Detection of Above-Ground Physiological Indices of an Apple Rootstock Superior Line 12-2 with Improved Apple Replant Disease (ARD) Resistance

(1) Background: The cultivation of resistant rootstocks is an effective way to prevent ARD. (2) Methods: 12-2 (self-named), T337, and M26 were planted in replanted and sterilized soil. The aboveground physiological indices were determined. (3) Results: The plant heights and the stem thicknesses of T337 and M26 were significantly affected by ARD. Relative chlorophyll content (June–October), Pn (August–September), and Gs (August) of T337 and relative chlorophyll content (June–July, September), Pn (September–October), and Ci (September) of M26 were significantly affected by ARD. ARD had a significant effect on Fv/Fm (June), qP (June–July), and NPQ of T337 (June–October, except August) and Fv/Fm (June) and NPQ (June-October, except July) of M26. Additionally, ARD affected Rfd of M26 and T337 during August. SOD (August and October), POD (August–September), and CAT (July-August, October) activities and MDA (September–October) content of T338 as well as SOD (July–October), POD (June–October), and CAT (July-October) activities and MDA (July, September–October) content of M26 were significantly affected by ARD. ARD significantly reduced nitrogen (October), phosphorus (September–October), and zinc (July) contents of M26 and potassium (June) content of T337. The above physiological indices were not affected by ARD in 12-2. (4) Conclusions: 12-2 could be useful as an important rootstock to relieve ARD due to strong resistance.