Seasonal patterns of fruit drop and the influence of flower position and bloom date on fruit set were studied for ‘Woodard’, ‘Bluegem’, and ‘Tifblue’ rabbiteye blueberries (Vaccinium ashei Reade). The pattern of fruit drop was similar for the 3 cultivars, with most the drop occurring within 3 to 4 weeks of full bloom. Fruit drop was most severe for ‘Tifblue’, which set only 21% to 27% of its flowers, compared with 46% to 60% for ‘Woodard’ and 53.5% to 55% for ‘Bluegem’. Position of flowering shoots in the bush and time of flower opening had no consistent effect on the percentage set, although flowers in a terminal position on the shoot generally set a higher percentage of fruit than those in a lateral position for ‘Woodard’. Spray application of gibberellic acid (GA) or (2,4-dichlorophenoxy)-acetic acid (2,4–D) at various times during bloom did not affect yields. The percentage of fruit set was poorly correlated with yields within a season for ‘Woodard’ and ‘Bluegem’, indicating that flower number is also an important determinant of yields. However, poor fruit set for ‘Tifblue’ was associated with low yields.
Root conductivity was measured in decapitated 18-month-old citrus rootstocks using a modified pressure chamber apparatus. Carrizo citrange [Citrus sinensis (L.) Osbeck × Poncirus trifoliata L. (Raf.)], a frost-hardy species, exhibited a log-linear decrease in conductivity over a temperature range from 40 to 10°C. Rough lemon (C. jambhiri Lush.), a frost-susceptible species, also exhibited decreasing conductivity from 40 to 20°, but conductivity was similar at 10 and 20°. No endogenous diurnal cycling of root conductivity was observed in Carrizo citrange root-stocks.
Potted `Tifblue', Woodard', and `Climax' rabbiteye blueberry plants (Vaccinium ashei Reade) were exposed to artificial or natural chilling regimes (< 7C) ranging from 100 to 1000 hours during the dormant season to determine the effects on budbreak and fruit set. Insufficient chilling increased the days to 50% vegetative and floral budbreak in all three cultivars. The amount of floral budbreak increased in `Tifblue' and `Woodard', but decreased in `Climax' as chilling increased. Insufficient chilling did not decrease percent fruit set of hand-pollinated flowers in any cultivar, indicating that the fruit-setting potential of these cultivars is unrelated to chilling.
Two field studies conducted from 1990 to 1991 evaluated the effects of reclaimed water on growth and development of 1- and 2-year-old `Redblush' grapefruit (Citrus paradisi Macf.) trees on Swingle citrumelo [Citrus paradisi (L.) Osb. ×Poncirus trifoliata (L.) Raf.] rootstock. Treatments were arranged as a3 (water sources) x 3 (irrigation levels) factorial at two locations on an Arredondo (well drained) and Kanapaha (poorly drained) fine sand near Gainesville, Fla. Irrigation treatments included 1) reclaimed water, 2) reclaimed water plus fertigation, and 3) well water plus fertigation. The reclaimed water was formulated to simulate that of a sewage treatment plant at Vero Beach, Fla. Irrigation was applied at 20% soil moisture depletion, or at 19 or 25 mm·week regardless of rainfall. In both experiments, visual ratings of tree vigor, and measured tree height and trunk diameter, were significantly lower for trees watered with reclaimed water without fertilizer than for the others in both years. Moreover, there was no fourth leaf flush in 1991 with reclaimed water. There was a significant increase in leaf Na, Cl, and B concentrations for the reclaimed water and reclaimed water plus fertigation treatments in 1990; however, in 1991 only leaf B concentrations showed a similar trend. In 1991, there were no significant differences in leaf Cl concentrations. Visual symptoms of N deficiency were observed by the end of the first season in trees grown with reclaimed water. Irrigation levels generallv did not affect tree growth.
In Florida, gibberellic acid (GA3) is applied to citrus in the late summer or early fall to reduce senescence-related peel disorders of fresh fruit and to increase juice yield of processing oranges. Heavy rainfall may occur daily during this time that could reduce the efficacy of GA3 sprays. Experiments were conducted in 1998-99 and 1999-2000 to test the effect of timed “wash off” treatments on the peel color and peel puncture resistance (PPR) of `Hamlin' orange (Citrus sinensis [L.] Osb.) fruit that were previously treated with GA3. In Oct. 1998 and 1999, the canopy of 14- or 15-year-old trees were sprayed to runoff (≈10 L) with GA3 (45 g a.i./ha) and a non-ionic surfactant (Silwet, 0.05%). For the next 4 (1998-99) or 5 (1999-2000) h, three different GA3-treated trees each hour were then sprayed with ≈20 L of tap water to simulate rainfall that might remove or dilute the GA3. An additional three trees did not receive a GA3 or a washoff treatment. Fruit were harvested in Nov. 1998 and Jan. 1999 and Dec. 1999 and Jan. 2000 and evaluated for PPR and color. Data were subjected to regression analysis to determine the relationship between peel variables and time until washoff. In 1998-99, PPR and peel hue (level of green color) increased linearly with time until washoff, indicating that some GA3 uptake was still occurring after 4 h. In 1999-2000, PPR and hue increased linearly until about 3 h before washoff. Therefore, heavy rainfall within 3 to 4 h of application may reduce GA3 effectiveness, even when a surfactant is used.
Several studies suggest that optimum N rate and application frequency differ among citrus rootstocks. `Rhode Red' valencia orange trees [Citrus sinensis (L.) Osb.] on three rootstocks, C. volkameriana Ten. and Pasq., `Carrizo' citrange [C. sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.], and `Swingle' citrumelo [C. paradisi Macf. × P. trifoliata (L.) Raf.], were used to determine if N rate and application frequency should be adjusted, based on rootstock, during the first 3 years in the field. Treatments were arranged in a 3×3×3 (rootstock, N rates, N application frequency, respectively) factorial experiment. Annual N application rates ranged from 68 to 272 g/tree depending on tree age, and N was applied biweekly, weekly or monthly. Application frequency had no effect on trunk diameter or leaf N concentration in any year. Rootstock had a significant effect on growth in all 3 years, with trees on C. volkameriana being largest and having the greatest yields, followed by those on `Carrizo' and `Swingle', respectively. Trees on C. volkameriana were larger than those on the other rootstocks because they were larger at planting, grew over a longer period during the year, and often grew at a faster rate. Nitrogen rate had no effect on growth during the first 2 years in the field, but the highest N rate increased yields in year 3 for trees on C. volkameriana and `Swingle' rootstocks. Interaction between rootstock and N rate was nonsignificant for trunk diameter, but it was significant for yield, suggesting that trees on C. volkameriana responded more to increased N than did those on the other rootstocks.
Flooding damage causes millions of dollars in losses to horticultural crops every year. Plantings established on sites with poor drainage and/or an impervious soil layer may flood periodically after heavy rainfall or excessive irrigation. Planting sites with lowlying areas or where site preparation is inadequate for drainage of excess water add to the problem. Poor soil aeration associated with flooding may induce numerous soil and plant changes that adversely affect plant survival, growth, development, and yield. Organic and inorganic soil toxins may accumulate in flooded soils, adversely affecting plant metabolism and physiology.
The relationship of root (RLp) and stem hydraulic conductivity (SLp), root electrolyte leakage (EL), and stomatal conductance (gs) to flooding was investigated using 2-year-old ‘Tifblue’ and ‘Woodard’ rabbiteye blueberry (Vaccinium ashei Reade) plants. Soil redox potentials (Eh) decreased to about — 225 mV within 4 to 10 days of flooding, whereas Eh of unflooded soils were always > 400 mV. Root hydraulic conductivity decreased by 44% to 60%, compared to that of unflooded plants after 4 to 6 days of flooding in two of three experiments, decreasing by 29% to 81% by the end of 2 to 3 weeks. Root electrolyte leakage increased and SLp decreased after 6 to 10 days of flooding. Stomatal conductance decreased by 49% to 93% compared with that of unflooded plants after 4 to 6 days of flooding. Decreases in RLp and gs for flooded plants occurred concomitantly and are two of the earliest physiological responses of rabbiteye blueberry plants to flooding.
The authors’ objectives were to determine whether gibberellic acid (GA3) initially increases juice content of ‘Rohde Red’ valencia oranges and prevents or delays decreases in juice content after a freeze, and to determine whether there is an interaction between GA3, rootstock, and juice content. The experiment consisted of a 2 (+, –GA3) × 3 (rootstock) factorial using a completely randomized design with 10 replications per treatment. Gibberellic acid was applied to mature ‘Rohde Red’ valencia [Citrus sinensis (L.) Osb.] orange trees on three rootstocks—Citrus volkameriana Ten. & Pasq.(Volk), Swingle citumelo [C. paradisi Macf. ×Poncirus trifoliata (L.) Raf.], and Carrizo citrange [C. sinensis ×P. trifoliata]—at color break in Fall 2002, 2003, and 2004. Juice content, soluble solids content (SSC), titratable acidity (TA), ratio of SSC to TA, and kilogram solids per box were determined at about 2-week intervals after several freezes. In 2002–03 and 2004–05, juice content in the fall was greater and the rate of decrease in juice content lower for GA3-treated fruit than nontreated fruit for about 8 weeks after a freeze. In contrast, in 2003–04, juice content and rate of decrease in juice content were not different between treatments. Juice content was lower for fruit from ‘Rohde Red’ trees on Volk compared with those on Carrizo and Swingle, and more important, the rate of decrease in juice content after a freeze was greatest for trees on Volk in all three seasons. Soluble solids content, TA, SSC-to-TA ratio, and kilogram solids generally were not effected by GA3 treatment. Therefore, GA3 application at color break in the fall generally increased juice content and slowed the rate of decrease in juice content after a freeze compared with nontreated fruit. In addition, juice content differed significantly with rootstock, but there was no GA3 × rootstock interaction.