The clonal rootstock 'Sirio', previously known as 'I.S.5/22', was selected within the breeding programme for peach rootstock conducted at the Dipartimento di Coltivazione e Difesa delle Specie Legnose, University of Pisa. 'Sirio' was originated by open pollination of 'G.F.557' peach x almond rootstock. Other 'I.S.' clones were selected from the same seedlings based on the degre of induced vigour to the scion. 'Sirio' showed a good response to in vitro propagation, but also a poor rooting ability to propagation by cutting, stoolbed and trench layering. 'Sirio' was one of the weakest stocks within the 'I.S.' series, as it induced a 40% reduction in tree vigour when compared with 'G.F.677'. 'Sirio' was endowed with a good root system, and it adapted to fertile and permeable soils, allowing good control over vegetative growth and resulting in well balanced trees. It also showed resistance to chlorosis only slightly lower than that of 'G.F.677'. Trees grafted on 'Sirio' showed an early onset in production, higher yield efficiency, larger fruit size and better fruit skin colour than trees grafted on 'G.F.677'. On account of the low induced vigour in the grafted cultivar and its resistance to limestone, 'Sirio' was judged to be suitable for high density planting systems even in fertile and calcareous soils, which are usually unsuitable for 'G.F.677' because of the high vigour induced. The response of 'Sirio' to replanting situations is still unknown and specific trials are currently under way to assess this aspect. 'Sirio' has been patented by Azienda Agricola Angelo Errani (Brevetto vegetale n° 032 NV/94). An extension of this patent has been requested for France and Spain.
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