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  • Author or Editor: David W. Buchanan x
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Abstract

Roots of sour orange (Citrus aurantium L.), ‘Carrizo’ citrange [C. sinensis L. (Osbeck.) × Poncirus trifoliata L. (Raf.)] and ‘Swingle’ citrumelo [C. paradisi Macf. × P. trifoliata L. (Raf.)] seedlings were exposed to various high temperatures for 20 minutes and heat injury was determined by electrolyte leakage procedures, microscopic examination, and visual observations. Temperatures at the midpoint of sigmoidal curves fitted through electrolyte leakage data for excised roots were 51.6° ± 0.5°C, 52.5° ± 0.7°, and 53.5° ± 0.5° for ‘Carrizo’ citrange, sour orange, and ‘Swingle’ citrumelo rootstocks, respectively. Electrolyte leakage results with excised roots were supported by microscopic examination and visual observations of whole plants.

Open Access

Abstract

Mexican avocado seedlings and grafted ‘Irwin’ mangos grown under soil temperatures of 21, 27 and 32°C responded differently. The soil temperature statistically influenced the growth of the avocado seedlings but not the mangos. A soil temperature range of 21 to 27° was best for the growth of the avocado seedlings but temperatures greater than 27° reduced growth. The number of growth flushes was greater at 27° than either 21 or 32°. The avocado seedlings were tall and upright at 21° and were short and spreading at 32°.

The mineral composition of both the avocado and the mango leaves changed with soil temperatures. The content of N and P in avocado and mango leaves was highest at 32° and lowest at 27°. The K content of the avocado leaves increased with temperature, but the Fe and Zn content decreased. In the mango Mg and Fe content was highest at 27° and lowest at 21°. Calcium content of the mango leaves decreased with soil temperature.

Open Access

Abstract

‘Orlando’ tangelo (Citrus reticulata Blanco × Citrus paradisi Macf.) trees not irrigated in the fall, but protected by under-tree sprinkling during a frost, sustained the lowest percentage of leaf and fruit damage as determined 6 weeks after the frost. Trees irrigated both in the fall and during a frost, or those receiving no fall irrigation or under-tree sprinkling, were intermediate in fruit damage. Fall irrigation without sprinkling the night of a frost contributed to the most severe damage to leaves and fruit. Soil moisture content of irrigated blocks was significantly greater than for non-irrigated blocks during the fall, yet afternoon leaf xylem water potential and stem water content were comparable. Leaf freezing point of detached leaves of ‘Orlando’ and navel orange (Citrus sinensis (L.) Osbeck) was poorly correlated with leaf xylem water potential, abaxial diffusion resistance, and relative water content. Leaf freezing and killing temperature was unaffected by fall irrigation and ranged from -5.8 to -6.8°C from October until December in 1978 and 1979.

Open Access

Abstract

The influence of root temperature on whole-plant water relations and cold hardiness in seedlings of 2 citrus rootstocks—rough lemon (Citrus jambhiri Lush.) and Carrizo citrange [C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.]—and ‘Valencia’ scions on both rootstocks was examined. Plants were exposed to root temperatures of 5°, 10°, or 15°C for 5–8 weeks, while shoots were exposed to a nonacclimating air temperature of 30°. Root temperatures of 5° decreased leaf xylem water potential and increased cold hardiness. Statistical differences in diffusive resistance and transpiration were observed only at the 5° root temperature. Root temperature did not significantly alter leaf relative water content in either seedlings or budded plants. A decrease in soil and root temperature alone, without a simultaneous reduction in air temperature, can provide an effective cold-acclimating environment for citrus.

Open Access

Abstract

Boron, calcium, and naphthalene acetamide (NAAm) foliar sprays were applied alone or in combination to ‘York Imperial’ apple trees under Eastern Pennsylvania orchard conditions. Mineral content of the leaves and fruit and number of cork spots in the fruits were determined.

B applications alone or in combination with Ca and/or NAAm increased leaf and fruit B content. All Ca applications increased the leaf Ca content, the fruit P content, and the leaf and fruit K and Fe content, but had no effect on fruit Ca content. NAAm sprays increased the leaf Mg and Al content. NAAm applied in combination with Ca increased the leaf Ca content. The NAAm effects appear to be associated with the valence of the element, having no effect on monovalent elements, some effect on divalent elements, and the strongest effect on the trivalent element, Al.

Th B-Ca and B-Ca-NAAm spray treatments reduced the number of cork spots per fruit. Regression analysis indicated that as the B and Ca content increased in the leaves, and fruit peel and flesh the cork spots decreased. Cork spots increased as the P and K content of the leaves increased. Core data showed that cork spots decreased as the B and Mg content increased and the B × Mg interaction decreased. There was no relation between number of cork spots and the leaf and fruit content of Mn, Fe, Cu, Zn, or Al, despite significant effects of the treatments on these elements.

Open Access