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  • Author or Editor: Yan Chen x
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From 1986 through 1993 wild rose species were investigated throughout China to catalog and to characterize the rose germplasm resources in mainland China. Many of the 94 rose species and 144 rose varieties in China have not been extensively utilized. The basic features of Chinese rose species are as follows. (1) There are many valuable and rare Rosa species in China. These species are sources of many unique and outstanding characters such as intense fragrance, white and yellow flower color, recurrent flowering and resistance to stress. More than 80% of the rose species in China are native to only China. (2) Although most Rosa species are still in the wild state, a few species cultivated from very early time have many forms available. (3) The number of rose species gradually increases from Northeast to Southwest China. The distribution centers of Rosa species in China are Sichuan and Yunnan Provinces. Chinese rose species can be introduced and used directly in gardens, or in breeding programs to develop new roses.

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Annual vinca, Catharanthus roseus, is exceptionally adaptive to the summer heat and the sandy loam or clay soil in the southeastern region and provides season-long blooms once established in landscape plantings. A wide variety of colors, sizes, and applications are available for landscape use. However, diseases such as alternaria leaf spot and phytophthora leaf blight are prevalent in this region in vinca plantings. Effective disease control requires frequent fungicide application that is expensive and may pose negative effects on the environment. Proper planting techniques including date of planting, fertilization rate at planting, and variety selection may improve plant growth, reduce disease severity, and save landscape service business labor in disease management. Plants of three varieties: open-pollinated `Cooler Hot Rose', F1 hybrid `Titan Rose', and trailing variety `Mediterranean Lilac' were planted on 1 Apr. or 1 May in landscape plots. Plants were at the same growth stage at the time of planting and were fertilized with Osmocote 14–14–14 (3 months) at 0, 35, 70, or 140 g·m2. Plant growth index indicates that plant growth increased significantly at increasing fertilization rates; however, plant overall quality ratings were not significantly different among fertilized plants. Disease incidence in July suggests that late planting may reduce alternaria leaf spot in open-pollinated and hybrid upright type vinca. Disease severity in August was more pronounced on trailing vinca and more severe when plants were not fertilized or fertilized with the highest fertilization rate. Tissue analysis indicates that trailing vinca `Mediterranean Lilac' may require less fertilization than upright type.

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While herbaceous perennials continuously gain popularity in southern landscape plantings, the nutrient requirements of many species in this group are still unknown. The business goal of lawn and garden care companies emphasizes aesthetic value of the urban landscape. Improper nutrient management, such as the overapplication of fertilizers, is inefficient and may result in increased pest problems and risks of contaminating ground and surface waters by nutrient runoff. Seven herbaceous perennials (lantana, rudbeckia, purple cone flower, daylily, mexican heather, cigar plant, and guara) were planted in simulated landscape beds. Fertilizers applied included one or two OsmocotePlus 16-8-12 tablets (7.5 g), OsmocotePlus 15-9-12 (5 months) at 0, 33, 66, and 131 g/m2 at planting, or applying OsmocotePlus 15-9-12 (5 months) 33 g/m2 or one OsmocotePlus tablet at the time of planting plus another 33 g/m2 topdressing after flowering. Plant growth of rudbeckis, purple cone flower, and lantana were highest at 131 g/m2 applied at planting, but resulted in similar overall plant quality as with 33 or 66 g/m2 treatments. Daylily growth was similar across fertilization treatments, and overall quality decreased at high fertilization rates with more severe daylily rust observed on these plants. Applying one OsmocotePlus 7.5-g tablet resulted in similar plant quality with applying OsmocotePlus 33 and 66 g/m2, but significantly reduced the amount of fertilizer used. Additional topdressing after flowering did not further increase plant quality in fall, but may affect the overwintering survival of perennial plants.

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A high priority in rose (Rosa spp.) breeding research is the transfer of disease resistance, especially to black spot (Diplocarpon rosae Lib.), from wild diploid Rosa species to modern rose cultivars. To this end, amphidiploids (2n = 4x = 28) were induced with colchicine from five interspecific diploid (2n = 2x = 14) hybrids involving the black spot resistant diploid species R. wichuraiana Crép, R. roxburghii Thratt., R. banksiae Ait., R. rugosa rubra Hort., and R. setigera Michaux. Two application procedures (agitation of excised nodes in colchicine solution or tissue culture of shoots on medium with colchicine), five colchicine concentrations (0.0, 1.25, 2.50, 3.76, and 5.01 mmol), and five durations (2, 3, 5, 8, and 10 d) were used. After colchicine treatment, the materials were cultured in vitro and the surviving explants were examined for the “gigas” characteristics typical of doubled diploids. Chromosome counts of morphologically suspect genotypes confirmed 15 amphidiploids among 1109 plants that survived colchicine treatment. Although the effect of colchicine treatment varied some among interspecific hybrids, 2.50 mmol for 48 h of node agitation or 1.25 mmol for at least 5 d of shoot culture were optimal.

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Nitrogen (N) fertilization is critical for successful production of cut flowers in a hydroponic system. In this study, two sunflower cultivars: single-stand `Mezzulah' and multi-stand `Golden Cheer' were grown under two N fertilization rates: 50 mg·L-1 and 100 mg·L-1 in a recirculating hydroponic system. At the same time, `Mezzulah' sunflowers were biologically stressed by exposing each plant to 2000 second-stage juveniles of the plant parasitic nematode Meloidogyne incognita, race 1. The experiment was conducted in May and repeated in Sept. 2004, and plant growth and flower quality between control and nematode-infested plants were compared at the two N rates. The two cultivars responded differently to fertilization treatments. With increasing N rate, the dry weight of `Mezzulah' increased, while that of `Golden Cheer' decreased. Flower size and harvest time were significantly different between the two cultivars. However, N had no effect on flower quality and harvest time. Flower quality rating suggests that quality cut stems can be obtained with 50 mg·L-1 N nutrient solution. Nematode egg count suggests that plants in the nematode treatment were successfully infested with Meloidogyne incognita, however, no significant root galling was observed, and plant growth and flower quality were not affected by nematode infestation.

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Two key trends of sustainable agriculture are reducing the amount of inputs such as pesticides, fungicides, or fertilizer and finding ways to reduce or reuse agricultural waste. Leafy plant waste can be burned to produced smoke-water extracts that have effective antimicrobial and germination properties. Damping-off disease caused by Pythium spp. leads to significant losses at the papaya seedling stage and is usually managed with fungicides. Five smoke-water extracts derived from burning different plant residues—namely, rice straw smoke-water (R-SW), wheat straw smoke-water (W-SW), pangola grass smoke-water (P-SW), cornstalk smoke-water (C-SW), and bamboo leave smoke-water (B-SW)—were prepared. These were mixed into the V8 media used for culture of Pythium aphanidermatum. In vitro treatment with 5% P-SW, C-SW, or B-SW reduced mycelial growth rate significantly, whereas 5% B-SW inhibited mycelial growth completely. All 1% smoke-water preparations reduced zoospore production significantly, but the inhibition rate of 3% R-SW, 3% W-SW, 1% P-SW, 1% C-SW, and 1% B-SW reached 100%. For in vivo experiments, P. aphanidermatum was inoculated in 1 kg of potting soil and mixed with B-SW in concentrations of 1% to 5%. The papaya seedlings treated with 2% to 5% B-SW maintained the growth parameter without damping-off symptoms.

Open Access

In this study, in vitro induction of tetraploid Lychnis senno Siebold et Zucc. and its cytological and morphological characterization were conducted. For polyploid induction, nodal segments with axillary buds from in vitro grown plants were kept for 3 days in MS (Murashige and Skoog, 1962) liquid or solid media added with a series of concentrations of colchicine. Out of total 588 recovered plants, 15 tetraploids and 6 mixoploids determined by flow cytometry analysis were obtained. The tetraploid contained 48 chromosomes, twice the normal diploid number of 24, as observed under light microscope. The tetraploid plants exhibited much larger but less stomata than diploid plants. Moreover, significant differences in stem height and leaf size between the diploid and tetraploid plants were noted. The tetraploid plants were more compact than diploids.

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Abstract

Several tuber-bearing Solanum species with different levels of frost hardiness and different capacities for cold acclimation were studied for the interrelationship of freezing and heat tolerance after cold and heat acclimation. Cold acclimation could increase the frost hardiness in some species as previously reported, but except for S. commersonii it did not change the heat hardiness in species studied. Heat acclimation, on the other hand, could increase the heat hardiness in all tested species without affecting their frost hardiness. There is no systematic relationship between freezing and heat tolerance and no correlation in heat hardiness between the controls and the heat acclimated plants. The results indicate that the mechanisms of cold and heat acclimation in the potato appear to be independent of each other.

Open Access