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In Florida, pounds soluble solids per box (% soluble solids × % juice × weight) can be 60% higher in some years compared to the lowest years. Pounds solids, soluble solids and juice content data were obtained for the different citrus growing districts in Florida for a 20-year period from the USDA and Florida Agricultural Statistics Service. Weather data for each district was obtained from US National Weather Service records. Total rainfall and average daily temperature were calculated for 2–month periods from prior to the normal bloom period until harvest. Juice data was regressed against weather data and the previous years pounds solids using a stepwise multiple regression program. R2 values for early oranges, `Marsh Seedless' grapefruit and `Valencia' were 0.48, 0.48 and 0.72, respectively. Prebloom and bloom rainfall and temperatures were frequently positively correlated, while summer rainfall often was a negatively correlated independent variable to final pounds solids. Additional data and physiological implications will be discussed.
Abstract
Antitranspirant sprays of 5 film-forming materials were compared on mature Citrus sinensis (L.) Osbeck cv. Valencia trees for film persistence and reduction of fruit weight loss after harvest. These materials were also sprayed on young ‘Pineapple’ (C. sinensis) or ‘Valencia’ orange trees growing in 7.6 liter containers on which weight loss was subsequently measured for 48-hour periods after watering. Spray solutions of equal or known film-forming ingredients (solids content) of 1 to 4% (weight/weight) were applied and compared. Plantgard film did not significantly increase the leaf epicuticular coating nor did it reduce fruit weight loss or young tree water use. Mobileaf, Vapor Gard, Nu-Film-17, and Wilt Pruf NCF did result in heavier leaf coatings and less fruit weight loss than the controls. Mobileaf and Vapor Gard reduced potted tree water use. Some loss of effectiveness and coating thickness occurred 5 months after application, but only a small nonsignificant change in effectiveness occurred during the first 2 months after application. Mobileaf and Vapor Gard appeared to give the best antitranspirant protection for the initial 2 months and Vapor Gard for 5 months.
Abstract
Levels of several inorganic elements were determined at one time in samples of trunk phloem from 3 adjacent pairs of healthy and blight-affected ‘Marsh Seedless’ grapefruit (2 groves) and ‘Pineapple’ orange (1 grove) trees on rough lemon rootstock. A smaller number of elements were determined seasonally over a 1½-year period in the trunk phloem from 3 similar pairs of healthy and declining trees per grove. Zn, Mn, and N levels in the trunk phloem of blighted trees were significantly higher than in healthy trees, and B levels were significantly lower in the one-time sample analysis for Zn, Mn, Cu, K, Na, Mo, B, Cl, and N. Zn and Mn levels were significantly increased in blighted trees for all samples during the seasonal analysis for Zn, Mn, Cu, K, and Na. Cu and K levels were significantly higher in blighted trees only on some sampling dates. Zn levels continued to increase with time in blighted trees. None of the other elements showed a consistent pattern of change with time. In a study of 5 elements in north- vs. south-side trunk phloem, only Zn in healthy trees was different consistently in each side of the tree.
Attention to the management of insects that feed on foliar flush growth has increased in Florida citrus as a result of the establishment of invasive plant diseases associated with insects that develop exclusively on flush. Citrus can be monitored to identify peak periods of flush abundance to time insecticide applications for these insects; however, guidelines for quantifying flush abundance are lacking. We therefore investigated sampling procedures for estimating flush abundance. A sampling method was devised to enable a quantitative estimation of flush shoots, defined as any shoot with immature leaves. A sample unit was the area within a 15 × 15 × 15-cm frame slipped into the outer edge of a tree with the end of a branch inside the frame. The number of flush shoots originating within the sample unit was counted. Three sample units were examined per tree in 45 randomly selected trees weekly during 2005 in each of two blocks of trees, one containing young ‘Marsh’ grapefruit (Citrus paradise Macf.) and one containing mature ‘Temple’ orange (tangors) [C. reticulate Blanco × C. sinensis (L.) Osbeck]. A pronounced abundance of flush was generally indicated by means of one or more flush shoots per sample in the particular trees studied. Variation in numbers of flush shoots per sample was similar within and among trees, differed significantly among sample dates, and did not differ significantly between the two blocks of trees overall sample dates. Taylor's power law coefficients indicated that, over all sample weeks, flush shoots were randomly distributed within the young grapefruit trees and only weakly aggregated within the block of mature oranges. Projections indicated that a sampling plan consisting of 40 trees (one sample per tree) would provide density estimates acceptable enough for general estimates at mean densities of one or more shoots per sample. An index of pest abundance based on mean pest density per flush shoot and mean density of flush shoots per sample is proposed.
Permanent chlorosis of leaves on plants fertilized with urea containing high levels of the contaminant biuret has been observed in several crops including citrus. Little has been reported as to the cellular changes that result from such chlorosis. Branches from `Ruby Red' grapefruit (Citrus paradisi Macfadyn) and `Hamlin' orange [C. sinensis (L.) Osbeck] were sprayed with urea solutions containing 1.05% biuret. As visible symptoms developed, leaf tissue samples were prepared for transmission electron microscopy. For comparison purposes, leaves from similar trees showing chlorosis from age-related senescence and Zn deficiency were also sampled. The progressive development of chlorosis in biuret-affected leaves was characterized by: the loss of starch, thylakoidal and granal membranes in chloroplasts along with the enlargement and increase in number of plastoglobuli or lipid bodies. The lipid bodies were liberated alone or in association with membrane vesicles to the cytoplasm and vacuoles. The number and volume of the individual chloroplasts became smaller. Concurrent loss of cytoplasmic content and the enlargement of the vacuolar space were also observed in the biuret affected leaf tissue. Similar findings were observed in the cells of senescent leaves. In cells of leaves showing nutritional deficiency, losses in cytoplasmic content and vacuolar enlargement were observed but there was neither complete loss of thylakoidal or granal membranes nor the release of lipids from the plastids. It was concluded that 1) the cytological characteristics of the biuret-affected samples were more similar to age-related senescent samples than to chlorosis from Zn deficiency and 2) that complete loss of the lipid bodies from the chromoplasts to the cytoplasm and vacuole in the biuret-affected samples and in age-related senescence in citrus leaves was responsible for the permanent nature of the chlorosis.
Abstract
Mature ‘Valencia’ oranges when sprayed 2 months prior to harvest in the spring of 1969 with a 1 or 3% solution of Pinolene, a liquid polyterpene plastic film former, were greener at harvest, lost less wt, and had better appearance than control fruit after 9 weeks of storage. Fresh and fixed sections of peel from control and plastic-treated ‘Hamlin’ orange fruit from trees sprayed 2 months before harvest with a 1% solution of Pinolene were observed with a scanning-electron microscope after harvest. The surfaces of control fruit showed considerable variation with some areas having essentially no epicuticular wax platelets while other areas were completely covered. On sprayed fruit, plastic often partially masked the wax platelet edges. On control fruit, the openings to the outer stomatal chambers were usually unobstructed although the stomatal pores between the guard cells were often plugged. In most cases, the openings to the outer stomatal chambers of sprayed fruit were partially or completely obstructed with plastic.
Abstract
Zn content was higher in trunk bark (cambium to outer scrapings) than in the adjacent wood in healthy and blight-affected sweet orange (Citrus sinensis (L.) Osb.) and grapefruit (C. paradisi MacF.) trees. Zn levels were elevated in trunk bark and wood of blight-affected trees on rough lemon (C. limon (L.) Burnt, f.) rootstock, whereas affected seedling trees or trees on ‘Cleopatra’ mandarin (C. reticulata Blanco) rootstock that were tested had high Zn levels only in the bark. Bark Zn content was much higher above the bud union than below in blight affected trees on rough lemon or trifoliate (Poncirus trifoliata (L.) Raf.) rootstocks, but Zn content was high above the bud union in healthy trees only on rough lemon rootstock. The inner half of the bark, an area representative of the active secondary phloem, had much more Zn than the outer half of the bark or the most recently developed xylem. The outer half of the bark served as a barrier against outside contamination. Accumulation of Zn in wood occurred only when the phloem Zn was high.
Abstract
Positional differences among leaf and fruit surface temperatures and water relations of ‘Ruby’ grapefruit (Citrus paradisi Macf.) were related to fruit load and juice quality. Southern top canopy positions experienced the highest temperatures and lower water potentials and yielded more fruit with more soluble solids than other canopy positions. Canopy depth was also an important determinant of fruit yield and early season juice quality. Based on data from 3 trees during 2 seasons, there were greater fruit loads with higher °Brix and lower acidity in the outside canopy positions than in the inside positions. Upper canopy positions tended to have lower acidity and consequently higher °Brix/acid ratios than the lower positions. Abaxial fruit hemispheres were smaller and had a lower percent juice than their paired adaxial fruit hemispheres. Grapefruit from sunlit canopy positions mature earlier than fruit from shaded positions. Since there were more fruit with higher soluble solids in the most exposed canopy positions, daily heat stress and leaf and fruit water stress were not limiting factors in grapefruit yield and juice quality with respect to different tree canopy positions.
Abstract
The effects of succinamic acid, 2-2-dimethyl hydrazide (Alar) and controlled late-season night temperatures on maturity indices of the sun-exposed and shaded sides of ‘Stayman’ apples were studied. The inhibitory effects of Alar on maturity were apparently reduced by warmer night temperatures. Warmer nights decreased soluble solids and red color but increased softening and acidity. These effects are attributed to an increased night respiration rate. Maturity indices data suggest that metabolic activities of the sun-exposed and shaded sides of the fruit respond differentially to increases in night temperature.