Breeding of ‘Y-2',a early-fruiting and dwarfing rootstock for apple

Abstract:Using dwarf rootstocks for high density planting has many advantages, such as early fruiting,high yield, top fruit quality, easy to mechanical work, convenient to standardized and efficient production,etc, has become a trend and direction of development of world apple production, while The dwarfing rootstock is the main way to achieve dwarf and high density apple cultivation, many countries had more focused on rootstocks research than varieties since then. At present, the apple production of the most widely used M series, MM series, etc. rootstocks in China, some problems had been found in the past years, such as poor compatibility with the varieties, weak cold and drought resistance ability, not suitable for a wide range, tree lodging, etc. These limited the effect of dwarf rootstock. Therefore, based on the Malus baccata(L.) Borkh., containing abundant wild apple rootstocks resistant germplasm resources, in Shanxi province,China, with large groups of seedling breeding method, breeding and suitable for the Loess Plateau in northwest arid, dry areas planted with new varieties of rootstock independent intellectual property rights, have great significance to the sustainable development of the apple industry.‘Y-2'dwarfing rootstock was derived from Malus baccata(L.) Borkh. in Northwest of Shanxi province, China. After several years of evaluation, it had some traits as follows: First, it had flowering and fruiting ability earlier 3 to 4 year than the standard rootstock, yields of‘Fuji'in the fourth year were 6 000 kg·hm^-2 by the spaceing of 1.5 m×4 m,but output was zero from the common northwest Shanxi baccata. Second, Grafting‘Fuji'‘Danxia'and‘Gala'as interstock, six-year old tree height were standard rootstocks 48.46%, 37.68% and 61.23%, be-longed to extrem-dwarfing rootstock when grafting‘Fuji'‘Danxia', but belonged to dwarfing rootstock when grafting‘Gala', the overall evaluation was dwarfing rootstock. Third, it had strong cold, drought and disease resistance, good compatibility, excellent fruit quality than the standard rootstock.‘Y-2'rootstock was adapted to the Loess Plateau or the regions with similar climate, but should be carefully used in saline area. Because of its weak rooting, usually‘Y-2'were used as interstock in production, and the interstock length was about 20 cm.‘Y-2'dwarfing rootstock showed a high value in apple cultivation by many regional trials, especially suitable for high fertilizer orchards or using to planting bonsai culture. It can for high density planting by the spaceing of 1-1.5 m×3.5-4 m, the suitable planting were 1 650 to 2 850 trees per hm2. Pollination trees must be utilized which were planted every line or single seedling about 15 percent of the whole‘Y-2'orchards. The trunk of tree used‘Y-2'interstock should be maintained 1 to 1.2meters with spindle or small canopy shape, based mainly in the summer pruning including engraved bud,twisted tip, bent branches, and other measures, while opened the light path by thinning in winter pruning.It was similar to common orchards such as fertilizer and water management, fruit management, disease and pest control, etc.