Selected crucial morpho-physiological indices of family may predict the rootstock quality in Magnolia ×soulangeana

The distinct rootstock genotypes have different effects on grafting, and it is of great significance to evaluate rootstock quality in advance. Magnolia ×soulangeana, a robust hybrid of Magnoliaceae extensively cultivated in China, is an ideal rootstock for magnolia grafting. However, its complex genetic background leads to the instability of graft survival. In this study, a total of 17 morphological and physiological indices were measured, and significant differences were also detected among nine M. ×soulangeana candidate rootstock families. Based on principal component analysis, neither the individual morphological indices nor physiological indices could sufficiently judge the quality of rootstocks. Through the comprehensive evaluation, we identified that nine indices associated with seedling biomass, root morphology, net photosynthetic rate, antioxidase activity, and organic content could be the crucial indices in family assessment. Consequently, the result showed that the EQ6 was the superior family, and the EQ5 was the inferior one. When using EQ6 and EQ5 as rootstocks, the result of the micrografting verification test showed EQ6 had a graft survival rate 15.55% higher than EQ5. In short, family variation of morphological and physiological traits relates to rootstock quality, implying that it is necessary to use crucial morpho-physiological indices for screening the high-quality rootstock in M. ×soulangeana. These findings will provide technical support for magnolia grafting production practice.