SUMMARY Broadleaf weeds cause considerable yield losses to sunflower production in all regions of the world. Resistance to the imidazolinone herbicides, imazethapyr and imazamox, found in a population of wild sunflower, could have great value for controlling many broadleaf weeds. The herbicide resistance was successfully transferred from resistant wild sunflower plants to a cultivated sunflower inbred line, HA 425. The objective of this investigation was to determine the inheritance of resistance to the herbicide imazamox in HA 425. Segregation ratios of plants in F 2 and testcross populations indicated that resistance was controlled by two genes, a major gene having a semi-dominant type of gene action ( Imr1 ), and a second gene ( Imr2 ) with a modifier effect when the major gene is present. Resistance in sunflower can only be achieved with homozygocity ( Imr1, Imr1, Imr2, Imr2 ) of both resistance genes in an inbred line or in a hybrid. Completely resistant hybrids require having resistance factors in both parents.
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Bruniard et al. (2001) studied this question.
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