Breeding report of a new black walnut variety BH06

BH06 is a new variety of black walnut selected from the Xinjiang black walnut seedlings by natural hybridization among the eastern black walnuts from Nebraska, USA, which were originally introduced from Henan Province. In 1993, Xinjiang Academy of Forestry Sciences introduced eastern black walnut seeds from the U.S. for the first time, carried out seedling and planting, and completed the introductory acclimatization cycle by flowering and fruiting in the fourth year. In 2001, we introduced six one-year-old grafted seedlings of eastern black walnut cultivars on Persian walnut rootstocks from the National Black Walnut Breeding Demonstration Base in Henan Province, and planted them respectively in the southern Xinjiang Forestry Academy of Sciences (XFAS) Jia Mu Experimental Station and the northern Xinjiang Forestry Academy of Sciences Manas Experimental Station, showing good demonstration effects. In 2016, this species passed the variety certification by Xinjiang Forest Tree Variety Certification Committee and was named“Xinjiang Black Walnut”. On the basis of this variety certification, BH06 black walnut was selected and bred as an excellent protective timber forest type. This variety has a straight central leader, vigorous growth, obvious apical dominance and small branching angle. The annual branches are brownish green, the biennial branches are light brown, and the triennial branches are brown. Leaves are odd pinnately compound, with leaflets 15-21, part of the terminal leaf degeneration, leaf margin serrulate, leaf ovate-lanceolate, and leaf color dark green. The fruit is fusiform, rough on the fruit surface, with obvious ribbed larger protrusions, larger, uniform and neat. The average single fruit mass is about 16.43 g, the transverse diameter is 36.12 mm, the longitudinal diameter is 32.71 mm, the lateral diameter is 28.05 mm, the shell thickness is 2.58 mm, and the kernel weight is 4.72 g. The average growth of 6-year-old tree height and diameter at breast height of the offspring of BH06 black walnut sibling families are 4.87 m and 8.31 cm, respectively, which are significantly better than those of common black walnut offspring seedlings. The fruit is medium, flat and round, with hidden buds at the base of the second- year branches. Kernel yield is 28.76 percent, with excellent quality. Fruit ripens in late September in Aksu area of Xinjiang; fruiting mainly takes place on medium fruiting branches (5- 15 cm), and there is strong axillary bud fruiting ability (1 fruiting sequence bearing 1 fruit mainly), with monoecious and dioecious traits. Resistance to drought, salinity, wind and sand, and cold is high. The protection forest in agricultural area and urban garden green space in the north slope of Tianshan Mountain, Yili River Valley and Tarim Basin plain oasis can be popularized and applied. For planting on flat or gentle sloping land, soil conditions with a deep layer of soil (≥150 cm), good drainage, water table ≥1.5 m and pH ≤8.5 should be selected. pH ≤8.5 is preferred for planting under soil conditions. Planting spacing of 1.5×2.0 m or 1.0 m×1.5 m is suitable. Ordinary black walnuts can be used as rootstocks, the excellent scions from BH06 black walnut are collected, grafting or budding in spring or summer can cultivate asexual grafted seedlings, and grafting survival rate can reach up to 90% or more. In the first three years of planting, cut off the competing branches in time; after the fourth year of planting, cut off the competing branches on the main leader and the lower one-third of the lateral branches on it.