Funding for this research was provided by:
Natural Science Foundation of Hebei Province (C2019204270)
Science and Technology Research Project of the Universities of Hebei Province (QN2019159)
Research Foundations for Returned Scholars from Overseas of the Human Resources Dept. of Hebei Province (C20190345)
Received: 7 November 2019
Accepted: 24 March 2020
First Online: 15 April 2020
Ethics approval and consent to participate
: Walnut is one of widespread fruit trees in China, and it is not an endangered species. The walnut trees were from the Experimental Field of Hebei Agricultural University. No specific permits are required for sample collection on walnut.
: Not applicable.
: The authors declare that they have no competing interests.