Studies on the Effect of Temperature on the Sugar Production in Sugar Beet : 1. The effect of temperature on the growth.

Abstract

The effect of temperature on the growth of sugar beet at different stages of growth has been studied. The sugar beet plants of variety GW 359, grown in Wagner pots under natural condition, were subjected to temperature treatments in which the plants were grown under the temperature of 15°C, 20°C and 30°C for 30 days. One group was exposed to similar temperature conditions in its early stage of growth, one in its middle stage and the other one in its later stage (Fig. 1). Plants were harvested at the end of treatments for determination of dry matter production, leaf area, leaf numbers and total-sugar concentration. Results obtained are as follows. 1 Throughout all the growth stages, the total dry matter increase of whole plant is highest under 20°C At the early stage, the increase of total dry weight is more in the plants which have been exposed to 30°C than those exposed to 15°C. But this becomes reverse at the middle and at the later stages. Dry weight of tap root increases most under 20°C, then under 15°C and least under 30°C. As regards the top of plants, it is found that the dry matter increase of the petiole is generally retarded under 15°C (Table 1). 2 The total leaf area always becomes maximum under 20°C, then under 30°C and least under 15°C. From the other results on leaf number and leaf area per one leaf blade, it is clarified that as the beneficial effect of high temperature on leaf expansion of one leaf blade is very little in comparison with its harmful effect on leaf number increase, the total leaf area is less under 30°C than under 20°C and that the less total leaf area under 15°C is due to the harmful effect of low temperature both on leaf expansion and on leaf number increase (Table. 2, Fig. 2). In the early stage, a positive correlation between the leaf area and total dry matter increase is seen. But no such correlation is seen between them at the middle stage and at the later stage (Table 1, Table 2). These phenomenon can be explained by the following assumption: As the plant grows, the non-photosynthesizing organ begins to occupy more and more portion of the whole plant and as the results, the dry mattes production becomes more and more influenced by respiration rather than by photosynthesis. 3 The ratio of dry matter increase of tap root to top is generally higher under low temperature with an exception of middle stage at which this ratio becomes highest under 20°C (Fig. 3). 4 The lower the temperature, the higher the total sugar concentration of leaf blade, petiole and tap root. As regards the total-sugar concentration of tap root, it is found that its difference is little among three plots at early stage, but it becomes remarkable at the later stage. This different effect of temperature with different stage is also true with the dry matter increase ratio of tap root to top, as described above. These facts suggest that sugar beet possesses self reguratory mechanism for modifing the effect of temperature on sugar accumulation in tap root (Fig. 4). 5 At the early and at the middle stages, the beneficial effect of the temperature of 15°C on total-sugar concentration in tap root is so little that sugar produced under 15°C is actually less than that produced under 20°C, which is the beneficial temperature for dry matter increase of tap root. In the later stage, however, the total-sugar content in tap rot becomes more under 15°C than under 20°C, as the beneficial effect of the temperature of 15°C on sugar concentration is more in comparison with the beneficial effect of temerature of 20°C on dry matter increase. Under the temperature of 30°C, the sugar content of the tap root is always least due to the harmful effect of high temperature on sugar concentration and dry matter increase of the tap root (Fig. 5).