Effects of different types of pollens on fruit size, shape and hardness in Ruixianghong apple

Abstract：【Objective】In order to select excellent pollen that can improve the fruit size, fruit shape and hardness of Ruixianghong apple, the present experiment was undertaken.【Methods】We selected 21 different types of pollens to control pollination of Ruixianghong with natural pollination serving as the control. The fruit setting rate was investigated, the vertical and horizontal diameters of fruit during development were measured after pollination, and the fruit weight, deflection rate and hardness of the harvested fruit were also measured. The pollination effect was comprehensively evaluated by combining membership function and cluster analysis.【Results】The effects of different pollination combinations on fruit setting rate, fruit longitudinal and transverse diameter growth, fruit shape index, fruit weight, fruit hardness and density at maturity were different. The longitudinal and transverse diameters of the fruits pollinated by each variety mainly increased in the early stage and tended to stop increasing at harvest. At the early stage of fruit development, the increase of fruit longitudinal diameter was greater than that of transverse diameter, and the increase of longitudinal diameter and transverse diameter of most pollination combinations showed a downward trend at harvest. In the process of fruit growth and development, the fruit longitudinal diameter and fruit shape index of Ruixianghong were larger after it was pollinated by Maypole and Hybrid superior line 2 and the fruit transverse diameter growth and fruit shape index were larger after it was pollinated by Freedom and B118, while the longitudinal diametergrowth and fruit shape index were smaller after it was pollinated by Hybrid superior line 3 and Zha’ai 76. The fruit weight of Ruixianghong was the largest (289.86 g) after it was pollinated by Maypole, which was significantly higher than that of the control and other pollination combinations, 20.79% higher than that of the control (239.98 g), and Hybrid superior line 2. The fruit weight of Ruixianghong decreased after it was pollinated by Zha’ai 76 (183.47 g) and Hybrid superior line 3 (169.80 g). The fruit weight was the smallest after it was pollinated by Pink Lady, which was 156.52 g, and the difference between treatments was significant. The effects of other pollination combinations on fruit weight were different, but the difference was not significant. There was no significant difference in the effect of different types of pollens on fruit shape index. The average fruit shape index was about 1.0, indicating that pollination had little effect on the fruit shape, and the variety had excellent high-L/D retention. The fruit deviation rate (4.33%) was the lowest after it was pollinated by Ruixianghong pollen, which was significantly reduced by 64.88%, compared with the control (12.33%). The fruit deflection rate with Jin Shiji pollen was the highest (18.73%), which was significantly different from the control. Except for the pollen of Ruixianghong, the fruit deflection rates with Hybrid superior line 1 (5.25% ), Malus sp. Beijing No. 1 (8.00% ), B118 (8.33% ), M. prunifolia (Willd.) Borkh. (9.40% ), Anna (9.67% ) and Maypole (9.67% ) were less than 10%, which were qualified as grade Ⅰ fruits. Compared with natural pollination, they were significantly reduced by 57.42%, 35.12%, 32.44%, 23.76%, 21.57% and 21.57%. The fruit deflection rate of other pollination combinations was greater than 10%. The results showed that Ruixianghong maintained the fruit with high-L/D characteristic, increased the fruit weight and reduced the deviation rate after it was pollinated by Maypole. The fruit weight of Ruixianghong was smaller and the fruit deflection rate was higher after it was pollinated by Zha’ai 76, Pink Lady and Hybrid superior line 3. In terms of fruit density, compared with natural pollination (1.01 g · cm-3 ), Ruixianghong significantly increased fruit density after it was pollinated by Hybrid superior line 3 and M. sieversii (Ledeb.) Roem.. The fruit density of Ruixianghong decreased after it was pollinated by Zha’ai 76 (0.77 g · cm-3 ) and Pink Lady (0.75 g · cm-3 ), but the difference was not significant. In terms of fruit hardness, the fruit hardness of Ruixianghong significantly increased (10.13 kg · cm- 2 ), followed by the pollens of Nagafu No.2 (9.94 kg · cm-2 ). The fruit hardness of Ruixianghong was the lowest (8.32 kg · cm-2 ) after Freedom served as a pollinator, and then M. sieversii (Ledeb.) Roem. (8.45 kg· cm-2 ), which was significantly reduced by 7.75%, compared with the natural pollination (9.16 kg· cm-2 ). The membership function method was used to establish a comprehensive evaluation on the efficacy of different pollens. The results showed that the top pollens were Maypole, Freedom, M. sieversii (Ledeb.) Roem., Liaofu, Anna, etc. The fruits pollinated by Pink Lady, Zha’ai 76, Nagafu No. 2, India and Jin Shiji ranked lower than the control. The pollination effects of 21 types of pollens can be divided into 4 categories by means of mean cluster analysis. The fruit deviation rate was large, the fruit shape index was small, the fruit weight was relatively small compared with other pollination combinations, and the Zha’ai 76, India and Pink Lady, which ranked lower, were divided into one category. The comprehensive ranking of Maypole, Freedom and natural pollination, LG2, M. sieversii (Ledeb.) Roem., Liaofu, Golden Delicious, Anna and Orin were divided into one category; B118, M. prunifolia (Willd.) Borkh., Hybrid superior line 1, Ruixianghong and Malus sp. Beijing No. 1, Hybrid superior line 2, Jin Shiji, Envy and Nagafu No. 2 were divided into one category.【Conclusion】Maypole has the best comprehensive effect after it serves as a pollinator, which is characterized by large fruit, small hardness and low deflection rate. It is the preferred pollen for Ruixianghong.