Results of Multi-site Interstem Trials with Apple Trees Erfolge mit Zwischenveredlungen bei Obstbäumen

Summary An interstem trial was planted in the spring of 1988 with the tender apple cultivars ‘Elstar’ and ‘Jonagold’ on M.9 rootstock with thirteen interstem cultivars to study their possible effects on tree hardiness and growth vigour. The interstems used were: ‘Gloster’, ‘Golden Delicious’, ‘Summerred’, because of their hardiness shown in an earlier Dutch trial, ‘Heyer12’, ‘Antonovka’, ‘Hibernal’, ‘Dolgo’, ‘Honeygold’, ‘Yellow Transparent’, ‘Ottawa 3’, ‘Haralson’ and ‘Paulared’, because of their reputed hardiness elsewhere, and ‘Dubbele Zoete Aagt’ as the standard interstem used in The Netherlands. Two-year-old trees directly on M.9 served as controls. The material used was free of known viruses, except for ‘Hibernal’ where this was not quite certain. The trees were made in one nursery and planted at one site in Denmark and three in The Netherlands in single rows at distances ranging from 3.00 x 1.20 to 3.25 x 1.50 m and raised as slender spindles. The trial lasted till winter 1994/95 with ‘Jonagold’and one year longer with ‘Elstar’. No damaging frosts occurred during years that the trees were in the field, so no conclusions could be drawn with regard to the winter hardiness of the interstem cultivars involved. Growth control was obtained, especially with ‘Elstar’. With both cultivars, growth reduction occurred most consistently with ‘Dolgo’, ‘Ottawa 3’, ‘Paulared’ and ‘Summerred’. Little growth control was obtained with ‘Gloster’ and ‘Golden Delicious’ and especially ‘Antonovka’. Some, growth-reducing interstems (‘Paulared’, ‘Summerred’) had a thin trunk relative to that of the scion cultivar, for others (‘Dolgo’ with both cultivars and ‘Ottawa 3’ with ‘Jonagold’) the opposite was true. Productivity per tree was not much affected by the interstems, with the exception of ‘Hibernal’ allowing high productions and ‘Ottawa 3’ lagging behind with ‘Elstar’. However, compared to the controls, productivity per cm2 scion trunk-cross sectional area (TCA) was increased in many cases, especially with ‘Elstar’. With ‘Elstar’, interstems of ‘Heyer 12’, ‘Hibernal’, ‘Paulared’ and ‘Summerred’ especially were effective. With ‘Jonagold’, ‘Heyer 12’, ‘Dolgo’ and ‘Ottawa 3’ interstems rated high. Fruit size was not greatly affected by the interstem and if it was there was no clear relation with productivity per cm2 TCA. Where growth was reduced fruit colouring was improved. Except for trees on an ‘Ottawa 3’ interstem, where in some years lower leaf contents of N, P, K, Ca and Mg were found, no clear interstem effects were observed in the mineral content of leaves or fruits. The results are discussed and it is concluded that where both growth control and increased hardiness are wanted, ‘Summerred’ is a valuable interstem. When vigour control is not the main aim, other hardy interstems are promising as well, such as ‘Hibernal’ with its good effect on productivity. Given the many interactions found, it is stressed that without thorough experimentation the use of the before-mentioned interstems for other cultivars under other conditions bears risks.

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