THE EFFECT OF FUNGICIDES AND PLANT-GROWTH REGULATORS APPLIED AS A SEED TREATMENT ON THE FREEZING TOLERANCE OF WINTER-WHEAT

Several plant growth regulators and fungicides, which inhibit gibberellin synthesis, were tested for their effect on the development of freezing tolerance of winter wheats (Triticum aestivum em Thell). Seeds of Norstar and Norwin were treated with either triadimenol; prochloraz, alone or in combination with imazalil; tetcyclasis; and carbathiin. The first four compounds are potent plant growth regulators that inhibit the production of gibberellins. The first three compounds, triadimenol, prochloraz and imazalil are also registered seed fungicides. Carbathiin, also a seed fungicide, has no known plant growth regulator activity. Prochloraz alone or in combination with imazalil and carbathiin initially delayed germination of both cultivars; after 144 h, however, germination was 90% or better for all treatments except the seeds of Norwin treated with carbathiin which were only 84% germinable. None of the fungicides increased the freezing tolerance of the Norstar crowns; however, carbathiin, tetcyclasis, triadimenol, prochloraz alone and in combination with imazalil (intermediate rate) reduced freezing tolerance. The freezing tolerance of Norwin, a semi-dwarf winter wheat, was reduced by tetcyclasis at the low and intermediate rate. In samples collected in the spring, the carbathiin treatment reduced the freezing tolerance of both Norwin and Norstar. None of the treatments affected the growth of the Norstar crowns in late October, Only triadimenol (intermediate rate) and tetcyclasis (intermediate and high rate) increased the crown moisture content. The carbathiin seed treatment increased the growth of Norwin crowns in the autumn. Nearly all of the treatments increased the crown moisture content of the Norwin crowns. In estimating spring vigour, only triadimenol (low rate) and tetcyclasis (intermediate rate) increased the leaf number of Norstar crowns, whereas nearly all treatments except tetcyclasis (intermediate rate) and prochloraz alone or in combination with imazalil increased leaf number of Norwin crowns. All rates of triadimenol and tetcyclasis, at the low rate, stimulated development of more roots for Norwin. The above seed treatment provide little or no benefit for the survival of winter wheats to a freezing stress.