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  • Author or Editor: George C. Martin x
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Abstract

The development of phloem sieve tube files in receptacles of pollinated, nonpollinated, and auxin-treated strawberry flowers (Fragaria × ananassa Duch. ‘Fern’) was examined from 0 to 120 hr after emasculation and treatment and correlated to fruit set and growth. The receptacle dry weight of nonpollinated flowers increased very little during the first 120 hr after emasculation. Conversely, receptacle dry weights of the pollinated and auxin-treated flowers began to increase within 24 hr after emasculation and continued to increase throughout the rest of the experimental period. No differences were found in the appearance of the phloem and xylem cells produced in the receptacles among the three treatments. Although the number of sieve tube files in all treatments increased with time, there was no consistent difference in the number of files between growing and nongrowing receptacles. These results indicate that there is no correlation between the degree of phloem sieve tube development and fruit set/initial growth of strawberry receptacles.

Open Access

Abstract

One of the more effective means of developing a smaller than standard apple tree is to graft the desired variety onto East Mailing (EM) IX rootstock. This combination results in a tree from 1/3 to 1/2 standard size. A decisive explanation for the mechanism of dwarfing by EM IX has not appeared in the literature. Of the suggested factors which might result in dwarfing by EM IX rootstock, those which involve organic constituents appear to be most plausible. It has been shown that EM IX is not deficient in fat, starch, reducing sugars, and disaccharides (3, 10). Also there is evidence to indicate that neither the root system (11) nor water (4) is limiting the growth of a dwarfing rootstock.

Open Access

Previous studies have demonstrated that phosphorus, which stimulates ethylene biosynthesis, induces abscission of olive leaves directly without the involvement of ethylene. In the present study this possibility was further explored by comparing the effects of an ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), and an ethylene action inhibitor, 2,5-norbornadiene (NBD), in olive [Olea europaea (L.) `Manzanillo'] and citrus [Citrus sinensis (L.) Osbeck `Shamouti']. In olive, leaf abscission was always induced in the presence of KH2PO4 with or without AVG and NBD (alone or in combination), but it was much more pronounced when KH2PO4 was applied alone. In citrus, KH2PO4 did not induce leaf abscission in the presence of NBD during the first 48 (detached shoots) or 60 hours (leaf explants) despite the high levels of ethylene production by the tissues. Our results demonstrate that phosphorus can, at least partly, act independently of ethylene action in inducing leaf abscission in olive but not in citrus.

Free access

Abstract

Single applications of auxins that normally induce parthenocarpic fruit set in June-bearing and everbearing strawberries (Fragaria × ananassa Duch) (e.g., NAA, 2-NOA, and IAA) do not induce set in the day-neutral cultivar Fern. The only auxin found to date that induces set in day-neutrals with a single application is Et-IAA. The translocation and metabolism of [14C]Et-IAA applied to receptacles was followed in order to gain insight into mechanisms involved in set. Ninety to ninety five percent of the recovered 14C activity remained in the receptacles throughout set and initial development (0 to 6 days) after Et-IAA application. Growth of treated receptacles followed the rapid metabolism of [14C]Et-IAA. Twelve hours after application, 16% of the radioactivity remained in the Et-IAA fraction. This level decreased to <5% by 144 hr after application. The majority of the radioactivity (55–60%) was contained in highly polar compounds. Little activity was recovered in the free IAA fraction. Chemical names used: 1-naphthaleneacetic acid (NAA); 2-naphthoxyacetic acid (2-NOA); 1H-indole-3-acetic acid (IAA); IAA ethyl ester (Et-IAA).

Open Access

Abstract

Soluble sugar and starch levels and translocation of 14C-Iabeled photoassimilates in receptacles of pollinated, nonpollinated, and auxin-treated strawberry flowers (Fragaria × ananassa Duch. ‘Fern’) were examined from 0 to 144 hr after anthesis and correlated with fruit set and initial growth. Receptacle dry weight of nonpollinated flowers increased very little during the experimental period, whereas receptacles of pollinated and auxin-treated flowers showed a gain in dry weight within 24 hr, which continued throughout the experimental period. However, 14C accumulation in flower receptacles did not reflect the initial differences in growth, indicating that recently fixed 14C-labeled photosynthate was not the source for the observed dry weight increases. Analysis of carbohydrate pool sizes in treated receptacles indicated no consistent correlation between pool sizes and fruit set and initial growth. Thus, fruit set and initial growth in strawberry is not limited by the capacity of receptacles either to mobilize current source leaf assimilates or accumulate carbohydrates.

Open Access

Abstract

Olive (Olea europaea L.) leaves are characterized by their ability to respond to exogenous ethylene by a 100- to 400-fold enhanced ethylene production irrespective of leaf age or time of year when sampled. The autoenhancement of ethylene production from intact or detached leaves is positively correlated with the concentration of external ethylene. A lag time of 72 to 120 hr occurred before the autoenhancement of ethylene production could be observed. An autoinhibition of ethylene production was usually observed during the first 24 to 48 hr. The effect was, however, much less pronounced. This autoinhibition of ethylene production apparently does not involve wound ethylene. Olive fruit normally produce only negligible amounts of ethylene, and the enhanced ethylene evolution, which was observed after the fruits were exposed to exogenous ethylene, was found to be exogenous ethylene that was trapped by the fruit tissue during its exposure to ethylene. In leaves, however, autoenhancement of ethylene production evidently is a physiological response that may induce a senescing process in the leaves rather than abscission.

Open Access

Abstract

In a 16-year field study, all graft combinations of Persian walnut, Juglans regia scions with other rootstock species were susceptible to blackline. ‘Sinensis #5’, a selection of J. regia, did not exhibit symptoms of blackline when used as an interstock. In no case was blackline observed in graft combinations between J. regia.

Open Access

Abstract

The possibility of using 31P-nuclear magnetic resonance (NMR) spectroscopy to detect ethephon (ET) in olive leaves has been examined. 31P-NMR spectroscopy can be used as a nondestructive technique (tissues excised but not extracted) with the unique attributes of monitoring ET hydrolysis internally and without radiochemicals. A characteristic spectral peak for the parent ET molecule was found 17-21 ppm (a measure of relative frequency, not concentration) downfield from the H3PO4 reference, and a nonreactive, minor contaminant spectral peak was found at 26-27 ppm. Absolute spectral peak location (“chemical shift”) is pH-dependent. The ET hydrolysis product, orthophosphate, produces a spectral peak at 2 to 3 ppm, which coincides with the broad spectral peak attributed to major endogenous phosphate compounds in leaves, such as inorganic phosphate. The lower limit of 31P-NMR detection of ET in solution was 10−3 m; however, spray applications of ET were not detectable in olive leaves unless concentrations of 5 × 10−2 m or more were used, which is far greater than current agricultural use levels for mechanical harvest of olive. Nevertheless, 31P-NMR spectroscopy was useful in following ET uptake and decomposition for more than 48 hr in olive leaves from xylem-fed shoots, and the resolution of the ET spectral peak into separate, adjoining peaks presents the potential to identify and quantify subcellular compartmentalization of ET according to pH-induced chemical shifts. Such knowledge would contribute to understanding long- and short-term in vivo decomposition of ET to ethylene. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).

Open Access

Abstract

An inhibitor was present in both seed coat and embryo of a high and a low chilling cv. of unstratified peach seeds and its concn decreased as stratification proceeded, Embryonic tissue retained more of the inhibitor than the seed coat. As the concn of inhibitor decreased, seed germination increased. The inhibitor was tentatively identified as abscisic acid (ABA) by chromatography. A bound inhibitor was also present in the seed parts of both cvs., and its concn increased in the embryo as stratification proceeded. More ABA and bound inhibitor were present in the high-chilling cv. than in the low-chilling counterpart, indicating that they may be related as factors which cause a cv. to require long periods of chilling. Application of ABA reduced germination percentage on stratified seeds without seed coats. Application of gibberellic acid (GA) and N-benzyladenine (BA) combined had a synergistic effect in promoting germination of dormant seeds.

Open Access

Abstract

Tree cages were used to modify temperature around ‘Starking Delicious’ apple (Malus domestica Borkh.) trees and to establish 4 bloom dates: April 2, 15 and May 7, 22. Determination of soluble solids, acid, firmness and chlorophyll indicated that the time from bloom to maturity was longer for fruit from earlier than normal bloom. Fruit from delayed bloom accumulated less soluble solids than that from normal or earlier bloom dates. Ultimate fruit size decreased with each successive bloom. Fruit from the 2 early bloom dates apparently was harvested before the preclimacteric minimum. Fruit from delayed bloom was harvested after initiation of the climacteric. Loss of fruit firmness in storage increased with successive harvests. Storage scald and green fruit color were associated with warm night temperatures just before harvest rather than with length of growing season.

Open Access