Study of the influence of cherry rootstocks on the growth and productivity of cultivars grown in South Bulgaria

The rootstocks (Prunus mahaleb seedling, MaxMa 14 and GiSelA 6) were studied for their influence on the growth and reproductive characteristics of three well-known cherry cultivars in Bulgaria, the early ripening 'Burlat', the medium ripening 'Van' and the late ripening 'Katalin.' The study was conducted in South Bulgaria near the town of Plovdiv in a typical cherry-growing region with relatively low fertile soil with drip irrigation provided. One-year-old nursery trees were planted at the density of 571 trees ha- 1 (5.0x3.5 m) in the autumn of 2012. Trees were formed as free growing crown. In terms of growth characteristics the rootstock GiSelA 6 forms significantly less trunkcross sectional area and crown volume in all three cultivars. The growth of this rootstock weakens early and requires strong pruning to maintain it. The most commonly used in the region rootstock Prunus mahaleb seedling induces the formation of the largest trees. MaxMa 14 forms larger plants than GiSelA 6 but the growth begins to weaken after the fourth vegetation. GiSelA 6 demonstrates a significant flower bud formation in combination with the cultivars 'Van' and 'Katalin' at the beginning of the second vegetation, but there was no yield because of late frost. The rootstock GiSelA 6 produced the largest cumulative yield tree- 1 and demonstrated the highest productivity in terms of trunk-cross sectional area and crown volume for all three cultivars. The other two rootstocks gave similar cumulative yield during the studied period but MaxMa 14 has higher yield efficiency coefficients compared to Prunus mahaleb seedling. The fruit weight of trees on MaxMa 14 and Prunus mahaleb seedling is significantly higher than that of GiSelA 6. At the end of the sixth vegetation 8% of the trees on GiSelA 6 rootstock died, whereas no tree mortality was recorded in combinations with MaxMa 14 and Prunus mahaleb seedling rootstocks.