| Seedlings of dwarfing self-root stock apple trees are produced by asexual propagation, usually grow fast and strongly and early bear with high yields,disease resistance and fruit quality,due to elimination of effects from genetic heterogeneity of seedling rootstock.This technology has now been widely used in America,Japan,Holland,and other developed countries.In China,intermediate stocks produced by dwarfing the seedling rootstock,are always the dominant germchits,due to their high adaptability and being easy to be reproduced. Research on Seedlings of dwarfing self-root stocks was lacking.With improvements on the orchard site condition,fruit growers' planting technology and culture methods of seedling,it is of great importance to investigate effects of dwarfing self-root stocks on the tree development and fruit yields and quality.Therefore,field trials for comparison on self-root stocks and intermediate stocks were carried out in several different site conditions in Baishui, Luochuan,Fuping,Yaozhou,Linwei and other main apple production counties in Shaanxi,to investigate the tree growth,fruiting and resistance.Main obtained results are as follows:1.Dwarfing self-root stock apple trees are early fruiting with higher fruit yield,quality and disease resistanceCompared with intermediate stock apple trees,self-root stock M26 apple trees fruited 2 years earlier,with its flower amount being one fold higher,color-up time 10-12 days earlier, fruit chroma 20-45%higher,harvest time 3-10 days earlier,fruit shape index 0.05-0.07 higher, averaged fruit weight 14-44 g higher,and high-quality fruit ratio 44-67%higher.The final tree biomass is also a bit higher than the intermediate stock apple trees,with fresh weight of 100 hundred leaves being 12.9%higher,obviously lowered disease and pest affected ratios, and similar drought and cold resistance.Of the four cultivars of self-root stock M26 apple trees, only one(Gala) showed lower stem quality with 11%plants with more than 10°slanting,and 1.3%plants spliting open at stock-scion connection sites in rain storm.2.Quality of seedling is the key factor for orchard development of dwarfing self-root stock apple treesQuality of seedling is the key factor for successful orchard development of dwarfing self-root stock M26 apple trees.During the first two year after transplanting,self-root stock M26 apple trees must developed to have enough biomass.The indexes for seedling quality included:Being the first grade elf-root stock according the national standard,no virus,and the basic stocks being culture seedlings.3.Properate cultivation technologies should be developed for self-root stock M26 apple trees(1) Rational planting density.Plant and row space is 2 m X(3.5-4) m for orchards with excellent water-fertilizer condition and fine management,and(2～3) m X 4 m for usual orchards.(2) Reasonable dwarfing stock depth.The obligate heights of dwarfing stocks are closely relevant with the adult tree biomass and size.The stock seeding should be 5-10 cm higher above the ground for orchards with excellent water-fertilizer condition,and 3-5 cm in the ordinary areas.(3) Appropriate optimized trimming technologies.Self-root stock M26 apple seedling has a lower stem quality,and it is of great importance to strong the stem,growth potential by an appropriate trimming technologies.The thin-spindle tree shape is suitable for trees growing in orchards with excellent water-fertilizer condition and intensive management,and free-spindle tree shape for ordinary areas due to its well developed roots and high resistance.(4) Optimized field management on water,fertilizer,fllower and fruit.Due to shallow distribution of roots,high root density in surface layers,and more uptake roots and less main roots,special attention should be paid to fertilizer management of self-root stock M26 apple trees,such as fertilization timeing and methods,and fertilizer varieties.For organic fertilizers, application rate should be decreased with an increased application times.If the trees in newly built orchards keeps too much leaves in late autumun,man-aided leaf falling should be done so that the tree could get into the bormancy stage in time.Self-root stock M26 apple trees are easy to form flowers with a higher flower amount,which is one fold higher than the ordinary cultivars.Therefore,pre-flowering trimming is vry important for eliminating the unfruiting branches.The apprearance of fruits produced by the self-root stock M26 apple trees are bright and clean,and it is not necessary to cover the fruit the special bag for mid- and early-harvest cultivars.4.It is practical and feasible to develop seedlings of self-root stock M26 apple trees in main apple production areas of Shaanxi.Seedlings of dwarfing self-root stock M26 apple trees with a higher comprehensive resistance compared to the intermediate stocks,could be developed in the areas with 600-1100 altitude,where the intermediate stock trees had widely been developed. |
