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  • Author or Editor: D. E. Ramos x
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Abstract

Leaf number, area and chlorophyll content, and specific leaf weight were greater in light-exposed spurs of ‘Hartley’ walnut (Juglans regia L.) than those grown in the shade. Starch content increased early in the season in shaded spurs, but the accumulation ceased while the nuts stored dry matter. In exposed spurs, starch increased steadily until harvest. After harvest, starch level decreased in exposed and shaded spurs. Light intensity did not affect percentage composition of spurs and fruit with respect to carbohydrates or oil content in kernels. Increased exposure to light resulted in higher percentage of return bloom, greater spur growth, and more pistillate flowers per spur the following season.

Open Access

Abstract

The pistillate flower of walnut is a complex structure (10, 13, 14) and is referred to as a pistil for simplicity. Pistils emerge terminally on shoot or spurs after different degrees of vegetative extension from mixed buds (9, 14). Such growth can range from essentially nil to about 1 m. Pistils are borne on a short peduncle (Fig. 1). Two pistils per peduncle are most common, but one or three, or (rarely) more, can occur. Flowers are wind-pollinated and all cultivars are considered to be cross- and self-fruitful (9, 14). Pistils become receptive very shortly after emergence from the shoot apex when the two stigma lobes begin to separate. Fertilization of ovules is necessary for nut development to maturity, but pollination and fertilization are not required for early growth of the ovary (14). Ovaries of nonpollinated flowers will enlarge at rates similar to those of fertilized ones for several weeks before abscising, when about 1 to 2 cm in diameter.

Open Access

Abstract

Quantitative assessments of the degree of susceptibility to experimental infection by Erwinia rubrifaciens Wilson et al. were made on 54 cultivars of Juglans regia L., J. hindsii Jepson, and J. nigra L. on J. hindsii and Paradox rootstocks. Forty-five of the 54 cultivars were susceptible and developed symptoms characteristic of deep bark canker. On Paradox rootstock, ‘Pioneer,’ ‘Early Erhardt,’ ‘Willson-Franquette,’ ‘Sinensisy5,’ ‘Conway-Mayette,’ ‘Scharsch-Franquette,’ ‘Meylan,’ and ‘Sinensis-7’ showed canker extension rates greater than ‘Hartley’; whereas, on J. hindsii rootstock only ‘Sinensis-5’ and ‘Sinensis-7’ showed canker extension rates greater than ‘Hartley.’ All cultivars were ranked into 4 susceptibility groups according to their rates of canker extension: group I (0 mm/day), group II (0.01 to 0.10 mm/day), group III (0.101 to 0.200 mm/day) and group IV (0.201 to 1.0 or greater mm/day). Of 54 cultivars only 8 ranked in group I (non-susceptible); 28 ranked in group II (dry-canker types); 11 ranked in group III (moderately susceptible); and 7 ranked in group IV (highly susceptible). ‘Hartley,’ the only cultivar commonly associated with the disease in commercial plantings ranked in group IV. Cultivars of either J. hindsii or J. nigra were ranked in group I. Erwinia rubrifaciens was recovered from 45 of 54 cultivars, 14 months after experimental inoculation and 23 of 54 cultivars after 26 months. The pathogenic bacterium was recovered from cultivars of group I (that displayed no visible symptoms). It is hypothesized that natural populations of J. hindsii and J. nigra may harbor E. rubrifaciens and may have been the original inoculum source.

Open Access

Abstract

Crowded conditions in ‘Serr’ walnut orchards predispose trees to initiate numerous catkins which reduce crop potential in 3 ways: a) catkins replace potentially fruitful buds at several nodes; b) they occasionally induce abscission of the terminal bud; and c) they utilize much reserve food, requisite for pistillate flower set, especially, because the cultivar is protandrous.

Open Access

Annual pruning was compared with nonpruning for 8 years and to two biennial pruning treatments for 4 years in a mature full-canopied `Ashley' walnut (Juglans regia L.) orchard. Light penetration and nut distribution through the canopy was improved by pruning. Nut size and percent edible kernel was consistently lower in nonpruned trees than in trees pruned annually or biennially. Yield from annually pruned trees was not significantly different from that of the nonpruned trees because of the removal of fruitful spurs. Yield of biennially pruned trees was similar to annually pruned or nonpruned trees in the year following pruning, but yield was usually greater during years in which trees were not pruned.

Free access

To be useful for indicating plant water needs, any measure of plant stress should be closely related to some of the known short- and medium-term plant stress responses, such as stomatal closure and reduced rates of expansive growth. Midday stem water potential has proven to be a useful index of stress in a number of fruit tree species. Day-to-day fluctuations in stem water potential under well-irrigated conditions are well correlated with midday vapor-pressure deficit, and, hence, a nonstressed baseline can be predicted. Measuring stem water potential helped explain the results of a 3-year deficit irrigation study in mature prunes, which showed that deficit irrigation could have either positive or negative impacts on tree productivity, depending on soil conditions. Mild to moderate water stress was economically beneficial. In almond, stem water potential was closely related to overall tree growth as measured by increases in trunk cross-sectional area. In cherry, stem water potential was correlated with leaf stomatal conductance and rates of shoot growth, with shoot growth essentially stopping once stem water potential dropped to between −1.5 to −1.7 MPa. In pear, fruit size and other fruit quality attributes (soluble solids, color) were all closely associated with stem water potential. In many of these field studies, systematic tree-to-tree differences in water status were large enough to obscure irrigation treatment effects. Hence, in the absence of a plant-based measure of water stress, it may be difficult to determine whether the lack of an irrigation treatment effect indicates the lack of a physiological response to plant water status, or rather is due to treatment ineffectiveness in influencing plant water status. These data indicate that stem water potential can be used to quantify stress reliably and guide irrigation decisions on a site-specific basis.

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