Physiological and biochemical basis of hazelnut rhizogenesis promoted by embedded stock etiolation

Abstract: 【Objective】Physiological and biochemical basis of hazelnut rhizogenesis promoted by stock embed etiolation was investigated. This study provides theoretical foundation and technical support for the cutting propagation in hazelnut and other woody plants.【Methods】One-year-old hardwood branches of hybrid hazelnut cultivar‘Da Wei'were collected from the hazelnut orchard of Institute of Forestry and Pomology of Beijing Academy of Agriculture and Forestry Science, which is situated on North Latitude 39°97' and EAST Longitude 116°23', in November 2015. Then the one-year-old hardwood branches of hybrid hazelnut were stored in sand at low temperature. In mid-March 2016, the one-year-old hardwood branches of hybrid hazelnut were horizontal embedded in moistened sand in greenhouse at 25 ℃ and(80±5)% RH(relative humidity). The greenhouse was equipped with automatic watering and mist systems as well as shading devices. After 30-40 days, basal region etiolated softwood cuttings were obtained. Nonetiolated softwood cuttings were obtained from normal growth shoots outdoor. The etiolated and non-etio-lated softwood cuttings, 0.5 cm in diameter, 8-10 cm in length, were used for root induction. Leaves from the basal part were excised and 2-3 leaves in upper part were reserved. The etiolated and non-etiolated softwood cuttings were treated with 0 and 2 000 mg·L-1IBA for 2-3 s. And then the cuttings were inserted to a depth of 2 cm into a mixture of peat, perlite and sand(1:1:1). During rooting, cuttings were sprayed everyweek with 0.05%(m/V) bavistin. The contents of soluble sugars, soluble proteins, flavonoid, phenolic acids, indole-3-acetic acid(IAA) and abscisic acid(ABA) in the etiolated and non-etiolated softwood cuttings were determined. The contents of IAA and ABA were also determined during the induced initial stage of rooting of softwood cuttings.【Results】The rooting rate in the etiolated softwood cuttings was significantly higher than that in the non-etiolated softwood cuttings. The best condition for rooting of softwood cuttings in hazelnut was etiolation combined with the application of exogenous IBA. Enhanced rooting in etiolated softwood cuttings was concomitant with increase in the contents of soluble sugars, soluble proteins and phenolic acids and with decrease in contents of flavonoid and ABA. The soluble sugars level increased significantly to 77.62 mg·g^-1 from 48.57 mg·g^-1. The soluble proteins level increased significantly to 25.39 mg·g^-1 from 15.47 mg·g^-1. The phenolic acids level increased significantly to 3.51 mg·g^-1 from1.64 mg·g^-1. While the flavonoid level decreased obviously to 0.87 mg·g^-1 from 1.83 mg·g-1and ABA level decreased obviously to 50.14 ng·g^-1 from 72.30 ng·g-1. The IAA level increased slightly, but there was no significant difference. After 7 d of root induction, IAA level in etiolated softwood cuttings increased significantly to 135.53 ng·g^-1 from 83.09 ng·g^-1. ABA level in etiolated softwood cuttings increased slightly,but the difference was not statistically significant. IAA/ABA value in etiolated softwood cuttings increased significantly to 2.31 from 1.66. After 7 d of root induction, the IAA level in non-etiolated softwood cuttings increased to 80.48 ng·g-1from 78.54 ng·g-1. The ABA level in non-etiolated softwood cuttings increased to 83.41 ng·g^-1 from 72.30 ng·g^-1. IAA/ABA value IAA/ABA value decreased to 0.96 from 1.09.The changes of IAA level, ABA level and IAA/ABA value in non-etiolated softwood cuttings after 7 d of root induction were not significant. After treatment with 2 000 mg·L^-1, IAA level in etiolated softwood cuttings increased significantly to 229.33 ng·g^-1 from 83.09 ng·g^-1 after 7 d of root induction. ABA level in etiolated softwood cuttings increased to 60.35 ng·g^-1 from 50.14 ng·g- 1after 7 d of root induction, but there was no significant difference. IAA/ABA value in etiolated softwood cuttings increased significantly to 3.80 from 1.66 after 7 d of root induction. After treatment with 2 000 mg·L^-1, IAA level in non-etiolated softwood cuttings increased significantly to 137.41 ng·g^-1 from 78.54 ng·g^-1 after 7 d of root induction.ABA level in non-etiolated softwood cuttings increased to 76.52 ng·g^-1 from 72.30 ng·g^-1 after 7 d of root induction, but there was no significant difference. IAA/ABA value in non-etiolated softwood cuttings increased significantly to 1.8 from 1.09 after 7 d of root induction.【Conclusion】Embedded stock etiolation can enhance the rooting rate of softwood cuttings in hazelnut. Etiolation combined with the application of exogenous IBA is the best condition for rooting effect of softwood cuttings in hazelnut. Etiolation can improve the contents of soluble sugars, soluble proteins and phenolic acids and decrease the contents of flavonoid and ABA. Etiolation promotes the transportation of IAA and the accumulation of IAA in the basal region of softwood cuttings in hazelnut. And etiolation also accelerates the absorption and transformation of exogenous IBA. IAA/ABA value is a mark to judge the rooting capability of softwood cuttings in hazelnut. The larger the value is, the higher the rooting rate of softwood cuttings in hazelnut.