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Yoshiko Yambe, Kiyotoshi Takeno, and Takashi Saito

Seed germination percentage of multiflora rose (Rosa multiflora Thunh.) was much higher under continuous white light than in complete darkness. Red light was the most effective in inducing germination, and far-red light was ineffective. Exposure to red light for 1 min increased germination; this effect was saturated at an exposure of2 min. The red-light effect was reversed by subsequent exposure to far-red light. The results indicate that rose seeds are positively photoblastic, and that the photoreceptor involved is most likely phytochrome.

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M. Capellades, R. Fontarnau, C. Carulla, and P. Debergh

The surface structure of rose (Rosa multiflora L. cv. Montse) leaves formed in vitro under several environmental conditions (light level, relative humidity) and with various growth regulator treatments was studied by light and scanning electron microscopy. The epidermis from leaves developed in cultures grown under a higher light level and a lower relative humidity (80 μmol·s-1·m-2 and 75% RH) than the conditions used in commercial laboratories (25 μmol·s-1·m-2 and 100% RH) showed anatomical modifications of the epicuticular wax, stomata, and epidermal cells similar to that of greenhouse-grown plant leaves. These results indicate that cultured plantlets can resemble greenhouse-grown plants under modified environmental conditions. In vitro pretreatment will reduce transplant losses and shorten the acclimatization period in the greenhouse.

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Andrew D. Cartmill, Fred T. Davies Jr., Alejandro Alarcon, and Luis A. Valdez-Aguilar

Sustainable horticultural production will increasingly have to rely on economically feasible and environmentally sound solutions to problems associated with high levels of bicarbonate (HCO - 3) and associated high pH in irrigation water. The ability of arbuscular mycorrhizal fungi (AMF; GlomusZAC-19) to enhance plant tolerance to HCO3 - was tested on the growth, physiology and nutrient uptake of Rosamultiflora Thunb. ex J. Murr. cv. Burr (rose). Arbuscular mycorrhizal colonized and noninoculated (non-AMF) plants were treated with 0, 2.5, 5, and 10 mm HCO - 3. Increasing HCO - 3 concentration and associated high pH and electrical conductivity (EC) reduced plant growth, leaf elemental uptake and acid phosphatase activity (ACP), while increasing alkaline phosphatase activity (ALP). Inoculation with AMF enhanced plant tolerance to HCO - 3 as indicated by greater plant growth, leaf elemental uptake (N, P, K, Ca, Fe, Zn, Al, Bo), leaf chlorophyll content, higher mycorrhizal inoculation effect (MIE), lower root iron reductase activity, and generally lower wall-bound ACP (at 2.5 mm HCO3 -), and higher soluble ALP (at 10 mm HCO3 -). While AMF colonization (arbuscules, vesicles, and hyphae formation) was reduced by increasing HCO - 3 concentration, colonization still occurred at high HCO - 3. At 2.5 mm HCO3 -, AMF plant growth was comparable to plants at 0 mm HCO3 -, further indicating the beneficial effect of AMF for alleviation of HCO3 - stress.

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Genhua Niu, Denise S. Rodriguez, and Lissie Aguiniga

the 6.0 dS·m −1 and 9.0 dS·m −1 treatments as early as 3 weeks after the treatment initiation. However, the survival rate of this rootstock was slightly higher than the other two rootstocks at the end of the experiment. Rosa multiflora had lower

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Genhua Niu and Denise S. Rodriguez

contents. Substrate ψ m in the control ranged from 0 to −15 kPa. Fig. 1. Substrate matric potential (ψ m ) during the mild cyclic drought-stressed period for four rose rootstocks: Rosa × hybrida ‘Dr. Huey’, R . × fortuniana , R. multiflora

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Genhua Niu and Denise S. Rodriguez

tolerance was higher when grafted onto Rosa ‘Manetti’ and ‘Natal Briar’ than R . odorata (syn. R . indica L. ‘Major’), R . multiflora ‘Rum 9’, and ‘Dr. Huey’. However, the relative salt tolerance of the five rootstocks alone (without grafting with

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Yunliang Peng, Wanrong Chen, and Maurice Moens

Methods to screen for resistance to root-lesion nematode Pratylenchus penetrans in Rosa were modified to screen-rooted materials. Sixty days after rooting, plants were transplanted into 50-mL pots filled with river sand and each inoculated with 500 P. penetrans in 400 μL water 10 days later. The inoculated plants were fertilized weekly and incubated in a growth chamber or a greenhouse for 5 months when nematodes were extracted from the sand and root system and enumerated. When used for screening of the 131 Rosa accessions, this approach allowed the observation of a large variation in host suitability. While a majority of the accessions supported the multiplication of P. penetrans, previously reported resistance of R. multiflora `K1' and R. virginiana to P. penetrans was confirmed. Rosa laevigata anemoides allowed a significantly lower nematode multiplication than the currently prevalent rootstock R. corymbifera `Laxa'.

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Yoshiko Yambe and Kiyotoshi Takeno

The germination percentage of Rosa multiflora Thunb. achenes was greatly increased when they were treated with 1% Driselase, a macerating enzyme, for 36 hours. The seeds germinated more rapidly when the achenes were treated with the enzyme for a longer period. Treatment with Cellulase Onozuka improved seed germination at a lower concentration than did Driselase. Pure preparations of pectinase and cellulase had effects similar to treatment with the enzymes noted. Treatment with pectinase was more efficient than treatment with cellulase. These enzymes likely loosened the bond between cells along the suture of the pericarp and forced the pericarp to split.

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David Wm. Reed, Yin-Tung Wang, and Brent H. Pemberton

Roses are adapted for growth and production on acid to slightly acid soil. When grown on alkaline soil sites, without extensive soil modification and acid forming and/or iron chelate fertilization, growth is reduced and severe iron chlorosis is prevalent. This study screened 24 Rosa rootstock species and selections on one acid and two alkaline soil sites for 2 consecutive years. Plants were observed for chlorosis, chlorophyll content, fresh and dry weight production and overall quality. A final reciprocal grafting study using susceptible and tolerant selections was conducted to assure the scion could realize the adaptability of the rootstock. Overall, the following five selections consistently exhibited greater growth and decreased chlorosis on the alkaline sites: R. odorata, R. canina, R. manetii, R. sp. “Mexican”, R. fortuniana, and R. multiflora selection K-l. All other R. multiflora selections performed poorly. On the acid soil site, all rootstocks grew well. When susceptible selections were budded onto tolerant rootstocks, the scions exhibited a higher degree of tolerance. Tolerant selections budded onto susceptible rootstocks exhibited increased chlorosis and decreased growth.

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Yin-Tung Wang

Cuttings of a thornless mutation of Rosa odorata (RO) and R. multiflora (RM) were rooted in Feb., budded with Rosa `Queen Elizabeth' on 21 Apr. 1987, and planted in 2.6- or 5.2-liter containers. Five weeks after budding, over 50% of the buds on the thornless RO had developed into shoots, while only 4% of the buds on the RM were growing. After an additional 10 weeks, 80% and 60% of the buds on the thornless RO and RM, respectively, had development into shoots. Six months after budding, plants in the 5.2-liter pots produced 1 to 2 folds more flowers than those in 2.6-liter pots. Plants from all four production treatments were planted in a field with alkaline soil on 3 Nov. 1987. During the next four years, plants on RM showed severe chlorosis and had 5% and 45% survival for those produced in 2.6- and 5.2-liter pots, respectively. Those on the thornless RO had 85% and 100% survival when produced in 2.6- and 5.2-liter pots, respectively after four years. Leaves of plants on the thornless RO rootstock had higher concentrations of chlorophyll than those on the RM. However, analyses of leaves did not reveal differences in elemental concentrations among treatments.