The article considers the possibility of walnut cultivation in the Moscow region - in conditions far from its ecological optimum. The studies were carried out in 2013-2021 on the experimental site of the department of flora of the Main Botanical Garden of RAS, where in 1977 Alexei Konstantinovich Skvortsov established a collection of walnuts. The material for planting was the seed progeny of varieties and forms from various cities, including Moscow. The purpose of this work was the selection of promising forms for the creation of varieties adapted to the conditions of central Russia. The criteria for selecting the best genotypes were: winter hardiness, frost resistance, precocity, earlier entry into fruiting, autogamous type of flowering, lateral type of fruiting, fruits in the clusters, restraint in growth and high commercial qualities of fruits. As a result of the phenological observations, it was revealed that acclimatized walnut plants go through a full cycle of seasonal development, start the growing season late (April 29 − May 6) and end it early (October 1−11). The shoots are completely woody before the onset of cold weather, so the plants are quite winter-hardy in ordinary mild winters. The critical temperature in Moscow was -29.9 °C in January 2017. Low temperatures caused the death of reproductive buds, annual and perennial wood in almost all trees, and the most weakened specimens fell out completely. To date, the walnut gene pool is represented by 87 specimens aged from 37 to 44 years, of which 47 are single-stemmed and multi-stemmed trees and 40 are bushes. Samples were noted that, after the winter of 2017, normally bloomed and formed single fruits, despite the fact that the summer of 2017 was the coldest in the 21st century. As a result of studying the created genetic collection, 12 promising forms were identified. They are characterized by the presence of several breeding-valuable traits and regularly bear fruit. Further vegetative reproduction and varietal testing of the selected material is planned, which will allow solving a number of breeding and production problems to create a local range of walnuts.

Walnut is one of the most economically significant nut crops. Evaluation of the genetic structure of the domestic walnut gene plasma using modern molecular genetic approaches is a relevant research task. The walnut samples collected by Tsitsin Main Moscow Botanical Garden of Academy of Sciences (MBG RAS) are of particular importance for breeding practice aimed at increasing winter freezing tolerance of plants. The seed material for this collection was introduced from different regions of the former Soviet Union, including Tajikistan, Kyrgyzstan, Ukraine, Belarus, as well as regions of Russia. The MBG RAS collection presents interest as a breeding material for mobilizing the genetic resources and replenishing the gene pool of the South of Russia with new, economically valuable walnut varieties. This work aims to analyze the genetic diversity of a J. regia genotype sample, which includes the most valuable forms from the MBG RAS collection, in order to establish their genetic relationships with samples representing the walnut gene pool of the South of Russia. The genetic analysis of the studied walnut species and varieties was carried out using eight SSR markers: WGA001, WGA376, WGA069, WGA276, WGA009, WGA202, WGA089, and WGA054. The polymorphism of microsatellite DNA markers established during genotyping indicated a high heterogeneity between the MBG RAS walnut sample and genetic resources in other regions. An analysis of genetic relationships using UPGMA and PCoA clustering methods revealed the genetic isolation of most samples in the MBG RAS collection from walnut varieties in the South of Russia. The most genetically distant samples in the MBG RAS collection were found to be 199, 196, 236, 256, 106, and 134. Therefore, these samples should be introduced in the gene pool of North-Caucasus Federal Scientific Center of Horticulture, Viticulture, and Wine-making and Nikitsky Botanical Garden with the purpose of increasing the heterogeneity of their gene pools.