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W.L. Chen and D.M. Yeh

Elimination of in vitro contamination and shoot multiplication were studied with Aglaonema Schott ‘White Tip’. Apparently, contamination was reduced, but explants browned when 200 mg·L−1 streptomycin was used as either a pretreatment or incorporated into the medium. Reduced occurrence of contamination and browning was achieved in axillary bud explants excised from the stock plants that had not been watered for 2 months. Six shoots per explant elongated normally in Murashige and Skoog (MS) medium containing 30 μm benzylaminopurine (BA). MS medium containing 20 μm thidiazuron (TDZ) also resulted in six shoots per explant, but these shoots failed to extend beyond a rosette. Only microcuttings from 30 μm BA treatment were used for the ex vitro rooting trial, and indole-3-butytric acid (IBA) at 9.8 or 19.7 mm applied to the base of the microcuttings resulted in 100% ex vitro rooting and the longest roots.

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Albert T.Y. Mak and D.M. Yeh

Effects of nitrogen application on growth, stomatal conductance, transpiration, and chlorophyll content were studied in Spathiphyllum Schott 'Sensation' grown in sphagnum peat (SP)- and coir dust (CD)-based media with top-irrigation or subirrigation. Maximum shoot dry weight occurred at 8 mM N in plants grown in SP-based medium under top-irrigation and subirrigation, and in CD-based medium under subirrigation. For plants in CD-based medium under top-irrigation, maximum shoot dry weight was obtained at 16 mm N. In SP- or CD-based medium, shoot dry weight was greater at 4 and 8 mm N under subirrigation than under top-irrigation. Stomatal conductance and transpiration were reduced by nitrogen deficiency (0 N), greatly enhanced by 4 mm N, and decreased gradually at higher N levels. Chlorophyll content increased with increasing N concentration up to 8 mm. The percentage of maximum total dry weight increased quadratically as leaf N content increased from 1.5% to 3.5%. Nitrogen at 16 and 32 mm increased the number of leaves with marginal necrosis. Reduced growth and more leaves with marginal necrosis occurred in SP- or CD-based media with EC > 1.25 dS·m-1 in the middle and bottom layers.

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D.M. Yeh and H.F. Lin

Identification of heat-tolerant chrysanthemum [Dendranthema ×grandifolia (Ramat.) Kitamura] genotypes for commercial production in hot areas of the world is desirable. The extent to which electrolyte leakage from chrysanthemum leaf discs, measured using a test for cell membrane thermostability (CMT), could be related to the delay in flowering induced by heat in the field-grown plants was determined. The relationship between the relative injury (RI) occurring in leaf tissue discs of chrysanthemum cultivars and treatment temperature was sigmoidal. A single temperature treatment at 50 °C resulted in injury values near the midpoint of the sigmoidal response curve and showed the greatest sensitivity in detecting genotypic differences in heat tolerance. The cultivars with a low RI value are those with the greater CMT and shorter heat-induced delay to flowering.

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C.Y. Kuo and D.M. Yeh

Guzmania lingulata (L.) Mez. `Cherry' were grown in coco chips and fertigated with half-strength Hoagland solution containing various concentrations of boric acid. Excessive boron induced changes in growth, relative chlorophyll content, and leaf anatomy were investigated. Plants treated with 5 mg·L–1 or higher boric acid concentration had reduced SPAD-502 readings and Fv/Fm values and increased leaf necrosis in the lower leaves. Boron was distributed unevenly within a leaf, with the maximum concentration in the leaf tip. Increased necrotic length and new leaves with necrosis were evident where average whole leaf boron concentration was higher than 170 μg·g–1 on dry weight basis. More leaf growth and higher transpiration or stomatal conductance were recorded in plants under 40% (average 676 μmol·m–2·s–1 PPF at noon) than 76% (average 270 μmol·m–2·s–1 PPF at noon) shade. Excessive boron was not found to affect epidermal cells or water storage tissue, but caused browning and shriveling of the chlorenchyma cells.