Differences in chilling tolerance among genotypes of sweetpotato (Ipomoea batatas (L.) Lam.)

We aimed to develop a simple method to identify the most chilling tolerant sweetpotato 
genotypes. Plants at the stage of five to eight most fully expended leaves were used in this 
experiment. Temperature was reduced in five sequent 144 hrs lasting steps (16/14), (14/12), 
(12/10), (10/8) and (8/6) °C. Structural changes, chlorophyll fluorescence parameter and content 
were utilized as selection criteria. The two more tolerant genotypes with orange flesh Abees and 
Beauregard indicated the overall picture of only minor morphological changes (<11%) in leaves 
and stem. They showed beside significant lower development of leaf necrosis, generally higher 
chlorophyll concentrations, a lower reduction of the electron transport rate (ETR) and much less 
photoinhibition. The protocol employed in this work, with a relative short hardening time, makes it 
possible to achieve rapid results with good reliability and to handle a large number of genotypes as 
required in breeding programs. Although the sweetpotato genotypes Beauregard and Abees, 
selected in this study, might be suitable for growth at low temperatures, even more practical 
cultivars could be developed by using the method described in this paper.