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 immersion in household bleach solutions (50% bleach and 2.6% NaOCl) adjusted to 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 non-dormant rice seeds in order to test the direct effect of sodium hypochlorite on rice seedling growth apart from an indirect effect related to elimination of microbial contaminants. Seeds were immersed for 2 h in each solution or water in each of the following treatments: (i) sterilewater followed by sterile water, (ii) HgCl₂ (1,000 μg/ml) followed by sterile water, (iii) HgCl₂ followed by KH₂PO₄ (0.3 M), (iv) HgCl₂ followed by NaOCl, and (v) NaOCl followed by sterile water. Sodium hypochlorite 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 treated with HgCl₂ followed by NaOCl, and NaOCl followed by sterile water, 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 stimulated rice seedling growth directly, as opposed to an indirect effect related to elimination of microbial contaminants or alleviation of dormancy.