Effects of Granular Ethephon on Male Sterility in Wheat 1

Granular ethephon (2‐chloroethylphosphonic acid) was studied as a gametocide on three winter and six spring wheat ( Triticum aestivum L.) cultivars. Applications were made during four stages in ontogeny viz, seeding, primary tiller emergence, initiation of spikelet primordia on the main culm, and during the early‐boot phase, in rate categories of 2 to 8, 26.9 to 109.2, and 164.5 to 822.0 kg a.i./ha. Sterility levels reached mean values of 65 (range 10 to 95), 71 (range 48 to 94) and 89% (range 36 to 100) for the respective rate categories. These values are means of pot/plot data and include different order tillers. Mean sterility levels rose with increase in the rate of gametocide; it was most effective when applied at the highest rate during reproductive development on the main culm. At low rates of application, winter cultivars were more responsive than spring cultivars perhaps because of their increased uptake with a more extensively developed root system. The granular form of ethephon may be more suited to practical use than the liquid form because the latter demands precision in the time of spraying and causes undesirable side effects. No apparent morphological or physiological abnormalities were observed with the granular form even at the very high rates used in these studies. A better understanding of the site and form of uptake may permit the use of lower rates with effective gametocidal action.