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Quantifying differences in growth of selected apple rootstocks under extreme simulated spring temperatures in environmental chambers

Lotze, E., Steyn, W. J.
Acta horticulturae 2017 no.1177 pp. 103-106
Malus domestica, Mediterranean climate, apples, bags, genetics, leaves, nutrient uptake, rootstocks, spring, summer, temperature
The South African apple industry utilizes rootstocks imported mainly from the northern hemisphere where the climate differs significantly from the Mediterranean-type climate apple growing regions in the Western Cape. Our aim was to determine if high growing temperatures differentially affect rootstocks in terms of mineral nutrient uptake, survival and growth rate, i.e., whether rootstocks differ in their adaptability to the harsh South African summer climate. Trials were conducted in 4 L black poly bags in environmental chambers during the spring of 2012/13 and 2013/14. Rooted liners of Geneva® 222, Geneva® 202, M.7, MM.109/M.9 and M.793 were used in 2012/13 and the same rootstocks were grafted to 'Fuji' for 2013/14. Temperature regimes varied between 30 and 38°C during 2012/13 and 15 and 35°C in 2013/14. Rootstocks did not show a differential growth response to temperature. Differences in growth between rootstocks were primarily a function of genetics. In 2012/13, M.7 had the highest root mass, foliage mass and total plant mass at harvest and differed significantly from M.793 and M.9 at 30 and 34°C - indicating better adaption (genetically) under these conditions over the few weeks duration of the trial. No significant differences in root, stem and foliage mass were observed between these temperatures. Geneva® 222 was the only rootstock that survived and grew at 38°C. Geneva® 222 was the best-adapted rootstock during 2012/13.