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  • Author or Editor: W. B. Collins x
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Abstract

Carbon dioxide enrichment of the greenhouse atmosphere, either in the period prior to tuberization or during the tuber development period of potato (Solanum tuberosum L.), increased tuber yield significantly at harvest, compared to yields from plants grown in a conventional atmosphere. Enrichment during the tuber development period provided the greatest increase in tuber dry weight. The data indicated that the increase in yield was attributable to an increase in the net assimilation rate of carbon dioxide enriched plants and a corresponding increase in the relative growth rate.

Open Access
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Abstract

The rooting of strawberry runner tips was studied in relation to soil moisture tension in the rooting medium and soil moisture supplies to the mother plants. In the first weeks of runner establishment the rate and amount of top growth was controlled largely by the moisture supply to the mother plant. Growth was decreased as moisture stress on the mother plant was increased. For the most part, root habit of the runner was independent of influence from the mother plant. Variations in soil moisture tension in the rooting medium had little influence on top growth of the runner except for leaf area but did influence root growth significantly. Secondary root growth was restricted by both very wet and very dry soil conditions. The results confirmed that the initial number of main roots formed and their penetration was independent of moisture tension in the rooting medium. Organic matter additions to the rooting medium did not influence moisture effects appreciably.

Open Access

Abstract

The identity of a growth-regulating substance that occurs in flower buds of lowbush blueberry (Vaccinium angustifolium Ait.) subjected to short-day inductive conditions was investigated. The results of Avena bioassay tests and thin layer chromatography led to the conclusion that the growth regulator was similar in its properties to the gibberellins. Under continued exposure to short-day conditions the induced flower buds developed into naturally parthenocarpic fruit.

Open Access

Abstract

Two mist systems, one in a mature orchard and the other in a young hedgerow, delayed bloom 15 days for ‘Bartlett’ and 8 days for ‘Bosc’ pear (Pyrus communis L.), while a low pressure sprinkler system delayed bloom for 14 days for ‘Bartlett’ and 8 days for ‘Bosc’ in 1976. Bloom delay generally increased fruit set and seed content of the fruit. Return bloom was greatly reduced in the mature orchard ‘Bartlett’ mist and ‘Bosc’ sprinkler plots in 1976 and, in turn, cropping was reduced the following year on these plots. Yield during treatment years was generally lower in the delayed areas. Fruit growth rates were accelerated in the bloom-delayed trees, but total fruit volume was less than the non-delayed fruit. Leaf nitrogen levels were reduced in all bud delayed treatments. Pear psylla oviposition was delayed in the mist system. Fire blight, caused by Erwinia amylovora (Burr.) Winslow et al., absent in 1975, was found in the misted ‘Bosc’ and in the sprinkled plots of both cultivars in 1976.

Open Access

Abstract

Mature orchard misting and sprinkling and young hedgerow misting for bloom delay of pear (Pyrus communis L.) reduced fruit sizes of ‘Bartlett’ 6% and of ‘Bosc’ 12%. Harvest maturity, indicated by fruit pressure testing, was delayed 0 to 6 days for ‘Bartlett’ and 2 to 7 days for ‘Bosc’. The effect of bloom delay on fruit size and maturity was greater on ‘Bosc’ than ‘Bartlett’. Bloom delay had a greater effect on fruit sizing at harvest (3.5 days for every 6 days of bloom delay) than on harvest maturity (1 day for every 6 days delay). Soluble solids, not affected in pears from the mature plots, were slightly lower in the misted hedgerow. Titratable acids were not influenced by bloom delay.

Open Access

A random sample of 6000 individuals from a recombinant Solanum phureja - S. stentomum hybrid population and 250 individuals of Solanum phureja were twice inoculated with potato virus Y (PVY) strain “o” using the air brush technique. Symptomless seedlings were field transplanted for further evaluation and 1508 seedlings were judged to be resistant to PVY (33%). At harvest, a mild selection pressure for tuber appearance was applied and 602 clones were selected.

Selected clones were re-evaluated for PVY resistance in the greenhouse: twice inoculated with PVY, tested by ELISA (Enzyme-linked immunosorbent assay), graft-inoculated with tobacco PVY infected scions, and subjected to a second ELISA test. To assess immunity to infection by PVY, the ELISA negative clones were bioassayed using tobacco cv. “Burley 21” as a plant indicator. We identified 224 PVY immune clones (4.8%).

Simultaneously, the first year PVY selected clones were twice inoculated with U.S. common strain of potato virus X (PVX). Clones free of PVX symptoms were tested by ELISA. Negative clones were re-inoculated with PVX and symptomless clones were re-tested by ELISA. To assess immunity to infection by PVX, negative clones were bioassayed using Gomphrena globosa as a plant indicator. We identified 7 immune (1.3%); 4 highly resistant and 4 resistant clones. Eight clones showed high levels of resistance to both PVY and PVX (high resistance to immunity).

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