Effects of exogenous paclobutrazol and sampling time on the efficiency of in vitro embryo rescue in the breeding of new seedless grape varieties oleh Teng-fei XU, Yu-rui GUO, Wen-yuan WANG, Xiao-jian YUAN, Yan-nan CHU, Xiao-wei WANG, Yu-lei HAN, Yue-jin WANG, Rui SONG, Yu-lin FANG, Lu-jun WANG, Yan XU