Agronomic comparison of two sets of SSD barley lines differing for the ym4resistance gene against barley mosaic viruses

The ym4 gene has been extensively used in breeding for resistance against b arley mosaic viruses. The objective of this study was to investigate whethe r resistant lines carrying this gene were lower yielding than susceptible l ines derived from the same cross when grown on a disease-free soil. Eightee n 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, suscept ible 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 s usceptible ones by 0.3 t ha(-1). In this case lodging was high and it was s hown that susceptible lines were more susceptible to lodging. They also hea ded 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 s tudy clearly showed that selecting for ym4 can lead to indirect selection o f unfavourable traits. ((C) Inra/Elsevier, Paris.).