Enhancing root regeneration and nutrient absorption in double-rootcutting grafted seedlings by regulating light intensity and photoperiod

Abstract

Double-root-cutting (DRC) grafting is a recently developed grafting method that makes it possible to produce grafted seedlings without using plug trays through cutting off the roots of both scion and rootstock during grafting. To date, little information is available about how to enhance the survival and quality of DRC grafted seedlings. Since light not only drives photosynthesis but also induces shoot-root communication via multiple mechanisms including direct light transmission, hormones and mobile proteins, we hypothesized that light could stimulate the delivery of the signal associated with nutrient requirement from shoot to root and further trigger root regeneration of cut rootstock in DRC grafted seedlings. To test this hypothesis, in this study, we investigated the effects of light intensities (0, 100, 150, 200 and 250 μmol m−2 s-1) and photoperiods (0, 6, 12, 18 and 24 h light) on the survival rate, graft union formation, rootstock root regeneration, nutrient absorption and scion growth in DRC grafted cucumber seedlings. Overall, under light conditions with a 200 μmol m-2 s-1 and a 12 h photoperiod, DRC grafted seedlings achieved the highest values in both survival rate and seedling quality index. The healing process of graft unions was efficiently promoted under light intensities ranging from 100 to 250 μmol m-2 s-1 and under photoperiods ranging from 12 to 18 h. The specific absorption rates of most nutrients (e.g. N, P, K, Ca, Mg, S, Zn and Mo) for the scion-rootstock connection region and the average growth rate of root length were enhanced under lighting conditions compared to dark conditions. These results provide acceptance for the hypothesis and infer that a 12-h photoperiod with a light intensity of 200 μmol m-1 s-1 could be applied to produce high-quality DRC grafted seedlings through enhancing graft union formation, rootstock root regeneration and nutrient absorption.