ホウ素過剰による秋ギクの葉縁褐変と日持ち低下に及ぼす二, 三の要因

Abstract

Summary Effect of boron (13) concentration (0.2, 5 and 10 ppm) in nutrient solution on the major mineral and B content, and ethylene (C2H4) and carbon dioxide (C02) production was investigated in relation to the occurrence of marginal leaf-burn and deterioration of vase life in chrysanthemums grown in sand. The nutrient solutions containing B were applied the last 3 weeks before harvest. Marginal burns appeared on the upper leaves of the plant at 10 ppm B 16 days after treatment and thereafter, developed towards the lower leaves and involucre. Symptoms were found on upper leaves at 5 ppm B only at harvest. However, plants at 0.2 ppm B did not exhibit B toxicity symptoms. Vase life of cut flowers decreased by 15 to 17 days at 5 and 10 ppm B compared with 0.2 ppm B. B in leaves increased significantly with increasing B concentration in nutrient solution. B was much higher in the leaf margin than in the internal leaf areas. Potassium (K) in leaves gradually increased after treatment, but was slightly decreased at harvest. K was much higher in the internal leaf areas than margin. Total-N, P, Ca, Mg and Na in the leaves were not influenced by B concentration in nutrient solution. B in various parts of the flower increased significantly with increasing B concentration in nutrient solution. The 13 content in decreasing order was involucre > ray floret > tublar flower > receptacle. K in various parts of the flower decreased slightly with increasing B concentration in nutrient solution. The K content in decreasing order was receptacle > ray floret --- involucre > tublar flower. The cut flower having marginal leaf-burn produced more C2114 and CO2 than those with the normal leaves. However, they decreased markedly by removal of the leaf margin. When petals or leaves of the cut flower began to wilt, the vessels of the stem end were plugged with a brownish substance. The substance was stained well with ruthenum red, methylene blue and safranin, although it was not stained with congo red and aniline blue. Therefore, it is possible that the vessel plugging substance is a pectinlike compound. As a result, the marginal leaf-burn is apparently caused by high concentrations of B along the margin of leaves. Higher accumulation of B in leaves or ray floret, and plugging of pectin-like compounds in vessels of the stem may be one of the causes for deterioration of the vase life.