重炭酸塩がアジアナシ台木種の鉄欠乏クロロシスに及ぼす影響 Responses of Two Asian Pear Rootstocks (Pyrus spp.) to Fe-deficiency Chlorosis Induced by Addition of Bicarbonate to Nutrient Solution

本研究では,二種のナシ台木種(Pyrus xerophila Yu,Pyrus betulaefolia Bunge)を水耕栽培し,重炭酸塩が鉄欠乏によるクロロシスに与える影響を調査した. P.betulaefoliaは重炭酸塩添加処理後わずか20日で鉄欠乏からくるクロロシスを生じた.一方,P.xerophilaでは,障害がほとんど発生せず.葉のクロロフィル含量(SPAD値),茎の鉄含量ともにP. betulaefoliaに比べ高かった.これらの結果より,P. xerophilaは石灰質土壌下で誘導される鉄欠乏症に対して,P. betulaefoliaに比べ耐性を持つことが示唆された.また,両種とも根の先端部の鉄(III)還元力は重炭酸塩処理により増加し,P. xerophilaの還元力はP. betulaefoliaの約2倍であった.このように,根の先端部における鉄(III)還元力の測定は,鉄欠乏症耐性ナシ台木種を選抜するための指標として適当と認められた.

To evaluate the tolerance of two Asian pear rootstock species, Pyrus xerophila Yu and Pyrus betulaefolia Bunge, to lime-induced Fe chlorosis, seedlings were grown in a nutrient solution with or without bicarbonate. After 20 days in the bicarbonate solution, P. betulaefolia seedlings became chlorotic, a symptom of Fe-deficiency, whereas those of P. xerophila did not. Leaves of the P. xerophila had higher chlorophyll (SPAD value) while the stem amassed more Fe than did those of P. betulaefolia, which indicates that the former may be more tolerant to lime-induced Fe chlorosis than may be the latter. Furthermore, higher Fe^<3+>-chelate reductase activity in root tips was observed in two pear rootstocks grown in the bicarbonate solution; seedling of P. xerophila had twice the activity than had those of P. betulaefolia seedlings. Hence, we propos that Fe^<3+>-chelate reductase activity in roots tips may be a useful physiological index to select rootstock genotypes that are tolerant to Fe-deficiency chlorosis.