Development of tissue culture system for pear cultivars

The pear is one of the most economically important fruit crops in the temperate climatic zone. Concerning the Czech Republic, there were 790 ha of commercial pear plantations in 2014. In 2012, a project has been started to test the resistance of pear landraces and older cultivars grown on the territory of the Czech Republic to fire blight in in vitro culture and field conditions. A key part of the project was also testing the applicability of different in vitro culture media and methods of artificial inoculation in in vitro culture conditions. In the present study, successful micropropagation, which can be carried out during the whole year, provided an alternative method to produce stock material of particular cultivars for experiments with artificial inoculation. 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. Selected genotypes were successfully established in vitro using 0.15% mercuric chloride as disinfection solution. Shoots developed were subcultured onto fresh MS media for six consecutive 4-week passages. Five MS media containing 1, 2 and 4 mg L-1 BAP (6-benzylaminopurine), 0.5 and 1 mg L-1 TDZ (thidiazuron) were tested. Selected pear cultivars differed in their multiplication and development potential on tested media. Multiplication coefficients and statistical evaluation are stated in the paper. The effect of selected growth regulators on callus formation and shoot morphology is also presented. In conclusion, obtained data show that in vitro propagation of used pear cultivars can be accomplished in amount sufficient for artificial inoculation studies. We obtained multiplication coefficient higher than 3.0 for all tested pear genotypes. Generally, the highest proliferation rate was obtained for pear cultivar 'Bitterbirne Lukas' that produced 4.9 in vitro shoots on MS medium containing 4 mg L-1 BAP. The physiological mechanisms that determine the need for growth regulators during the different stages of in vitro development are currently being investigated.