Differences in Density and Size of Idioblasts containing Calcium Oxalate Crystals in Petioles among Cultivars of Taro (Colocasia esculenta (L.) Schott. and C. gigantea Hook, f.)

Abstract

The petioles of 37 Japanese taro cultivars (Colocasia esculenta (L.) Schott. and C. gigantea Hook, f.) which belong to 14 cultivar groups were examined to compare the densities and sizes of their calcium oxalate crystal idioblasts. Two types of raphide idioblasts were observed in petioles of all cultivars examined: the nondefensive raphide idioblasts, which are elongated cells containing a tightly connected raphide composed of many needle-like crystals; the defensive raphide idioblasts, also elongated cells, but containing a loosely connected raphide. The densities of raphide idioblasts differed among cultivar groups, whereas in some cultivar groups, they closely resembled each other. No definite differences in the densities of raphide idioblasts were recognized among the cultivars within the same cultivar group except for a few. The densities of druse idioblasts were higher than those of raphide idioblasts in all cultivars examined. Definite differences in the densities of druse idioblasts were recognized among cultivars within the same group. The 14 cultivar groups were divided into 2 types according to the density of raphide idioblasts in the petioles: the low density type, 'Migashiki', 'Mizu-imo', 'Shoga-imo', 'Tono-imo', 'Yatugashira', 'Hasu-imo', 'Egu-imo' and 'Akame-imo'; the high density type, such as: 'Hasuba-imo', 'Ishikawa- wase', 'Dotare', 'Kurojiku', 'Binroshin' and 'Takenoko-imo'. The densities of raphide idioblasts of cultivars with edible petioles were less than those of cultivars with edible corms. The size of the raphide and druse idioblasts was comparatively small in the cultivars with edible petioles. These results indicate that the densities and sizes of raphide idioblasts are useful as the selection indices in breeding of taro cultivars with edible petioles.