Breeding of avoiding late frost walnut variety of early- fruiting ‘Yunlin 7’

Abstract: Northeast Yunnan have severe late-frost and lack of the walnut varieties which have ability to avoid the late-frost damage.‘Yunlin 7', a new early-bearing walnut variety with excellent characteristics, was selected from seedings in Ludian county by Yunnan Academy of Forestry and Ludian county forestry bureau in 2016. It was initially selected out in resources investigation in 2009 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 1 200 square meters was built in Sanba state farms in Ludian Forestry Bureau of Ludian county, Yunnan province in 2010. Through five years' investigation and comparison about graft compatibility, nut quality, bearing habit and yield, it was identified as superior line in 2016. Regional adaptability testing of this superior line was carried out at three sites (Kunming, Dali and Lijiang, Yunan) over one years in 2012, using Juglans sigillata as control 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. It was name as‘Yunlin 7'in 2012 and audited through the Committee for Forestry Varieties in Yunnan province in 2016. The bud of the tree is round with a tip on the top. Leaflet is broadly lanceolate and the number of it is five to eleven. Male flowers bloom earlier than female ones. The nut has an elliptical shape, slightly tip on the top, flat and tight suture line, with average of vertical, transverse and lateral diameters of 3.40 cm. The average fruit weight is14.66 g, shell thickness is 1.03 mm. The oil content is 69.4%. The protein content is 18.9%. The kernel rate is 58.05%. The kernel is light yellow and plump with strong aroma. In Ludian county, Yunnan province, the tree germinates in late March. Male flowers bloom from the end of April, and female flowers bloom in 4 to 5 days later than male flowers. So, the variety of‘Yunlin 7'is protandrous. Fruit rapid growth period is from June to August. Nut ripens in early September. The fruit bud rate is 93.3%. The floral bud rate is 88.7%. The top of fruit bud rate is 34.2%. The lateral bud rate is 65.8%. The fruit setting rate is 84.6%. Juglans sigillata walnut suffered serious frozen injury in the winter of 2007. So the trees of‘Yunlin 7'have higher resistance to frost. The northeastern region in Yunnan, Guizhou, Sichuan, Hubei and Chongqing are the suitable cultivation area for the variety of‘Yunlin 7'.