Winter-hardiness and frost-resistance of plum ñultivar-rootstock combinations
WINTER-HARDINESS AND FROST-RESISTANCE OF PLUM (PRUNUS DOMESTICA L.) ÑULTIVAR-ROOTSTOCK COMBINATIONS
V.A. KRYVOSHAPKA, O.I. KITAIEV, V.A. SOBOL, PhDs
Institute of Horticulture, NAAS of Ukraine, 03027, Kyiv-27, 23 Sadova st., e-mail: email@example.com
The authors presents the results of determining the nine plum cultivar-rootstock combinations winter- and frost-resistance means of combining the field and laboratory methods of researches.
The fruit crops frost resistance and winter-hardiness belong to the most important economic and biological characteristics which determine the range of their spread and production value. The insufficient winter-hardiness inhibits the spread of any cv, no matter how attractive it were as to the fruit quality.
In order to determine the winter-hardiness the samples were chosen in different periods of deep and forced dormancy. Further on the damage of the shoots tissues and generative buds at low temperatures in natural conditions was assessed by means of the microscopic analysis of anatomical section.
The potential frost-resistance was determined by freezing in the laboratory of the Plant Physiology and Microbiology of the Institute of Horticulture of the National Academy of Agrarian Sciences of Ukraine. One-year increments with buds were frozen in the CRO/400/40 refrigerator. That enables to cool the samples to a temperature of minus 40 °C. The freezing was carried out by means of reducing the temperature (5 °C per hour) gradually to -25, -30 and -35 °C. Upon reaching the predetermined freezing temperature, the samples were held at it for four hours for creating nucleation conditions and development of ice-formation. The degree of the tissues frost damage was evaluated according to their burrowing intensity on the certain transverse anatomical sections. The estimation was conducted on the basis of the microscopic analysis by six-point scale (0-5 points).
The observations under the natural conditions revealed the rather high winter-hardiness of all the cultivar-rootstock combinations. The variety Oda appeared the most resistant to the shoots tissues and generative buds damage, then Stanley and Bogatyrska was characterized by least resistance.
The shoot tissue damage was not critical under the laboratory conditions at freezing temperatures of minus 25 and minus 30 ºC, most of the cultivar-rootstock combinations. The generative buds damage under minus 25 also did not achieve the critical level, while under minus 30 ºC it was quite strong (2.6-3.1 points). Under this temperature, with proper care, the plants recover after the stress state, but the yield losses were considerable.
On the average, during the investigation years it were the buds of the studied cvs on the rootstock Evrika that appeared to be the most sensitive to freezing up to -25 and -30 °C.
Under freezing temperature of minus 35 ºÑ the substantial part of the cultivar-rootstock combinations, the summary damage point of the shoot tissues was above the critical level (30.0-35.5). The bud damage was significant (3.5-4.0 points).
On the whole, according to the comprehensive assessment of the plum cultivar-rootstock combinations in the natural and laboratory conditions, all the experiment variants were characterized by the high winter-hardiness and frost-resistance, namely the highest – Oda on the seed rootstock and on VVA-1 as well as Stanley and Bogatyrska on VVA-1.
Key words: plum, cultivar, rootstock, laboratory freezing, critical tissue damages, winter-hardiness and frost-resistance.