INTENSIFICATION OF FRUIT PLANT BREEDING BY ARTIFICIAL STRESSES

Breeding for winter hardiness can be accelerated by modeling major injury factors of the region under controlled conditions.

The results of cooperation of physiologists and breeders at the Horticultural Middle Zone Institute (Moscow, USSR) in the solution of this problem had been already reported at the previous Symposium (Gogoleva at al., 1978).

The present paper contains the main data, obtained in the period from 1976 to 1984.

The programme of tests was arranged on the basis of long field observations of plant injuries under natural conditions (Fig. 1). It has been found that plants can be injured in the Middle Zone early frosts, hard winter frosts, frosts following thaws or sun heating of trunks and branches, and also by steadily increasing frosts following thaws (Gogoleva at al., 1978, Smagina at al., 1981, Tyurina at al., 1978). These 4 factors used for laboratory tests with apple, sour cherry, bird-cherries and cerapadus are shown on Fig.1.

The breeding for frost resistance includes such important item as search for the donors of the main frost resistance components or better complex donors used for cross-breeding with valuable commercial cultivars. Inspection of plantings and wild forms following severe winters help much in searching for the donors. A lot of data was supplied by the winter of 1978–79. In some regions frosts were as low as -40°, -50°C (Alexeev, 1983). Wood injuries of many apple varieties were first observed in the areas where frosts were down to -35°C. At the temperature of -40°C practically all large-fruit varieties had wood frost injuries, and at -42°, -45°C many trees were killed. Inspection of more than 700' varieties and several thousand of forms allowed us to single out only several varieties of Malus domestica, which are more frost resistant

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