IN-VITRO SCREENING-PROCEDURE FOR OSMOTIC TOLERANCE IN PRUNUS

Significant growth differences (p less than or equal to < 0.01) were o bserved for two micropropagated Prunus accessions after 14 days in cul ture when 685 mM mannitol was included in Quoirin and Lepoivre nutrien t medium. While there was an 11% growth increase in fresh weight durin g the 28-day culture period for accession K537-067, explants from New Jersey Plumcot No. 3 increased fresh weight an average of 123%. Simila r tests were conducted to determine the repeatability of this short te rm in vitro screening procedure. Explants of Mananna 2624 were subject ed to two levels of mannitol, 275 mM and 550 mM, included in the Quoir in and Lepoivre nutrient medium. Three successive 28-day tests were co nducted. Explants were examined at both 14 and 28 days after the onset of the experiment for net growth changes. Addition of mannitol to the nutrient medium at concentrations of 275 mM and 550 mM decreased expl ant fresh weights of Marianna 2624 to 36% and 28% of controls, respect ively, at 28 days past initial culture. Initial fresh weight and fresh weight changes at day 14 were significantly different (p less than or equal to 0.05) between tests. No significant differences existed betw een tests with regard to weight changes at 28 days past initial cultur e. This information may aid Prunus breeders in the choice of procedure s for inducing drought stress and screening large numbers of plant acc essions.