Three Types of Grafting Techniques Available for Research of Root-Shoot Communication in Cotton (<I>Gossypium hirsutum</I>) Seedlings under Low-Potassium Condition

Abstract

Grafting have been widely used to limit the effects of soil and vascular diseases, to increase yield and fruit quality, to induce resistance against low and high temperatures, to enhance nutrient uptake and to study the shoot-root relationship. Up to now, the main objectives of cotton grafts are to propagate somatic regenerated plants, transgenic plants and rare germplasm materials etc., and almost not come down to the research on long-distance signaling in plant. Recently, premature senescence caused by low potassium (K) has become one of the constraints for high yield and fine quality in cotton production. Before using grafting as a tool to investigate the shoot-root communication during this course, applicable grafting methods should be developed firstly. Therefore, we established normal (one scion and one rootstock), Y-type (two scions and one rootstock) and A-type (one scion and two rootstocks) grafting techniques with cotton seedlings (before one-leaf stage) grown in hydroponic condition. The effects of K + concentration in culture solutions, difference of scion age and rootstock age, different grafting sites and remaining cotyledons of rootstock or not on the survival rate of grafted cotton seedlings were examined. Considering either high survival rate or fast inducement of leaf senescence by low-K after grafting, the following methods were applicable for normal and Y-type grafting: the rootstocks emerged (3 days after germination) in sands without K, were transferred to one-half strength modified Hoagland solution containing 0.1 mmol L −1 K + (moderate K deficiency) and cultured for 5 days to just appearance of the 1st true leaf; the scions were grown only in sands for 5 days after sowing with fully expanded cotyledons and grafted in cotyledon node of rootstocks with their two cotyledons remained. For A-type grafting, the applicable procedure was as followings: the scions and rootstocks were all cultured with the same procedure for normal and Y-type graftings, the scion was grafted in the part of 2-3 cm below cotyledon node of rootstock. The mean survival rates of normal, Y-type and A-type graftings were more than 95%, 85%, and 90%, respectively. These three types of cotton grafting method were not only available for the research of root-shoot communication, but also 364 作 物 学 报 第 35 卷 for the research of shoot-shoot and root-root signals exchange.