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  • Author or Editor: Gene Albrigo x
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Three hurricanes in Florida starting in late Summer 2004 caused severe leaf loss, which stimulated many fall shoots. Flush occurred after each hurricane and by December, shoots were 6- to 12-weeks-old when cool temperatures capable of causing flower bud induction started. To evaluate the potential for these flushes to mature buds that could be induced to flower, flushes that were stimulated on potted trees in a greenhouse were allowed to mature 4, 6, 8, or 10 weeks before moving trees to flower-inducing conditions for 6 weeks (15 °C day/10 °C night). Plants were then returned to the greenhouse, which was kept at 20 °C or higher (ambient), until buds sprouted. Only 1% of sprouting buds on shoots that matured for 4 weeks had flowers. In shoots that matured for 6 weeks, 18% of sprouting buds had flowers. After 8 weeks of growth, 57% of the buds that sprouted were flower buds, while after allowing 10 weeks for shoots to mature, induction resulted in 76% of the sprouting buds producing flowers. Consequently, 8 weeks of development were necessary for citrus shoots to develop mostly mature buds that responded to flower inductive conditions. This is about the same amount of time required for new citrus leaves to fully mature.

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Abstract

A polyterpene antitranspirant spray applied to mature ‘Valencia’ orange trees in March. 1971 showed little weathering over the next 6 months. Scanning electron photomicrographs of lower surfaces of leaves sampled 1 month after a 3% Pinolene spray revealed the material was deposited as droplets on the young expanding leaves but formed a more continuous film on mature leaves. Many of the stomatal openings were covered on mature leaves. Leaves from 1 and 3% Pinolene treatments had 68% and 187% more epicuticular coating, respectively, than control leaves when compared 2 months after application. At 6 months, there was 40% and 134% more surface coating on leaves of the treated trees than on the control leaves.

Open Access
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Abstract

The outer stomatal openings on Citrus sinensis cv. Valencia fruit and leaves were formed by rupturing of the cuticle and possibly some of the outer epidermal cell wall. Small, 5µ diam, structures surrounded by wax were visible on the young fruit surface. The wax on immature fruit was soft, forming a continuous film with little surface structure. With maturation the progressive formation of more and harder epicuticular wax resulted in more visible structure. The eventual cracking and lifting of the wax film indicated loss of its ability to expand with the slow developing cuticle - cell wall complex. Leaves developed some surface wax structure but no platelet wax was formed. The leaves expanded rapidly and the leaf surface wax remained soft during this time.

Open Access
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Abstract

Upon microscopic examination, no stomata were found within 3 mm of the button in an area typically immune to stem end rind breakdown. Stomata outlined the oil glands 7 to 10 mm from the button in peel susceptible to this disorder. Heavy deposits of epicuticular wax were also found in the area void of stomata. Total epicuticular wax was inversely correlated to postharvest wt loss of ‘Valencia’ oranges (r2 = 0.94). A 1-min petroleum ether extraction of soft wax components increased wt loss 66% over washed-only fruit and resulted in etched patterns in the wax platelets suggesting that the soft and hard waxes are not uniformly mixed. A 1-min wax extraction with CCL4 : hexane (1 : 1 v/v) removed 85.6% of the surface wax and increased wt loss to 3 times that of the washed-only fruit over 24- and 48-hr time periods.

Open Access

Grapefruit are susceptible to melanose from initial set until fruit diam. is 6-7 cm, which can span 3 months. Common Indian River melanose-control practice has been application of Cu fungicides at petal fall, with reapplication every three wks. through the infection period. Research data were previously used to develop a computer model to estimate Cu levels on fruit and indicate when reapplication is needed to prevent potential infection. The purpose of this study was to compare melanose control using spray timings suggested by the computer model vs. standard 3 week intervals vs. non-sprayed checks and was conducted over 3 years in mature grapefruit groves near Ft. Pierce, Fla. All applications were made using airblast at 1180 L· ha-1. Melanose and melanose-like Cu injury could not be distinguished and were combined in a melanose/Cu marking (MCM) score for each fruit. Separate fruit samples from the interior and exterior of tree canopies were randomly selected from each tree. In no year was there a significant difference in interior fruit MCM from computer model vs. calendar spray timings when treated with standard rates of Cu fungicide. However, rainfall never occurred when calendar-sprayed fruit were projected to be at low Cu levels. In 2 of 3 yrs. exterior fruit in the non-sprayed checks had less MCM than those from trees treated with Cu, indicating that Cu injury predominated over melanose on exterior fruit. In these fruit, MCM increased linearly with maximum fruit Cu concentration, which was lower on trees managed using the computer model. The computer model appears to be a sound approach to managing melanose, but economic benefit over calendar-based spray timing may only become apparent when practiced over numerous groves and seasons.

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Temporal studies were conducted from mid- to late-harvest season of `Ruby Red' grapefruit (Citrus paradisi Macf.) to evaluate the effect of on- and off-tree storage, fruit size, and juice vesicle position on the development of granulation. Juice vesicle fresh and dry masses were highest at the stem and stylar positions of the fruit section and were not affected significantly by time of harvest or by storage. Juice vesicles isolated from each position were subjectively evaluated for the presence of granulation. Granulation was highest in stylar juice vesicles obtained from large fruit (≈600 g) that were harvested late in the season (March and May) and stored in air at 21 °C for 60 days. Large fruit harvested in March and May and examined immediately, and fruit harvested in January and stored for 60 days had low granulation scores. Thus, fruit remaining on the tree until May are less susceptible to the disorder than those harvested in March and held in storage until May. Levels of alcohol-insoluble solids (AIS), largely composed of pectins and other cell wall materials, were significantly higher in juice vesicles that were granulated. The results suggest that storage itself was not responsible for the marked accumulation of AIS in granulated juice vesicles. Rather, some interaction of fruit size with maturation, as well as other factors such as tree age and rootstock, likely contributed to the development of granulation.

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In order to evaluate possible reduced nitrate leaching while maintaining yield, `Hamlin' orange and `Flame' grapefruit trees on `Carrizo' or `Swingle Citrumelo' rootstocks were grown from planting using only foliar urea or soil-applied nitrate or ammonium N. An intermediate treatment of foliar and ground N was included also. From the 4th year, yields were recorded for 3 years. As previously reported, canopy growth was greater for the foliar urea treatment for the first 3 years. For 2 of the next 3 bearing years, the grapefruit trees in the foliar urea N treatment produced significantly less yield than the soil-applied treatment and the intermediate treatment was intermediate. The orange trees in the foliar urea treatment produced significantly less fruit than the soil N treatment in only 1 of 3 years, but the yields were numerically less every year. Results for fruit quality and nitrate leaching will be reported also. Foliar urea application alone was more costly and less productive than a soil N program.

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In Florida, pesticides, nutritional and growth regulators are often sprayed in tank mixes to reduce sprayer use. Many individual spray components are phytotoxic and result in spray burns in combination or if applied with adjuvants. The toxicity level of standard spray materials is not known and new product testing for phytotoxicity is not routine. Three tests were developed to allow testing of cellular and whole fruit susceptibility to spray chemicals. Cell suspension cultures initiated from `nucellar derived' embryonic callus of `Hamlin' sweet orange were grown in log phase for 2 weeks with various levels of test chemicals. Fresh weight increase was measured. Peel disks of orange or grapefruit were grown for 4 weeks on solid media. Color changes and callus growth were used to evaluate phytotoxicity. Dilute sprays and droplet applications to on-tree-fruit were used to evaluate individual and combinations of chemicals with and without spray adjuvants. The 3 tests combined effectively demonstrated levels of phytotoxicity and are useful for testing new citrus production chemicals.

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Citrus flowering is a complex phenological process influenced by a number of interacting factors. Low winter temperatures are recognized as an important factor, but the flowering response has not been quantified under Variable natural conditions. A study was conducted to monitor the flower bud induction response of `Valencia' and `Hamlin' sweet orange trees [Citrus sinensis (L.) Osbeck] to naturally occurring winter weather conditions during the 1999 and 2000 seasons. The flowering response was quantified and related to shoot age, bud position along the shoot, local weather information, and crop load status. Results indicate that buds on previous summer shoots developed 2.52 and 3.59 to 1 flower on spring shoots, for `Hamlin' and `Valencia', respectively. In addition, buds at apical positions produced more flowers than buds located far from the apex. These basal positions buds required higher induction levels. Under Florida conditions, greater accumulation of hours of temperatures 11 to 15 °C increased floral intensity by the combined effect on the number of sprouting buds with reproductive growth and the number of flowers per flowering bud. Some statistical analyses indicated that high winter temperatures reduced flowering in `Valencia' and `Hamlin' oranges. The presence of fruit consistently reduced reproductive response for both cultivars. Crop load reduced flowering by an average of 41.5% compared to no crop and varied by cultivar. A discussion on the different induction requirements as well as on the differential effect of crop load on flowering by cultivar is presented.

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Cool ambient temperatures (5 to 20 °C) and water deficit are the only factors known to induce flowering in sweet orange (Citrus sinensis). Whereas the effects of cool ambient temperatures on flowering have been described extensively, reports on the mechanisms underlying floral induction by water deficit in sweet orange (and other tropical and subtropical species) are scarce. We report changes in the accumulation of transcripts of four flower-promoting genes, CsFT, CsSL1, CsAP1, and CsLFY, in sweet orange trees in response to water deficit or a combination of water deficit and cool temperatures under controlled conditions. Exposure to water deficit increased the accumulation of CsFT transcripts, whereas transcripts of CsSL1, CsAP1, and CsLFY were reduced. However, when water deficit was interrupted by irrigation, accumulation of CsFT transcripts returned rapidly to pre-treatment levels and accumulation of CsSL1, CsAP1, and CsLFY increased. The accumulation of CsFT transcripts in trees during the combined water deficit and cool temperatures treatment was higher than in trees exposed to either factor separately, and accumulation of CsAP1 and CsLFY transcripts after the combined treatment was also higher. These results suggest that water deficit induces flowering through the upregulation of CsFT and that CsFT is the leaf integrator of flower-inducing signals generated by the exposure to water deficit and cool temperatures in sweet orange.

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