EFFECT OF MATURATION DURATION ON DESICCATION TOLERANCE IN HYBRID LARCH (LARIX X LEPTOEUROPAEA DENGLER) SOMATIC EMBRYOS

Cotyledonary somatic embryos of Larix X leptoeuropaea that developed a fter various maturation times on media containing abscisic acid showed different frequencies of conversion into plants. Drying of these soma tic embryos under high relative humidity (RH) before germination impro ved plantlet recovery and eliminated differences in the performance of somatic embryos matured for different times. However, dehydration of somatic embryos under 98% RH to a water content below that of zygotic embryos excised from mature seeds (0.97 and 1.36 g H2O/g dry weight, r espectively) showed a strong positive correlation between longer matur ation time and desiccation tolerance. Drying somatic embryos at 4 degr ees C under 59% RH for 1 wk resulted in desiccation to a water content of 0.30 g H2O/g dry weight, which was the closest to the hydration st ate of zygotic embryos in dried, stored seeds (0.20 g H2O/g dry weight ). Under this condition, only somatic embryos matured for 5 wk germina ted and produced plantlets at a relatively high frequency (73 and 41%, respectively).