Vegetative growth and fruiting habits of the superior strain 'Yanfu 7' apple grafted on different rootstocks

Abstract:【Objective】Dwarf and intensive planting in apples has the advantages of early fruiting, high quality and high efficiency, and is suitable for mechanical management. It has become the main form of apple planting nowadays, and is the development direction of apple industry in our country. The current study characterized the vegetative growth and fruiting habits of the superior strain‘Yanfu 7'apple grafted on different rootstocks with an aim to provide reference for cultivation of high quality‘Yanfu 7'apple with high efficiency.【Methods】The experimentation was carried out with a randomized block design. In2008, the apple trees grafted on Malus micromalus, M7 and M9 were planted in the field. All the data collected were treated with SPSS 18.0 statistical software. Means were generated from 3 replicates with 10 trees in each plot. Tree height, crown diameter and trunk circumference were measured annually from2008 to 2015. The rate of flowering trees was recorded during the blooming period each year from 2009 to2011. In 2011 and 2012, we investigated the numbers of total branches and vegetative branches in each tree and the ratio of the latter to the former was calculated. We also recorded the numbers of long bearing branches, medium bearing branches, and short bearing branches and calculated the ratio of each type of bearing branches to the total bearing branches. From 2010 to 2015, total output and yield per acre were recorded. In 2015, single apple weight was collected with a YP1002 N type electronic balance and fruit colorindex was calculated as ∑(number of fruit at one level× representative value of the fruit level)/( the total number of fruit×the highest extremum) ×100. The vertical and horizontal diameters of the fruit were measured with vernier calipers for calculating shape index(the ratio of vertical diameter/transverse diameter)of fruit. Content soluble solids was measured with an Alpha ATAGO PR-101 digital refractometer and fruit hardness with a GY-4 type hardness instrument【.Results】Our results showed that tree height, shoot growth and stem cross-section area could be used to evaluate the growth potential affected by rootstocks.The tree size, including tree height, crown diameter and trunk girth, was in the order of Malus micromalus> M7 > M9. Shoot amount per mu and short bearing shoots were increased, while vegetative shoots were reduced with the increase in dwarfness of the rootstock. The greater dwarfing effect of the rootstock was, the more branches produced and greater proportion of short branch was, which was favorable for the transformation from vegetative growth to reproductive growth. Some researchers suggested that by increasing the proportion of short shoots dwarfing rootstocks promote allocation of photosynthetic products to the fruit and promote early bearing and productivity. The study showed that‘Yanfu 7'apple grafted on all of the tested rootstocks formed buds in the second year and bore fruit in the third year. The grafted apple trees on Malus micromalus and M7 reached the early stage of full fruiting period, while those on M9 entered the full fruiting period in the fifth year. Yield increased greatly with increased dwarfness of the rootstock, which is consistent with the above results. In full fruiting period, the difference among apple trees grafted on different rootstocks was not significant. With the increase in dwarfing degree of the rootstocks,the fruit quality except for fruit shape index and firmness was improved. Fruit quality was significantly enhanced in the trees on M9 compared to those on Malus micromalus.【Conclusion】The order of tree growth vigor was Malus micromalus> M7 > M9, while the order of shoot number per 666.7 m² and the percentage of short bearing shoots was M9>M7> Malus micromalus.‘Yanfu 7'on M9 exhibited earlier bearing character and higher productivity than trees on M7 and Malus micromalus. Therefore, the rootstock of M9 contributed favorably to the early fruiting and high yield.