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- Author or Editor: C. Nishijima x
Analysis for hormones in plant material received impetus from the early studies of Went (4). Since that time, scientists have used living plant materials to estimate the presence of specific hormones. Among the advantages of the bioassay are sensitivity to the nanogram and in some cases, picogram range, ease of use, functionality with high levels of contaminants, and low cost of operation. The disadvantages include lack of specificity, variable response, and, in most instances, the need to use a species foreign to the one under examination.
Flowers of caged ‘Winter Nelis’ pear (Pyrus communis L.) set parthenocarpic fruit that persisted until maturity after a single treatment with the gibberellin GA3, GA3 + CaCl2 or the pear gibberellin GA45. Cytex (a zeatin-like cytokinin), abscisic acid (ABA), GA9, GA17 and GA25 were ineffective. The persisting fruits treated with GA3 or GA3 + CaCl2 were significantly smaller than the controls and the GA3 + CaCl2 treated fruits were significantly smaller than those treated with GA45.
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.
At “June drop”, the abscission zone occurs predominantly between the fruit and the receptacle. The abscising fruits had low levels of a growth promoter and high levels of a growth inhibitor, tentatively identified as ABA. Persisting fruits had higher levels of the growth promoter and lower levels of the growth inhibitor than did abscising fruit. Treatment of immature fruits with the chemical thinners 3-CPA or ethephon induced levels of growth regulators in the abscising fruits equivalent to those in abscising non-treated fruits.
Concentration of abscisic acid (ABA), abscisic acid-glucose ester (ABA-GE), indoleacetic acid (IAA), zeatin (Z), zeatin riboside (ZR) and gibberellic acid (GA) were measured in ‘Winter Nebs’ pear (Pyrus communis L.) receptacles from anthesis to 12 days thereafter. Concentration of GA or IAA may signal subsequent growth rate for GA3-treated and pollinated receptacles. No correlations with growth were evident for Z or ZR. ABA-GE began massive accumulation prior to the senescence and abscission of control receptacles.
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.
Withholding irrigation of walnut trees (Juglans regia L. cv. Ashley) for one growing season significantly reduced trunk growth and kernel weight. Tree survival and return cropping were unaffected. When irrigation was resumed kernel weight was significantly heavier than that from trees irrigated the previous year.
Olive (Olea europaea L.) field experiments involving natural flower and fruit populations are fraught with variability, resulting in large coefficients of variation. We provide evidence that coefficients of variation can be reduced successfully by judiciously selecting four experimental twigs per tree and using only those twigs with an internodal growth ≥2 cm, two inflorescences per node, and that are selected from trees with near-maximum bloom density. Although counting flowers at full bloom may establish the population uniformity, only a single node; e.g., node 5, is needed for analysis. Increasing the number of trees will reduce variance more than increasing the number of twigs or nodes.
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.
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.