Formation characteristics of tree structure, fruit yield and quality in the apple stock-scion combination of 'Yue Yanghong' with '77-34' interstock and Malus baccata Borkh. rootstock

Abstract: 【Objective】The new '77-34'rootstock and cold resistant'Yue Yanghong'apple cultivar were independently selected and bred by Liaoning Institute of Pomology.Up to now, there have been no reports on the growth, yield and quality formation of'Yue Yanghong'with interstock of '77-34'.The goal of this study was to understand the change patterns of tree structure parameters, branch type proportion, yield and fruit quality in tall spindle shaped'Yue Yanghong'with interstock of '77-34'and rootstock of Malus baccata Borkh from juvenility to fruiting stage.【Methods】The materials were'Yue Yanghong'trees with interstock of'77-34'or'GM256'and rootstock of Malus baccata Borkh.Annual tree growth, dynamic changes of the growth, branch type proportion, yield and fruit quality were measured from 2 to 7 after the trees were planted.In 2016, the trees were divided into 4 groups according to different canopy heights, and fruit yield and quality in different groups were compared.Measured parameters included fruit mass, fruit shape index, firmness, soluble solids, TSS/TA ratio, color difference value, etc.【Results】Interstock of'77-34'and'GM256'showed differences in growth, fruit quality, the tree yield and fruit components.From 2010 to 2016, the growth rate of tree height, coverage rate and bough number in'77-34'interstocked trees were all higher than in'GM256'interstocked trees.The canopy diameter of'77-34'trees was higher than 'GM256' trees.The crown diameter in East-West direction was greater than in North-South direction.The ratio of variety/interstock trunk circumference with'77-34'interstock was significantly higher.The rootstock has a better graft compatibility with the interstock of'77-34'than with'GM256'.Compared with'GM256', the total number branches was larger, the spur shoot proportion was higher;andthe growth rate of total branches was higher in'77-34'.The total branch amount of'77-34'in 2015 (7 years) was similar to that of'GM256'in 2016 (8 years) .The higher spur shoot proportion and the total number of branches provided guarantees for the high yield and stable yield in trees with'77-34'interstock.In 2012, the trees with'GM256'and'77-34'interstocks began to bear fruit.The fruit number and yield in trees with both interstocks increased rapidly from 2012 to 2015.The growth rate became stable from 2015 to 2016, and the output in'77-34'trees was higher than'GM256'trees for five consecutive years.The output of'77-34'and'GM256'was 54 147.06 kg · hm-2 and 43 444.67 kg · hm-2 in 2016, being 16.29% and 26.80% higher than that in 2015, respectively.The yield stability in trees with'77-34'interstock was better than those with'GM256'.The fruit mass and firmness in trees with both interstocks increased year by year in2013—2016, the firmness of'77-34'was higher than'GM256'.The soluble total sugar content of'77-34'fruit was higher than that in'GM256'fruit from 2012 to 2015.There were differences in fruit intrinsic quality and color values of'77-34'and'GM256'between different years.The L value in'77-34'fruit was higher than in'GM256'fruit from 2012 to 2016;the a was higher in 2013—2016.b value was higher in'GM256'in 2013 but in other years it was lower in'GM256'.In a word, the color of surface of'77-34'fruit was better than that of'GM256'fruit, with gorgeously red, better background color and higher brightness.There were differences in fruit quality in trees with different height canopy.The fruit mass, fruit shape index, TSS/TA ratio and color difference value in trees with higher canopy of both interstocks were better than those with lower canopy.Because of the poor light intensity in the lower canopy, and the fruit development was poor with poor inner quality.Within the same tree group, fruit mass, hardness, TSS/TA ratio and color values of'77-34'fruit were higher than those of'GM256'.The canopy part 2.0 to 3.0 m in height was the part with concentrated distribution of fruit, contributing43.48% and 38.05% of the total yield in'77-34'and'GM256'trees, respectively.The canopy below1.0 m height was with the lowest fruit contribution, accounting for 13.68% and 12.20%, respectively.【Conclusion】'Yue Yanghong'trees with the interstock of'77-34'and rootstock of Malus baccata Borkh.were less dwarfed than those in interstock of'GM256', which had lower total branch number and proportion of spur shoots.The two interstocks had similar early bearing trait, but the yield and quality of fruit were better in trees with'77-34'than with'GM256'.Taking into account various traits, 'Yue Yanghong'with the interstock of'77-34'and rootstock of Malus baccata Borkh.was better than those with the interstock of'GM256'.