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Postproduction quality, net C exchange, and petal abscission in response to ethylene were compared following forcing at 21(day)/16C(night) or 18/13C(18-hour photoperiod) of two cultivars of Pelargonium × domesticum L.H. Bailey. Fewer petals of 2- to 6-day-old florets abscised in response to 60 minutes of 0.7 μl ethylene/liter on plants forced at low temperature than on plants forced at 3C higher temperature. Forcing temperature did not affect floret longevity or the number of florets opening during forcing, but the floral display under simulated consumer conditions was prolonged in low-temperature plants by the continued development of buds. Dark respiration rates at 21C were lower in leaves from plants forced at low temperature than in leaves of plants forced at the higher temperature. Differences in postproduction quality between plants forced at high and low temperatures may have been related to the reduced rate of carbohydrate depletion in low-temperature plants.
Abstract
Investigations were carried out to isolate, identify, and characterize major volatile components of tomato fruit. Simultaneously, the confirmation was extended to the reported tomato volatiles. The volatile extracts from field and artificially-ripe fruits were compared qualitatively as well as quantitatively. The changes occurring in the volatile components of the fruit at the onset of senescence also were delineated.
A typical chromatogram from field ripe tomatoes contained 60 peaks. The functional group properties of individual peaks were derived by chemical analysis and approximate concentrations of individual groups were calculated. Among alcohols and carbonyls, 3-pen tanol, 1-nonanal, 1-decanal, and 1-dodecanal, and among esters, propyl acetate, geranyl acetate, and citronellyl butyrate were tentatively identified as volatile compounds of tomato fruit. Linalyl acetate, citronellyl butyrate, and geranyl butyrate were identified for the first time as the components of tomato volatiles.
The concentrations of short-chain (C4-C6) compounds were higher in the artificially ripe fruits while the long-chain (C9-C12) carbonyls and the terpene esters were predominant in the field ripe fruits. These differences were discussed. It was indicated that major contributions of the long-chain carbonyls and the terpene esters are essential for ripe tomato aroma. An attempt has been made to theorize the mechanisms of the biogenesis of these compounds. During senescence the amounts of alcohols, aldehydes, ketones, acetates, and propionates generally decreased. However, the concentrations of diacetyl and butyric acid esters increased.
An inexpensive system for maintaining desired water potentials throughout seed germination was developed. During hydration, a water reservoir at the base of inclined petri dishes allowed continual saturation of filter paper on which seeds were placed. During dehydration, seeds were exposed to equilibrium vapor pressures above saturated salt solutions. Constant temperature, necessary to prevent condensation of water vapor, was achieved via a small (0.2 A) fan that furnished and circulated heat throughout an insulated chamber in which salt solutions were placed. By operating the chamber above ambient laboratory temperature, interior cooling was not required. The system allowed manipulation of the rate, degree, and frequency of dehydration episodes to which germinating seeds were exposed.
During this three year study, irrigation water was withheld from trees in a commercial drip irrigated french prune orchard (Butte County, CA), during different periods within the double sigmoid fruit growth pattern (stage I - III), and postharvest. Tree water stress associated with early season water deprivation was minimal, due to the presence of stored soil moisture and low evaporative demands. For mid and late season water deprivation there was no fruit growth stage that was particularly sensitive to water stress, although severe and prolonged stress caused smaller fruit with lower quality. For the three year average, irrigation treatments caused no statistically significant effects on fruit set or drop relative to the control, however most of the stress treatments increased return bloom relative to the control, resulting in higher fruit loads and higher yields. These results suggest that moderate water stress may enhance economic prune productivity.
Abstract
The pistillate flower of walnut is a complex structure (10, 13, 14) and is referred to as a pistil for simplicity. Pistils emerge terminally on shoot or spurs after different degrees of vegetative extension from mixed buds (9, 14). Such growth can range from essentially nil to about 1 m. Pistils are borne on a short peduncle (Fig. 1). Two pistils per peduncle are most common, but one or three, or (rarely) more, can occur. Flowers are wind-pollinated and all cultivars are considered to be cross- and self-fruitful (9, 14). Pistils become receptive very shortly after emergence from the shoot apex when the two stigma lobes begin to separate. Fertilization of ovules is necessary for nut development to maturity, but pollination and fertilization are not required for early growth of the ovary (14). Ovaries of nonpollinated flowers will enlarge at rates similar to those of fertilized ones for several weeks before abscising, when about 1 to 2 cm in diameter.
To be useful for indicating plant water needs, any measure of plant stress should be closely related to some of the known short- and medium-term plant stress responses, such as stomatal closure and reduced rates of expansive growth. Midday stem water potential has proven to be a useful index of stress in a number of fruit tree species. Day-to-day fluctuations in stem water potential under well-irrigated conditions are well correlated with midday vapor-pressure deficit, and, hence, a nonstressed baseline can be predicted. Measuring stem water potential helped explain the results of a 3-year deficit irrigation study in mature prunes, which showed that deficit irrigation could have either positive or negative impacts on tree productivity, depending on soil conditions. Mild to moderate water stress was economically beneficial. In almond, stem water potential was closely related to overall tree growth as measured by increases in trunk cross-sectional area. In cherry, stem water potential was correlated with leaf stomatal conductance and rates of shoot growth, with shoot growth essentially stopping once stem water potential dropped to between −1.5 to −1.7 MPa. In pear, fruit size and other fruit quality attributes (soluble solids, color) were all closely associated with stem water potential. In many of these field studies, systematic tree-to-tree differences in water status were large enough to obscure irrigation treatment effects. Hence, in the absence of a plant-based measure of water stress, it may be difficult to determine whether the lack of an irrigation treatment effect indicates the lack of a physiological response to plant water status, or rather is due to treatment ineffectiveness in influencing plant water status. These data indicate that stem water potential can be used to quantify stress reliably and guide irrigation decisions on a site-specific basis.
In both laboratory and field experiments, excessive pollen has been found to be a major cause of pistillate flower abscission (PFA) and reduced yields of sensitive English Walnut cultivars (CVs) (especially “Serr”). In the field, PFA and reduced yields develop when substantial overlap of male and female walnut bloom occurs. PFA and poor yields can be further aggravated when pollenizing CV's have been included into an orchard to maximize pollen availability for the commercial CV Field experiments, conducted in 1992 and 1993, demonstrated that mechanically shaking trees to remove male flowers pre-bloom from either pollenizer CV's or the main CV reduced pollen load, PFA, and substantially improved yields.
Prunes trees are believed to be relatively tolerant of water stress, and because prune fruit are dried, a low fresh to dry weight ratio of the fruit will reduce energy requirements for fruit drying and will represent an economic benefit to the grower. In previous research, we found that, under some orchard conditions, irrigation deprivation was associated with a number of economically beneficial effects, including a lower fresh to dry weight ratio of the fruit, increased return bloom, and final saleable crop yield. Analysis of these results was complicated by the effects of irrigation on alternate bearing, and the fact that tree water stress could be substantially different under different soil conditions for the same level of irrigation deprivation. Taking these factors into account, however, indicated that economic yield in prune could be maintained or increased by managing trees at a moderate level of water stress. An experiment was established to determine whether midday stem water potential could be used to guide irrigation and achieve a target level of water stress during the growing season, and whether a moderate level of water stress would be economically beneficial to prune production. By managing prune trees at a moderate level of water stress (midday stem water potential reaching about –1.5 Mpa by the end of the season) over 3 years, an average savings of 40% in applied irrigation water was obtained. Modest increases in return bloom, and an improved fruit dry to fresh weight ratio, occurred in moderately water stressed trees, although overall yield was not changed. The substantial savings in water, without reducing yield, should represent a net economic benefit to growers, depending on the price they pay for water.