Physiological and anatomical characterization of a late-storage root-forming mutant of sweetpotato

Abstract

A late-storage root-forming mutant ('KM95-A68') of sweetpotato [Ipomoea batatas (L.) Poir.] was characterized to clarify the genetic and physiological mechanisms of storage root formation. This mutant originated from a somaclonal mutation of 'Kokei No. 14'. Storage roots of 'KM95-A68' are rare and, when formed, develop 2 or 3 weeks later than those of 'Kokei No. 14' from which it originated. Morphological characteristics of the canopy and leaf photosynthetic rates of 'KM95-A68' were similar to those of 'Kokei No. 14'. No apparent differences were observed in the anatomy of root cross sections of 'KM95-A68' and 'Kokei No. 14'. An apparent increase in the root zeatin riboside (ZR) levels were observed in 'Kokei No. 14' at storage root formation. Root ZR levels differed between 'Kokei No. 14' and 'KM95-A68'. The onset of increase in root ZR levels was delayed by 2 or 3 weeks in 'KM95-A68' in comparison to 'Kokei No. 14'. Maximum root ZR levels in 'Kokei No. 14' were 2.2 times higher in comparison to 'KM95-A68'. This appeared to be a factor in delayed storage root formation of 'KM95-A68'. Results of reciprocal grafts of 'KM95-A68' and 'Kokei No. 14' indicated that the late storage root-forming characteristic of 'KM95-A68' is a characteristic that arises from the root itself.