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  • Author or Editor: L. Cheng x
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Abstract

Dianthus caryophyllus L., a quantitative long day plant, was used for studies of the effect of photoperiod on the different stages of plant development. The anatomical structure of the vegetative shoot apex and the changes during floral transformation are described. These stages were not affected by the various photoperiod lengths, i.e., 9, 13, and 18 hr.

The developmental cycle of D. caryophyllus may be divided into 3 stages: vegetative, floral initiation, and floral development. The influence of photoperiod on the duration of each of the 3 stages was different. The length of the vegetative stage was inversely related to the length of the photoperiod (the longer the photoperiod, the shorter the vegetative stage). Daylength had no effect on the period of floral initiation, but did affect the period of floral development (i.e., the longer the photoperiod, the longer the developmental stage). The rate of stem elongation under all treatments increased exponentially until the floral initiation state, and then the plants grown under photoperiods of 13 hr or longer elongated significantly faster than those under the 9-hr photoperiod. After flower initiation was completed, the rate of stem elongation suddenly increased linearly until the flower opened. In contrast to the vegetative shoot, the rate of stem elongation of flowering plants was completely independent of photoperiod, and the rate was the same in the 9, 13, and 18 hr photoperiods.

Open Access

`Flying Dragon' Poncirus trifoliata L. Raf. is a dwarfing rootstock for citrus. Inheritance of dwarfing ability was studied in a population of open-pollinated seedlings of `Flying Dragon'. Molecular marker genotypes suggest that all seedlings originated from selfing. Progeny seedlings were budded with `Cutter Valencia' orange and planted in the field to evaluate the dwarfing effect of the seedling rootstock. At 5 years after planting, rankit analysis of the frequency distributions of trunk cross-sectional area and canopy volume suggested the presence of two overlapping distributions of 34 dwarf trees and 7 nondwarf. This ratio is consistent with inheritance of rootstock dwarfing as a single dominant gene for which `Flying Dragon' is heterozygous. Two morphological characteristics of `Flying Dragon', curved thorns and twisted trunk growth, were closely linked to, or pleiotropic effects of, the dwarfing gene. Bulked segregant analysis was used to identify three RAPD markers linked to the dwarfing gene. `Flying Dragon' was identical to nondwarfing cultivars of trifoliate orange at 40 homozygous and heterozygous isozyme and RFLP markers; therefore, it is likely that `Flying Dragon' originated as a mutant of a nondwarfing genotype and has not undergone sexual recombination since this event.

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Double-stranded ribonucleic acid (dsRNA) analysis of apparently healthy red mulberry (Morus rubra L.) yielded four distinct dsRNA banding profiles. dsRNA type 1 contained three dsRNA bands with approximate molecular weights (MWs) of 12.0, 1.0, and 0.9 × 106, respectively. dsRNA type 2 contained two dsRNA bands with MWs of 1.0 and 0.9 × 106. dsRNA type 3 contained four dsRNA bands with MWs of 1.0, 0.9, 0.89, and 0.88 × 106. dsRNA type 4 contained three dsRNA bands with MWs of 1.0, 0.88, and 0.87 × 106. No virus particles were associated with any of the samples analyzed. All four types of dsRNA were resistant to DNase I and RNase A in high salt and susceptible to RNase A in low salt. Mulberry dsRNAs were somewhat similar to endogenous dsRNAs (edsRNA) associated with other hosts. This is the first report of edsRNA associated with a deciduous tree.

Free access

New roots of Malus domestica Borkh MM106 apple rootstock were divided into two categories, 1) feeder roots and 2) extension roots based on morphology and their ability to take up NH4 +, were studied. The roots were harvested in August from 1-year-old potted plants growing under natural conditions in Corvallis, Ore. Extension roots were thicker and longer than feeder roots. Average diameter and length were 0.89 and 45.29 mm for extension roots and 0.27 and 5.36 mm for feeder roots. Root special length (cm/g FW) and surface area (cm2/g FW) were 11.94 and 33.17 for extension roots and 108.97 and 93.38 for feeder roots. Maximum uptake rate, Imax, Km, and root absorption power, α (α = Imax•1/Km), for NH4 + absorption were 6.875, 0.721, and 9.48 for extension roots and 4.32, 0.276, and 15.63 for feeder roots. Feeder roots had stronger affinity to NH4 + (low Km) and higher NH4 + absorption power (high α value) than extension roots. The feeder roots were better able to uptake NH4 + at lower external solution concentrations than extension roots according to the nutrient depletion curve, which indicates feeder roots being more efficient than extension roots in nutrient absorption when NH4 + availability was low.

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The nutrient uptake kinetics by new roots of 1-year-old potted clonal apple rootstocks (M7, M9, M26, M27, MM106, and MM111) were determined by the ion depletion technique at the stable development stage of trees in August. The total roots of five of the rootstocks (except MM111) consisted of more than 60% feeder roots and less than 12% extension roots. MM111, the most vigorous rootstocks tested, had 60.7% feeder roots and 24.5% extension roots. Root: top ratio was negatively related to the growth inhibiting character of the rootstock. Nutrient uptake by excised new roots was found to fit into Michaelis-Menton kinetic model for all rootstocks tested. The kinetic characteristics (maximum uptake rate, Imax, apparent Michaelis-Menton constant, Km, and root absorption power, (α = Imax•1/Km) between rootstocks differed significantly. MM111 had the highest Imax for NH4 + absorption and M9 for NO3 -. Root affinity to ions was highest with MM106 for NH4 + and with M26 for NO3 -. Root absorption power (α = Imax•1/Km) was greatest in MM106 for NH4 + and M9 for NO3 -. At this developmental stage the data suggest no relationship between nutrient uptake and dwarfing character of the rootstocks.

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Abstract

Scanning electron microscopy was used to investigate leaf epicuticular wax of Prunus instititia L. ‘Pixie’ from aseptically cultured plants before and after acclimatization to the greenhouse. Leaves from plants acclimatized for 2 weeks in the greenhouse had more adaxial wax than those from non-acclimatized (culture flask-grown) plants. Acclimatized plants had more adaxial than abaxial wax. No abaxial wax was observed on leaves of non-acclimatized plants. Stomata were present on the abaxial leaf surface only of both acclimatized and non-acclimatized plants. Epicuticular wax layers surrounded guard cells of acclimatized plant leaves but were not present on non-acclimatized plant leaves. Weight changes in non-acclimatized plant leaves coated with silicon rubber on adaxial, abaxial, and both surfaces indicated that excised leaf water loss occurred only through the abaxial surface. Water loss from plants during the acclimatization process thus may be due to abaxial cuticular and stomatal transpiration.

Open Access

Potted apple trees (Malus domestica L. `Gala') were drenched with either water or an antitranspirant (N-2001). After treatment, no additional water was applied to the plants. Abscisic acid (ABA) content of immature and mature leaves was determined by radioimmunoassay after 0, 1, 3, and 5 h and 1, 2, 4, 7, 8, and 9 days after treatment. ABA content of mature and immature leaves of antitranspirant-treated plants peaked 1 and 4 days after treatment, respectively, and remained constant thereafter. In contrast, with increasing water stress, the ABA content of mature and immature leaves of control plants without antitranspirant peaked at 7 and 8 days, respectively. The overall level of ABA in mature leaves of both treatment groups was significantly greater than in immature leaves. The water saturation deficit increased, water and turgor potentials of leaves decreased, and stomatal conductance decreased in response to antitranspirant application. The changes in water relations parameters and stomatal conductance were highly correlated with changes in leaf ABA content.

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The `Flying Dragon' cultivar of Poncirus trifoliata L. Raf. is a strongly dwarfing rootstock for Citrus cultivars, reducing canopy volume of 9 year-old `Valencia' orange trees to 1/3 that of trees on standard rootstocks Open-pollinated seed of `Flying Dragon' was screened with isozyme markers to distinguish zygotic from nucellar (apomictic) seedlings. All zygotics had genotypes consistent with an origin by self-pollination. Zygotic seedlings were budded with `Valencia' orange scion and planted in the field. Of 46 progeny evaluated as rootstocks, 35 produced small trees similar to those on nucellar `Flying Dragon' and 11 produced large trees. This ratio is consistent with the 3:1 segregation expected for a single dominant gene. The dwarfing gene was closely linked, or pleiotropic with a gene causing curved thorns and stems. Several RAPD markers close to the dwarfing gene were identified with bulked segregant analysis. `Flying Dragon' apparently originated as a mutation because it had au identical genotype to non-dwarfing strains of trifoliate orange at all 38 isozyme and RFLP markers tested

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Control of bitter pit in `Honeycrisp' apples (Malus ×domestica) from trees treated during the growing season with foliar sprays of trifloxystrobin fungicide and calcium was evaluated in four replicated trials over 2 years. All trials were in commercial orchards of `Honeycrisp' trees that were 3 to 6 years old. The effectiveness of combining boron with foliar applications of calcium chloride (CaCl2) was evaluated in two trials, and effectiveness of harpin protein, used either alone or in alternating sprays with CaCl2 was assessed in one trial. Trifloxystrobin applied twice during the 30 days before harvest reduced bitter pit incidence at harvest in one of the four trials, but the reduction was transitory, no longer being evident when fruit were re-evaluated after 63 days of cold storage. Harpin protein did not affect disorder incidence. Calcium sprays failed to control bitter pit in treatments where the total elemental calcium applied was less than 2.7 lb/acre (3.03 kg·ha–1) per year for tree canopies that were sprayed to drip using 100 gal/acre (935.4 L·ha–1) of spray solution. In the two trials where some treatments involved application of at least 2.9 lb/acre (3.25 kg·ha–1) of elemental calcium per season, the incidence of fruit with bitter pit at harvest was reduced by 76% to 90%. Effectiveness of calcium sprays for bitter pit control was not enhanced by superimposing trifloxystrobin, boron, or harpin protein treatments. Flesh firmness at harvest was lower in calcium-treated than in non-treated fruit, and fruit maturity was more advanced on trees receiving boron sprays than on trees receiving no boron. In one trial, where the first calcium application was made approximately 2 weeks after petal fall and 4 days prior to a fruit thinning spray, crop load of trees that received calcium sprays, measured as number of fruit per cm2 trunk cross-sectional area, was 38% greater than on trees that received no calcium sprays. CaCl2 provided better control of bitter pit in `Honeycrisp' than any of the other materials tested.

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Shoot regeneration was obtained from leaf tissues of American (Ulmus americana) and Siberian elm (U. pumila) seedlings germinated in vitro and in greenhouse. Murashige and Skoog (MS, 1962) media supplemented with 4 levels of BA (0, 5, 10, 15, 20 μM) and 3 levels of IBA (0, 2.5, 5.0 μM) were tested in a factorial design to find an optimal hormonal combination for shoot regeneration. Shoot regeneration was obtained from both species within 3-4 weeks in a wide range of media. The highest regeneration rate (50%) of American elm was in the medium containing 10 μM BA and 2.5 μM IBA. Incubation under the light was essential for a higher rate of regeneration. Gelrite was found as a better solidifying agent than agar. The progress is under way to achieve transgenic elms by combining this regeneration system with Agrobacterium-mediated transformation.

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