Effects of Seed Treatment with SAN 789 F, a Homopropargylamine Fungicide, on Germination and Contents of Squalene and Sterols of Wheat Seedlings

Abstract

Wheat seedlings ( Triticum aestivum L. cv. Arina) contained mainly sitosterol and campesterol as the principal sterol compounds (71 and 21% of the total amount of free sterols, respectively), whereas stigmasterol (3%) and other unidentified sterols (together 5%) were much less abundant. Squalene, an important intermediate of sterol biosynthesis, was only found in traces. Seed treatment with SAN 789 F ( N-(5,5-dimethyl-3-hexynyl)- N-ethyl-1-naphthalenemethanamine), a homopropargylamine fungicide, induced two primary effects on sterol biosynthesis: First, squalene accumulated temporarily in large amounts within 48 hr after treatment, indicating an inhibition of squalene epoxidase; second, the content of free sterols slightly decreased within 14 days after treatment, probably as a consequence of squalene epoxidase inhibition. An additional effect of the seed treatment was an inhibition of growth occurring immediately after germination, whereas later, seedlings started to regrow. In contrast to a seed treatment with a wettable powder formulation (10 WP), seeds treated with an encapsulated "slow-release" formulation (CS 250) accumulated much less squalene. In addition, the growth of seedlings was only slightly inhibited by treatment with the CS 250 formulation. A reduced growth inhibition was also achieved when seedlings were treated between 3 and 7 days after germination. These results suggest that accumulation of squalene rather than a deficiency of free sterols is responsible for the inhibition of germination induced by the treatment with SAN 789 F. The inhibitory effects of the fungicide on growth and on squalene epoxidase were drastically reduced, when the homopropargylamine delivery to the seed was delayed by either a late application or the use of an encapsulated formulation.