GAMETOCIDAL POTENCY OF ETHYL 4' FLUOROOXANILATE IN RICE

Relative efficacy of three oxanilate formulations namely ethyl 4'fluorooxanilate, ethyl 4'bromooxanilate and ethyl 2'nitrooxanilate in comparison to the check gametocide sodium methyl arsenate was studied for selective induction of male sterility on the rice variety Pusa 150 at two concentrations and three stages of.development. Ethyl 4'fluorooxanilate applied with 1500 ppm at stamen-pistil primordia stage or at stage between polIen mother celI formation and meiosis proved most effective with highest polIen and spikelet sterility, widest action spectrum and least phytotoxicity. Gametocides of wide action spectrum ensure higher seed yield and genetic purity. Pilot study on hybrid seed production revealed ethyl 4'fluorooxanilate applied as single spray at stamen-pistil primordia stage to be superior to sodium methyl arsenate with higher percentage seed set, test grain weight and seed yield. Ever since the reports on the existence in rice of exploitable hybrid vigour, research efforts to identify potent gametocides have been on along with equal thrust given to development of cytoplasmic-genetic male sterility system. [1-10]. Of the three major groups of chemicals viz., ethylene-releasing compounds, carcinogenic arsenic compounds and growth harmones evaluated over the last three decades surprisingly none has been found to qualify as ideal for use in commercial hybrid seed production. Whereas some have been reported effective but carcinogenic, others either effective but phytotoxic or partially effective though safe. Considering further the unique advantages of two-line hybrid breeding approach using either chemical hybridizing agent (CHA) or environment sensitive male sterility system over the cytoplasmic-genetic male sterility-based three-line breeding efforts in search of ideal CHA's still continue. Following reports that oxanilates selectively impair pollen