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- Author or Editor: L. J. Edgerton x
Abstract
A horticulturist assigned this topic 30 years ago would start with a brief review of the nature of the abscission zone in the ripening apple fruit, and then spend the remainder of the time telling about research and experience on ways to delay the abscission process. The principal concern of that era was the loss frequently experienced by growers from preharvest drop of ripening fruits of ‘McIntosh’, ‘Delicious’ and several other cultivars. Anatomical studies of the apple pedicel and abscission zone by MacDaniels (18) contributed to an understanding of the abscission process, and orchard studies on nutrition and production led to practices by which growers could reduce their losses during the harvesting period. Then the research by Gardner et al. (13) with growth regulators paved the way for the effective control of harvest drop through the foliar application of a spray solution containing an auxin such as a-naphthaleneacetic acid (NAA). Many other growth regulators have been added to the list and are being used in special situations or for specific cultivars. These include 2-(2,4,5-trichlorophenoxy)propionic acid (fenoprop) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and the growth retardant, succinic acid-2,2-dimethylhydrazide (SADH).
Abstract
The new growth regulator 2-chloroethanephosphonic acid (Ethrel) was applied to apple and peach branches or young trees at several stages of development from prebloom to harvest. Application at 1000 to 2000 ppm during the prebloom to early postbloom stages on several apple cultivars virtually eliminated all fruit with little or no phytotoxicity. Peach foliage and shoots were more sensitive to the chemical. Vegetative growth was checked and flower bud formation promoted in some cases. From one week after bloom to 4 weeks after bloom, fruit set could be reduced but it was not possible to eliminate the fruit in all cases without phytotoxicity. Application from then until a few weeks before maturity had little effect on abscission. Fruit abscission at maturity was promoted with application of Ethrel.
Abstract
The growth retardants, CCC and Alar, were compared for their effects on fruit set and fruit quality of apple. Early season sprays were applied to ‘Golden Delicious’ and midsummer applications were made on ‘Idared’. Pre-bloom sprays of Alar increased fruit set on ‘Golden Delicious’. Pre-bloom applications of CCC and post-bloom applications of Alar tended to reduce set. Neither chemical influenced fruit size, flesh firmness or percent soluble solids of ‘Golden Delicious’ at the concentration used in this study. Pre-bloom sprays of both retardants increased the severity of fruit russet on this cultivar; post-bloom sprays did not affect russet. On ‘Idared’, Alar reduced fruit size and increased red color; it also increased flesh firmness at harvest but not after storage to March. CCC did not affect any measured characteristic of ‘Idared’ apples.
Abstract
Fruit maturity induced by (2-chloroethyl)phosphonic acid (ethephon) in apples (Malus domestica Borkh.) and sour cherries (Prunus cerasus L.) was enhanced by tetrachloroisophthalonitrile (chlorothalonil). Chlorothalonil alone had no effect on any of the fruit maturity parameters measured, but in combination with ethephon, enhanced ripening in apple (color development, soluble solids, softening, and loosening) and loosening of sour cherries. Apple fruit ethylene production was advanced by this combination. The addition of chlorothalonil to ethephon sprays to loosen sour cherries permitted the use of lower ethephon concentration and eliminated gummosis in branches caused by standard rates of ethephon.
Abstract
On current season’s growth of sour cherry (Prunus cerasus, cv. Montmorency) injury induced by (2-chloroethyl)phosphonic acid (ethephon) occurred at and below the nodes in tissues adjacent to the 3 leaf traces supplying each leaf. In the secondary xylem close to the cambium, separation and breakdown of cell walls resulted in the formation of gum cavities; injury occurred also in cortical tissues adjacent to the leaf traces. In older portions of the branch more severe injury occurred where large gum cavities formed in the outer secondary xylem and in cortical tissues. Superficial swelling, cell proliferation and surface cracks occurred on the branches near the nodes accompanied by exudations of gum. Injury and cell wall dissolution may be related to cellulase activity stimulated by ethylene released from the break down of ethephon within the tissues.
Abstract
Uniform, actively growing apple seedlings, 10-15 cm high, were sprayed with 1000 ppm succinamic acid 2-2 dimethyl hydrazide (Alar). The apical portion of treated and control seedlings was collected at the following intervals after treatment: 3, 27 hr; 3, 6, 8, 14 days; 5 weeks. Sections through the apex were prepared, stained and examined microscopically for mitotic figures. As compared with controls, the frequency of mitotic figures in the stem apex of treated plants progressively decreased through 3 days, thereafter the number of figures increased to 69% of that in untreated plants on the 14th day. In the rib meristem frequency of mitosis declined slightly at 3 hr, then progressively until the 3rd day, after which the number of figures increased progressively to the 14th day when it was 28% of that in untreated plants. Only a temporary decrease in mitotic activity occurred in young leaf primordia during the first 6 days. Five weeks old treated seedlings were examined for histological abnormalities associated with extreme shortening of internodes.
Abstract
2-chloroethylphosphonic acid (Ethrel) was applied alone and in combination with NAA or 2,4,5-TP on apple cultivars which had previously been treated with succinic acid 2,2-dimethyl hydrazide (Alar). On ‘McIntosh,’ Ethrel applied 1 to 2 weeks before harvest overcame the abscission delay induced by the earlier Alar application, hastened red color development and slightly diminished the increased firmness imparted by Alar. The addition of NAA to the Ethrel treatment counteracted the abscission stimulation but did not alter the other effects of Ethrel associated with its release of C2H4. Thus, Alar-treated fruits reached maturity earlier under the influence of Ethrel, and with the addition of NAA or 2,4,5-TP a satisfactory retention force was maintained until harvest. ‘McIntosh’ receiving these combinations were of comparable or better quality in comparison with control fruits or fruits treated with Alar alone after storage in CA and in 32°F air.
Abstract
Radioactive (2-chloroethyl)phosphonic acid (ethephon) was applied to leaf and fruit surfaces 6 to 10 days before normal harvest date. Samples were collected periodically following application and analyzed with appropriate extraction and counting procedures. The level of radioactive ethephon increased in the fruit for about 48 to 72 hr, then decreased to a low level after 6 days. No intermediate metabolites were detected in the fruits. It was found that the majority of the ethephon in the fruits moved there from the application on adjacent leaves; relatively small amounts moved directly into the fruit from surface application. Radioactive ethylene was detected within 12 hr after application of the 14C-ethephon on the leaf surfaces.
Abstract
Bud explants of apple (Malus domestica Bork.) grown aseptically in vitro have been shown to respond to several chemicals in a manner similar to intact trees treated with the same chemicals, except that much lower concentrations are required. The method should be useful as a screening test for chemicals which have shoot-regulatory properties.
Abstract
Single and multiple foliar sprays of a commercial formulation containing silicon dioxide, when applied on ‘Golden Delicious’ starting at the petal fall stage, significantly reduced fruit russeting. In 4 trials the 2-spray treatment (petal fall and petal fall + 8 to 10 days) gave better control than a single application at petal fall. In a single trial a third application 21 days after petal fall gave no further reduction in russet. The treatments did not significantly alter fruit size, shape, seed number or maturity date.