Annual Variation of Growth and its Relation to Meteorological Factors in Potato Plants : II. An aspect of annual variation in tuber starch weight

The tuber starch weight in three varieties of potato plant was observed 5-8 times during the growing season (June to September) for ten years (1972-1981) at the Hokkaido National Agricultural Experiment Station. 1. The starch yield in each variety showed a significant correlation with the growth rate of the tuber starch weight (tuber GR), and not with the bulking period (Table 1). 2. At the early bulking stage, high solar radiation, little precipitation and a maximum temperature between 22-23°C enhanced the tuber growth, but restricted the shoot growth, resulting in a low shoot fresh weight at the main bulking stage, especially in the early variety (Figs. 1 and 2). The meteorological factors accounted for 68% of the variance in the distribution ratio for the tuber on a fresh weight basis. 3. At the main bulking stage, the tuber GR showed a significant correlation with the shoot fresh weight in the early variety, but with the shoot efficiency (tuber GR/shoot fresh weight) in the late varieties. The shoot efficiency was higher under the conditions of high solar radiation, little precipitation and a minimum temperature of about 15°C (Table 2, Fig. 3). The meteorological factors accounted for 54% of the variance in the shoot efficiency (Fig. 4). 4. At the late bulking stage, the tuber GR showed a significant correlation with the shoot fresh weight in the late varieties.