INTERVENTION BY GIBBERELLIN AND CYTOKININ IN THE RELEASE OF APPLE EMBRYOS FROM DORMANCY: A REAPPRAISAL

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Abstract
Summary: Embryos of Pyrus malus L. cv. Golden delicious, were isolated from the fruits and cultivated in aseptic conditions on solid media. Rate of cotyledon greening, evolution of germination percentage and growth of organs after germination were used to determine the extent of dormancy. Treatment with gibberellins and by chilling both induced an increase in the rate of cotyledon greening, in germination percentage as well as stimulating root growth. However, even the most active gibberellins, GA4, GA7, GA9, applied simultaneously at high concentration (5 mg l−1), could not completely reproduce the effects of optimum chilling treatment (9 to 12 weeks at 5 °C).While progressive increases in germination percentages were found with duration (chilling) or concentration (gibberellins), there was no direct relationship between concentration and response in the case of kinetin. Low concentrations (10 or 100 ug l−1) were inactive, whereas concentrations equal to or greater than 1 mg l−1 induced large increases in germination percentage. The concentrations which stimulated germination also inhibited growth, especially of the root.