Micropropagation ofPyrus andCydonia and their responses to Fe-limiting conditions

Abstract

Appropriate micropropagation regimes were determined for fourPyrus species (P. amygdaliformis Vill.,P. betulaefolia Bunge,P. calleryana Dene., andP. communis L.) andCydonia oblonga L. Shoot multiplication was optimal at 10 or 20μM N6-benzyladenine and high light intensity (135μE m−2 s-1). Root formation of thePyrus species was stimulated by exposure of shoots to high levels (10 or 32μM) ofβ-indolebutyric acid (IBA) for 7 days or a dip in 10 mM IBA for 15 s, followed by a passage on auxin-free medium.α-Naphthaleneacetic acid was more effective than IBA in stimulating rooting ofC. oblonga. The effects of Fe-limiting conditions in vitro were determined by comparing the responses of shoots and rooted plantlets to medium containing FeEDTA or FeSO4, with or without bicarbonate. Symptoms of Fe deficiency were genotype-dependent and most severe in the presence of FeSO4 and bicarbonate. Chlorosis was pronounced inCydonia, absent fromP. amygdaliformis andP. communis, and intermediate inP. betulaefolia andP. calleryana, indicating a good correlation between in vitro and field responses. Similar responses were obtained with rooted and unrooted shoots. These findings suggest that in vitro cultures may be used for studies of Fe-chlorosis as well as screening for tolerant rootstocks.