Study On The Regulation Of PGRs On Branching Of Nursery And Young Apple Trees

Cultivating high quality nursery trees and promoting laterals of young trees can lay foundation on the early and heavy bearing of fruit trees. The early benefit is high if the growers plant the feathering apple trees on dwarf rootstock with early and heavy bearing in Europe and the United States. As we know, the single-trunk seedlings bear limited laterals in the planted year and the next year. At present, the intensive planting with dwarf rootstock is generalizing in the current apple production in China. Given bud-notching can only creat limited branches with a lot of labor and the buds formed in that year can not germinate under natural conditions. Thus, the technology of promoting branching of PGR_s with simple operation and high efficiency is very important. On the one hand, the effects of spraying different combination and concentration PGRs from June 1st to July 27th on branching, the dynamic changes of growth and content of endogenous hormones during the prosess of bud germination were studied with‘Red Fuji’and‘Orin’cultivars grafted on dwarf inter-rootstock in the spring of that year. On the other hand, based on painting or spraying PGRs from April 5th to July 25th, effects of different treatments and time on positioning and quantitative branching and growth were studied with young‘Red Fuji’apple trees, and the effects of spraying PGRs on the regrowth of new shoots located on the lower part of central leader and promoting secondary branches were researched as well. In order to screen the suitable combination, concentration and treatment period of PGRs, provide theoretical guidance and techniques of training and branching of nursery and young apple trees on dwarf rootstock, and lay foundation on the further study on the regulation of hormones on axillary bud germination mechanism of apple trees. The main results were as follows:1. The axillary buds of‘Tianhong 2’nursery apple trees could germinate treated by 6-BA combination in every different time, but the average length of laterals treated by 6-BA + GA₃ was longer than that treated by 6-BA only. And the axillary buds apparently expanded, germinated, and growed to 1 cm long on the fifth day, the seventh day, and the ninth to tenth day respectively. The laterals located from 5 cm to 45 cm down the shoot tip at treatment, that is, the branching site moved upward as the tree growed taller. However, the percent of trees with laterals, length of branching site, numbers of laterals, type of branches, total length of branches, length of super long branch, rate of branch diameter to trunk diameter, nursery tree height and trunk base diameter were different. But the branching effect was the best when treated on June 15th, Approximate 15 buds germinated from 9.1 to 54.3 cm down the shoot tip at treatment on average, and the percent of nursery trees with germinated buds was 100 %. The average trunk base diameter which was 17.2 mm significantly increased with a large growth quantity of total laterals growed to 249.6 cm long. And the average length of super long branch was 45.3 cm, the ratio of branch diameter to trunk diameter was 0.47, the nursery tree height was 201.2 cm, which can meet the standard of apple nursery trees with suitable feathers on dwarf rootstock of China, Europe and the United States.2. The axillary buds of‘Orin’could germinate and grow into branches treated by KT-30 + GA₃ combination with suitable concentration, dose, and spraying time. Approximate 21.6 buds germinated from 5 to 62 cm down the shoot tip at treatment on average, and the percent of nursery trees with germinated buds was 100 %. The branches mainly growed into medium and short branches, the branching ability, length of super long branch, and the ratio of branch diameter to trunk diameter was 39.8 %, 55.2 cm and 0.41 on average respectively. The trunk base diameter which was 18.4 mm was significantly increased, but there was no significant difference between the nursery tree height of treatment and control which was 221 cm.3. Comparison to the control （the single-trunk nursery tree）, the diameter of taproot and lateral root of grade 1 of feathering tree were significantly increased, and the number of lateral roots of grade 1 was increased as well. However, the number and diameter of lateral roots of grade 2 were no significant difference between feathering trees and the control.4. On the one hand, IAA content decreased obviously at the initial stage of‘Tianhong 2’nursery apple trees treated by 6-BA （2 days） and then rised slowly, meanwhile, the content of ZR_s and GA_s rised rapidly, however, both the two decreased 6 to 8 days later in the bud. On the other hand, IAA content continued to reduce significantly and ZR_s content decreased slightly after treatment, both the content of IAA and ZR_s rised 6 days later, the trend of GA_s content was oposite in the stem. Besides, ABA content decreased both in the bud and stem. Thus, spraying 6-BA could make ZR_s transport to axillary bud from local stem, inhibit IAA to transport to the main stem from shoot tip, promote the IAA in the axillary bud to transpot to the main stem, and then the axillary bud germinated.As the effect of 6-BA decreased, the curves of 4 hormones content began to fall back on the sixth day or the eighth day, meanwhile, hormones started to reach new balance with the germination and growth of axillary buds.5. The effects of 6-BA + GA₃ or KT-30 + GA₃ combination on branching of young apple trees were better than 6-BA or KT-30 only. Because the growth quantity of total branches was larger, branching ability was stronger and the branching ability showed a gradually rising trend as the concentration of GA₃ elevated. Besides, the germination rate of buds could get to 80 % above and the numbers of total branches were significantly increased when the buds were treated in earlier April, later April, May, June and earlier July separately. Especially, buds with the highest germination rate and strongest branching ability could growed into long branches with strong growth vigor, good maturity and suitable ratio of branch diameter to trunk diameter when treated from later May to earlier June.6. The stopped growing new shoots located in the lower part of one-year-old central leader could regrow after spraying 6-BA + GA₃, and the treated shoots obviously began to regrow on the 7th day, meanwhile, the control did not change. The growth of the leading new shoot on the top of central leader slowed as the new shoots in the lower part regrowed rapidly 7 to 35 days after treatment, however, there was no significant difference between the length of treatment and control when stopped growing in winter. The number of main branches on the central leader of treated trees was significantly increased, approximate 13.5 super long branches were promoted, of which the average length was 47.9 cm, and the rate of branch diameter to trunk diameter was 0.36 on average.7. Approximate 10.8 secondary branches of per shoot were induced when the main shoots of young apple trees formed in the current year were treated by 6-BA in mid June. And the distance from the first secondary branch to the last was 33.8 cm on average, the secondary branches mainly growed into spurs, of which the average length was 2.5 mm, and the percent of branches with flowers was 18.06 % on average.