In vitro Germination of Early Ripening Sweet Cherry Varieties (Prunus avium L.) at Different Fruit Ripening Stages

In vitro embryo culture enabled satisfactory germination of immature seeds produced in crosses from early ripening sweet cherry varieties (Prunus avium L.). Three varieties -'Rita', 'Bigarreau Burlat' and 'Carmen'- were crossed with 'Early Star' as male parent. Germination rate was affected by the developmental stage of both fruit and embryo. Fruit ripening stage was a critical factor for culture infection rate that increased with maturity. In-ovule embryo culture on Murashige and Skoog medium without hormones improved the embryo size but did not increase the germination rate due to a further increase in infection rate. Ex-ovule embryo culture on Murashige and Skoog medium supplemented with BA 1 mg L-1, NAA 0.5 mg L-1, 20 g L(-1)sucrose, 10 g L-1 sorbitol and 6 g L(-1)agar during the stratification time increased embryo length. Germination was performed on Brooks and Hough medium at the 22 +/- 1 A degrees C with 16/8 h light/dark photoperiod. The highest germination rate (75 %) was reached in embryos that were 3-4 mm in length, after 30-days stratification at 4 A degrees C. Embryos in fruits at green-yellow stage that were 3-4 mm long were morpho-physiologically developed to produce bipolar seedlings, without combined application of embryo culture and micropropagation.