Effect of dwarfing interstocks on tree growth,yields and fruit quality of ‘Miyazakifuji' apple

Abstract:【Objective】High density planting using dwarfing rootstocks is the main planting system for apple in China. Screening of rootstock-scion combinations is important for high density planting, and dwarfing potential, adaptability, productivity, and fruit quality are the main indexes for the evaluation of rootstock-scion combinations. Yanshan region is one of the major apple producing areas in China. Due to low temperature in winter and hot and rainy weather in summer, apple trees are suffering from double restrictions of freezing damage in winter and vigorous growth in summer, which highlights the need for cold resistant rootstocks with greater dwarfing potential in Yanshan region. In this study,‘SH3'‘SH6'‘SH18'‘SH38'‘Mark'‘11-8'‘77-34'‘GM310'and‘Liaozhen 2', which had previously shown to be cold resistant, were used as the dwarfing interstocks, and Malus domestica Borkh.‘Miyazakifuji', an dominant variety in Yanshan region, was used as the scion. Horticultural characteristics such as tree growth vigor, yields and fruit quality were compared for screening the optimal rootstock-scion combinations.【Methods】‘Miyazakifuji'were grafted onto the above 9 dwarfing interstocks with M. robusta Rehd. as the basal rootstock in 2008. The grafted plants were transplanted in 2010. Growth of the tree were quantified by tree height,canopy diameter, circumference(include rootstocks and scion) and total shoot number, and proportions of different types of shoots were measured in 2015. Flowering plants was counted in 2011. Fruit yields and quality, fruit weight, flesh firmness, soluble solid content, titratable acids content were measured every year from 2013 to 2015, and fruit shape index and color index were measured in 2013. The effects of dwarfing interstocks on fruit quality were evaluated based on membership values of functional ingredients calculated by the method of membership function, and all the collected data were analysed using SPSS19.0.【Results】The tree height and canopy diameter of different rootstock-scion combinations were in a descending order of‘SH38'>‘SH6'>‘SH18'>‘11-8'>‘77-34'>‘GM310'>‘SH3'>‘Liaozhen 2'>‘Mark'. The growth of shoots(only 5 cm) was the weakest in trees with interstocks of‘Liaozhen 2'and‘Mark'and their total amount of shoots was 137 and 224 per tree(1.7×105-2.8×105per hm2) with a long shoot rate of 4.8% and 1.0%, respectively. For interstocks of‘SH38'‘SH6'‘SH18'‘11-8'‘77-34'‘GM310'and‘SH3', there was no significant difference(P>0.05) in tree height and canopy diameter and their shoot length was in the range of 32.6-51.9 cm, total amount of shoots was 339-549 per tree(4.2×105-6.9×105per hm2),short and middle shoots rates were higher than 80%. In 2011, trees with‘Mark'as interstock had the highest rate of flowering(86.7%), followed in descending order by those with‘11-8'‘SH6'and‘SH38'with a flowering rate of 73.3%, 66.7% and 63.3%, respectively, and‘77-34'combination had the lowest rate of flowering(26.7%). Yields in trees with‘SH3'‘SH6'‘SH18'and‘SH38'increased significantly with a total yield in three years ranged from 49.2 to 54.3 kg per tree(6.2×104-6.8×104kg·hm- 2), while the yields of the other 5 combinations were significantly less than those of the trees with SH series as interstock.‘Mark'combination produced less than 5 kg per tree(0.63×104kg·hm- 2).Fruit weight of‘SH6'combination was the highest and significantly greater than those of the‘GM310'and the‘11-8'combinations. Fruit firmness of the‘SH3'combination was the highest, and that of the‘SH6'combination was the lowest. There was no significant difference between the other combinations.Fruit from the trees with‘SH3'‘77-34'‘SH18'and‘SH38'as interstock had a soluble solids content above 14.0%, while those from trees with‘11-8'and‘GM310'were the lowest. Rootstocks did not significantly affect titratable acid content in fruit. Fruit from‘11-8'combination had a significantly smaller fruit shape index than those from the other 7 combinations. Fruit color index of‘Liaozhen 2'combination was 0.92, smaller than those from the other combinations. The highest fruit color index was found in fruit from the‘77-34'and the‘SH3'combinations. Characters of early flowering and fruiting of the 9 combinations were evaluated by using fuzzy membership function with the normalized coefficients of variation as weight of the selected 11 indexes(tree height, conpy diamater, total shoot amount, flowering plant rate, accumulative yields, fruit weight, fresh firmness, soluble solids content, titratable acid content, fruit shape index, and red color index). The results showed that‘SH38'had the best comprehensive characters, including tree vigor control, early flowering, and high yield and quality, followed by‘SH3'‘SH6'‘SH18'‘11-8'‘Mark'‘Liaozhen 2'‘77-34'and‘GM310'.【Conclusion】Cold resistance, dwarfness, and early flowering and fruiting are the primary indicators for rootstock selection in Yanshan region. According to the comprehensive evaluation,‘SH38'‘SH3'and‘SH6'dwarfing interstock are relatively good choices for high density planting of‘Miyazakifuji'in this region.