IN VITRO MULTIPLICATION OF OLD PEAR CULTIVARS

In 2012, a project was started to evaluate the resistance of pear landraces and older cultivars grown in the Czech Republic to fire blight. A key part of the project was also testing of applicability of different in vitro culture media and methods of artificial inoculation under in vitro culture conditions. Therefore, the purpose of this study was to develop an efficient protocol for rapid in vitro shoot multiplication of older pear cultivars and landraces. The donor shoots were obtained in March from mature trees grown at the Research and Breeding Institute of Pomology (RBIP) Holovousy Ltd., Department of Genebanks (Holovousy 1, 50801, Horice, Czech Republic). Selected genotypes were successfully established in vitro using mercuric chloride as sterilization solution. For initiation of multiplication, five Murashige and Skoog (MS) media containing 1, 2 and 4 mg L^-1 BAP (6-benzylaminopurine) or 0.5 and 1 mg L^-1 TDZ (thidiazuron) were evaluated. Multiplication rate was defined as the number of newly formed shoots (>10 mm) per initial shoot tip after four weeks of culture. The effect of the two growth regulators on callus formation and shoot morphologywas determined. Selected pear cultivars differed in their multiplication and development potential on the evaluated media. Generally, the highest proliferation rate was obtained for pear cultivar ‘General Leclerc’ that produced 7.3 in vitro shoots (>10 mm) on MS medium containing 1 mg L^-1 TDZ. Results obtained in our study confirmed preliminary findings that TDZ was an important plant growth regulator for proliferation and growth in pear micropropagation.