INFLUENCE OF THE ROOTSTOCK ON THE MORPHOLOGICAL DIFFERENTIATION OF THE FLOWER BUDS IN TWO CHERRY CULTIVARS

Abstract

The studies were conducted during 2004-2006 on 8 to 10-year-old trees of ‘Bigarreau Burlat’ and ‘Stella’ sweet cherry (Prunus avium) grafted on the rootstocks P 1 (seedling of P. mahaleb L.), Gisela 5 (P. cerasus × P. canescens), Weiroot 13 and Weiroot 72 (both P. cerasus). From the beginning of May to the end of September (every 7 days), spurs were collected from the two-year-old wood and their lateral buds were examined under a stereomicroscope. Rootstock did not influence the growth termination date of the long shoots, irrespective of the fact that the length of the apical shoot depended on their vigour. The onset of the morphological differentiation of the flower buds (connected with the appearance of the bract primordia) was observed 2 to 3 weeks after the growth termination of the apical shoot. This fact can be used for optimizing the application of fertilization, irrigation, and plant protection, etc., to influence the processes of flower bud formation. The type of rootstock did not influence significantly the rate of initiation of the bud scales (including the bracts), nor that of the remaining parts (flower sepal, petal, stamen and pistil primordia) on the differentiating flower buds. No significant differences were discovered in morphological differentiation of the flower buds, nor between the cultivars on the various rootstocks, regardless of the difference in time of fruit ripening. Trees on Gisela 5 (in comparison with P 1) formed the greatest number of flower primordia per flower bud, whereas the remaining rootstocks were intermediate. The floral bud scales differed in shape by cultivar – in ‘Bigarreau Burlat’ there was a small notch in the upper part of the bud scale, whereas in Stella’, they were more rounded, with a bigger notch in the upper part, forming essentially two parts. These differences are best established in the 4th to 6th bud scales. This difference could be used to identify the two cultivars in fall and winter, when there is a lack of fruit. It is advisable to study the morphological characteristics of the bud scales in other sweet cherry cultivars too, with a view to enriching their pomological characterization.