In vitro storage of some pear genotypes with the minimal growth technique

Shoot cultures of 9 pear genotypes collected from different areas of Azad Jammu and Kashmir (northern Pakistan) were maintained on MS medium supplemented with 30 g L^–1 of sucrose + 7 g L^–1 of agar^ + 1 mg L^–1 of BAP. For in vitro preservation shoot tips were excised from these cultures and transferred onto different media, i.e. full strength, ¼ strength, ½ strength MS medium, and full strength MS medium containing 2.5% or 3.5% (w/v) mannitol. The cultures were assessed for their survival after storage periods of 3, 6, 9, and 12 months. To test the regenerability of the cultures they were transferred onto fresh culture medium. The genotypes differed significantly in their survival; however, they were statistically similar in terms of regenerability when transferred onto fresh medium. Shoots of the Khurolli and Bagugosha genotypes remained quite healthy, with relatively high survival rates (53.25% and 50.50%, respectively), whereas those of the Desi nakh genotype had the lowest survival rate (41.02%). Full strength MS medium containing 2.5% (w/v) mannitol gave the highest survival and regenerability rates (55.82% and 52.31%, respectively) in cultured shoots. Preservation for the shortest period (3 months) resulted in the highest survival (63.41%) and regeneration (58.81%). Genotypes and storage period interaction showed maximum shoot survival in Kashmiri nakh stored for 3 months, while Raj btung cultures stored for 12 months responded poorly, with the minimum survival rate. Addition of mannitol at the lower concentration of 2.5% (w/v) was an effective technique to lengthen subculture duration, possibly because of a gradual increase in osmotic pressure in the medium, which resulted in reduced availability of water to the growing cultures.