Genetic dissection of crown root traits and their relationships with aboveground agronomic traits in maize oleh Xiao-qian SHA, Hong-hui GUAN, Yu-qian ZHOU, Er-hu SU, Jian GUO, Yong-xiang LI, Deng-feng ZHANG, Xu-yang LIU, Guan-hua HE, Yu LI, Tian-yu WANG, Hua-wen ZOU, Chun-hui LI