Biology Division, Bhabha Atomic Research Centre, Trombay, Bombay
In order to elicit information regarding the effect of diethyl sulphate (dES) on rice (Oryza staiva, L.) and also to examine if different varieties show a differential response to this chemical, dormant seeds often varieties, seven indicas, two japonicas and one javanica (bulu), were treated for two hours with 0.2 per cent., 0.3 per cent., 0.4 per cent, and 0.5 per cent, solutions. Distilled water was used for controls. Treated seeds were sown in a split-plot design and reductions in seedling emergence and height used as measures of chemical damage.
The effects on both the seedling emergence and height generally exhibited a dose dependent relationship. In general, the effect on height was more pronounced than that on emergence. Statistical analyses of results delineated the doses between which seedling emergence and height fell significantly below that of untreated controls. Such differences were obtained for emergence at the cone, of 0.3 per cent., while for height the lowest cone, of 0.2 per cent, was sufficient, although varietal differences were quite evident.
The emergence differences due to dES treatments, in relation to control, were not significant in three of the indicas and the javanica variety; in the rest of the indicas the differences were significant at cone. greater than 0.3 per cent. Both the japonicas showed significant differences at all concentrations, except the lowest. Only two indica varieties, namely A 157 and K 42, exhibited somewhat similar response only at the two highest concentrations. However, the japonicas showed relatively much higher and significant reductions with each increasing dose. The LD 50 amounted to circa 0.5 per cent. concentration for both the japonicas but only one indica.
The height differences due to dES treatments, in relation to control, were not significant up to 0.4 per cent. cone, in one indica, up to 0.3 per cent. conc. in four other indicas and the javanica and up to 0.2 per cent. in the remaining two indicas. In the case of the japonicas, the reduction effect at any given dose was significantly different than that at any other dose. Among the indicas, three varieties, viz., A 157, H.R. 47 and K 540, showed such differences at conc. of 0.5 per cent, and/or 0.4 per cent. The japonicas responded the same way as they did for emergence. The LD 50 amounted to between 0.3 per cent, and 0.5 per cent. concentrations only for the japonica varieties.
The japonicas were thus found to be more susceptible to diethyl sulphate than either the indicas or the javanica variety, which exhibited gradations of treatment effects. The above differences were apparently not related to certain agronomic traits like duration, grain size and shape and aroma. Differences with regard to chemical permeability through husk in different varieties is not known. However, the genetic diversity in varieties is assumed to be mainly responsible for their differential response to diethyl sulphate.
