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  • Author or Editor: M. N. Westwood x
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Pyrus calleryana Dene, is ar. exceptional species because of its resistance to a wide variety of insects, diseases and other pests. The selection of the striking ornamental clone shown on the cover resulted from a chance observation in the long-term pear rootstock research program, which began nearly 70 years ago in Oregon.

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Viruses and virus-like disorders have been observed in plants for many years. The economic importance of some are obvious, e.g. cull fruit or dead plants, but until recently the effects of some of the less serious viruses had not been determined in detail. Prior to World War II a good deal of the virus research was done in England and the U.S., but since then such work has expanded rapidly throughout the world.

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Since the release of Pyrus calleryana Done. cv. Bradford by the U.S. Department of Agriculture (4) this species has become popular as a street tree and in landscapes in areas where it is hardy. Because of problems in maturing ‘Bradford’ trees in the nursery, with subsequent problems of dieback in storage and poor transplanting success, some nurseries have sought selections of P. calleryana with all of the good characteristics of ‘Bradford’ but with better growing and handling traits. Also in some climates ‘Bradford’ does not exhibit red leaf coloration in the fall, and a number of selections have been made that are more colorful.

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Of the 90 plant collections listed by Wyman (The arboretums and botanical gardens of North America, Chronica Botanica X: 395-497, 1947) 54 indicated their chief function as either education, research, or both. These terms have different meanings to different people but either function could best be carried out if the collected species were authentic and correctly labelled.

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One of the key limiting factors in fruit production is bud or tree damage from fall or winter freezes. This is due to the selection of cultivars by criteria other than hardiness and to man’s attempt to extend otherwise good cultivars beyond their hardiness range.

Open Access

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The nutritional status of ‘Bartlett’ pear growing on P. communis seedling, Old Home × Farmingdale (OH×F), and several Pyrus species seedling rootstocks was compared to those growing on Bartlett seedling rootstock at 3 locations over a 2-3 year period. Few significant differences were found in leaf element content of scions growing on Bartlett seedling rootstock and those on the rootstock clones or other Pyrus seedlings. Nitrogen was higher in the scions on 5 of the OH×F rootstocks but did not seem related to yield efficiency. Generally the leaf element content of Mg and Mn was lower and Fe higher in leaves of trees growing on the OH×F clonal rootstocks when compared to trees on Bartlett seedling. Nutrient uptake and passage through graft unions appeared unrelated to the degree of graft compatability, based on the similarity of nutrient levels of ‘Bartlett’ scions grafted directly on quince rootstock and those with an Old Home interstem. Root system genetics seems to be the controlling factor of nutrient uptake rather than the interstock.

Open Access

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In a test designed to study the effect of cross pollination on pear fruit set Stephen (4) found that seeded fruits result almost entirely from cross pollination rather than selfing. He found also that seedless set was mainly from selfing, although a small proportion was parthenocarpic. When he first caged entire trees against insect pollination during the period of open bloom, an average set of seedless fruits resulted. However, after caging during bloom each year for four years, seedless set was gradually reduced to only a few fruits. Stephen extended this study and found (5) that renewed exposure of the caged trees to cross pollination resulted in a good set of seeded fruit. If only one leader of a previously caged tree was exposed to cross pollination, it alone produced fruit. The following year, however, when the entire tree was again caged to prevent cross pollination, a substantial set of seedless fruit occurred on all leaders.

Open Access

Abstract

Considerable work has been done on the effects of gibberellins on parthenocarpic set and growth of apple fruits. Bukovac (1) has reviewed the literature in this field and has presented further evidence that seedless fruits induced to set by gibberellins A3 and A4 (GA3 and GA4) are distinctly more elongate than normal seeded fruits. More recently Dennis and Edgerton (2) found that GA made seeded fruits of one variety of apple more elongate than controls, although shape was not altered on several other varieties. Westwood and Blaney (6) reported several factors other than applied GA that also affected apple shape. Among these were crop density (i.e. leaf: fruit ratio), varietal strain, cluster position, and rootstock. To further study the effect of GA on fruit shape without confounding it with seedlessness, a test was set up using seeded fruits in which crop density and rootstock were held constant.

Open Access

Abstract

Effects of cultivars, rootstock, and long-term growth regulator and herbicide treatments on above-ground tree damage from a December 1972 freeze were recorded soon after the freeze and again 7 years later. Ultimate injury was greatest with ‘Jonared’ and least with ‘Golden Delicious’ apple (Malus domestica Borkh.) in the growth regulator plot, while in the herbicide plot it was opposite for the 2 cultivars. There was not a good relationship between injury to specific plant parts (flower buds, spurs, leaders, and lower trunks) observed soon after the freeze, and ultimate tree mortality. Growth regulator treatments significantly increased freeze damage to flowers and spurs, but ultimate tree mortality was reduced by daminozide sprays. Clean cultivation increased flower and spur mortality but did not reduce yield or increase tree mortality compared to the sod treatment. Trees on Mailing (M) 5, M 7 and M 9 rootstocks showed greater initial trunk injury than those on seedling roots, but only those on M 9 showed significantly greater ultimate mortality.

Open Access

Abstract

The pear cultivars ‘Anjou,’ ‘Bartlett’. ‘Bose,’ ‘Cornice,’ ‘Seckel’ and ‘Packham's Triumph’ grown on 9 rootstocks were observed for tolerance to pear decline, tree size, bloom density, yield, fruit weight and leaf nutrient content. Cultivars on Old Home clonal rootstock or Old Home on nurse roots of Mailing Quince A, Winter Nelis seedling or Bartlett seedling were smaller, had lower yield efficiency and greater uptake of Ca, Mg and Mn than when worked directly on Winter Nelis or Bartlett seedling rootstocks or Pyrus calleryana Decne. Winter Nelis and Bartlett seedling rootstocks were similar in performance but Winter Nelis seedlings had a lower yield efficiency than did Bartlett seedlings. Both had better uptake of Fe and Zn but were less precocious than P. calleryana. Fruit size was increased on P. calleryana and P. betulaefolia Bunge seedling rootstocks, particularly when topworked with ‘Seckel’. Cultivars with Call rootstock had greater uptake of K than other rootstocks. A hybrid of P. nivalis Jacq. as a rootstock was inferior to other seedling rootstocks.

Open Access