Growth characteristics of apple cultivar Gravenstein plants grafted onto the transformed rootstock M26 with rolA and rolB genes under non-limiting nutrient conditions

The growth characteristics of the apple cultivar (Malus domestica) Gravenst ein (GR) grafted onto the transformed rootstock M26 were investigated. The transformed rootstocks used in the experiments included two clones with the rolA gene (rolA1 and rolA2) and one clone With the rolB gene (rolB). The g rafted plants consisted of GR/rolA1, GR/rolA2 and GR/rolB and the control p lants GR/M26 (the untransformed rootstock). Ingestad's experimental system was employed for growing the plants to maintain non-limiting nutrient condi tions and to achieve accurate and comparable results. The results show that the grafted GR/rolA1, GR/rolA2, and GR/rolB plants had a similar relative growth rate to the GR/M26 plants, indicating no effect of the transformed r ootstock on relative growth rate under non-limiting nutrient conditions. Mo reover, the transformed rootstocks influenced neither the leaf area ratio, specific leaf area values nor dry matter allocation. However, the GR/rolA1 plants did show a reduced stem length and a decreased internode length comp ared to the control and the other two transgenic clones. Also, the GR/rolA1 and GR/rolA2 showed a significant lower specific root length value compare d to the control. The present results suggest that the dwarfing effect does not relate to the relative growth rate of the rootstock. The transformed c lone rolA1 and rolA2, especially rolA1, might be potential dwarfing rootsto cks for apple production. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.