Search Results
Abstract
Diurnal leaf and fruit water Potentials (Ψ) of sweet cherry (Prunus avium L.) showed that fruit pedicel Ψ was always lower at 6 AM then leaf Ψ but leaf Ψ as usually lower during the day. Varietal differences in Ψ occur but fruit maturity does not appear to have an effect. Minimum fruit pedicel Ψ was reached at about 2 PM and then recovered to the earlier higher Ψ as water uptake occured during the night.
Abstract
Alfalfa greening, (green stain, green mottle, or superficial cork) is a physiological disorder of ‘Anjou’ pear fruit, Pyrus communis L. This disorder is characterized by green streaks, blotches, and specks on the skin occurring most frequently at the stem end; it may also extend to the calyx end where superficial cork is also frequently present. Mineral analysis of the peel and whole fruit of alfalfa greening-affected fruit indicated that the disorder was associated with higher nitrogen, potassium, and phosphorus content but lower calcium levels than normal fruit.
Abstract
Excised Cornus stolonifera Michx. stems cultured axenically in a liquid medium were acclimated to cold when subjected to short photoperiods and low temperatures. Foliate explants acclimated effectively and defoliated ones did not when they were cultured on White's medium which contained 0.083 M sucrose. Several other concentrations of sugars (0, 0.01, 0.1, and 0.5 M glucose and 0, 0.01, 0.05, and 0.1 M sucrose) did not enhance cold acclimation of foliated explants. The exogenously supplied sugars reduced stem growth, promoted leaf abscission, and enhanced the development of typical autumnal red coloration in leaves and stems. The highest sugar concentration (0.5 M glucose) caused death of the explants.
While a minimal level of photosynthate (sugar) is almost certainly required for the active metabolic phases of cold acclimation in hardy woody species, our studies provided no evidence that sugars bear a direct causal relationship to cold acclimation.
Abstract
Mature ‘Red Delicious’ apple trees (Malus pumila Mill) were sprinkled intermittently with an overhead irrigation system after completion of winter rest. A 2-minute sprinkling cycle operated automatically whenever the ambient air temperature of the orchard exceeded 7°C until the control trees reached full bloom. Evaporative cooling of the treated trees reduced bud temperatures to within 2°C of the wet bulb temperature. Treated trees reached full bloom 17 days after the untreated controls.
The citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), is a key pest in most citrus-growing regions worldwide. Adult citrus leafminers oviposit primarily on young elongating flush of Citrus as well as other Rutaceae and some ornamental plants. Larvae feed on the epidermal cell layer of developing leaves and injury to leaves provides a pathway for infection by the bacterium Xanthomonas citri subsp. citri (Hasse), the causal agent of Asiatic citrus canker. In this study, we quantified abundance of citrus leafminer larvae on progeny of 87 seed parent genotypes of Citrus and Citrus relatives (family Rutaceae) in the field in East–central Florida to identify those that have low abundance of leafminers. Progeny from the 87 parent genotypes varied in abundance of the leafminer. Progeny of 15 parent genotypes had a high mean abundance of more than six leafminers per flush shoot. All but one of these genotypes were in the Citrus genus. Progeny of 16 parent genotypes had zero, or nearly zero, leafminers, but none were from the Citrus genus. However, many of these 16 genotypes were from genera closely related to true citrus (subtribe Citrinae) and are sexually compatible with Citrus. Progeny of two parent genotypes in the subfamily Toddalioideae and Glycosmis pentaphylla (Retz.) Corr. also had a low abundance of leafminer. Glycosmis pentaphylla also is a poor host for the Asian citrus psyllid, Diaphorina citri Kuwayama, and has biochemical resistance to the citrus weevil, Diaprepes abbreviatus (L.), so this genotype as well as others identified as poor hosts for the leafminer may prove useful in breeding programs aimed at reducing the abundance of multiple insect pests on citrus.