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- Author or Editor: Heinz K. Wutscher x
- HortScience x
An 8-ha block of 9-year-old Valencia orange trees, surrounded on three sides by drainage ditches, was divided into four equal-sized plots. A 4-m deep sampling well was drilled in the middle of each plot and a short piece of perforated pipe was placed above the water level in the bank of one of the drainage ditches to intercept seepage water. Water from the well in the third plot and the corresponding seepage pipe contained consistently NO3-N in the 20-ppm range, in contrast to the other sampling points, ranging from 0.1 to 9 ppm. Electrical conductivity was higher in plots 3 and 4, downstream from plots 1 and 2, in the ground water flow. Sodium in the water followed the same pattern P and K were the same, and pH was higher in plots 1 and 2 than in 3 and 4. Soil pH (5.2–5.8) and water-extractable NO3-N showed no patterns, organic matter (0.79% to 0.12%) and soil moisture (5.5% to 6.3%) were higher in plots 3 and 4. Leaf nitrogen (2.60% to 2.90%) was highest in the high-nitrate plot 3. The soil on the east side of this plot showed a higher nitrate-holding capacity compared to the other plots in an anion-exchange capacity procedure.
Seven-year-old `Hamlin' orange on Swingle citrumelo rootstock were sprayed with 30% methanol and 0.05% Silwet surfactant. There were four treatments: one spray application 48 days, two spray applications 48 and 32 days, and three spray applications 48, 32, and 20 days before harvest on December 2, 1993, with five untreated control trees. The treatments were arranged in five replications of randomized, complete blocks throughout the orchard. There were no significant differences in fruit weight, fruit diameter, rind color, rind thickness, juice content, soluble solids, total acids, solids/acids ratio, and juice color of 30 fruit samples collected from each tree. Leaf samples collected at harvest and analyzed for 12 elements showed higher Na and Cl levels in the leaves of the trees treated with methanol once than in those treated three times.
Abstract
Diseases caused by viruses and mycoplasmalike organisms are among the most serious citrus production problems. Mycoplasmas are, of course, much larger than viruses and contain both RNA and DNA. Many are obligate parasites, but some are not (54, 55). From a horticultural point of view, mycoplasmalike diseases of citrus are much like virus diseases. The first citrus disease shown to be caused by a virus was psorosis in 1933 (32). About 20 virus and viruslike diseases of citrus are recognized now (53, 55, 56); to cite an exact number is difficult because, like taxonomists, citrus virologists disagree on which diseases should be lumped together and which should be considered separately. Recent summaries of citrus virus research have been published (7, 54, 55, 56, 80, 89, 126). Table 1 summarizes the more important virus and viruslike diseases of citrus.
Abstract
One-year-old ‘Hamlin’ and 2-year-old ‘Valencia’ orange [Citrus sinensis (L.) Osbeck] trees on rough lemon (C. limon Burm. f.) rootstock were grown in solution culture for 7 months. The solutions of the two treatments were identical, except for Si. The KNO3 in the –Si solution was substituted by K2SiO3 and NH4NO3 to supply 66 ppm Si in the +Si solution. Solution pH was initially adjusted with HNO3 and NH4OH and maintained at 7 ± 0.5 by addition of dolomite. Plant weight at 28-day intervals showed significant differences in fresh weight increase between treatments only in the first 2 months. Analysis of eight different tree tissues for Si and 14 other elements showed strong correlations between Si levels and levels of P, S, Mg, Fe, Mn, Zn, Cu, and Mo, especially in the leaves, bark, and feeder roots. Si accumulated mostly in the leaves and the feeder roots, a pattern that was also found in field-grown, 17-year-old ‘Hamlin’ on rough lemon trees.
Abstract
Roots have a strong influence on plant composition, but differential ability to absorb nutrients is only part of a maze of interactions affecting mineral concentrations in plant tissues. Most reports on rootstock effects on mineral nutrition are based on leaf analysis, but all other tissues are involved. Rootstock and scion effects are reciprocal, and the influence of the scion can be as strong as that of the rootstock. Variation in distribution pattern, capability of nutrients to move across bud unions, environmental and soil factors, fruit load, and, above all, the genetic makeup of stock and scion are intimately involved. There is a large amount of literature on rootstock effects on scion composition, but generally other horticultural properties outweigh nutritional effects when a rootstock is chosen. This is especially true for the major elements. The main use of nutritional properties of rootstocks has been to avoid toxicities, especially those of Cl and B, which are difficult or impossible to avoid by other means, and to avoid deficiencies.
Abstract
NO3-N concentrations in 35-year-old ‘Hamlin’ orange (Citrus sinensis L. Osbeck) and ‘Marsh’ grapefruit (C. paradisi Macf.) trees on rough lemon (C. limon Burm. f.) rootstock were highest in the feeder roots (212-962 ppm), followed by the leaves (160-300 ppm) and trunk wood (0-304 ppm). Only in 3 of 10 orange trees and in 1 of 10 grapefruit trees was NO3-N detected in the bark. Nitrate-N concentration in the leaves and the wood and the percentage of NO3-N in total N in the wood were higher in orange than in grapefruit trees.
Abstract
Healthy ‘Valencia’ and blight-affected ‘Pineapple’ orange [Citrus sinensis (L.) Osbeck] trees, both on rough lemon [C. limon (L.) Burnì, f.] rootstock, had a seasonal pattern of higher Zn in the outer 2.5 cm of the trunk wood in the winter and lower Zn in the summer. The 5-year means for the ‘Valencia’ trees were 5 ppm Zn in February and 3 ppm Zn in July; the blighted ‘Pineapple’ trees contained 21 and 16 ppm Zn (2-year means), respectively. There was no clear seasonal pattern for water-soluble phenolics.
Abstract
Leaf NO3 concentration in ‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] and ‘Marsh’ grapefruit (Citrus paradisi Macf.) declined in midsummer when temperature and rainfall were at their maximum. Total N concentration remained steady after declining in the spring. The decrease in NO3-N concentration during the hottest time of the year contrasts with a peak at this time in dry citrus-growing areas.
`Hamlin' orange (Citrus sinensis L. Osbeck) was grown on 15 rootstocks: four citrumelos [C. paradisi Macf. × Poncirus trifoliata (L.) Raf.], five mandarin × trifoliate orange hybrids (C. reticulata Blanco × P. trifoliata), two pummelo × trifoliate orange hybrids [C. grandis (L.) × P. trifoliata], Vangasay lemon (C. limon Burm. f.), Norton citrange (C. sinensis × P. trifoliata), and two Smooth Flat Seville (C. aurantium L. hybrid?) hybrids. These scion–rootstock combinations were compared to trees on Swingle citrumelo, the most widely used citrus rootstock in Florida. One Smooth Flat Seville hybrid was eliminated early because of poor growth and variability in size, and the Vangasay lemon rootstock was eliminated because of severe freeze damage. At age 5, the trees on Norton citrange developed citrus blight and were eliminated. Remaining in the experiment for 7 years, `Hamlin' trees on six of the 13 rootstocks produced more fruit than trees on Swingle citrumelo. Of these six, HRS 852 (Changsha mandarin × English large-flowered trifoliate orange) was the best overall rootstock, with trees on it producing large quantities of high-quality fruit on medium-sized canopies.
Abstract
Juice color of ‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] on 30 rootstocks was determined at three harvests. Late harvest increased color scores. The mean color score over 3 years varied from 34.3 for juice of ‘Hamlin’ on trifoliate orange [Poncirus trifoliata (L.) Raf.] and Chu Kag mandarin (C. reticulata Blanco) to 33.2 on rough lemon [C. limon (L.) Burm. f.] and 32.9 on sour orange (C. aurantium L.). Scores >35 were found in single years, but no rootstock improved the color above a score of 36, the minimum for Grade A juice.