Breeding of a new Shimen walnut cultivar ——‘Zaoshuo'

Abstract: ‘Zaoshuo',a new early-bearing walnut variety with excellent characteristics,was selected from natural crossing seedlings of‘Xinjiang'walnut introduced to Lulong county in 1960 s and Shimen walnut,a local variety in Lulong county,and approved in 2014. It was initially selected out in resources investigation in 2002 for its large fruit size,excellent quality,high yield,no obvious stem diseases and good continuously fruiting ability. By the method of top grafting,variety comparative testing orchard of 3 335 square meters was built in Chongyukou village of Lulong county,Hebei province in 2003. Through four years' investigation and comparison about graft compatibility,nut quality,bearing habit and yield,it was identified as superior line in 2007. Regional adaptability testing of this superior line was carried out at five sites(Qipanshan Fruit Farm in Lulong county;Chongyukou village,Yanheying town,Lulong county;North Seedling Breeding Farm;Hebei Academy of Forestry Science;Xilingdi village Yuanshi county Shijiazhuang city) over three years from 2007 to 2009,using‘Liaoning No.1'and‘Kuixiang'as check varieties. Results showed that this superior line had stable characters and outstanding economic value,which meet the breeding objective of big nut,suitable shell thickness,easily taken kernel,strong stress resistance,strong aroma and high quality of‘Shimen'walnut. It was name as‘Zaoshuo'in 2012 and audited through the Committee for Forestry Varieties in Hebei province in 2014. The tree has moderate vigor,open gesture,high germinating rate,high branching ability and early bearing characters. One year old branches were red brown with little sparse lenticels. The bud is round with a tip on the top. Leaflet is elliptical and the number of it is seven to nine,mostly nine. The quantity of male flowers is less. The color of stigma is yellow. Female flowers bloom earlier than male ones. The nut has a round shape,smooth shell,slightly tip on the top,flat and tight suture line,with vertical,transverse and lateral diameters of 4.33 cm,4.42 cm and4.11 cm respectively. The average fruit weight is 16.65 g,shell thickness is 1.25 mm. Degraded packing tissue and membranous diaphragm makes it easy to get the whole kernel. The kernel rate is 56.5%. The contents of fat and protein are 66.8% and18.4%,respectively. The kernel is light yellow and plump with strong aroma. In Lulong county,Hebei province,the tree germinates in early April. Male flowers bloom from the end of April to early May,and male flowers bloom in late April. So,the variety of‘Zaoshuo'is protogynous. Fruit rapid growth period is from late May to late June. The core-hardening stage of nut is from late June to late July. Nut ripens in late August or beginning of September. The fruit growing period is about 120 days.The germination rate is 43.4%. Branching ability is 3.2%. About 80% top grafting trees have fruits in second year. The average fruit branch rate of mature tree is 64.3%. Fruiting rate of lateral bud is 82.2%. Average number of fruit setting per inflorescence is 1.6. The trees of of‘Zaoshuo'has higher resistance to disease and cold. In the experimental orchard without protective measures,diseased fruit rate,diseased leaf rate and diseased plant rate of stem diseases of‘Zaoshuo'were 2.3%,8.6%and 3.0%,respectively;compared with‘Liaoning No.1'4.2%,11.2% and 4.5%,respectively。‘Shimen'walnut suffered serious frozen injury in the winter of 2009. Investigation indicated that the rate of frozen injured trees of‘Zaoshuo'is 61.84%,compared with‘Liaoning No.1'and‘Zhonglin No.1'79.17%,100% respectively. So the trees of‘Zaoshuo'has higher resistance to frozen. Taihang mountain area in Hebei province,hilly region and piedmont plain of Yanshan mountain are the suitable cultivation area for the variety of‘Zaoshuo'. Grafted seedlings begin fruiting in the second year after planted,and enter full fruit period in the fifth year. In the sixth year,yield per plant may reach 6 kg or more. Yield of the variety‘Zaoshuo'in early stage is high.