Uptake of 14C-SAN 789 F and 14C-cyproconazole into germinating wheat following seed treatment at different soil matric potentials

Abstract

The effects of fungicide uptake into germinating wheat and adsorption to the soil were studied following seed treatment with 14C-SAN 789 F, a fungicide of the homopropargylamine class, and 14C-cyproconazole, a triazole fungicide, at soil matric potentials between −2 and −70 kPa. Seed treatment with the strongly lipophilic SAN 789 F provided highly-concentrated seed dressing zones over the whole range of soil matric potentials. As a consequence, SAN 789 F was efficiently absorbed by seedlings over 3 d (approximately 35% of the total recovered amount). On the other hand, the moderately lipophilic cyproconazole provided more diffuse seed dressing zones at soil matric potentials of −2 and −10 kPa resulting in reduced uptake rates. At −70 kPa, however, cyproconazole produced similar seed dressing zones as SAN 789 F, but was absorbed by the seedling more efficiently than SAN 789 F (approximately 50% after 3 d). Quantitative analyses of the amount of 14C-SAN 789 F and 14C-cyproconazole incorporated into different plant tissues revealed that both compounds accumulated mainly in the testa (approximately half of the amount), that the embryo and the pericarp accumulated considerable amounts (approximately 25% each). Only traces were found in the radicle and endosperm. When seeds were treated with SAN 789 F, moderate phytotoxic effects were observed independent of the size of matric potential. In contrast, seed treatment with high concentrations of cyproconazole resulted in moderate phytotoxic effects at matric potentials of −2 and −10 kPa and strong effects at −70 kPa. Thus, phytotoxic effects of these two fungicides are mainly caused by the rate of fungicide uptake into germinating seeds. Moreover, uptake of these fungicides depends on both the soil matric potential and the size of seed dressing zones.