SEARCH FOR A MORE DWARFING ROOTSTOCK FOR 'JONAGOLD' APPLE

Up until now we have not find a better rootstock than M.9 in our rootstock experiments. Nevertheless, there are two rootstocks for ‘Jonagold’, namely J.TE.G. and P16 that show promise. J.TE.G. is 15% less vigorous than M.9. The production efficiency and colouring remain the same, but there is more production of A2++ class fruits in the 70-85 mm size class because of its smaller fruit size. P16 is 30% less vigorous. The production and the fruit size are somewhat smaller than those of M.9Nic29. The combination of less vigour and the somewhat lower yield causes the production efficiency of P16 to be clearly better than that of M.9Nic29. Colouring on the other hand can be a problem. Where the vigour of M.9 is too strong, other selections of M.9 with less vigour can be used. The most suitable selections to this purpose are M.9Fl56, M.9NAKT337 and M.9NAKT339. These selections have the weakest growth and fruit size is smaller than or comparable to that of M.9Nic29. With respect to colouring, there is no improvement. Also the use of M.27 as rootstock springs to mind, but M.27 is not always suited to replace M.9. In many cases a tree with vigour between M.9 and M.27 is needed. One way to achieve this is the use of M.27 as an interstock, in the hope that the advantages of M.9 (yield and size) and of M.27 (colouring and labour) will be found in the interstock tree. In practice however this does not seem to be so. Another possibility is the use of ‘Idared’, ‘Granny Smith’ or ‘Delcorf’ as interstock. These interstocks provide a clear growth reduction, without influencing yield too much.