Development of Sulfonylurea‐Resistant Rapeseed Using Chemical Mutagenesis

Abstract

Residual levels of sulfonylurea (SU) herbicides in the soil have limited rapeseed ( Brassica napus L. var. napus ) production in the Pacific Northwest. In a greenhouse screening procedure, the test herbicide suppressed the growth of susceptible rapeseed plants but allowed normal growth of resistant plants. Mutant (M 2 ) populations of ‘Cascade’, ‘Bridger’, and ‘Cathy’ winter rapeseed, ‘R‐500’ spring rapeseed ( B. rapa L. subsp. rapa ), and ‘Tilney’ spring mustard ( Sinapis alba L.; syn F. hirta Moench.) were screened with DPX‐G8311, a 5:1 mixture of the SU herbicides chlorsulfuron (2‐chloro‐ N ‐[[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)amino]carbonyl]benzenesulfonamide) and metsulfuron {(methyl l‐[[[[(4‐methoxy‐6‐methyl‐l,3,5‐triazin‐2‐yl)‐amino]carbonyl]amino]sulfonyl]benzoate)}, applied preemergence at 7.5 g a.i. ha −1 . Approximately 243 000 M 2 seedlings were screened and 178 were selected for additional tests. In progeny tests, several M 3 and M 4 families were identified that survived 6.5 g a.i. ha −1 DPX‐G8311 applied preemergence but failed to survive the same rate of DPX‐G8311 applied postemergence. DPX‐G8311 was applied preemergence at 0 to 64 g a.i. ha −1 , to one M 3 and six M 4 families to determine a dose × family response relationship. Calculated 50% growth reduction (GR 50 ) values for both number of nodes produced and dry weight accumulation were up to 25 times greater for the selected M 3 and M 4 families than for the susceptible cultivar Cascade. Rapeseed lines resistant to soil residual levels of SU herbicides but susceptible to SU herbicide foliar applied would allow rapeseed to be planted after a small‐grain cereal to which a SU herbicide had been applied.