Abstract
A shoot with leaf color mutation in a Japanese pear (‘Osa-Gold’) was found among trees treated by chronic gamma-ray irradiation. Seven nurseries raising plants from mutated specimens were surveyed in 2004 and 2009. In 2004, shoots with yellow-green leaves and with yellow-green margin variegation leaves were observed. The comparisons of observation in 2004 and 2009 showed that yellow-green mutant was stable and five types of shoots sprouted from the branches with variegated leaves in 2004 were observed in 2009. These findings showed that the variegated mutant was apparently unstable; however SAM structure in the yellow-green variegations was also stable and the development of L2 and L3 were merely different depending upon leaves. Furthermore, the results of microscopic observation, the phenotypes of cross pollinated seedlings, twin sector variegations showing the yellow-green variegated leaves indicated that the leaf-color mutant was heterozygous and showed a semi-dominant gene. Furthermore mutant cells in the SAM of the variegated shoot occupied the L2 layer. The methods of utilizing these mutants are discussed.
