Effect of fipronil seed treatments on the germination and early growth of rice

Fipronil seed treatments were evaluated to determine whether they directly influence germination and subsequent seedling growth in rice (Oryza sativa L). Continuous seed exposure to fipronil (four days) at 2000 mg litre(-1) s ignificantly impaired germination (P < 0.001). When exposure was restricted to a 1-h period 48 h after the initiation of germination, early post-germi nation growth was also impaired (assessment two days after exposure, P < 0. 05). The proportion of seeds satisfying our criteria for normal germination fell by 2.3 and 2.6% respectively across 17 cultivars. Cultivar effects we re highly significant (P < 0.001). When exposure to fipronil (2000 mg litre -1) was restricted to 2 h at initial seed wetting no significant growth imp airment occurred. No significant differences (P > 0.05) were found between shoot lengths or root system dry weights of control plants and plants devel oping from seed exposed continuously (two days) to fipronil at rates of up to 2000 mg litre-1 during germination and harvested nine days after sowing. Treating germinated seed with fipronil for Ih immediately prior to sowing at rates of up to 4000 mg litre-1 did not result in significant changes (P < 0.05) in plant growth parameters at either nine or 25 days after sowing. No evidence of fipronil having a direct phytostimulatory effect on rice was obtained. (C) 1999 Society of Chemical Industry.