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I.L. Goldman and J.F. Watson II

A severe dwarf mutant affecting vegetative and reproductive growth arose spontaneously in our red beet (Beta vulgaris L. subsp. vulgaris) breeding nursery and was used in crosses with inbred lines to characterize its inheritance. Segregation data in backcross and F2 generations were collected. Chi-square goodness-of-fit tests did not deviate significantly from the expected ratios for a monogenic character for each genetic background-generation combination. We propose the symbol dw to describe the genetic control of this dwarf phenotype. Greenhouse experiments were conducted to determine whether the mutant was sensitive to exogenous application of gibberellic acid (GA). GA3 and GA4/7 in concentrations of 0 to 1000 ppm were applied to apical meristems during flower stem development in vernalized dwarf plants. Data on flower stem length and leaf length were collected over a 6-week period during reproductive growth. Recovery of wild-type flower stem length was obtained with application of both types of GA. A 30-fold increase in flower stem length over untreated plants was accomplished by GA application. Results of these phenocopy experiments suggest the mutant gene is involved in GA synthesis.

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Qingrong Sun, Yinping Shi, Qiangsheng Wang and Hongyan Sun

Laiyang dwarf cherry (Prunus pseudocerasus Lindl. Var. Laiyang dwary cherry) is an important dwarf type of Chinese cherry. It is both directly used for production and used as rootstock of sweet cherry (P. avium L.). Material used in this study was Laiyang dwarf cherry seed, which is open-pollinated. The fruit surface is sterilized with 70% ethanol on sterile working table, the seed is removed from fruit, and embryo is taken out of cracking seed shell. Explants include whole embryo, embryo without cotyledons, and cotyledons. Basal media are MS and 1/4MS major elements, sugar 30 g·L–1, agar 5.5 g·L–1, adjusted pH 5.8. Hormone used included 6-BA,IBA and 2,4-D for a total eight treatments. Culture temperature was 25° ±2°C, and photoperiod was 14 h. Results show 1) the plant regeneration rate from cotyledons is highest, second is from embryo without cotyledons, lowest is from whole embryo; 2) when BA is in the range of 0.7 to 5 ppm, plant regeneration is higher at a high concentration than that at low concentration; 3) at the same concentration, plant regeneration rate on the medium supplemented with 2,4-D is higher than that on the medium supplemented with IBA; 4) plant regeneration rate is higher on the medium containing cytokinin and auxin is higher than that on the medium only containing cytokinin; and 5) plant regeneration rate of continuous light culture cotyledons is higher than that of first dark culture 2 weeks cotyledons. Effects of light and dark/hormone and explant type on plant regeneration rate is discussed.

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Shahrokh Khanizadeh, Yvon Groleau, Odile Carisse, Vicky Toussaint, Raymond Granger and Gilles Rousselle

‘SJM150’ (St-Jean Morden 150) is a new rootstock resulting from a cross made in 1960 between Malus baccata ‘Nertchinsk’ and ‘M.26’ (‘Malling 26’ = M.16 × M.9). It is a new dwarfing apple rootstock developed at the Agriculture and Agri

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Shahrokh Khanizadeh, Yvon Groleau, Odile Carisse, Vicky Toussaint, Raymond Granger and Gilles Rousselle

‘SJM127’ (St-Jean Morden 127) is a new rootstock resulting from a cross made in 1960 between Malus baccata ‘Nertchinsk’ and ‘M.26’ (‘Malling 26’ = M.16 × M.9). It is a new dwarfing apple rootstock developed at the Agriculture and Agri

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Timothy K. Broschat

`Petite Yellow' dwarf ixoras (Ixora spp.) were grown in an alkaline substrate (3 limestone gravel: 2 coir dust) or a poorly aerated composted seaweed substrate to induce iron (Fe) chlorosis. Chlorotic plants were fertilized every 2 months with soil applications of 0.1 g (0.0035 oz) Fe per 2.4-L (0.63-gal) pot using ferrous sulfate, ferric diethylenetriaminepentaacetic acid (FeDTPA), ferric ethylenediaminedi-o-hydroxyphenylacetic acid (FeEDDHA), Hampshire Iron (FeHEDTA plus FeEDTA), ferric citrate, iron glucoheptonate, or DisperSul Iron (sulfur plus ferrous sulfate). Additional chlorotic ixoras growing in a substrate of 3 sedge peat: 2 cypress sawdust: 1 sand were treated every 2 months with foliar sprays of Fe at 0.8 g·L-1 (0.11 oz/gal) from ferrous sulfate, FeDTPA, FeEDDHA, ferric citrate, or iron glucoheptonate. Only chelated Fe sources significantly improved ixora chlorosis when applied to the soil, regardless of whether the chlorosis was induced by an alkaline substrate or a poorly aerated one. As a foliar spray, only FeDTPA was effective in improving chlorosis in dwarf ixora. Leaf Fe content either showed no relationship to plant color or was negatively correlated with plant chlorosis ratings.

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Ralph Scorza, Daniele Bassi and Alessandro Liverani

A study was conducted to determine genetic control of the columnar or pillar (PI) growth habit, and to evaluate the effects of interactions of various genes that influence peach [Prunus persica (L.) Batsch (Peach Group)] growth habit. The PI habit (brbr) examined in this study was inherited as a monogenic trait expressing incomplete dominance. The heterozygous Brbr derived from crosses between standard (ST) and PI genotypes was recognized as an upright (UP) tree with narrower branch angles than ST trees but wider than PI trees. The combination of brbr and brachytic dwarf (DW) (dwdw) produced dwarf-pillar (DWPI) trees. The effects of the heterozygous Brbr in combination with dw and/or compact (CT) (Ct) could not be recognized by visual observation. Compact pillar (CTPI) trees resulted from the expression of Ct_ brbr. These trees were distinguished from globe-shaped (GL) trees (Ct_Brbr) by the more upright growth habit of the CTPI trees. This genetic study highlights the genetic plasticity of tree growth habit in peach. The investigation of novel growth habits extends our concept of the peach tree. Some growth habits such as PI may have commercial potential for high-density peach production systems. Others, such as DWPI and CTPI may have potential as ornamentals.

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Shahrokh Khanizadeh, Yvon Groleau, Odile Carisse, Vicky Toussaint, Raymond Granger and Gilles Rousselle

dwarf trees equal to ‘Ottawa 3’ (O.3) but with better precocity (early fruiting), higher yield efficiency (based on yield/trunk cross-sectional area), lower suckers, and wider branch angles. ‘O3A’ is similar to ‘O.3’ in susceptibility to two races of

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Victoria E. Anjichi and Edmund J. Holcomb

The flowering of Dwarf Bearded Iris as a potted plant requires knowledge of the effect of chilling time and photoperiod on the plant. An experiment was conducted to determine what combination of these two factors would lead to flowering. The treatments were chilling time (0,4, and 8 weeks) and irradiance treatment (short day, long day, and HID lighting). Iris rhizomes were potted into 6 inch pots, kept moist and placed in a 4°C cooler for the various lengths of time. These were then transferred to the different irradiance levels and allowed to flower in the greenhouse.

The plants that received 8 weeks of chilling flowered earliest, followed by those that received 4 weeks of chilling. The plants that were placed under HID lighting flowered earlier than those that were placed under long day light treatment. The plants that received short day light treatment did not flower except for those that received-8 weeks of chilling.

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Meriam Karlsson and Jeffrey Werner

Dwarf carnation (`Monarch Yellow' and `Monarch Purple') was germinated and grown at 20 °C for 3 weeks. Following transplant (21 d from seeding), seedlings were grown at 16 °C and either 9 or 16 hr daylength. Irradiance was adjusted to 10 mol/m2 per day. Growth and development in response to photoperiod was significantly different for the two cultivars in the `Monarch' series. Flowering at long days was faster with 118 d from seeding for `Monarch Yellow' and 128 d for `Monarch Purple'. Under short days, flowering was observed 128 d from seeding in `Monarch Yellow' and 144 d for `Monarch Purple'. Ten days with short photoperiod initiated at transplant followed by long days resulted in more branching without significantly delayed development for `Monarch Yellow'. No effect on branching or rate of development was observed in `Monarch Purple' with 10 initial short days compared to long days throughout.

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Gennaro Fazio, Herb S. Aldwinckle, Terence L. Robinson and James Cummins

The Geneva® Apple Rootstock Breeding program initiated in 1968 by Cummins and Aldwinckle of Cornell University and continued as a joint breeding program with the USDA-ARS since 1998, has released a new dwarf apple rootstock named Geneva® 41 or G.41. G.41 (a progeny from a 1975 cross of `Malling 27' × `Robusta 5') is a selection that has been tested at the N.Y. State Agricultural Experiment Station, in commercial orchards in the United States, and at research stations across the United States, Canada, and France. G.41 is a fully dwarfing rootstock with vigor similar to M.9 T337, but with less vigor than M.9 Pajam2. It is highly resistant to fire blight and Phytophthora with no tree death from these diseases in field trials or inoculated experiments. G.41 has also shown tolerance to replant disease. Its precocity and productivity have been exceptional, equaling M.9 in all trials and surpassing M.9 in some trials. It also confers excellent fruit size and induces wide crotch angles in the scion. It appears to be very winter hardy and showed no damage following the test winter of 1994 in New York. Propagation by layering in the stool bed G.41 is not consistent and may require higher layering planting densities or tissue culture mother plants to improve its rooting. G.41 also produces some side shoots in the stool bed. The nursery liners of G.41 produce a smaller tree than G.16 liners, but similar to M.9, which is very acceptable. Unlike G.16, G.41 is not sensitive to latent viruses. G.41 has similar graft union strength to M.9 and requires a trellis or individual tree stake when planted in the orchard. Suggested orchards planting densities with this rootstock are 2,000-4,000 trees/ha. This rootstock has been released for propagation and commercial sale by licensed nurseries.