Estimation of frost and winter resistance of Calluna vulgaris (L.) Hull and its cultivares in conditions of Right-Bank of Forest Steppe of Ukraine

Objective – to investigate the frost resistance of Calluna vulgaris (L.) Hull and its cultivars by the method of direct laboratory freezing of annual shoots. Compare with field studies of winter hardiness of it in 2016–2017.

Material and methods. Objects of research are C. vulgaris and its 10 cultivars (Alicia, Mullion, Golden Carpet, Golden Wonder, Winter Red, Dirry, H.E. Beale, Red Star, Silver Knight, Bonita) from the collection of M.M. Gryshko National Botanical Garden of the NAS of Ukraine. The shoots were freezed in the laboratory of plant physiology of the Institute of horticulture of the NAAS of Ukraine in the refrigerating chamber "CRO/400/40". Field winter hardiness was assessed visually on 8point scale of S.Ya. Sokolov during 2016–2017.

Results. The potential frost resistance of C. vulgaris and its cultivars is determined using the laboratory method of direct freezing of shoots. The degree of damage to phloem (cortex), cambium, xylem (wood), cores in the apical, middle part of the shoot, in the section through the node, and bud tissues was determined using binocular microscope. It was revealed that common heather and its varieties are characterized by different degrees of frost resistance.

Conclusions. C. vulgaris and his cultivars are sufficiently frostresistant in conditions of Right-Bank of Forest Steppe of Ukraine. C. vulgaris plants are more resistant to low temperatures compared to cultivars. The most sensitive to the effect of frost are the bud and apical part of the shoot (up to 80.0 and 72.6 %, respectively). The least sensitive is the middle part of the shoot in the section through the internode. Plants of the cultivars H.E. Beale, Golden Wonder, Golden Carpet suffer the most from the effect of low temperatures. C. vulgaris, ‘Dirry’, ‘Winter Red’, ‘Alicia’ had less damage. More than 50 % of tissues of annual shoots are damaged at temperature –30 °C set in the laboratory conditions. According to a visual assessment of winter hardiness, the cultivars Silver Knight, Golden Wonder, Red Star, H.E. Beale suffer the most from winter conditions.