THE RESULTS AND METHODS OF BREEDING NEW CULTIVARS OF PLUMS FOR THE CENTRAL PROVINCES OF THE NON-CHERNOZEM ZONE IN U.S.S.R.
The following data can give an idea of winter temperature in this zone. The average monthly temperature for January in Moscow province for the last 60 years was -10.5°C and the absolute minimum temperature was -53°C. The average monthly temperature for January and the absolute minimum temperature were -12°C and -42.4°C accordingly.
The alteration of thaws and abrupt falls of temperature as low as -22, -25°C act very injuriously on the fruit buds in winter. The vegetational period here is short, a lack of warmth and precipitation (an average of 560 mm a year) is observed.
The northern boundary of the feasible culture of the common plum runs along the line Leningrad-Gorky. There are individual microregions rather favourable for cultivating the common plum (Prunus domestica) south from this line. Damson (Prunus insititia) and large-fruited blackthorn (spontaneous hybrids P.spinosa L. x P.domestica L.) occur in a small number.
The plum-tree is cultivated both on its own roots and as grafted plants. The advantage of plants with their own roots over grafted ones resides in the fact that they display the ability to recover rapidly after heavy winter injury.