SODIUM-HYPOCHLORITE - EFFECT OF SOLUTION PH ON RICE SEED DISINFESTATION AND ITS DIRECT EFFECT ON SEEDLING GROWTH

Bacteria were completely eliminated from rice seeds following immersio n in household bleach solutions (50% bleach and 2.6% NaOCl) adjusted t o pH 7.0 in 0.5 M potassium phosphate, while fungi were eliminated at pH 5.0 and below. Mercuric chloride was used to disinfest nondormant r ice seeds in order to test the direct effect of sodium hypochlorite on rice seedling growth apart from an indirect effect related to elimina tion of microbial contaminants. Seeds were immersed for 2 h in each so lution or water in each of the following treatments: (i) sterile water followed by sterile water, (ii) HgCl2 (1,000 mu g/ml) followed by ste rile water, (iii) HgCl2 followed by KH2PO4 (0.3 M), (iv) HgCl2, follow ed by NaOCl, and (v) NaOCl followed by sterile water. Sodium hypochlor ite solutions were prepared in 0.3 M potassium phosphate, which gave a final pH of 7.3. Seedling growth in treatments in which seeds were tr eated with HgCl2 followed by NaOCl, and NaOCl followed by sterile wate r, was significantly greater than those treatments in which seeds were treated with sterile water followed by sterile water, HgCl2 followed by sterile water, and HgCl2 followed by KH2PO4. Sodium hypochlorite st imulated rice seedling growth directly, as opposed to an indirect effe ct related to elimination of microbial contaminants or alleviation of dormancy.