CONTROLLED FREEZING AS A LOW-TEMPERATURE TOLERANCE TEST FOR APPLE ROOTSTOCKS

Abstract

In the years 2009-2010, frost resistance of artificially frozen plants of nine Polish apple rootstocks (P 2, P 14, P 16, P 22, P 59, P 60, P 66, P 67 and P 68) bred at the Research Institute of Pomology and Floriculture (recently renamed Research Institute of Horticulture), and of M.7, M.9, M.26, M.106 rootstocks and Antonovka seedlings was tested. Controlled freezing was performed in a freezing chamber manufactured by Binder GmbH, Germany. Prior to exposing the rootstocks to freezing temperatures, they had been kept in sealed plastic bags in a cold store (0°C). During freezing, 10 rootstocks of each genotype were inside the same plastic bag to protect them from drying. Freezing was performed on 3-5 March 2009 and on 15-17 February 2010. On each freezing date, the plants were subjected to the temperatures of -8°C, -10°C and -12°C for 3 hours. During freezing, the temperature was lowered at a rate of 2°C per hour, and after freezing it was raised at the same rate until it reached 0°C. Rootstocks of the listed clones treated in the same way but not frozen served as the control. After freezing, the plastic bags with rootstocks were again placed in a cold store and subsequently planted in a field at the beginning of April. After planting, the rootstocks were cut back to a height of 5 cm above the soil level and their regeneration was evaluated during the growing season. The best regeneration (average for two years of evaluation) showed rootstocks P 60, P 67 and P 68; rootstocks P 59, P 66 as well as M.7, M.9, Antonovka seedlings and M.106 also regenerated well.