Effects of Fusarium proliferatum on Aboveground Physiological Indicators of Superior Apple Rootstock Line 12-2 (Malus spectabilis) with Improved Apple-Replant-Disease Resistance

Abstract

(1) Background: Cultivating resistant rootstocks is an effective way to mitigate apple replant disease (ARD), and we developed superior apple rootstock line 12-2 (self-named), which shows improved ARD resistance. (2) Methods: We used ARD-associated pathogen Fusarium proliferatum MR5 (MR5) to test the fungal infection in the 12-2 line. Seedlings of the 12-2, T337, and M26 rootstock lines were planted in a substrate with potato dextrose broth and MR5 spore solution, and aboveground physiological indicators were measured. (3) Results: MR5 had the greatest effect on the leaf growth of T337 and M26. The incidence rates of infectious symptoms in the T337 and M26 lines were 68 and 100%, respectively. MR5 significantly affected the leaf chlorophyll content, ETR, and NPQ of T337 and M26, as well as Pn and Tr of M26. MR5 tended to reduce the leaf photosynthetic parameters of T337, but the decreases were not significant. The leaf reactive-oxygen-species levels of T337 and M26, the leaf antioxidant-enzyme activities of M26, and the superoxide-dismutase activity of T337 were significantly affected by MR5. MR5 also had a significant effect on the leaf malondialdehyde, proline, and soluble-sugar contents of T337 and M26. None of these aboveground physiological indicators were affected by MR5 in the 12-2 rootstock. (4) Conclusions: The 12-2 rootstock was more resistant to ARD-associated MR5 and could serve as an important test material for resistant-apple-rootstock breeding in China.