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 significantly impaired germination (P< 0.001). When exposure was restricted to a 1-h period 48h after the initiation of germination, early post-germination 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 were highly significant (P<0.001). When exposure to fipronil (2000 mg litre^-1) was restricted to 2h at initial seed wetting no significant growth impairment occurred. No significant differences (P > 0.05) were found between shoot lengths or root system dry weights of control plantsand plants developing 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 1 h immediately prior to sowing at rates of up to 4000mg 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. [ABSTRACT FROM AUTHOR]