Rootstocks apple … Plenty of Choice

In recent years, much has been written on Geneva rootstock by the inteternational professional literature. These rootstocks are characterized by increased resistance against replanting problems, slightly more growth than M9, no root fields, insusceptibility against fire blight and above all, good productivity. Around the start of the 21st century, a small trial was executed at WUR WPR Randwijk, using these Geneva rootstocks. The former researcher Frank Maas assessed these rootstocks positively. Unfortunately, the program was discontinued, and these rootstocks were picked up more quickly in other countries than in the Netherlands. 

Fortunately, in 2016 we were given the opportunity to pick up where they left off with the tree growers such as Van Diepen and the material was set up for a large Elstar trial with different rootstocks. This trial is financially supported by the relevant tree growers and partly from the sponsors contributions.  

Ultimately, the trees were ready at the end of 2017 and we were able to do a trial planting in spring 2018. 

In the field trial, the current standard rootstock M9 - T337 is compared with different Geneva rootstocks, B9, Mark and Voinesti 2. The rootstocks are always planted at 10 centimeters or 25 centimeters high. This results in a total of 18 treatments in 4 repetitions. 

The second growing year, the differences between the various types of rootstocks were remarkable. The table below shows the yield in the second year. With the standard (M9) the harvest more than 8 kg, which is good  for a re-implantation situation. However, the various Geneva numbers and Mark produced a lot more, with G11 resulting in a leg height of 25 cm and 14.1 kg per tree as the absolute leader. 

The measurements of the trunk circumference showed considerable differences as well. The growth of the various rootstocks differs, with B9 and M9 growing at a similar pace. Voinesti is clearly weaker than M9 and the Geneva rootstocks and Mark grow significantly faster. At the end of the third year of growth, it can be concluded that for G202, the trees are clearly growing too quickly. 

Following the good harvest in 2019, G11 and G16 in particular showed a very uniform good flowering. Currently , the trial plot shows large differences in yield once again. Not only G11 and G16 seem to score very well, but Mark and G41 also exhibit good results. Contrarily, Voinesti seems clearly too weak under these replanting conditions. 

Obviously, this trial should be continued for several more years. However, it seems that in a few years' time we will not only be able to select for plant variety, but also for a rootstock. For weaker varieties, we were already convinced of the added value that the Geneva rootstocks provide. Even with a strong variety like Elstar, Geneva rootstocks clearly seem to be the better choice for replanting. A striking advantage of this trial can be found in the resistance to critters such as mice. In this trial, part of the plot was affected by mice. By stamping down the soil around the roots, watering them and adding extra fertilizer, all the trees survived and were in good condition . However, after the mouse infestation, trees on Geneva rootstocks were in good health, while the trees on M9, B9 and Voinesti were somewhat too weak afterwards. The greater vigor of the rootstocks therefore also results in a more robust tree! 

Trees on Geneva rootstocks are more expensive. Fewer  rootstocks are obtained from a stoolbed and they sometimes prove a bit more difficult in the nursery. In addition, a license for this rootstock is required. However, the clearly higher yield seen in this trial in the first few years of this trial justifies the higher tree price in our humble opinion. 

We expect that within a few years the supply of trees on G11 and G41 will gain momentum.  We advise every apple grower to follow this trial closely. The move to Geneva rootstocks can provide a clear improvement for organic cultivation. 

To be continued….