EFFECTS OF TEMPERATURE AND PHOTOPERIOD ON THE LEAF GROWTH AND YIELD OF CHINESE CABBAGE
Lee Shu-hsien Lee Shi-tsun (Chekiang University of Agriculture) (Nanking Agricultural College)
The present experiment was conducted in order to determine the effects of temperature and photoperiod on the growth and yield of leaves of Pak-choi Chinese cabbage (Brassica chinensis L.) variety "Se-Yu-Man." Plants were grown by pots under three kinds of photoperiods, viz., long-day (24 hours per day), short-day (8 hours) and natural day length. They were grown respectively in the green-house, with temperature from 10-15 ℃ (minimum) to 30-35 ℃ (maximum), and in the open, with temperature from 0 to -5 ℃ (minimum) to 10-20 ℃ (maximum) during the winter and early spring of 1962-1963. It was found that the weight per plant grown in the open, was about three times more than that in the greenhouse, especially those under natural and short-day conditions. How-ever, no appreciable difference was found between that in the open and that in the greenhouse of the long day treatments. When grown in the greenhouse with higher temperature, the growth rate of leaves, as measured by fresh weight increase, was more rapid in the early stage, but slow down earlier in the later stage. While that in the open, the reverse was the case. The final weight was therefore greater in the open with short-day length, and less in the greenhouse with long-day length. The growth of leaf area in response to the effect of temperature and photoperiod was very similar to that of the leaf weight. But it was more pronounced on weight than on area. In the course of the growth from seedling to a mature plant, the ratio of the petiole with respect to the total weight of the leaves was smaller in the early stage, and larger by the time of harvest. Generally, in the early stage, the weight of the petiole was less than that of the blade; while that in the later stage, the weight of petiole was much greater than the blade, especially for those grown under cool and short-day conditions. As to the yield formation of an edible plant of "Se-Yu-Man", it was relatively more affected by the weight of leaves than the number of leaves per plant, which was less sensi-tive to the environmental conditions. However, the number of leaves per plant under short-, or natural-day length may be somewhat greater than that under long-day. But the increase of them was almost all of young ones, which had little contribution to the total weight of a plant. In order to form high yield of a Pak-choi Chinese cabbage, it is considered to be first to have sufficient number of leaves per plant, and then to increase the weight of the leaves. Plants grown under cool and short-day condition usually produced wider leaves with smaller leaf-shape-index, and those under hot and long-day, usually produced longer leaves with larger leaf-shape-index. The two directions, length(y) and width(x) were shown to confirm with allometic relation formula, y = cxk, to be log y = 0.513 + 0.647 log x and that of leaf width (x) and leaf shape index (y/x) to be log (y/x) = 0.513 - 0.353 log x.