Angliavandenių įtaka kultūrinių kriaušių mikroūglių užsigrūdinimui žemoje teigiamoje temperatūroje.

For pear cultivars growing in Lithuania like for many other orchard plants, low temperature and temperature luctuations during various periods of over wintering can cause heavy losses. Climatic conditions often constitute a serious hazard to genetic resources of many plant species maintaining in field collections. Therefore, in vitro techniques are being developed and used to store germplans of vegetatively propagated plants. Low temperature often is used for growth slowdown during long-term storage. Cold hardiness is genotype dependent and specific reaction to storage condition is characteristic to different genotypes. Therefore, knowledge about capabilities of plants to cold acclimate and withstand low temperature stress is needed for development of new cultivars and methods of long-term storage of germplams. The aim of this study is to evaluate accumulation of rafinose family carbohydrates and mannitol at low positive temperatures (during cold acclimation) in vitro, to assess effect of cold acclimation temperature, photoperiod regime, medium content of phytohormones and carbohydrates on pear cold hardiness in vitro. Cold hardiness was evaluated based on cold damage assessment and ion leakage after freezing treatment of micro-shoots. The study revealed that content of monosaccharide carbohydrates did not change during cold acclimation, however, content of rafinose family oligosaccharides increased considerably in acclimated pear micro-shoots. Differences in cold acclimation conditions had little effect on accumulation of galactinol and rafinose. Change of stachyose content in pear microshoots during cold acclimation varied and was dependent on pear genotype, cold acclimation conditions and composition of growth medium. Results of experiments on freezing of pear microshoots revealed that cold acclimation lowered cold injury of pear microshoots and increased their viability. Absolute value of critical temperature (KT50) of cold acclimated microshoots (ex- cept 'Senryo') was increased by 0.5--1.2 --C, as compared to control. This increase was most pronounced for micro-shoots of 'Oranževoje', and the lowest value was for clone No. 0408. Mannitol supplement in growth medium caused significant increase in cold hardiness in vitro of microshoot of the selected evaluated cultivars. [ABSTRACT FROM AUTHOR]