液肥濃度と無機養分がキクの黄斑発生に及ぼす影響

　Yellow-leaf-spot, a physiological abnormality occurring in leaves of several chrysanthemum (Chrysanthemum ×morifolium) cultivars harvested from September to October, is a very serious problem in Japan, of which causes have not been well established. Water stress, high temperature, high irradiation or nutrient stresses are possible physiological factors which may lead to yellow-leaf-spot. In the present study, effects of nutrient levels and mineral composition on the occurrence of yellow-leaf-spot were investigated. ‘Seikou-no-makoto’ and ‘Seikou-no-masaru’ plants were grown in 5 nutrient solutions (N 0, 60, 120, 180, 240 ppm based on Enshi-shoho). In ‘Seikou-no-masaru’ no yellow-leaf-spot occurred. However, in ‘Seikou-no-makoto’, the nodal position with spotted leaves and rate of yellow-leaf-spot increased as nutrient levels increased. ‘Seikou-no-makoto’ plants were supplied with 6 different nutrient solutions containing 3 times N, P, K, Ca, Mg or Fe in 1/3 concentration of Enshi-shoho solution for 3 or 14 days. The nodal position with spotted leaves and rate of yellow-leaf-spot was not affected by mineral composition. The nodal position with spotted leaves and rate of yellow-leaf-spot increased with increasing days of application. Both cultivare were supplied with 7 different nutrient solutions with lacked N, P, K, Ca, Mg, Fe or only microelement (no mineral) in 1/2 Enshi-shoho solution for 10 days. In ‘Seikou-no-masaru’, no yellow-leaf-spot occurred. It occurred only in ‘Seikou-nomakoto’. yellow-leaf-spot occurred in control, P, K, Ca, Mg, Fe deficiency and no mineral, but only slightly in all cases. These results suggest that the occurrence of yellow-leaf-spot was dependent on genotype, and that excessive or deficiency specific elemental mineral stress had no significant effect.