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- Author or Editor: George C. Martin x
- Journal of the American Society for Horticultural Science x
Abstract
Spray application of 2-chloroethylphosphonic acid (ethephon) to walnut trees caused dehiscence of hulls and enabled complete nut removal with a single mechanical shaking operation as much as 3 weeks earlier than normal. Walnuts were hullable and the quality was generally superior to that of the controls. In some instances considerable leaf fall resulted from the treatment.
Abstract
Large differences in abscisic acid (ABA) concentrations were found among persisting fruit of ‘Winter Nelis’, seeded ‘Bartlett’ and parthenocarpic ‘Bartlett’ pear (Pyrus communis L.) even though fruit set and fruit growth rates were similar. Concentration of ABA was positively correlated with rate of fruit and seed growth in these 3 pear types. The concentration of ABA was greater in the seed than in fruit flesh, and in the integuments plus endosperm than in the embryo.
Fruit removal force (FRF) and percent leaf drop (LD) of fruit-bearing olive (Olea europaea L.) shoots were examined 120 hours after being sprayed with ethephon at 600 mg·liter-1 and held under controlled-environmental conditions analogous to those found in the field in California at harvest time in mid-October. FRF was not significantly affected by solution pH, but FRF of all treated shoots was significantly lower than that of the untreated controls. Only at pH 5 was percent LD significantly greater than that of the controls, but, of the shoots treated with ethephon, the lowest percent LD occurred at pH 3. Percent LD after treatment with ethephon at pH 3 was not affected by application time, but FRF was significantly less than the controls' when shoots were treated at 7 am or 12 pm but not at 5 pm or 10 pm. Adding NAA to the ethephon solution raised FRF and adding BA lowered FRF compared to ethephon alone. Adding NAA or BA did not mitigate percent LD significantly. Adding BA advanced anthocyanin production in fruit. Ethephon penetration of rachides was ≈70% that of petioles. Correlation between ethephon penetration of petioles and percent LD was greater than that between penetration of rachides and FRF. Correlation was significant for both tissues only in the 12 pm pH 3 treatment; correlation was also significant for petiole penetration and percent LD at pH 5. Autoradiographic studies of the 14C-ethephon penetration showed no pH effect, greater penetration into petioles than rachides, and that radioactivity was limited largely to intercellular spaces, with accumulation in vascular bundles, especially xylem. Regardless of treatment, FRF and percent LD are negatively correlated (r 2 = 0.615). Mean results to be expected using ethephon as an olive harvest aid under these conditions are an FRF of ≈3 N and a percent LD of ≈15%. The desired low FRF and percent LD were obtained by applying ethephon alone at pH 3 at 7 am. Raising ethephon solution pH does not increase harvest effectiveness. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon), naphthalene acetic acid (NAA), 6-benzylaminopurine (BA).
Adding Al2O3 to 8-hydroxyquinoline citrate (8-HQC) solution did not alter the sensitivity of the leaf abscission zone to external ethylene. Exogenous ethylene at 791 nl·liter-1 for 72 to 120 hours and at 193 nl·liter-1 for 120 hours induced leaf abscission, whereas no leaf abscission occurred at 47 nl·liter-1 for 72 to 120 hours. Ethylene at 791 nl·liter-1 for 72 to 120 hours increased ethylene evolution, but the amount of ethylene evolved from the explants does not seem to be enough to induce leaf abscission. Three different ethylene inhibitors—aminooxyacetic acid (AOA), CoCl2, and aminoethoxyvinylglycine (AVG)—were used to determine whether P-induced leaf abscission was mediated through elevated ethylene evolution. Although AOA and CoCl2 failed to inhibit ethylene evolution from the explants stem-fed with NaH2PO4, AVG inhibited ethylene evolution. Each inhibitor, except 5 mm CoCl2, promoted leaf abscission when administered alone or with P. Our results reveal that P-induced olive leaf abscission may occur without elevated ethylene evolution. At 40 or 75 mm NaH2PO4, abscission did not occur until explants were removed from N2 and placed in ambient air.
Abstract
Spur buds of apricot were sampled at intervals from late July, 1968, until bloom in 1969, and from 1 month after bloom until the end of September. The samples were freeze-dried and then extracted with 80% methanol. The extracts were partitioned into 4 phases: water, neutral ethyl acetate, acidic ether, and acidic butanol, and then bioassayed for auxins, inhibitors and gibberellins. Although an inhibitor and gibberellin-like activity were present in the extracts, no consistent auxin-type activity was found. The end of rest was correlated with a decrease in the level of inhibitor and gibberellin-like activity, with the inhibitor increasing again towards anthesis. The onset of rest in May, 1969, was correlated with a decrease in inhibitor and increase in gibberellin-like activity. The inhibitor was present in scales and floral parts of buds, while gibberellin-like activity was confined mainly to the floral parts.
Abstract
A sample of freeze-dried apricot buds collected during December, 1968, and January, 1969, was extracted with 80% methanol. The extract was partitioned into 3 phases: water, neutral acetate, and acidic ether. The acidic ether phase contained most of the inhibitor that was present in the methanolic extract. Thus, further purification and identification was done with this fraction exclusively.
The similarity of Rf values of abscisic acid and of the apricot bud inhibitor when TL-cochromatographed using 10 different solvent systems, the equal retention times of their methylated derivatives when gas chromatographed, the congruency of their ultraviolet light spectra, and their inhibition of growth of apricot seedlings indicate that the apricot bud inhibitor is similar, if not identical, to abscisic acid.
Abstract
Fruit-bearing olive (Olea europaea L.) shoots were exposed to more than 100 ethylene (C2H4) treatments to determine if C2H4-induced abscission varied between leaves and fruits in response to manipulation of treatment concentration, duration, and total amount of exogenous C2H4. Nearly three-quarters of the treatments induced greater fruit abscission than leaf abscission on a percentage basis. The potential for optimization of C2H4-induced fruit abscission relative to leaf abscission was examined by calculating the fruit-to-Ieaf (F:L) abscission ratio. Of the treatments inducing at least 75% fruit abscission, the dose range of 150 to 370 μmol C2H4 gave ratios up to 13.3; however, results were highly variable and closely dependent on the interaction of concentration and duration. Response surfaces were created to depict this interaction. Desirable levels of fruit abscission occurred at durations > 30 hr and concentrations > 2 to 3 μl·liter−1. However, excessive leaf abscission occurred at durations of 24 to 48 hr, depending on concentration. Acceptable F:L ratios were found for about 30% of the surface, with the highest ratios occurring for treatments of 3 to 5 μl·liter−1 for 28 to 34 hr.
Abstract
The presence of gibberellin A29 (GA29) in extracts of pericarp of immature prune, was established by combined gas chromatography-mass spectrometry (GC-MS). Another gibberellin (GA) in the extract was determined by GC-MS to be a di-hydroxy A9 derivative different from any of the 46 GAs of known structure. An inhibitor of wheat coleoptile elongation present in pericarp and seeds was tentatively identified as abscisic acid (ABA), based on Rf values on thin-layer chromatograms (TLC) and retention times of the methyl ester on gas liquid chromatographic (GLC) columns.
Abstract
The acid methanol extract from the exocarp of l,2-l4C(2-chloroethyl)ohosphonic acid 14c-CEPA treated peach fruits contained 4 radioactive substances in addition to 14c-CEPA. In the petroleum ether extract 3 such substances were found. The total radioactivity of these substances, compared to the 14c-CEPA and its inherent contaminants recovered from the peach fruit exocarp, did not exceed 3%. Neither the petroleum ether nor acid methanol fractions contained a true metabolite of CEPA as a result of reactions involving living tissue. The nature of the radioactive fractions and their significance is discussed. Additional examinations were made on the stability of these fractions and their distribution in the fruit. Sugars were involved in the formation of one of the major radioactive fractions.
Abstract
Penetration of ethephon into peach fruits was determined using l,2-14C(2-chloroethyl)-phosphonic acid (l4C-CEPA). Most of the activity accumulated in the fruit exocarp, with only minute amounts in the mesocarp. No notable lateral translocation was apparent. The results suggest that active degradation of the compound takes place in the young fruit while in the older peach fruits the rate of l4C-CEPA degradation takes place at a slower rate.