A simple and robust in vitro assay to quantify the vigour of oilseed rape lines and hybrids

At present, there is no general laboratory assay described that allows quantification of the yield potential of plant lines obtained in breeding or research programmes. The only way to evaluate the performance of a plant line is by greenhouse and field trials over several years on different locations. In this paper, an in vitro physiological method is described that allows prediction of the yield vigour (amount of seeds ha–1) of hybrids and open-pollinating varieties of Brassica napus. The assay relates the vigour of a B. napus line or a hybrid to, first, the capacity of cultured hypocotyl explants to reduce 2,3,5-triphenyltetrazolium chloride (TTC), and second, to the sensitivity of this TTC-reducing capacity to acetylsalicylic acid (ASA), an active analogue of salicylic acid. Vigorous lines have a higher capacity to reduce TTC than less performing lines. TTC is reduced by the mitochondrial dehydrogenases and the efficiency of the formazan formation depends on the activity of cytochrome oxidase. The amount of TTC that is reduced in a certain time reflects the respiration rate. ASA, on the other hand, lowers the TTC-reducing capacity of the most vigorous lines, and enhances the TTC-reducing capacity of the less performing lines. The central role of salicylic acid in plant defence responses and respiration may explain the influence of ASA on the TTC-reducing capacity. From the results, it can also be concluded that the yield potential in B. napus is already present from the seedling stage onwards and persists until seed setting.