Morphological and physiological behaviour of sweet cherry 'somaclone' HS plants in field

The somaclonal variant HS (HS), regenerated from Prunus avium `Hedelfinger’ (H) leaf explants, had previously been molecularly and physiologically characterized both in vitro and in early ex vitro condition showing reduced apical dominance. Somaclone HS, here assessed for several morphological and physiological field performances showed reduced vegetative vigour as determined by trunk circumference and tree height nevertheless natural architecture of the tree was preserved. HS canopy was less crowded compared to H as leaves were shorter with a shorter petiole, they were better spaced out as indicated by internodes length and they had a significantly thinner cuticle and wax layer compared to that found on H leaves surface. Leaf histological analysis also evidenced that HS had thicker mesophyll and palisade the latter composed of more than one layer which, together with increased stomatal density, are distinguishing signs of extensively sun exposed leaves. HS showed a reduction in leaf chlorophyll b and β-carotene content. On the other hands no significant differences were found between the two genotypes in terms of net photosynthesis, intercellular CO2 concentration, leaf transpiration and water use efficiency. HS flowered one year later than H and fertility parameters such as floral buds and number of flowers per bud were reduced. In consideration of the fact that the large size of trees has contributed to make P. avium commercial cultivars unpopular with modern orchardists, HS could be used as either germplasm in breeding programs aiming to reduce tree vigour or a rootstock.