Genetically modified (GM) plants offer an ideal model system to study the influence of single genes that confer constitutive resistance to pathogens on the ecological behaviour of plants. We used phytometers to study competitive interactions between GM lines of spring @entity3505 @entity3505 carrying such genes and control lines. We hypothesized that competitive performance of GM lines would be reduced due to enhanced transgene expression under pathogen levels typically encountered in the field. The transgenes pm3b from @entity3505 (resistance against powdery mildew Blumeria graminis) or @entity70535 and glucanase genes from @entity2247 (resistance against fungi in general) were introduced with the ubiquitin promoter from @entity2829 (pm3b and @entity70535 genes) or the actin promoter from @entity579 (glucanase gene). Phytometers of 15 transgenic and non-transgenic @entity3505 lines were transplanted as seedlings into plots sown with the same 15 lines as competitive environments and subject to two soil nutrient levels. Pm3b lines had reduced mildew incidence compared with control lines. @entity70535 and @entity70535 /glucanase lines showed the same high resistance to mildew as their control in low-nutrient treatment and slightly lower mildew rates than the control in high-nutrient environment. Pm3b lines were weaker competitors than control lines. This resulted in reduced yield and seed number. The Pm3b line with the highest transgene expression had 53.2% lower yield than the control whereas the Pm3b line which segregated in resistance and had higher mildew rates showed only minor costs under competition. The line expressing both @entity70535 and glucanase genes also showed reduced yield and seed number under competition compared with its control. Our results suggest that single transgenes conferring constitutive resistance to pathogens can have ecological costs and can weaken plant competitiveness even in the presence of the pathogen. The magnitude of these costs appears related to the degree of expression of the transgenes.

Competitive performance of transgenic XXXX resistant to powdery mildew.

@entity2247 :: ('4513', 'Species') :: ['barley'] @entity2829 :: ('4577', 'Species') :: ['maize'] @entity3505 :: ('4565', 'Species') :: ['Triticum aestivum', 'wheat'] @entity579 :: ('4530', 'Species') :: ['rice'] @entity70535 :: ('542525(Tax:4577)', 'Gene') :: ['chitinase', 'Chitinase']
@entity3505 :: (4565,Species) :: ['wheat']
