Effects of Benlate 50 DF on microtubules of cucumber root tip cells and on growth of cucumber seedlings

The aim of this study was to determine whether the fungicide Benlate 50 DF has adverse effects on the microtubules of cucumber root tip cells and on growth of the young seedlings. Germinating cucumber seeds and young seedlings were exposed to six concentrations of Benlate ranging from 1 mg/liter to 10 g/liter. Although seed germination was not affected by Benlate, seedling growth, especially number and length of branch roots, was reduced in proportion to the concentration of Benlate and length of treatment. Significantly lower mitotic indices were obtained from root tips exposed to 0.1, 0.6, 1, or 10 g/liter of Benlate. By means of immunofluorescence microscopy, the major microtubule arrays of root tip cells exposed to Benlate were compared and contrasted to those of controls. A few abnormalities in microtubule arrays were found at or after cytokinesis, and were of two types: 1) persistence of phragmoplast microtubules; and 2) presence of an array of microtubules between two recently divided daughter nuclei in the plane that would normally be occupied by the new cell wall. These abnormalities are somewhat similar to those induced by caffeine, and, as with caffeine treatment, possibly reflect impaired or/and incomplete cytokinesis that results in production of binucleate cells. A few binucleate cells were observed in root tips exposed to 10 g/liter of Benlate.