Response of three winter wheat cultivars to difenzoquat

Summary The response to difenzoquat of the three winter wheat cultivars, Hobbit, Maris Huntsman and Score is compared. In an experiment in which plants with three to four leaves were sprayed with 0, 1, 2 and 4 kg ai ha −1 difenzoquat Maris Huntsman was most tolerant while Score appeared least tolerant. Difenzoquat reduced the main shoot height and lamina length, and increased tiller number. At the high doses the main shoot was often killed, particularly in Hobbit and Score, which showed stunting and tillering with the 1‐kg dose. DNA synthesis, monitored by 14 C‐thymidine incorporation in excised meristematic segments, and 14 C‐difenzoquat penetration and translocation were compared in the three cultivars. 1 × 10 −4 m difenzoquat inhibited DNA synthesis by 7·9, 29·3 and 45·5% in Maris Huntsman, Score and Hobbit respectively. This is likely to contribute to the different responses of Maris Huntsman and Hobbit as 14 C‐difenzoquat penetration and translocation were similar. However, there was a greater accumulation of 14 C activity in the apical meristem of Score, which is likely to contribute to the greater susceptibility of this cultivar, as is the greater inhibition of DNA synthesis and higher level of spray retention.