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Abstract
Differential thermal analysis on winter flower buds of Cornus florida revealed that numerous small low temperature exotherms occurred between -15 and -23° C. These exotherms resulted in the death of the winter bud florets. Only a single exotherm near -20° C was observed in individual florets. These observations indicate that the florets of the winter flower bud survive subfreezing by supercooling and that the temperature of the exotherms may be correlated with the minimum temperature occurring at the northern range of the species.
Abstract
To determine the frost hardiness of some important Camellia species and their cultivars, dormant twigs wintering in Tokyo were collected mainly in midwinter and artificially hardened at −3°C for 15 days to induce the maximum hardiness. Camellia japonica which extends north as far as 40°51′ was the most hardy species, resisting freezing from −18 to −20°C. A great difference in the hardiness was observed in the flower buds among many species and cultivars, ranging from −15 to −5° or above; though the leaves, vegetative buds and twig tissues were all hardy to temperatures from −10 to −15°C in the camellias tested. Except for C. japonica and its cultivars, the peduncle was found to be the least hardy tissue of the flower buds in the genus Camellia.
Abstract
There is need for rapid determination of cold resistance of plants in the field. Exotherm analysis was adapted to such needs for dormant fruit buds of peach (Prunus persica (L.) Batsch). Buds were excised with 1-2 mm of vascular tissue attached and then held near the thermocouple junction with an A1 foil wrap. Exotherms could be recorded from most of 25-30 buds per junction. Resolution was improved by slow rates of temperature decrease in the critical range (near l°/hour). At high rates of temperature decrease (8 to 15°/hour) buds were killed at higher temperatures. The distribution of bud mortality with temperature was very close to the standard skewed curve for buds evaluated by the tissue browning method.
Bulbous structures consisting of meristematic clumps (designated “shoot primordia”) were induced from a meristematic culture of a hybrid statice (Limonium altaica Mill. × L. caspium Mill., cv. Blue Symphonet). The shoot tips were cultured in 25 mL of liquid 1/2 Murashige & Skoog (MS) medium supplemented with 0.44 μm BA and 0.054 μm NAA and 3% sucrose at pH 5.8 by vertically shaking at 2 rpm on rotating stages (1 m in diameter) at 25 °C. One month after inoculation of shoot tips, numerous small globular structures were formed and propagated vegetatively at a high rate following subculture. Segments of shoot primordia had developed into plantlets 2 weeks after transfer to solidified 1/2 MS medium supplemented with 0.44 μm BA and 1% sucrose. Plantlets successfully acclimated and grew into normal plants in a greenhouse. Cold-hardened, precultured small segments of shoot primordia were successfully cryopreserved in liquid N by vitrification. Vitrified and warmed segments plated on solidified 1/2 MS medium produced shoots about 21 d after plating. Cultured masses of shoot primordia appear promising for large-scale production and cryopreservation of annual and biennial statice. Chemical names used: 6-benzyladenine (BA); 1-naphthaleneacetic acid (NAA).
Abstract
Shoot tips isolated aseptically from dormant buds of apple (Malus domestica Borkh. cv. Fuji) survived immersion in liquid nitrogen following prefreezing below — 10°C without cryoprotectant. After thawing, they grew and multiplied shoots in vitro as did unprefrozen shoot tips. This study suggested the possibility of freeze preservation in liquid nitrogen of apple shoot tips.