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Xunzhong Zhang, Kehua Wang, and Erik H. Ervin

Recent advances in bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon] breeding and cultural management practices have enabled its use as a sports surface in U.S. Department of Agriculture cold hardiness zones 5 and 6. Use of these more cold-hardy bermudagrass cultivars further into transition- and cool-season zones increases the probability of freezing injury and increases the need for an improved understanding of physiological responses to chilling and freezing temperatures. Abscisic acid (ABA) has been shown to increase during cold acclimation (CA) and play a role in dehydration tolerance. This study investigated changes in ABA metabolism and dehydrin expression during CA and their association with freezing tolerance in four bermudagrass cultivars. Two cold-tolerant (‘Patriot’ and ‘Riviera’) and two relatively cold-sensitive (‘Tifway’ and ‘Princess’) cultivars were either subjected to CA at 8 °C day/4 °C night with a light intensity of 250 μmol·m−2·s−1 over a 10-h photoperiod for 21 days or maintained at 28 °C day/24 °C night over a 12-h photoperiod. In a separate study, exogenous ABA at 0, 50, 100, and 150 μm was applied to ‘Patriot’ bermudagrass without CA. ABA content in leaf and stolon tissues increased substantially during the first week of CA and remained relatively stable thereafter. ‘Patriot’ and ‘Riviera’ had greater ABA content and less stolon electrolyte leakage (EL) relative to ‘Tifway’ and ‘Princess’. Expression of a 25 kDa dehydrin protein increased during CA in all four cultivars. A significant correlation was found between ABA content and freezing tolerance. Exogenously applying ABA to ‘Patriot’ at 50, 100, and 150 μm significantly increased endogenous ABA content and the 25 kDa dehydrin expression and reduced stolon EL. The results suggest that alteration of ABA metabolism during CA is closely associated with freezing tolerance. Selection and use of cultivars with substantial accumulation of ABA and certain dehydrins during CA or in response to exogenous ABA could improve bermudagrass persistence in transition zone climates.

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H. Brent Pemberton, Yin-Tung Wang, and Garry V. McDonald

Case-cooled bulbs of Lilium longiflorum `Nellie White' were potted on 4 Dec. 1995 and forced to flowering using standard growing procedures. Plants were illuminated from shoot emergence to visible bud with supplemental high-intensity-discharge sodium vapor light at 70 μmol·m–2·s–1 from 1700 to 2200 HR each day. When the first primary flower bud (first initiated flower bud most proximal on the shoot) was 5 to 7 cm long, each plant was treated with 3 ml of either de-ionized water or 500 mg·liter–1 6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine (PBA). Sprays were directed at the flower buds and associated bracts. When the tepals on the first primary flower bud split, plants were placed at 2°C in the dark for 0, 4, or 21 days. After storage, plants were placed in a postharvest evaluation room with constant 21°C temperature and 18 μmol·m–2·s–1 cool-white fluorescent light. The first three primary flowers on PBA-treated plants lasted significantly longer than corresponding flowers on control plants, but there was no difference between flowers at the fourth and fifth positions. Also, the total postharvest life of the five primary flowers on PBA treated plants was 3 days longer than those on control plants. Storage time inversely affected the postharvest longevity of the first three primary flowers, but had no effect on the longevity of the fourth or fifth primary flowers or total postharvest life of the five primary flowers. There were no significant interaction effects between PBA treatment and storage duration on primary flower longevity.

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Shi-Ying Wang, William H. Carlson, and Royal D. Heins

Argeranthemum frutescens `Butterfly' and `Sugar Baby', Brachycome hybrid `Ultra', Helichrysum bracteatum `Golden Beauty', Scaevola aemula `New Wonder',Supertunia axillaris hybrids `Kilkenny Bells' and `Pink Victory', Sutera cordata `Mauve Mist' and `Snowflake', and Verbena hybrid `Blue' were grown in a glass greenhouse maintained at 20°C under seven different photoperiods (10-, 12-, 13-, 14-, 16-, 24-hr, and 4-hr night interruption). Black cloth was pulled at 1700 and opened at 0800 HR; incandescent lamps provided 2 μmol·m–2·s–1 to extend light hours to the designed photoperiods. Seedlings were pinched 3 days after transplant. Responses to photoperiod were clearly species-dependent. The tested species can be classified into three groups: 1) stem elongation and flowering were promoted in the long-day treatment (A. frutescens and S. axillaris hybrids), 2) only stem elongation was promoted in the long-day treatment (S. aemula, H. bracteatum, and B. hybrid), and 3) neither flowering nor stem elongation were affected by photoperiod (S. cordata and V. hybrid).

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K.H. Wang, A.R. Kuehnle, and B. Sipes

Burrowing nematode, Radopholus similis, reduces flower-yield-infected anthurium fields. Genetic resistance is one alternative to chemical control of the disease in anthurium. Seventeen commercial anthurium varieties, established in vitro on anthurium nutrient medium, were inoculated with burrowing nematodes to screen for tolerance. Three months after inoculation, plant responses were compared by number of nematodes recovered and by symptom index and plant weight loss with respect to non-inoculated plants. Results show that `Mauna Kea' and `Flamingo' anthuriums are among the most tolerant, while `Ozaki' is one of the most susceptible. These results are consistent with grower field evaluation. Nematode count is positively correlated with symptom index and weight loss. The mechanism of tolerance or resistance of anthurium toward burrowing nematode is unclear. However, due to the fact that burrowing nematode is a migratory endoparasite, a preinfectional resistance or tolerance mechanism is more likely to take place.

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Shi-Ying Wang, William H. Carlson, and Royal D. Heins

The effect of 6 weeks of storage at 2.5, 5.0, 7.5, 10.0, or 12.5°C in a glass greenhouse was determined on 11 vegetatively propagated annual species. Fresh weight (total, shoot, and root) and height of 30 plants per species in each storage temperature were measured at the end of storage. Another 30 plants were transplanted into 15-cm pots (three plants per pot) and grown under natural light in a 20°C glass greenhouse for 3 weeks. Three species showed chilling injury or died during storage at ≤7.5°C. Plant height and shoot fresh weight at the end of storage for most species increased linearly as storage temperature increased. Storage temperature did not affect the net increase in height or weight significantly during recovery growth, except for plants that exhibited chilling injury at the end of storage.

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Z. Mganilwa, M. Nagata, H. Wang, and Q. Cao

Based on seedling properties and stage of growth for cucurbitaceous and solanaceous vegetables, separate robots are being marketed for each. Full automatic grafting robots are used for solanaceous vegetables like tomato and egg-plant employing ordinary splice method by making a diagonal cut through the hypocotyl of both the scion and the rootstock. However, cutting one piece of cotyledon diagonally from the rootstock does grafting of cucurbitaceous vegetables like cucumber, melon, and pumpkin. This method had the advantage of easy recovery and high survival rate of seedlings. Only semi-automatic robots are marketed for this kind of plants because a fixed cotyledon orientation is required for grafting operation. Both the scion and the rootstock are loaded manually to their corresponding feeding devices. To replace the manual loading operation, this study proposed a neural network based automatic seedling loading system. The system automatically estimates the quality and determines the cotyledon orientation of seedling for guiding the loading device of the grafting robot. As a first step toward solution, we report the development of a model for seedling quality estimation and orientation detection using image processing and neural network techniques. The model has a learning ability and can judge seedlings according to the training patterns. A seedling leaves feature extraction model of 10 characteristics was proposed and a three-layer neural network was constructed. The experimental results indicate that the seedling leaves orientation was accurately detected with an average error of 3 degrees within 360 degrees of freedom and the machine vision system could properly classify seedlings into three classes (A-good, B-fair, and C-bad) according to the training pattern.

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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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Qianni Dong, Xinwang Wang, David H. Byrne, and Kevin Ong

Black spot disease, caused by the fungus Diplocarpon rosae Wolf, is one of the most serious diseases of garden roses. Both complete (vertical) resistance conditioned by dominant Rdr genes and partial (horizontal) resistance conditioned by multiple genes have been described. The use of resistant rose cultivars would reduce the demand of agrochemical applications. The characterization of 16 genotypes for resistance to black spot using two laboratory assays, the detached leaf assay (DLA) and the whole plant inoculation (WPI) approach, indicated that these techniques were well correlated. Thus, either method could be used to assess the resistance of the plants to black spot. Fifteen diploid hybrid populations from 10 parents segregating for partial (horizontal) resistance to black spot derived from Rosa wichuraiana ‘Basye’s Thornless’ (RW) were assessed for black spot resistance by quantifying the percentage of the leaf area with symptoms (LAS) and lesion length (LL) measured by the diameter of the largest lesion per leaf in DLAs. The narrow-sense heritability of partial resistance to black spot as measured by LAS and LL data of DLA was estimated to be from 0.28 to 0.43 when calculated with a genetic variance analysis and from 0.74 to 0.86 when generated from offspring–midparent regression. This suggests that the development of rose cultivars with high levels of stable partial resistance to black spot is a feasible approach for the rose industry.

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S. Y. Wang, H. J. Jiao, and M. Faust

An increase in ascorbic acid, reduced form of glutathione (GSH), total glutathione, total non-protein thiol (NPSH) and non-glutathione thiol (RSH) occurred as a result of induction by thidiazuron during bud break, whereas dehydroascorbic acid and oxidized glutathione (GSSG) decreased during the same period. Thidiazuron also enhanced the ratio of GSH/GSSG, and activities of catalase, superoxide dismutase (SOD), ascorbate free radical reductase (AFR), ascorbate peroxidase (POD), dehydroascorbate reductase (DHAR), ascorbate oxidase (AAO), and glutathione reductase (GR). The ascorbic acid content and the activities of catalase, SOD, AFR, POD, AAO, and DHAR peaked when buds were in the side green or green tip stage just prior to the start of rapid expansion, and declined thereafter. The GSH, NPSH, RSH, ratio of GSH/GSSG, and activity of GR increased steadily during bud development.

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H. Wang, S. Parent, A. Gosselin, and Y. Desjardins

Micropropagated plantlets of Gerbera jamesonii H. Bolus ex Hook. F. `Terra Mix', Nephrolepis exaltata (L.) Schott `Florida Ruffles', and Syngonium podophyllum Schott `White Butterfly' were inoculated with two vesicular-arbuscular mycorrhizal (VAM) fungi, Glomus intraradices Schenck and Smith and G. vesiculiferum Gerderman and Trappe. They were potted in three peat-based media to determine the effects of mycorrhizal peat substrate on acclimatization and subsequent growth of micropropagated plantlets under greenhouse conditions. Symbiosis was established between the three ornamental species and VAM fungi within 4 to 8 weeks of culture in the greenhouse, but not during acclimatization. Mortality of Gerbera and Nephrolepis mycorrhizal plantlets was reduced at week 8 compared to the noninoculated control. A peat-based substrate low in P and with good aeration improved VAM fungi spread and efficiency. Mycorrhizal substrates had a long-term benefit of increasing leaf and root dry weight of Gerbera and Nephrolepis. Mycorrhizal Gerbera plants flowered significantly faster than non-mycorrhizal plants.