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- Author or Editor: George C. Martin x
Abstract
Mist, low light, and low temperature during dormancy significantly promoted subsequent floral bud growth in peach (Prunus persica L. Batsch) while high temperature and high light intensity significantly decreased it. Chilling hours at 10°C bud temperature were half as effective as hours at 6°. No significant changes occurred in abscisic acid (ABA) levels in floral bud scales. ABA content of primordia within misted buds was significantly lower than of primordia in other treatments. The data support the concept that fog influences bud rest through temperature, light, and leaching effects. Results also indicate that ABA content in buds may not be the primary factor that determines termination of rest.
Abstract
In the laboratory, sections from leaves of peach [Prunus persica (L) Batsch. cv. Lovell] were treated with chemicals previously reported to have potential as peach fruit thinning agents. The resultant evolution of ethylene from the treated leaves was compared with the amount of peach fruit thinning by the same chemicals. A positive correlation exists between the level of ethylene evolution and the amount of fruit thinning by the chemicals tested.
Abstract
Forty days after treatment with 14 C-ethephon 23.6% of the applied radioactivity was recovered from the total fruit. The level was reduced to 19.0% after 95 days as a result of lower radioactivity in the extracted fruit; the surface level remained constant. Radioactive metabolites noted by 40 days after treatment were still prominent by 95 days.
Photoperiod is an important environmental signal for regulating developmental patterns in many plant species. In several species, photoperiodic regulation of gibberellin A1 biosynthesis has been implicated as the mechanism by which photoperiod may alter development. To examine this phenomenon in strawberry, Fragaria virginiana plants grown under long day (LD) and short day (SD) conditions with equivalent total PAR were examined to determine changes in vegetative growth and GA1 biosynthesis.
LD conditions (16 hr) promoted vegetative growth. Runner production, total leaf area, area of individual leaves, and petiole lengths, all increased under LD conditions. No runner production occurred under SD conditions (8 hr); however, the number of branch crowns increased.
Gibberellins A44, A19, A20, and A1, all from the GA1 biosynthetic pathway, were identified in plants under both LD and SD conditions. However, SD conditions appeared to affect the 2β-hydroxylation of GA20 to GA1. Whereas levels of most GAs decreased under SD conditions, levels of GA20 increased, and only trace amounts of GA1 were found, indicating a possible blockage of the pathway at this point. As GA1 is considered the active component of the pathway, blockage of GA20 conversion under SD conditions may explain the concomitant reduction in vegetative growth.
Previous studies, in which the role of phosphorus in abscission of olive leaves was examined in the presence of ethylene biosynthesis inhibitors, have suggested that phosphorus induces abscission directly, without 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) cv. Manzanillo] and citrus [Citrus sinensis (L.) Osbeck cv. Shamouti]. In olive, leaf abscission was always induced in the presence of KH2PO4, with or without AVG and NBD (alone or in combination), but was more pronounced when KH2PO4 was applied alone. In citrus, the effect of KH2PO4 alone on the induction of leaf abscission and ethylene production was much stronger than that observed in olive. However, in the presence of NBD, KH2PO4 did not induce leaf abscission in citrus during the first 60 hr. Similar results were obtained when NBD was replaced by AVG, but, in this case, abscission was inhibited for only 48 hr. In both cases, ethylene was detected after the inhibitory period had ended. The results obtained with citrus indicate that the observed effect of KH2PO4 on the ethylene-independent induction of leaf abscission in olive is not a general phenomenon and may differ in different species.
Abstract
Peach floral cup extracts were assayed for an inhibiting substance thought to be abscisic acid (ABA) at weekly intervals from November 11, 1969 to February 17, 1970. Inhibitor levels fluctuated during rest, but were relatively high at the termination of the rest period. Inhibitor levels then decreased after the chilling requirement was satisfied. Floral cup growth during the rest period was an exponential function.
Abstract
Walnut trees planted at 50’ × 30’ grew more slowly than xtrees at 50’ × 40’ or 50’ × 50’. Yields per tree were similar at all spacings early in the orchard’s life, but unit area yields later increased proportionately to the number of trees per acre. Long-term monetary returns above fixed costs were far greater as the number of trees per acre increased.
Abstract
A simple procedure for synthesizing and purifying the [14C]ethyl ester of IAA (Et-IAA) is described. This auxin has been found to stimulate parthenocarpic fruit set in day-neutral strawberries (Fragaria × ananassa Duch. ‘Fern’), which are non-responsive to various other auxins. Et-IAA may prove useful in eliciting physiological responses in systems shown previously to be auxin-nonresponsive. Chemical name used: 1H-indole-3-acetic acid (IAA).
Olive fruit persistence is a crucial component of yield and an important factor in estimating alternate bearing potential.
Unfortunately, measurement of fruit persistence exhibit considerable variation, with coefficients of variation greater than 100. Such a high degree of variation makes field studies on questions regarding flowering and fruiting unmanageable due to the large number of experimental units necessary. To determine the source of this variation and how it might be reduced, comparisons of flower and fruit number per node were made within branches and trees over the course of two seasons. Results show that while the largest population of flowers are most distal on the branch, the central portion of the branch contains the majority of the final fruit population and has the lowest coefficient of variation. Furthermore, variation in the number of flowers and fruits is greater between branches than between nodes or trees. The implications of these data on experimental design are discussed and a design is proposed for reducing variation and labor needs.
Trees that fruited during 1990 retained 67.3% of the inflorescence buds produced per branch in 1991 compared to 63.1% for trees that were defoliated immediately after harvest in 1990 and 21.3% by trees that were fruiting in 1991. Shading reduced bud retention similar to fruiting.
Defoliation after nut harvest accentuated the delayed costs of reproduction caused by previous season's fruiting whereas shading produced significantly greater immediate costs. Shading effects on the allocation of carbon to buds, leaves and shoots were similar to those of fruiting. Leaf net photosynthesis under shade conditions was reduced to 14.27% of control trees and this led to a significant reduction in the relative growth rates of all the organs surveyed.