First, second, third, and fourth authors: Department of Plant Pathology; and fifth, sixth, seventh, and eighth authors: Department of Soil Chemistry and Plant Nutrition, ARO, the Volcani Center, Bet Dagan 50 250, Israel
Go to article:
Accepted for publication 8 March 2006.
Deformation disease of Gypsophila paniculata mother plants reduces cutting yields as much as 50% but does not kill the mother plants. In preliminary experiments, fertigation of G. paniculata mother plants with a 20:20:20 compound fertilizer (N, P, K, plus microelements) at an N concentration of 720 mg/liter reduced the expression of deformation disease compared with the conventional N concentration of 360 mg/liter. The current study determined which component of the compound fertilizer reduced the disease. Experiments were carried out in 10-liter buckets packed with naturally infested 0- to 8-mm black tuff (Scoria = crushed volcanic stones). Irrigation was applied once a day at 0.5 liter per bucket with the nutrient under test being added at 1.0 liter per bucket via the water once a week. Treatments included: (i) four levels of 20:20:20 fertilizer; (ii) four levels of each of N, P, K, and Fe-Zn-Mn mixture (ME) corresponding to their concentrations in the compound fertilizer; (iii) different N sources (20:20:20, (NH4)2SO4, KNO3, NH4NO3, urea); and (iv) three pHs of the irrigation water at each of three NO3 and NH4 application levels. Increasing the 20:20:20 fertilizer concentration reduced the disease level from 82 to 96% with N at 180 mg/liter to 6 to 10% with N at 720 mg/liter. When either P, K, or ME was the sole variable, increasing concentrations had no significant effect on the disease, but elevating a mixed source nitrogen concentration from 0 to 180, 360, and 720 mg/liter (as 50% urea, 40% NH4NO3, and 10% KNO3) significantly reduced deformation similar to that observed with increasing concentrations of the 20:20:20 fertilizer. mong tested N sources, NH4 was the most effective in reducing the disease (almost to zero at an N concentration of 360 g/liter). Low disease incidence (0 to 10%) was always associated with effluent pH of 6 or lower. Irrigating with acidified water pH 5.5) in the presence of N, as NH4 at 180 mg/liter, additionally reduced disease from 56% under tap water (pH 7.8) rrigation to 11%. Similar acidification in the presence of NO - 3 N at 180 mg/liter was ineffective in reducing the disease, but ater basification in the presence of NO - 3 N reduced disease incidence from 93 to 38% 90 days after planting. The N, P, K, Fe, and Zn concentrations in gypsophila cuttings were similar under the three tested levels of NH4, NO3, and 20:20:20, whereas the concentration of Mn increased with increasing N. The Mn concentration in cuttings was inversely correlated with disease and is probably an important factor to understanding the physiological background of the deformation disease.
© 2006 The American Phytopathological Society