Determining the oilseed rape pod strength needed to reduce seed loss due to pod shatter

Seed pods of oilseed rape (Brassica napus) are fragile at harvest maturity and seed loss can be a significant fraction of potential yield if bad weather occurs when the crop is most vulnerable. Even in good weather, loss of up to 25% has been reported when harvest operations are late. Plant breeders need to be able to identify accurately single plants that provide resistance to pod shatter from amongst very large breeding populations. A'random impact' test, involving controlled agitation of samples of 20 pods to measure their breaking response, was used to compare 12 experimental lines, to fit a model and hence to estimate the sample half-lives found to range from 2.6 to 129 s. Using the fitted model, the treatment time for any fraction opened could then be estimated. For cultivar Apex to reach 25% of pods opened, equivalent to reported seed loss caused by bad weather in standing crops, the treatment time was found to be 17 s, with fiducial limits of 12 and 22 s. The 11% loss reported in field crops in normal conditions was achieved at 9.7 s agitation time, with fiducial limits of 5.1 and 14 s. The fraction of pods opened at 17 s for the other 11 lines was then estimated from the model. In two lines, less than 10% of pods opened, suggesting that these pods have a much better potential to survive intact than pods of current cultivars. The methodology proposed is potentially of value in oilseed rape breeding. (C) 2002 Silsoe Research Institute.