight hours. By contrast, we have shown that feeding has been usually independent of xylem tensions, as measured with a pressure chamber, and instead was a function of the amide content of xylem fluid. Moreover, the calculated net energy gain of insect feeding (or that contained within insect biomass) on xylem fluid of a given composition under a given tension have also been an a paradox. Experiments will be described that provide insight into the energetics of xylem fluid extraction.

Free access

Abstract

Three separate factorial experiments were designed to evaluate the effect of 10 adjuvants on net CO2 assimilation rate (A), leaf conductance to water vapor (g1), and transpiration rate (E) of pecan [Carya illinoensis (Wagenh.) C. Koch] ‘Elliott’, blueberry (Vaccinium ashei Reade) ‘Chaucer’, red top photinia (Photinia × Fraseri Dress), and azalea (Rhododendron × ‘Pink Ruffles’). Single applications of Bond, Leaf Act 80A, Nu-Film-17, Ortho X-77, Penetrator 3, Plyac, Sorba Spray ZNP, Sun Spray 7E, Triton CS-7, or Triton B-1956 at recommended rates did not affect A, g1, or E compared to a water spray. The main effect of plant species was highly significant in all three studies without adjuvant-species interactions. A significant adjuvant effect on A occurred with a second application of Nu-Film-17, Plyac, and Triton B-1956. The only significant effect, when treatments were analyzed separately by species, was that A of Plyac-treated blueberry was less than the control.

Open Access

Abstract

‘Sungem’ nectarine [Prunus persica (L.) Batsch] (Fig. 1) was released to provide an early ripening nectarine for commercial markets. All nectarines released by the Univ. of Florida begin with the prefix “Sun”. ‘Sun-gem’ is expected to be successful for homeowners, consumer harvest, local markets, and commercial growers with large acreage.

Open Access

Abstract

Nine pesticides (chlorothalonil, captan, benomyl, permethrin, methomyl, parathion, carbaryl, dicofol, and S) were sprayed on peach (Prunus persica L. Batsch ‘June Gold’) to determine pesticide-induced effects on leaf conductance (gl), transpiration (E), and net CO2 assimilation rate (A). Parathion was the only material to reduce A when applied <3 times. Net CO2 assimilation rate declined by 10% to 25% for parathion-, methomyl-, chlorothalonil-, benomyl-, and captan-treated trees after 3 applications; however, gl was reduced only for the parathion and chlorothalonil treatments. The pesticide-sensitivity of peach A appears to be much less than pecan and somewhat similar to apple. Chemical names used: 2,4,5,6-tetrachloro-l,3-benzenedi-carbonitrile (chlorothalonil); 3a,4,7,7a-tetrahydro-2-[(trichloromethyl)thiol]-lH-isoin-dole-l,3(2H)-dione (captan); methyl[l-](butylamino)carbonyl]-lH-benzimidazol-2-yl]carbamate (benomyl); (3-phenoxyphenyl)methyl 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate (permethrin); methyl N-[[(methylam-ino)carbonyl]oxy]ethanimidothioate(methomyl); 0,0-diethyl 0-p-nitrophenylphospho-rothioate (parathion); 1-naphthalenyl methylcarbamate (carbaryl); and 4,4′-dichloro-α-trichloro-methylbenzhydrol (dicofol).

Open Access

Abstract

The development of a high yielding, pink root-resistant [Pyrenochaeta terrestris (Hansen) Gorenz, Walker, and Larson], mild, sweet, shortday onion (Allium cepa L.) with improved shipping quality was the objective for the onion breeding program in the Texas Agricultural Experiment Station. ‘Texas Grano 1015Y’ (TG1015Y) is a very mild and sweet cultivar with those quality characteristics.

Open Access

Abstract

The development of a high yielding, pink root resistant, medium length storage shortday onion (Allium cepa L.) with improved shipping quality and maturing slightly later than ‘Texas Early Grano 502’ (TEG502) was the objective in the development of this cultivar. ‘Texas Grano 1025Y’ (TG1025Y) extends the South Texas onion season by 7 to 10 days beyond the ‘TEG502’ maturity season.

Open Access

Abstract

The development of a late maturing, high yielding, pink root resistant shortday onion (Allium cepa L.) with improved shipping quality was the objective for introduction of this cultivar.

Open Access

Abstract

The development of a late maturing, high yielding, disease resistant shortday onion (Allium cepa L.) with improved shipping quality and medium length storage characteristics was the objective leading to selection and increase of this cultivar.

Open Access