Effect of Nutrient Levels and Mineral Composition on the Occurrence of Yellow-leaf-spot in Chrysanthemum

　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.

９月から10月収穫の作型のキク（Chrysanthemum×morifolium）の葉身で発生する黄斑は水ストレス，高温，強日射，養分ストレスが発生要因として考えられている．本実験では無機養分の濃度，バランスが黄斑の発生に及ぼす影響を調査した．'精興の誠'を５種類の濃度の液肥（園試処方Ｎ０，60，120，180，240，300 ppm）で栽培した場合，液肥濃度が高くなるにつれ，黄斑が発生する範囲，程度共に増大する傾向が見られた．'精興の誠'と'精興の勝'に園試処方１/３濃度を基準とし，Ｎ，Ｐ，Ｋ，Ca，Mg，Fe それぞれを基準の３倍になるように作成した液肥を３または14日間与えた場合，'精興の勝'では黄斑発生は見られなかった．'精興の誠'では黄斑発生は見られたが，発生範囲，発生度ともに処理の影響は見られなかった．また，それぞれの無機養分を欠如させた液肥を作成し10日間与えた場合も黄斑発生に影響は見られなかった．これらの結果から，黄斑発生には遺伝的要因が関与しており，特定の無機養分の過不足により引き起こされるものではないと考えられた．