Agronomic comparison of two sets of SSD barley lines differing for the ym4 resistance gene against barley mosaic viruses

The ym4 gene has been extensively used in breeding for resistance against barley mosaic viruses. The objective of this study was to investigate whether resistant lines carrying this gene were lower yielding than susceptible lines derived from the same cross when grown on a disease-free soil. Eighteen susceptible and 18 resistant F7 lines derived from a three-way cross were grown over 2 years at four locations. In four out of eight trials, susceptible lines had on average a higher yield than resistant ones by 0.25 t ha(-1) (0 % humidity). In one trial, resistant lines significantly outyielded susceptible ones by 0.3 t ha(-1). In this case lodging was high and it was shown that susceptible lines were more susceptible to lodging. They also headed later (+1.4 days on average), were taller (+2.8 cm) and generally had a higher thousand kernel weight than resistant lines. Effect of the ym4 gene cannot easily be separated from possible effect of linked genes but this study clearly showed that selecting for ym4 can lead to indirect selection of unfavourable traits. ((C) Inra/Elsevier, Paris.).