Varietal difference of fruit producitivity in Japanese pears [Pyrus pyrifolia], 1: Yearly trends in matured trees

Wood formation in mature and aged trees of the major cultivars of Japanese pears, Pyrus pyrifolia Nakai. 1) The three major cultivars of Japanese pears, Shinsui, Kosui and Hosui were surveyed for fruit productivity per unit leaf area, mean fruit weight, fruit yield, the accumulation of wood portion and so forth from 1982 to 1997. Supplementary data were obtained from the cultivars Chojuro and Ishiiwase. 2) The shoot length of each tree tested was measured during the season of leaf fall. The relationship between shoot length and leaf area was analyzed for three cultivars. The total leaf area of each tree tested was estimated by using the relationship between shoot length and leaf area. Leaf area of the tree tested was kept constant in long terms. The leaf area index of most of trees was between 1.5 and 3.0. 3) All the trees tested were trained in the trellis system. The distribution of shoot length of Shinsui peaked between 100 and 150 cm, while Kosui and Hosui peaked at approximately 100 cm or below. The Chojuro cultivar had the shortest range of shoot distribution among the four cultivars. 4) Fruit yield per hectare of Shinsui was about 10 to 20 tons, while that of Hosui, Kosui and Chojuro was about 20 to 45 tons. The mean fruit weight of Shinsui was the smallest, at approximately 200 grams, compared to 300 to 450 grams of three other cultivars. The Shinsui cultivar had not only lower fruit productivity, and a smaller fruit weight than the three cultivars. The trends for fruit productivity per unit leaf area was also the same in the four cultivars in the same year. Fruit productivity decreased year by year for each of the four cultivars at 25 years of age or older. 5) Volume of wood, trunk and branches more than 2 cm in diameter, were estimated as truncated cones. Wood volume of individual trees increased significantly year by year, and this trend continued in the cultivars five years of age or older