The effect of light and temperature late in the season on the growth of sugar beet

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Abstract
SUMMARY: Sugar‐beet plants were subjected to all combinations of two day temperatures (12‐5 and 18‐5 oC), two night temperatures (8‐o and 14‐0 oC) and two light intensities (275 and 550 J cm‐2 of visible radiation in a 12 h day) during the last month of their growth. Cold day or night temperatures resulted in the plants having slightly smaller leaf areas, final dry weights and amounts of sugar in their roots than plants grown in warm temperatures. Plants grown in the cold also contained less water, particularly those given cold nights, so that they had smaller fresh weights and a greater concentration of sugar in the fresh, but not in the dry roots, than plants grown in warm conditions. Halving the light intensity had little effect on leaf area but decreased the net assimilation rate. The final dry weight of the shoot was not affected by changing the light intensity, but the dry weights of the roots of plants grown in dim light were 20 % smaller than in plants grown in bright light and they contained correspondingly less sugar. There was no effect of varying the light intensity on the concentrations of sugar in the fresh or dry roots. There was no evidence that cold night temperatures, either alone or in conjunction with bright conditions during the day, induced the storage root to accumulate sugar faster relative to non‐sugar dry matter, i.e. to ‘ripen’.