Development of a simple thermal time method for describing the onset of morpho-anatomical features related to sweetpotato storage root formation

A thermal time-based approach using growing degree days was used to describe the onset of morpho-anatomical features associated with storage root developmental stages in the sweetpotato cultivar ‘Beauregard.’ Initially, we calculated accumulated growing degree days corresponding to adventitious root initiation, the onset of storage root formation (appearance of anomalous cambium), and appearance of visible storage roots with localized thickening and pigmentation in sweetpotatoes grown under greenhouse conditions. Subsequently, we performed field calibration of this approach to verify the timing of these storage root developmental stages under natural growing conditions. Under field conditions, transplants required relatively fewer calendar days to achieve the thermal time corresponding to each developmental stage in comparison to greenhouse-grown plants. Further calibration of this approach for ‘Beauregard’ and other sweetpotato varieties grown in diverse environments will help enhance our understanding of the effects of management and agroclimatic variables on sweetpotato yield determination. This study demonstrates the advantage of using thermal time vs. calendar days in estimating storage root development in sweetpotatoes.