Quantifying the differential uptake of nutrients of different apple rootstocks under selected ambient summer temperatures in a pot trial in environmental chambers

The performance of new CG – versus present commercial apple rootstocks were evaluated in controlled climate chambers simulating warmer soil conditions due to climate change predicted for our growing regions.

Trees were all obtained from SAPO and placed at 4°C in the cold room for one month before being planted in pots. Two year old rootstocks with Fuji scions were transplanted into 4L bags at beginning of Sep 2013 and subjected systematically to 15, 30 or 35°C until the beginning of Nov 2013, when plants had to be harvested as some reached the ceiling of the growth chambers.

The only interaction between rootstocks and temperatures was noticed for root mass at harvest.  A significant increase in root mass occurred as temperatures rose from 15 to 35°C for M7, and a significant decrease in the case of M793. In GC 222 and 2404, there was a decline in root mass as temperatures increased. MM109 showed the highest root mass for 30°C.

Main effects after applying initial size of the trees as covariate showed significant differences between combinations for the following parameters: Stem mass at harvest was significantly higher for CG222 than the rest of the rootstocks. Stem diameter was significantly higher for CG222 than all rootstocks except for CG2404. M7 and MM109 had the smallest stem diameters. Shoot mass at harvest was significantly lower for CG2404 compared to CG222 and M7.  Total fresh weight at harvest was the highest for CG222 which differed significantly from the rest of the rootstocks.

The only significant differences between temperatures were found for shoot mass at harvest, where shoot mass at 35°C was significantly lower than for 15 or 30°C as expected.

The lack of interaction between temperature and rootstocks for most of the parameters did not justify mineral analyses of the new growth.