Reducing height and lodging in rapeseed with growth regulators

Abstract

The plant growth regulators (PGRs) ethrel (20% a.i. 2-chloroethane phosphonic acid), PP 333 (25% w/v a.i. paclobutrazol), cycocel (50% w/v a.i. chlormequat chloride), pix (5% w/v a.i. mepiquat chloride) and EL 500 (50% w/w a.i. flurprimidol) were applied to bulky crops of Jumbuck, Marnoo and RU 14 rapeseed at Cowra and Woodstock in central-western New South Wales, in an effort to reduce their height and lodging. The most effective growth retardants under evaluation were PP 333 and EL 500, and this was achieved without apparent phytotoxicity. Height reductions were enhanced as rates were increased from 0 to 2 Lha, and the heights of Jumbuck, Mamoo and RU 14 were reduced on average by 22% (from 159 to 124 cm), 26% (from 136 to 100 cm) and 14% (from 150 to 129 cm), respectively. Significant reductions in lodging accompanied these changes. Ethrel resulted in some phytotoxicity, while pix and cycocel had little or no measured effect on any plant characters. Jumbuck was the tallest variety and the most severely lodged, and under these conditions, yield responses to PGR were large (900 kg/ha or 54%). Shorter, erect plants produced an even, compact pod canopy, and as a result, ripening was more uniform, pod shattering reduced and harvesting more efficient. In situations where seed yields were increased, these practical considerations, rather than physiological responses (e.g. pod and seed set), were largely responsible. These findings support further research and commercial development of PGRs for use in canola production in the more favoured areas and support the inclusion of reduced plant height and increased stem strength as integral components of the overall breeding objectives for canola in Australia.