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The Journal of Horticultural Science & Biotechnology
Vol. 80 No: 5
Title:
In vitro leaf-shoot regeneration and somaclone selection for sodium chloride tolerance in quince and pear
Authors:
G. MARINO and L. MOLENDINI
pp: 561-570
Abstract:
The aims of this research were to set up in vitro procedures to obtain NaCl-tolerant somaclones of the quince rootstock ´BA 29` and pear cvs. ´Conference` and ´Abbé Fetel`, and to evaluate the selection-pressure effect of NaCl in the regeneration medium. Shoot regeneration was induced in leaf-explants on media enriched with 5.4 µM α-naphthalene acetic acid (NAA), 4.5 µM thidiazuron (TDZ) and variable concentrations of NaCl (0, 3 or 5 g l-1 for pear; 0, 5 or 10 g l-1 for quince). Regeneration was strongly negatively affected by the presence of salt in the culture media. It was inhibited by 5 g l-1 NaCl, and completely prevented by 10 g l-1 NaCl in ´BA 29`. No regeneration was obtained from ´Abbé Fetel` leaf explants, even at 5 g l-1 NaCl. Moreover, the few ´Abbé Fetel` and ´Conference` shoots regenerated at 3 and 5 g l-1 NaCl, respectively, could not survive transplantation. All shoots derived from each adventitious shoot were referred to as a somaclone and labelled with two numbers, the first referring to the NaCl concentration and the second being a progressive number. All were sub-cultured repeatedly on a standard medium before testing their salt tolerance in vitro. Somaclones and controls (shoots obtained by conventional micropropagation) were compared for proliferation, growth and rooting on standard and NaCl-enriched media (5 and 10 g l-1 NaCl for proliferation; 5 and 7.5 g l-1 NaCl for rooting). Shoot proliferation rate (PR), shoot relative growth rate [RGR = (final weight - initial weight)/initial weight], and proportion (%) of rooting of somaclones and controls were significantly reduced by salt in ´BA 29` and in the two pear cultivars, although great variability was found between somaclones regenerated at each NaCl concentration. No shoot proliferation occurred at the highest NaCl concentration. Most somaclones of ´BA 29` had higher shoot PR and RGR than controls on standard medium, and the presence of 5 g l-1 NaCl in the regeneration (induction, expression) media increased proliferation and growth across all NaCl concentrations. Moreover, a few somaclones regenerated at 5 g l-1 NaCl showed better root development on salt-enriched media. The most promising ´BA 29` somaclone seemed to be 5-3, whose RGR remained high in up to 10 g l-1 NaCl, and which showed a high proportion of rooting (75%) and root development at 5 g l-1 NaCl. Also notable for its slightly higher shoot PR, RGR and better rooting on 5 g l-1 NaCl-enriched media, was somaclone 5-4. Among the pears, most ´Abbč Fetel` somaclones (all from regeneration media lacking NaCl) grew and proliferated more than the controls across all NaCl concentrations. These differences were significant for somaclone 0-8. Some somaclones produced more and longer roots than controls on standard medium, while only a few very short roots were found in a few somaclones and none in the controls on NaCl-enriched media. Many ´Conference` somaclones had lower shoot PR than the controls up to 5 g l-1 NaCl, especially those regenerated in the absence of salt. Greater proliferation and growth were observed for somaclone 3-5, and better growth for somaclone 3-10 in the presence of salt. Moreover, some other somaclones regenerated in the presence of salt (i.e., 3-3, 3-5, 3-6 and, especially, 3-8) showed interesting rooting behaviour on NaCl-enriched media. Across all combinations, ´Conference` somaclone 3-5 seemed the most tolerant, with good proliferation, growth and rooting on NaCl-enriched media. Thus, the present results suggest that the regeneration-selection protocols described here can be useful for inducing somaclonal variation and NaCl tolerance in pear and quince, and indicate a positive NaCl selection-pressure effect in obtaining in vitro NaCl-tolerant variants of ´BA 29` and of ´Conference` pear.
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