Evaluation of KrymskReg.5 (VSL-2) and KrymskReg.6 (LC-52) as rootstocks for sweet cherry 'Kordia'

During a 6-year period the growth and production of trees of sweet cherry ‘Kordia’ grafted on rootstocks Krymsk®5 (VSL-2), Krymsk®6 (LC-52) and GiSelA 5 were compared. Shoot growth, increase in trunk diameter and intensity of flowering of ‘Kordia’ were almost similar on all three stocks. Fruit production per tree was significantly higher for ‘Kordia’ on rootstocks Krymsk®6 and GiSelA 5, while that on Krymsk®5 was similar to that on GiSelA 5. Both Krymsk rootstocks gave a small reduction in fruit size, and a slightly lower sugar and acid content. With Krymsk®6, smaller fruit size was related to the higher fruit load of the trees and may be avoided by thinning the tree to the optimum crop load. With Krymsk®5, the reduction in fruit size could not be attributed to overcropping. Fruit cracking, a big problem for cherry growers in areas with high risks of rain in the harvest period, occurred less on Krymsk®6 than on GiSelA 5 or Krymsk®5. Both Krymsk rootstocks produced significantly more root suckers than GiSelA 5. The highest numbers were observed for Krymsk®5, which produced on average 3.3 suckers per tree per during the first 6 years in the orchard. Krymsk®5 also developed burrknots. From this trial it is concluded that Krymsk®6 can be a good alternative rootstock to GiSelA 5, especially for less well drained soils and because its effect on reducing the occurrence of fruit cracking. However, because of its tendency to reduce fruit size, overcropping should be prevented. Therefore, Krymsk®6 is probably less suited for self-compatible cultivars than for cultivars setting fruit only after cross pollination.