Evaluation of frost resistance of rambler roses based on electrolytes leakage

Frost damage of shoots and buds of rambler roses have a negative effect on their growth and flowering. The aim of experiment was to verify the level of resistance to a low temperature during mild winter conditions using the electrolyte leakage method (electrical conductivity test EC) of the shoots fragments with the buds for eight rambler roses varieties of different origin: ‘American Pillar’, ‘Baltimore Belle’, ‘Excelsa’, ‘Lykkefund’, ‘Maria Lisa’, ‘Polstjårnan’, ‘Rose Mary Viaud’, ‘Wartburg’. The shoots were collected in three dates: 16.01., 12.02., and 17.02., 2019 year. After collecting materials were placed at the temperature of -3.5, -15, -20 and -40°C. The results of conductivity test were related to the damage observed on the cross-section of shoot and buds under a stereoscopic microscope. The shoots kept at -15 and -20°C showed different damages of shoot and bud tissues observed under a stereoscopic microscope depending on the cultivar. The shoots kept at -40°C showed complete frost damage of tissues. Moreover, the results prove about dehardening of shoots with approaching the spring. The most frost hardy cultivars were ‘Lykkefund’ and ‘Polstjårnan’, and the most susceptible – ‘Baltimore Belle’, ‘Excelsa’, ‘Wartburg’.