Articles
RESOURCES OF GENETIC IMPROVEMENT OF WALNUTS
On the basis of the study, rich genetic diversity by nut shape, shell firmness, by structure of inner endocarp’s layer, fruiting type and other characters has been revealed.
Under natural conditions, trees of J. regia f. plicata, f.lacunosa and f. macrolacunosa prevail.
Trees with well extracted seeds of J. regia f. typica are 1.3% only; those of f. lignosa (seeds are extracted in two undamaged halves) are 11.7%.
In the Nikita Botanical Garden’s Collection on rootstock J. regia more than 200 native clones involved from various areas of our country have been studied.
Promising clones have been selected by the following features:
- date of vegetation beginning;
- date of blooming start of staminate and pistillate flowers;
- date of fruit maturation;
- homogamous flowering type;
- fruit bearing in lateral buds;
- early start of fruit-bearing;
- optimal nut mass;
- seed protein content;
- cold resistance;
- higher resistance to anthracnose.
Long-year studies of walnut trees under natural conditions, varieties in collection plantations and of seed population in forest and other stands of similar kind have shown that USSR now possesses very rich natural resources which must be used more expediently in studies on genetic improvement of walnuts.
In addition to hybridization, effects of ionizing irradiation on the seeds were used which allowed to create forms which start fruit bearing on the second year.
Three-year seedlings yield 1.5 to 2.1 kg nuts per tree.