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  • Author or Editor: George C. Martin x
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Citrate-phosphate buffer induced olive (Olea europaea L.) leaf abscission at pH 3, 5, or 7. Of several sources of P-induced leaf abscission, NaH2PO4 was the most effective. Sensitivity to P was shown by leaf abscission, leaf desiccation, or both among 32 species representing 22 genera. Applied P accumulates in petioles, but its effect on abscission does not seem to depend on ethylene production. The low P content in the ethephon molecule may have an additive effect in ethephon-induced abscission. Stem-fed NaH2PO4 or ethephon resulted in total leaf and fruit abscission. Of the chemicals applied as a foliar treatment, only NaH2PO4 caused fruit abscission with minimal leaf loss. Adding Al2O3 to adsorb P in treatment solutions delayed the abscission effect of ethephon and NaH2PO4. Adding glycerol to NaH2PO4 increased fruit abscission from 50% to ≈80% and leaf abscission from ≈9% to 18%. The presumed effect of glycerol is from slowing the drying rate and thereby increasing P penetration into the fruit abscission zone. The pedicel-fruit cavity is a collection basin for spray accumulation that is not present in the leaf petiole attachment to the stem. This morphological difference probably leads to greater absorption of abscission-inducing materials by fruit. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).

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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

14C-ethephon applied to a walnut leaflet penetrated and translocated rapidly in young plants, but more slowly in older plants. The compound translocated to the kernel at higher levels when applied to a leaflet than when applied to the hull but in both cases levels of activity were low. Between 5 and 7 days after application the radioactivity in the kernel decreased markedly, 14C-ethephon in the leaves, hull, shell, and kernel was metabolized, but no side products remained in the plant tissue that could be detected by the techniques employed.

Open Access

Abstract

A method was devised for quantitation of methylated indoleacetic (MeIAA) using a nitrogen-phosphorus (N-P) detector gas chromatograph with sensitivity greater than 5 pg MeIAA. Parameters are described for use conditions of the N-P detector.

Open Access

Abstract

A gas chromatograph equipped with a nitrogen-phosphorus detector was used for quantitation of cytokinins. The described system, utilizing permethylated derivatives, will detect as little as 0.1 pg adenine, isopentenyl adenine, benzylamino purine, and kinetin, and 10 pg zeatin. As with all highly sensitive instrumentation, scrupulous procedures for sample preparation are essential.

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

Gibberellic acid reduces return bloom in many fruit tree species. Reducing bloom may cut costs of hand thinning apricot, peach and plum fruit. Sprays of 250 ppm GA, during floral bud evocation (June 1993) resulted in bud death and abscission as determined by light microscopy sections in `Patterson' apricot (Prunus armeniaca L). GA treatment in May did not cause observable effects. August treatments, immediately prior to floral initiation, did not impede differentiation. Treatment of `Elegant Lady' peach (Prunus persica [L.] Batsch.) buds with 75-250 ppm GA, in late June, 1993 (evocation phase) did not have any discernable effects in that season with respect to abscission or differentiation. Treated peach buds differentiated simultaneously with untreated buds in early August. The patterns of response to GA treatment imply `windows of opportunity' with respect to effectiveness of GA treatments. The specific response suggests that apricot buds possess differing levels of sensitivity to GA treatment and probably reflect distinct phases in transition to flowering. In August buds were already `determined' and were in a potentially floral state that was irreversible.

Free access

Abstract

Apricot shoots were defoliated and spurs were decapitated and defoliated on successive dates to determine the onset of rest in specific axillary buds. While the spurs were still growing and the leaves expanding decapitation alone would induce axillary bud growth. Later, when the spurs and leaves stopped growing both decapitation and defoliation were necessary to induce axillary bud growth. Eventually when the onset of rest occurred both decapitation and defoliation would not induce bud growth. Decapitation alone was enough to induce bud growth of terminal shoots. After the onset of rest decapitation and defoliation would not induce bud growth in the terminal shoot buds.

Open Access

Abstract

During 2 successive seasons, and several experiments, trees of Juglans regia cvs. Payne and Hartley were shaken and the walnuts were allowed to remain on the ground in sun or shade up to 72 hr before drying. Kernel temperature exceeded air temperature, sometimes by more than 10°C in those walnuts which were exposed to the sun, while those in the shade remained below air temperature. When the ambient air temperatures exceeded 35°C, extensive kernel quality loss occurred in shaded walnuts. At lower air temperature the market value of sun-exposed walnuts was decreased. Under high air temperature sun-exposed walnuts with hulls lost more market value than walnuts without hulls. Moisture content of the hull at time of exposure had no major effect on kernel quality. The greatest loss of kernel quality occurred when walnuts were exposed to midday sun.

Open Access