Growth rates and biomass production of micropropagated apple plants of M26 and Gravenstein on their own roots and in different micrografted combinations under non-limiting and limiting nutrient conditions

Micropropagated apple plants of semi-dwarf rootstock M26 (M26) and vigorouscultivar Gravenstein (GR) on their own roots and different micrograftcombinations were used in the experiment. The combinations included GRscion on GR root (GR/GR), M26 on M26 (M26/M26), GR on M26 (GR/M26), and M26on GR (M26/GR). The plants were grown under non-limiting and limitingrelative addition rates of nutrients. Under non-limiting nutrientconditions, M26 and GR showed a similar relative growth rate(RGR). Grafting reduced RGRsignificantly in the combination of M26/M26 compared to M26. The relativegrowth rate for the combination of GR/M26 was similar to the GR/GR plants,but it increased greatly compared to the M26/M26 plants. For the reversecombination of M26/GR, the RGR value decreasedsignificantly compared to either the M26/M26 or the GR/GR plants. TheRGR value and specific root length were lower forM26/GR than for GR/M26. No clear relationship between carbohydrateallocation and growth parameters of different plants was found undernon-limiting nutrient conditions. Nutrient limitation resulted in increaseddry weights and soluble sugars in the roots for all plants except forM26/GR. A reduced leaf area ratio and a lower RGR thanthe set relative addition rate of nitrogen were found for M26 and GR/M26under limiting conditions. These results suggest that the dwarfing effectis not directly related to RGR of rootstocks orscions, but rather associated with root morphology of grafted plants andthe ability of roots to absorb nutrients.