Growth characteristics of Japanese pear cultivar 'Kosui' (Pyrus pyrifolia Nakai) and researches after indexes and criteria for standardizing pruning

Summary Growth Characteristics of Japanese Pear Cultivar 'Kosui' (Pyrus pynfolia Nakai) and Researches after Indexes and Criteria for Standardizing Pruning Mamoru Sato In order to determine the effective indexes and criteria in standardizing pruning, the relation between tree growth and fruit productivity such as yield, fruit weight, development of axillary flower bud, fruit cracking was studied during 4 years from 1990 to 1993 by statistical analysis, using young tree for 10-years-old and mature tree for 24-years-old at the beginning year of this research. 1 . The following indexes were effective on pruning of 'Kosui'. Pruning index and criterion (1). The proportion of bearing division to primary scaffold limb (or secondary scaffold limb) (Length of primary scaffold limb from its grafted part to terminal lateral fruiting branch/ length of primary scaffold limb) * 100 (PBS : abbreviation) The proper value of this index is over 80% .The length of the lateral bearing shoot apt for the latest at the end of primary or secondary scaffold limb was evaluated over 150cm of shoot length for spur- type bearing shoot or 100cm for axillary flower type (length in which both included cut-backed residue of waiting shoot) at least.(2). The proportion of waiting shoot to fruiting branch (PWF) (Numbers of waiting shoot/numbers of lateral fruiting branch) * 100: Waiting shoot ("Yobisi") means the 1-year-old shoot sprouted from primary scaffold limb mainly, which was cut-backed at 30 - 45cm length for expecting the axillary flower bud to come easily. The proper value of this were evaluated at 20 - 40% for primary scaffold limb of young tree, 40 - 60% for first secondary scaffold limb of mature tree, 80% for second secondary scaffold. (3). Fruiting branch density (FBD) Bearing division length of primary scaffold limb/ (Number of lateral fruiting branches per primary scaffold limb - 1) The proper value of this was 30cm - 40cm. 2 . PBS influences yield and keeping the vigor at the terminal part of primary or secondary scaffold. FBD has not but close relation with yield,also affects more or less of leaf area of canopy. High PWF in primary scaffold limb or first secondary scaffold suppressed shoot growth and flower bud formation, while improved weight of fruit in second secondary scaffold branch.Moreover, fruit cracking was stimulated by higher PWF in first secondary scaffold, same as by lower FBD in second secondary scaffold. 3 . Yield and fruit weight of axillary-flower-type bearing branch were superior to them of spur type at the middle part of secondary scaffold branch. But there wasn't significant difference of the fruit weight between 3-year-old spur- type bearing branch and axillary flower type. Mainly, branch age of spur- type bearing branch influenced fruit weight on super. The number of super per fruit affected weigh and Brix of fruit on axillary flower type. Moderate fruiting ratio of spur /fruit in number was estimated to approximately 3.0 with 3-year-old spur- type bearing branch and axillary flower type . 4 . Summer pruning showed the high relevance to the level of axillary flower bud formation and the degree of sugar content of fruit. More flower bud on super and fruit weight were gained by summer pruning at 40 -45days after full blossom, while less Brix of fruit came in by summer pruning at 80days after. Yield and Brix of fruit were also affected number of shoots at basal part of bearing branch after summer pruning. Summer pruning was considered to be exercised only at the basal 40cm part of lateral fruit-bearing branch to avoid from lack. of folia area after pruning. The proper value of residual shoot number at basal part of bearing branch was evaluated to 0.7 - 1.0 at first secondary scaffold limb and 1.0 - 1.5 at primary or second secondary scaffold limb. 5 . It was effective on ensuring axi1lary flower bud formation to be cut-backed at the length of 30 - 40cm with shoots of 8.5 - 1lmm outside diameter ,while in the 'Yamase' zone 2-year-old waiting shoot method, which cut-back one shoot continuously between 2 years, was useful to improve flower bud formation. 6 . The ratio of wood-leaf (Cs/F) in fresh or dry weight of shoot occurred from basal part of fruit-bearing branch was helpful to prospect yield. Most yield was expected at 1.0 of Cs/F of shoot, which length was estimated 65 - 80cm. 7 . The moderate planting distance and LAI in field of 'Kosui' was evaluated to 7 m * 7 m and 2.7 from the analysis of the most productive secondary scaffold branch, which standardizing pruning was applied. Fruit weight which was produced by leaf of 1 square m in leaf area was calculated 1.35kg in fresh weight. Consequently, economical max of yield was estimated up to 36 - 40t/ha in Fukushima. Sum of all leaf area at every spur occupied over 50% to them of tree canopy.