Analysis of the Factors Causing Differences in the Leaf-Senescence Pattern between Two Soybean Cultivars, Enrei and Tachinagaha: Comparison of root length and exudation rate among grafted plants

摘要

To clarify the factors causing the differences in the leaf-senescence pattern between the soybean cultivars, Tachinagaha (T, late senescing cv) and Enrei (E, early senescing cv) , we grafted the T scion onto a T or E rootstock (T/T, T/E) andE scion onto an E or T rootstock (E/E, E/T) and investigated the effects of the roots on the senescence of scion leaves. At the early stage of ripening, the T and E scions on the T rootstock had a higher chlorophyll content than either the E orT scion on the E rootstock. Thus, the properties of the rootstock influenced the senescence of the scion. By contrast, at the late stage of ripening, the chlorophyll content of the T scion was higher than that of the E scion irrespective of thecultivar of the rootstock. Root length per plant was longer in the T rootstock than in the E rootstock irrespective of thecultivar of the scion. Moreover, root length did not change during the ripening phase. The exudation rate per plant and per unit leaf area at the early stage of ripening was higher in the plants with a T rootstock than an E rootstock and the exudation rate per plant and per unit leaf area were low and the differences between graft combinations were small at the late stage of ripening. From these results, it was clear that the physiological activity of the root (exudation rate) was more closely related to the delay of leaf senescence than the root length at the beginning of the ripeningphase.