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Abstract
‘Valencia’ oranges (Citrus sinensis (L.) Osbeck) with attached pedicels, harvested in April, May, and June, were exposed to 1 ppm ethylene or air for 0, 1, 3, 5, or 7 days. Ethylene lowered fruit removal force but the effect was less pronounced on fruit harvested in May than on fruit harvested in April or June. Endogenous gibberellins (GA) increased prior to regreening and development of the low-response period, and cell-wall hydrolase activity was lower in May than in April or June.
Abstract
‘Hamlin’ and ‘Valencia’ sweet orange fruit [Citrus sinensis (L.) Osbeck] explants responded to cycloheximide [CHI = 3-[2-(3,5-dimethyl-2-oxocyclohexyl)-2-hydroxyethyl] glutarimide] by increased ethylene and cellulase production, which decreased fruit removal force (FRF). Succinic acid-2,2-dimethyl hydrazide (SADH) applied with CHI increased ethylene production in ‘Valencia’ but not ‘Hamlin’ oranges. Cellulase and FRF remained unchanged when ethylene was removed by reduced atmospheric pressure. Partially regreened ‘Valencia’ oranges responded to SADH plus CHI with increased ethylene production. This possibly indicated that more CHI penetrated the rind when SADH was applied. Mature ‘Pineapple’ sweet oranges sprayed with CHI did not respond to SADH treatments with increased ethylene production.
Abstract
Ethylene production, hydrolytic enzyme activity, and fruit removal force (FRF) were more uniform and consistent when abscission chemicals were applied as dilute as compared to concentrated sprays to ‘Valencia’ orange (Citrus sinensis (L.) Osbeck). Cycloheximide (Acti-Aid), glyoxal-dioxime (Pik-Off), 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release), and Acti-Aid plus chlorothalonil (Sweep) were applied to ‘Valencia’ orange branches, each holding 100 to 120 fruit. The FRF's resulting from commercial concentrate and dilute sprays of Acti-Aid and Acti-Aid plus Sweep were similar to those in the branch tests. Equal amounts of chemical were applied in the dilute and concentrate sprays. Likely, the variation in coverage from concentrate sprays caused ethylene levels to vary greatly in the fruit (0 to 5.7 ppm). In turn, levels of hydrolytic enzyme activity varied as much as 10×, and fruit loosening was inconsistent (0 to 9.7 kg FRF). Release and Acti-Aid plus Sweep were more consistent than Pik-Off and Acti-Aid in dilute spray applications.
Abstract
Abscisic acid (ABA) introduced through the stem of ‘Pineapple’ and ‘Valencia’ oranges stimulated cellulase activity in the separation zones. ‘Pineapple’ orange was affected more than ‘Valencia’. Cellulase activity was greatest under normal atmospheres in which ethylene accumulated in the treated fruit. Under one-fifth atmosphere with little ethylene accumulation, cellulase was 2 to 2.5 times greater in separation zones of treated fruit than in non-treated fruit. ABA introduced through the stem was more effective than spray applications. ABA sprayed on the fruit was partly absorbed but did not increase ethylene production or cellulase activity, or decrease fruit removal force.
Abstract
Concentrations of 1% and 2% ascorbic acid stimulated evolution of ethylene from mature fruit of ‘calamondin’ (Citrus reticulata var. austera ? X Fortunella sp?) enclosed in flasks and from 2-year-old trees bearing mature fruit. Prolonged exposure of the trees to the evolved ethylene increased abscission of fruit and leaves. Low levels of ethylene bubbled into the containers also increased abscission of fruit and leaves.
Abstract
Cellulase activity in separation zones of ‘Orlando’ tangelo and ‘Valencia’ orange fruits was associated with the ethylene concn in their internal atm. The pull force required to separate the fruit from its stem decreased when ethylene increased cellulase activity.
Abstract
We collected lemon leaves from 25 trees growing in control and artificially salinized plots at Indio, California, 4 and 6 weeks after beginning of irrigation with water carrying 5,000 ppm total salt. Chloride content of the leaves was directly correlated with their ethylene production. Leaves with visible injury from high Cl produced more ethylene than those with no visible injury from salinized plots; foliage from the latter treatment produced more ethylene than those from nonsaline control plots. The correlation coefficient was significant at odds of 19:1 at 4 weeks and 99:1 at 6 weeks.
Abstract
Comparisons were made of the composition of ‘Valencia’ oranges, Citrus sinensis Osbeck, from orchards in 6 major climatic zones used for citrus culture in the U. S. Six orchards, selected in a compact area in each location, were measured and sampled at intervals during 2 crop seasons. The locations were: Orlando, Fla.; Weslaco, Tex.; Tempe, Ariz.; Indio, Calif.; Riverside, Calif.; Santa Paula, Calif. Statistical evaluations showed that the seasonal trends for most measurements differed significantly among locations.
Observations on flowering showed that full-bloom occurred from 1 to 2 months later in the Far-Western locations than in Texas and Florida. The extremes of the interval between an thesis and the beginning of ripening (a 9 to 1 ratio of total soluble solids to acid in juice) varied from 71/2 to 81/2 months in Weslaco, to 14 to 15 months in Santa Paula, but earliness or lateness of maturity could not be relatd in any simple, obvious manner to the characteristic of the seasonal temperature regimes in the 6 locations. In general, rinds were thinner, smoother and slower to color, and fruits larger, and juicier in Orlando and Weslaco than in the Far-Western locations. Total soluble solids and ascorbic acid in juice at comparable stages of maturity were not influenced in a predictable manner by location, although significant differences occurred in a given season. Of the juice constituents, the acids appear to be the most consistently influenced by climatic conditions during the rapid growth and maturation periods of fruit development. The warmer the climate, the more rapid was the rate of decrease of total acid concentration. Seediness of fruit was influenced by both location and season. Measurements of comparable samples of fruit obtained from widely divergent climatic parameters suggest that the numerous growth and metabolic processes involved in ripening of citrus fruits have independent internal controlling mechanisms. Apparently these processes interact in different ways with external environmental factors, and are not dominated by a pervasive, common internal maturity factor.