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Abstract
Concentrations of oxygen, carbon dioxide, ethylene, and methane did not differ significantly in soil containing blight-affected and healthy ‘Valencia’ orange trees [(Citrus sinensis (L.) Osbeck]. Methane was found in soils during all sampling, with the highest levels occurring during the July and October collections.
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”).
Abstract
CO2 exchange rate (CER), stomatal conductance (Cs), and transpiration in mature attached leaves of ‘Valencia’ orange [Citrus sinensis (L.) Osbeck] were determined outdoors from predawn to 1100 EDT. The maximum values of CER and Cs, which were about 7 μmol CO2·s−1m−2 and 0.27 cm·s−1, respectively, at solar photosynthetic photon flux density (PPFD) of 500-700 μmol·s−1m−2, remained at these levels as PPFD, temperature, and vapor pressure deficit (VPD) between leaf and air continued to increase. Transpiration rates, with maximum values ranging from 1 to 4 mmol H2O·s−1m−2, increased throughout the measurement periods of the morning as leaf-air VPD increased. Thus, photosynthetic water use efficiency decreased with increasing VPD.
Abstract
Citrus blight or young tree decline, is a wilt-like disease of unknown etiology which is characterized by restricted water movement and an upset in normal zinc distribution patterns. Diurnal leaf and fruit water potentials and leaf stomatal conductances of sweet orange Citrus sinensis (L.) Osbeck leaves on trees in various stages of decline were characterized to determine the progression of this disorder. All blight affected trees, regardless of severity of tree condition, had similar diurnal water relations. Blight affected trees have fewer and smaller leaves, less leaf area per tree, lower stomatal conductances, and lower diurnal transpiration rates than healthy trees. These differences did not result in any apparent changes in specific leaf weight, leaf osmotic potentials or in the critical leaf water deficits at which leaf turgor was lost. At equivalent transpirational fluxes, leaf water potential was much lower in blight affected trees than in healthy trees. Therefore, the water stress symptoms associated with blight are related to increased resistances in the water transport system and are not a result of lost stomatal function or changes in water relations characteristics of leaves that remain on blight affected trees.
Abstract
Carbon dioxide assimilation and ribulose-l,5-bisphosphate (RuBP) carboxylase activity were measured in 3 cultivars of pecan (Carya illinoensis (Wang) K. Koch cvs. Brooks, Stuart, and Mobile). Optimum leaf temperatures (27°C) and saturating irradiances (675 μEm−2s−1) were uniform among cultivars. Carbon dioxide assimilation was significantly higher in ‘Brooks’ and ‘Stuart’ than in ‘Mobile’ between April and June, but no differences were apparent among cultivars for the remainder of the season. The maximum rate observed was 13.5 mg CO2 dm−2hr−1. A lower rate occurred between mid-August and mid-September, which may limit available carbohydrate reserves for the following growing season. A significant decrease in RuBP carboxylase activity between May and August may have been a result of leaf senescence.