MICROPROPAGATION OF PYRUS AND CYDONIA AND THEIR RESPONSES TO FE-LIMITING CONDITIONS

Appropriate micropropagation regimes were determined for four Pyrus species (P. amygdaliformis Vill., P. betulaefolia Bunge, P. calleryana Dene., and P. communis L.) and Cydonia oblonga L. Shoot multiplication was optimal at 10 or 20 μM N6-benzyladenine and high light intensity (135 μE m-2 s-1). Root formation of the Pyrus species was stimulated by exposure of shoots to high levels (10 or 32 μM) of β-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 of C. 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 in Cydonia, absent from P. amygdaliformis and P. communis, and intermediate in P. betulaefolia and P. 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. © 1990 Kluwer Academic Publishers.