Common hazel (Corylus avellana L.) is a species that is widely distributed in various regions of the Russian Federation. It is a particularly valuable shrub due to its qualities. Its nuts, which have valuable food qualities, are of the greatest interest. To create a high-quality variety pool of the species, it is very important to study the polymorphism of its fruits and the occurrence of individual forms with selectable traits in various growing conditions. This is especially important in the mountain forests of the Northwest Caucasus, where the plant has significant polymorphism, which is least studied at the upper vegetation limit in the formations of the Oriental beech (Fagus orientalis Lipsky) and the Caucasian fir (Abies nordmanniana (Steven) Spach.). The goal of the research is to study the polymorphism of common hazel nuts and to predict the occurrence of species’ forms in these conditions. In the formations 467 fruits have been studied for 11 selection-significant indicators using a technique that takes into account the selection distribution of indicators and the iteration of averages, and the features of the statistical distribution of quantitative traits. To identify the relationship between the presence of fruit diversity and forms, long-term data on 1955 fruits and 258 forms selected as promising for further selection in the studied area have been used. It has been found that in the formations of the Oriental beech, the distribution of the indices of colour, shape, nut height, flavour and kernel yield, nut and kernel weight in common hazel significantly differs from the conditions that develop in the formations of the Caucasian fir. The distribution of hazel nuts does not have a statistically significant difference according to the strength of the shell, indestructibility of the kernel and the presence of husk on it, the total score of the selection value. In these formations, a very frequent occurrence of plants with a whole kernel of a very good taste, the selection category of ordinary, often with a light, easily split shell and a kernel without husk is predicted. An increase in the database on nut polymorphism does not exclude the transition of indices to neighbouring gradations when predicting the occurrence of forms.
Sukhorukikh et al. (Wed,) studied this question.