Temperature Alters Sweetpotato Storage Root Growth and Development.

Sweetpotato storage root initiation and growth is affected by temperature, yet little specific information is available on storage root initiation and growth in response to temperature. Information covering wide range of temperatures would be useful for predicting both growth and developmental rates in sweetpotato. Therefore, two studies were conducted to determine temperature effects on sweetpotato storage root initiation and development using sunlit plant growth chambers. In experiment I, sweetpotato, cultivar ‘Beauregard’ slips were planted in pots at five day/night temperatures of 20/12, 25/17, 30/22, 35/27 and 40/32°C for 55 days. In experiment II, four day/night temperatures of 25/17, 30/22, 35/27, and 40/32°C were imposed 16 days after planting for plants grown at optimum temperature (30/22°C) and continued for another 62 days. In both the experiments, optimum water and nutrients were provided throughout the experimental period.  In experiment I, two rows of three pots row^-1 were removed on a weekly basis leaving three rows with nine plants m^-2 until 55 days. In Experiment II, two rows of three plants row^-1 were removed at 16 days leaving three rows with nine plants m^-2 for the final harvest. At each harvest, root number (storage and adventitious) and dry weights of plants parts were determined.  Temperature, when imposed at the beginning of planting, did not affect either total or storage roots formed. The time to reach 50% of storage roots formed, and size and quality of the storage roots, however, were significantly affected by temperature. Total biomass produced increased up to 30/22 and 35/27°C and declined slightly at the 40/32°C. Storage root biomass increased with increase in temperature up to 30/22°C, and declined by 11 and 90% at 35/27 and 40/32°C, respectively. When temperature treatments were imposed after the storage roots are initiated, the number of total as well as storage roots produced was not affected by temperature, but the size and quality of storage roots were significantly affected by temperature. The optimum temperature for total biomass production was 30/22°C and declined by 9% at 35/27°C and 27% at 40/32°C. The optimum temperature for storage root growth was 25/17 and declined linearly by 31 g per 1°C increase in temperature. The functional algorithms developed from these datasets will be useful in predicting sweetpotato storage root formation.