Abstract:

The current study aims to investigate the influences of dwarfing intermediate stock SC1 on apple photosynthetic regulation characteristics and fruit quality. By using 15-year-old‘Honggala’and ‘Jinfu 4’grafted on Malus robusta rootstock（BLHT）（as two controls）and SC1 grafted on controls（as two treatments）as materials，the fluorescence quenching dynamics，the responses of leaf net photosynthetic rate（P_n）to photosynthetically active radiation（PAR）and leaf P_n to intercellular CO₂ concentration（C_i）as well as fruit quality indices of‘Honggala’and‘Jinfu 4’were measured and compared. Results showed that，in comparison with Honggala/BLHT and Jinfu 4/BLHT，the application of SC1 improved the capture efficiency of light energy（F_v′/F_m′），photochemical quenching coefficient（q_P），quantum efficiency（Φ_CO2）and actual PSⅡ efficiency under irradiance（Φ_PSII）of both the two scion cultivars. Meanwhile，the SC1 application suppressed the non-photochemical quenching coefficient（q_N）in Honggala and Jinfu 4. The leaf maximum net photosynthetic rate（P_nmax,P），light utilization range（I_u）and supplying rate of triose phosphate（V_tpu）of Honggala/SC1/BLHT and Jinfu 4/SC1/BLHT were also found to be significantly higher than those of Honggala/BLHT and Jinfu 4/BLHT. Besides，photosynthetic mesophyll limitations（L_M），CO₂ compensation point of dark respiration under light（Γ^*）and Michaelis constant of Rubisco to CO₂（K_c）and to O₂（K_o）were decreased significantly in Honggala/SC1/BLHT and Jinfu 4/SC1/BLHT than in Honggala/BLHT and Jinfu 4/BLHT. The application of SC1 also influenced greatly the fruit quality indices of Honggala and Jinfu 4. The coloring area and value of red chromaticity in peel were increased significantly in Honggala/SC1/BLHT than in Honggala/BLHT（by 13.7% and 43.2%）and in Jinfu 4/SC1/BLHT than in Jinfu 4/BLHT（by 42.5% and 37.6%）. The soluble solids content in flesh （increased from 14.1% to 15.2% in Honggala and from 14.9% to 15.9% in Jinfu 4）and total phenolic compounds content in peel and in flesh（by 66.9%-72.2% and 45.4%-84.4%，respectively）were increased significantly in fruits of Honggala/SC1/BLHT and Jinfu 4/SC1/BLHT compared to Honggala/BLHT and Jinfu 4/BLHT. Based on the result obtained in this study，it can be concluded that the application of dwarfing intermediate stock can alter the capture，partitioning and utilization efficiencies of light energy in apple leaves，decrease photosynthetic mesophyll limitation，enhance leaf biochemical reaction and photosynthetic rate，and finally lead to improved leaf photosynthetic capacity and boosted fruit quality.

Key words: apple, dwarfing intermediate stock, photosynthetic regulation, mesophyll limitation, fruit quality