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  • Author or Editor: William H. Griggs x
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Abstract

‘Bartlett’ pear trees were sprayed 2 weeks after full bloom or 4 weeks before harvest with a single application of succinic acid 2,2-dimethylhydrazide (Alar) at 1,000 or 2,000 ppm. Some trees that received 1,000 ppm were given a second application of Alar at 1,000 ppm 3 weeks after full bloom or 3 weeks before harvest. Alar was as effective as NAA at 10 ppm in preventing preharvest drop of fruits. Alar applied as a double spray early in the season or as a single or double spray late in the season was equally effective. Use of Alar as a preharvest drop spray provides great flexibility as it can be applied over a wide range of time. No undesirable side effects were noted from the use of Alar.

Open Access

Abstract

The gibberellins GA3 (200 ppm) and GA4+7 mixture (50 and 200 ppm) applied to blossoms of Pyrus communis L. cv. Winter Nelis previously bagged to prevent cross-pollination stimulated fruit set and growth for about a month, after which most of the fruits abscissed. Additional GA3 sprays were effective in retaining normal fruits until maturity. The addition of 2-(2,4,5-trichlorophenoxy) propionic acid (fenoprop) further reduced “June drop,” and also advanced maturity and caused breakdown and early preharvest drop of fruits.

Open Access

Abstract

‘Bartlett’ spurs carrying seedless or seeded fruits produced relatively high percentages of flower buds. Spurs carrying seedless pears for 31 days after bloom produced more flower buds than did spurs carrying seeded pears. Also, the exudate from seedless pears had more growth-promoting activity. Beyond 31 days there were no consistent differences in flower bud formation in spurs carrying seedless vs. seeded pears. Carrying seeded pears 31 days largely inhibited flower bud initiation in ‘Winter Nelis’. There was an inverse relationship between flower buds and seeds in fruits on spurs of both varieties defruited 61 days after bloom. The relationship was not distinct for spurs carrying fruits longer. Fluctuations in the growth-promoting activity of the fruit exudate indicate that the hormonal status, at the time the spur was defruited, influenced flower bud formation more than did number of fruits, seeds, or length of fruit-carrying period.

Open Access

Abstract

Seasonal changes in natural growth substances were studied by collecting the diffusate, via the pedicel, from intact seeded ‘Winter Nelis’, seeded ‘Bartlett’, and parthenocarpic ‘Bartlett’ pear fruits. The diffusate of ‘Bartlett’ fruits collected 10 to 25 days after full bloom (AFB) contained more auxin-like promoter than did that of ‘Winter Nelis’ fruits. With the exception of the 45-day sample, the diffusate from parthenocarpic ‘Bartlett’ fruits had more promoter from 25 to 70 days (AFB) than did either seeded pear. In contrast, more gibberellin (GA)-like materials diffused from ‘Winter Nelis’ fruits than from seeded or parthenocarpic ‘Bartlett’ fruits. With all types of pears the concentration of abscisic acid-like materials in the diffusate was similar until harvest when the concentration was greater for ‘Winter Nelis’ than for ‘Bartlett’. The combined effect of relatively low amounts of auxin-like and greater amounts of GA-like materials may explain why the presence of seeded pears during the postbloom period has a greater inhibitory effect on flower bud formation in ‘Winter Nelis’ than in ‘Bartlett’.

Open Access

Abstract

Flowers of cvs. Winter Nelis and Bartlett contained an equivalent amount of an acidic, auxin-like substance, which decreased in the following 30 days. Thereafter, until 70 days after full bloom (AFB), the substance increased in parthenocarpic ‘Bartlett’, remained relatively constant in seeded ‘Bartlett’, and declined in ‘Winter Nelis’. A neutral auxin-like promoter was detectable in flowers of the 2 cultivars, reaching a maximum between 40 and 65 days AFB. Also, flowers and fruitlets of both cultivars contained extractable gibberellin-like substances which were in greatest abundance about 25 days AFB. The concn of these GA-like promoters at this time was greater in parthenocarpic ‘Bartlett’ fruits than in seeded fruits of either cultivar. Relatively large amounts of an abscisic acid-like (ABA-like) inhibitor were present in ‘Bartlett’ and ‘Winter Nelis’ fruits for a short time AFB. The concn subsequently decreased in both cultivars, but in ‘Winter Nelis’ it increased again toward maturity. Pear extracts contained a bound inhibitor which was active after hydrolysis with β-glucosidase. Seeds of both cultivars and unfertilized ovules of parthenocarpic ‘Bartlett’ fruits had similar levels of an ABA-like inhibitor which increased concurrently with fruit growth. Inhibitors are present throughout fruit development, in contrast to promoters, which occur in sequential order.

Open Access

Abstract

Branch units of 20 ‘Bartlett’ pear trees were sprayed with 2-chloroethylphosphonic acid (Ethrel) at 250, 500, or 1000 ppm or with cycloheximide (beta-[2-(3,5-dimethyl-2-oxocyclohexyl)-2-hydroxyethyl] glutarimide) at 3, 5, or 20 ppm a wk before the beginning of normal harvest to weaken the abscission layer to facilitate mechanical harvest. Half the trees had been sprayed with naphthaleneacetic acid (NAA) to prevent preharvest drop. Nine days after application, Ethrel at 1000 ppm had significantly reduced the fruit removal force (FRF) on trees that had received no NAA. In contrast, the presence of NAA evidently nullified the abscission-promoting effect of Ethrel. All other treatments failed to reduce FRF significantly. None of the sprays caused discernible phytotoxic effects or hastened fruit maturity. However, after storage for 50 days at 0°C, 17% to 50% of the fruits that received Ethrel at 500 or 1000 ppm, broke down during ripening. Cycloheximide caused no breakdown, but 20% to 80% of the fruits aprayed with 5 or 20 ppm had necrotic spots at the calyx end.

Open Access

Abstract

Viability of walnut, Juglans regia L., pollen was not diminished by storage at subfreezing temperature, as previously indicated. Pollen stored 20 days at −19°C effected high percentages of fruit set in the orchard in 1969. Fruit set of the bagged flowers was relatively low in 1970, but the set effected by pollen stored a year at −19°C was not significantly different from that effected by fresh pollen. Laboratory tests indicated less than 1% germination for both freshly dehisced and stored pollen, and were unreliable for indicating the ability of walnut pollen to effect fertilization.

Open Access