Graduate Thesis Or Dissertation
 

Somatic manipulation of Pyrus and Cydonia : characterization and selection for iron efficiency

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  • Appropriate micropropagation regimes were developed for four Pyrus species (P. amygdaliformis Vill., P. betulaefolia Bunge, P. calleryana Dcne., and P. communis L.) and Cydonia oblonga L. Shoot multiplication was optimal at 10 or 20μM N⁶⁻ benzyladenine (BA) and high light intensity (135μm⁻²s⁻1). Root formation of the Pyrus species was stimulated by exposure of shoots to high levels (10 or 32μM) of β- indolebutyric acid (IBA) for 7 days or a dip in 10mM IBA for 15s, followed by a passage on auxin-free medium. a-Naphthaleneacetic acid (NAA) was more effective than IBA in stimulating rooting of C. oblonga. Adventitious shoots of Cydonia oblonga Quince A were induced from leaves cultured on MS-N6 medium containing thidiazuron (TDZ) and NAA. Optimal regeneration (78% of the cultured leaves with 3.2 shoots per leaf) occurred with 32μM TDZ plus 0.3μM NAA on young leaves obtained from micropropagated shoots. Adventitious shoots of Pyrus amygdaliformis and P. communis were obtained, but at much lower frequency. Effects of Fe-limiting conditions in vitro were determined by comparing the responses of shoots and rooted plantlets to media 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 in P. amygdaliformis and P. communis, and intermediate in P. betulaefolia and P. calleryana, indicating parallel responses between in vitro and field conditions. Similar responses were obtained with rooted and unrooted shoots. Tolerance to Fe-deficiency chlorosis was correlated with maintenance, under Fe-stress, of a high Fe²⁺/total Fe ratio, high Fe³⁺ reducing activity, and medium acidification. This adaptive response was diminished by bicarbonate. Roots of plantlets, shoot bases, root cultures and cell suspension cultures all manifested Fe-stress inducible Fe³⁺ reducing activity. The adventitious shoot regeneration protocol was successfully used to select somaclonal variants of C. oblonga with increased tolerance to Fe-deficiency chlorosis. Two variants, IE1 and IE2, were recovered which displayed higher Fe³⁺ reducing ability and acidification of the medium than the original C. oblonga clone. These variants may be useful as pear rootstocks in regions with calcareous soils.
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file details DOLCETSANJUANRAMOND1991.pdf 2017-08-08 Pubblico Scaricare