GERMINATION AND NET IN-VITRO GROWTH OF PEACH, ALMOND AND PEACH-ALMONDHYBRID EMBRYOS IN RESPONSE TO MANNITOL INCLUSION IN THE NUTRIENT MEDIUM

Nine Prunus accessions were evaluated for germination and plantlet gro wth in an in vitro osmotic screening test using mannitol as an osmotic um. Embryos from diverse peaches, almonds and peach-almond hybrids wer e cultured in Woody Plant Medium, and in this same medium modified wit h the inclusion of 350 mM mannitol. Embryos were stratified in vitro f or 60 days, induced to germinate for a two week period and then allowe d to develop and grow for another 20 days prior to harvest. Fresh weig hts of both roots and shouts as well as percent germination were recor ded at harvest. The main effects of nutrient medium, germplasm type (p each, peach-almond, almond) and specific Prunus accession were all hig hly significant (P = 0.01) with regard to fresh weight of roots and sh oots. Embryo germination was affected significantly by the inclusion o f mannitol in the nutrient medium and by the particular germplasm type (P=0.01 and P=0.05, respectively). Significant interactions of nutrie nt medium x Prunus accession and nutrient medium x germplasm type were also detected for both root and shoot fresh weights. Almond germplasm cultured in Woody Plant Medium with 350 mM mannitol produced signific antly more roots and shoots than either peaches or peach-almond hybrid s grown in the same medium. Peach-almond hybrid embryos were observed to germinate at a significantly higher frequency than peach embryos wh en averaged across both media. Results obtained in this study indicate a wide range of average plantlet fresh weight relative to the specifi c germplasm challenged in the osmotic screen.