MORPHOLOGICAL EFFECTS OF NAPHTHALIC ANHYDRIDE AND/OR THIOBENCARB ON IR-36 AND RD-19 RICE SEEDLINGS

Abstract

The root and shoot elongation as well as the anatomy of IR-36 and RD-19 rice seedlings treated with different concentrations of NA (1,8-naphthalic anhydride), thiobencarb (S-4-chlorobenzyl diethylthiocarbamate) and NA + thiobencarb was observed. Root elongation in the 2 cultivars was adversely affected by thiobencarb but not by NA treatment. Generally, the presence of NA in antidote-herbicide treatments seemed to reduce the inhibitory effect of thiobencarb on the root. Shoot growth was inhibited by thiobencarb and NA+ thiobencarb to a greater extent than root growth. Inhibition of root and shoot elongation was more pronounced in IR-36 than in RD-19 seedlings. Root growth inhibition by thiobencarb was not accompanied by any phytotoxic symptom at the histological level. In the shoot, thiobencarb injury was expressed by kinking of linear rows of cells and alteration of physical arrangement of mesophyll cells in developing leaves within the coleoptile. This anatomical effect was noted in all thiobencarb treatments with or without NA in both cultivars except in the NA +5 ppm thiobencarb treatment on RD-19 seedlings. Such anatomical observation can be correlated with the abnormal growth and emergence of leaves from grass coleoptiles which are the major phytotoxic symptoms induced by thiobencarb and other thiocarbamate herbicides.