Following seed treatment of wheat (T riticum aestivum L.) with 14Clabelled triticonazole at a dose of 1É8 g kg~1 seed, the uptake of radioactivity by shoots and roots was investigated from the two-to three-leaf stage up to the beginning of the booting phase, 80 days after sowing. Triticonazole equivalents taken up by wheat plants reached 5É7% and 14É6% of the applied dose in the shoots and the roots, respectively. Between the two-to three-leaf stage and the beginning of the booting phase, the concentration of triticonazole equivalents in the shoots decreased from 2É5 to 0É15 lg g~1 fresh weight. This was attributed to uptake of triticonazole by roots not keeping pace with shoot growth and increased retention in the roots of triticonazole taken up. The main factor limiting the uptake of triticonazole by the roots may be the rapid growth of the uptake-active apical root parts out of the dressing zone which had formed in the soil. Distribution of triticonazole equivalents taken up by the main shoot showed a decreasing concentration gradient from the oldest to the youngest leaf. An increase in the seed treatment dose was investigated as a way to increase the concentration of triticonazole in the shoots, but its inÑuence remained limited.1998 SCI ( Pestic. Sci., 53, 324È332 (1998)
The uptake of 14C-labelled triticonazole by wheat caryopses during imbibition was investigated. The uptake from an aqueous solution appeared to be driven by mass Ñow rather than by accumulation in seed lipids. During treatment with a liquid seed-dressing preparation of triticonazole, c. 1 kg triticonazole per caryopsis (2É4% of applied triticonazole) entered the seed. During germination in soil, another c. 1 kg triticonazole per caryopsis entered the seed in 24 h. In killed seeds, no penetration was observed between 24 h and 72 h after the beginning of imbibition. After seed treatment and imbibition in soil, triticonazole appeared to be located in the seed coats and embryo, but not in endosperm ; experiments suggested that the testa acted as a barrier. Under our conditions, the pathway from seed coats to shoots was not an important route for triticonazole uptake by the shoots.
A corn seed dressing with the fungicide triticonazole at 760 nmol/seed prevents head smut disease. In resting seeds, the dressing treatment was followed by the penetration of 19% of the product, 9% inside the tegument and 7% inside the pedicel. In growing seedlings, the inner content increased in the storage organs (endosperm + scutellum) as well as in the growing organs. The partition lipophilic phase/water certainly explains the high apparent fungicide concentration progressively reached inside endosperm and scutellum. However, no important transfer of fungicide from these organs to the growing parts seems to occur. It appears therefore that the fungicide transfer from the coating to the roots mostly occurs through dissolution of the product in the surrounding soil water and through root absorption. The efficient fungicide concentration inside the meristem is likely to be obtained during the early stages of development.
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