The cultivation of resistant rootstocks is one of the more effective ways to mitigate apple replant disease (ARD). We performed an ion current test, a pot experiment, and a pathogen infection test on the apple rootstocks 12-2 (self-named), T337, and M26. The ion current test showed that exposure to ARD soil extract for 30 min had a significant effect on K+ ion currents at the meristem, elongation, and mature zones of the M26 rhizoplane and on Ca2+ currents in the meristem and elongation zones. ARD also had a significant effect on Ca2+ currents in the meristem, elongation, and mature zones of the T337 rhizoplane. Exposure to ARD soil extract for 5 min had a significant effect on K+ currents in the meristem, elongation, and mature zones of 12-2 and on the Ca2+ currents in the elongation and mature zones. Compared to a 5-min exposure, a 30-min exposure to ARD extract had a less pronounced effect on K+ and Ca2+ currents in the 12-2 rhizoplane. The pot experiment showed that ARD soil had no significant effect on any root architectural or physiological parameters of 12-2. By contrast, ARD soil significantly reduced some root growth indices and the dry and fresh weights of T337 and M26 compared with controls on sterilized soil. ARD also had a significant effect on root metabolic activity, root antioxidant enzyme activity (except superoxide dismutase for T337), and malondialdehyde content of T337 and M26. Pathogen infection tests showed that Fusarium proliferatum MR5 significantly affected the root structure and reduced the root metabolic activity of T337 and M26. It also reduced their root antioxidant enzyme activities (except catalase for T337) and significantly increased the root malondialdehyde content, reactive oxygen levels, and proline and soluble sugar contents. By contrast, MR5 had no such effects on 12-2. Based on these results, 12-2 has the potential to serve as an important ARD-resistant rootstock.

(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.

Organic acids secreted by plants, such as p-hydroxybenzoic acid, ferulic acid, cinnamic acid, and benzoic acid, can inhibit seed germination and root growth. The effects of root and soil leaching liquor from orchards on the growth of M. hupehensis Rehd. seedlings under sand culture are studied; the seedlings are sampled at 15, 30, 45, and 60 d. Changes in the amount of root exudates are determined using HPLC. Low concentrations of root leaching liquor (A1) and soil leaching liquor (B1) significantly promoted plant growth and chlorophyll synthesis; high concentrations of root leaching liquor (A6) and soil leaching liquor (B4–6) inhibited growth. Low concentrations of soil leaching liquor had no significant effect on the POD, SOD, and CAT activities. A5–6 and B5–6 significantly decreased Fv/Fm and qP values, respectively, and increased NPQ values. All root and soil leaching liquor treatments inhibited the secretion of gallic acid, hydroxybenzoic acid, benzoic acid, and phloridzin, and promoted the secretion of caffeic acid. The root leaching liquor treatments inhibited the secretion of catechin and promoted the secretion of phloretin. The soil leaching liquor treatments promoted the secretion of cinnamic acid. The secretion of other phenolic acids is likely associated with the different concentrations of leaching liquor.

Background Cultivation of resistant rootstocks can effectively prevent apple replant disease (ARD), and grafting tests are an important means of evaluating the compatibility of rootstocks with scions. Methods The apple rootstocks 12–2 (self-named) and Malus hupehensis Rehd. (PYTC) were planted in a replanted 20-year-old apple orchard. The two rootstocks were grafted with scions of 13 apple varieties. Multiple aboveground physiological parameters of the grafted combinations were measured and evaluated to verify the grafting affinity of 12–2 with the scions as compared to Malus hupehensis Rehd. (PYTC). Results The graft survival rate and graft interface healing of 12–2 did not differ significantly from those of PYTC. Mechanical strength tests of the grafted interfaces showed that some mechanical strength indices of Redchief, Jonagold, Starking, Goldspur and Yinv apple varieties were significantly higher when they were grafted onto 12–2 compared to the PYTC control. The height and diameter of shoots and the relative chlorophyll content, photosynthetic and fluorescence parameters, antioxidant enzyme activities and malondialdehyde content of leaves showed that Fuji 2001, Tengmu No.1, RedChief, Gala, USA8, and Shoufu1 grew similarly on the two rootstocks, but Tianhong 2, Lvguang, Jonagold, Starking, Goldspur, Yinv and Luli grew better when grafted onto 12–2 than onto the PYTC control. The rootstock 12-2, therefore, showed good grafting affinity. Conclusion These results provide experimental materials and theoretical guidance for the cultivation of a new grafting compatible rootstock to the 13 studied apple cultivars.

Malus crabapple has high ornamental and ecological value. Here, the flavonoids in the petals of three pink Malus crabapple cultivars, Malus ‘Strawberry Parfait’ (GD), M. ‘Pink Spire’ (FY), and M. ‘Hongyi’ (HY), at the bud stage (flower buds are swollen, and the pistils and stamens are about to appear; L), full bloom stage (the flowers are fully open, and the stigma and anthers have recently appeared; S), and end bloom stage (the stigma and anthers are dry; M) were identified, and their abundances were determined. First, Kodak Color Control Patches were used to describe the colors of petals, and a colorimeter was used to determine the phenotypic values of flower colors. Flavonoids were determined using ultraperformance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS). In all three crabapple cultivars, the red and yellow hues of the petals gradually disappeared, the color of the flowers changed from bright to dull, and the petals gradually faded. The extent of fading of the red hue of the petals was highest in GD, followed by FY and HY. A total of 302 metabolites were detected in the three cultivars. The content of total flavonoids in the three cultivars significantly differed, but there were no significant differences among species. The total flavonoid content of the three crabapple varieties was highest in HY, followed by FY and GD. The content of the anthocyanins delphinidin-3-O-sophoricoside-5-O-glucoside, pelargonidin-3-O-(6″-O-malonyl)glucoside, pelargonidin-3-O-glucoside, peonidin-3-O-glucoside, and cyanidin-3-O-arabinoside decreased significantly, which resulted in the discoloration of GD petals from L to M. The flavonoids and flavonols in FY might interact with anthocyanins in metabolic pathways. The content of these five anthocyanins decreased slowly, which resulted in the weaker discoloration of FY and HY compared with GD. The content of the five anthocyanins in HY did not decrease significantly, but the content of chalcone increased significantly, which might facilitate the production of anthocyanin auxiliary pigments and result in less pronounced fading of the petals. Cyanidin-3-O-arabinoside and pelargonidin-3-O-glucoside were the key flavonoids of the three crabapple cultivars. The total content and changes in anthocyanins were the key factors affecting petal color development and fading. Nonanthocyanin polyphenols, such as flavonoids, flavonols, and chalcone, are auxiliary pigments that affect petal fading. Overall, the results of this study provide new insights into the mechanism underlying the fading of the color of Malus crabapple flowers, and these new insights could aid the breeding of cultivars with different flower colors.