SummaryPlant resistance (R) genes are highly effective in protecting plants against diseases, but pathogens can overcome such genes relatively easily by adaptation. Consequently, in many cases R genes do not confer durable resistance in agricultural environments. One possible strategy to make the use of R genes more sustainable depends on the modification of R genes followed by transformation. To test a possible transgenic use of R genes, we overexpressed in wheat the Pm3b resistance gene against powdery mildew under control of the maize ubiquitin promoter. Four independent transgenic lines were tested in the greenhouse and the field during 3 years. The four lines showed a five-to 600-fold transgene overexpression compared with the expression of the endogenous Pm3b gene in the landrace 'Chul'. Powdery mildew resistance was significantly improved in all lines in the greenhouse and the field, both with naturally occurring infection or after artificial inoculation. Under controlled environmental conditions, the line with the strongest overexpression of the Pm3b gene showed a dramatic increase in resistance to powdery mildew isolates that are virulent on the endogenous Pm3b. Under a variety of field conditions, but never in the greenhouse, three of the four transgenic lines showed pleiotropic effects on spike and leaf morphology. The highest overexpressing line had the strongest side effects, suggesting a correlation between expression level and phenotypic changes. These results demonstrate that the successful transgenic use of R genes critically depends on achieving an optimal level of their expression, possibly in a tissue-specific way.

Parasitoids are an important mortality factor for insects. Susceptibility to parasitoids should thus be under strong negative selection. Nevertheless, ample genetic variation for susceptibility to parasitoids is commonly observed in natural populations, suggesting that trade-offs may constrain the evolution of reduced susceptibility. This can be studied by assessing genetic variation for susceptibility and its covariation with other components of fitness. In a set of 17 clones of the peach potato aphid, Myzus persicae, for which good estimates of heritable variation for life-history traits were available, we found significant clonal variation for susceptibility to two of their common parasitoids: Aphidius colemani and Diaeretiella rapae. One clone, the only one harbouring a facultative endosymbiotic bacterium, Regiella insecticola, was entirely resistant to both parasitoids. Susceptibilities to the two parasitoids exhibited a positive genetic correlation close to unity, implying a general mechanism of defence. However, the susceptibility to parasitoids was uncorrelated to the clones' fecundity or rate of increase, providing no evidence for costs of the ability to resist parasitoids.

Long-term canopy storage of seeds in fruits (bradyspory) varies among species and is thought to be related to the fire regime experienced by the plant community. This study sought to quantify intraspecific variation in bradyspory among nine populations of Banksia serrata (Proteaceae) on the south coast of New South Wales. Marked differences were fotind between populations, ranging from more than 30% of follicles open at two coastal sites, to less than 5% of follicles open at two inland heath sites. Low levels of bradyspory occurred particularly in coastal sites which also had Banksia integrifolia, a non-bradysporous species, present. In addition to spontaneous follicle opening without fire, fall of infructescences to the ground after breaking of branches was observed to be a major contributor to seed release. At three sites where fire had not occurred for many years, the amount of seedling establishment since the last fire corresponded well with levels of bradyspory; there were no inter-fire recruits at the site with tie strongest bradyspory, while at the site with the weakest bradyspory there were numerous inter-fire plants, some with lignotubers large enough to be able to tolerate the next fire. It is argued that populations of iJ. serrata exhibit variable patterns of recruitment, depending on the site characteristics, ranging from complete dependence on fire for population maintenance to bet-hedging (spreading potential recruitment between fire events and inter-fire periods). Variations in populations and reproductive characteristics among sites make the application of demographic models to management decisions habitat-specific.

The aphid parasitoid Lysiphlebus fabarum is suspected to form distinct, host-associated lineages and exhibits poorly understood variation in reproductive mode including thelytokous and arrhenotokous populations. As a tool to study these issues, we developed 11 polymorphic microsatellite markers. The observed number of alleles ranged from two to 35, and the observed heterozygosity ranged from 0.01 to 0.64. Cross-species amplification tests demonstrated their utility for several congeners, but revealed very limited applicability to more distantly related species. The aphid parasitoid Lysiphlebus fabarum is suspected to form distinct, host-associated 2 lineages and exhibits poorly understood variation in reproductive mode including 3 thelytokous and arrhenotokous populations. As a tool to study these issues, we developed 4 eleven polymorphic microsatellite markers. The observed number of alleles ranged from 5 2 to 35, and the observed heterozygosity ranged from 0.01 to 0.64. Cross-species 6 amplification tests demonstrated their utility for several congeners, but revealed very 7 limited applicability to more distantly related species. 8 9 10

Since the introduction of genetically modified (GM) plants, one of the main concerns has been their potential effect on non-target insects. Many studies have looked at GM plant effects on single non-target herbivore species or on simple herbivore–natural enemy food chains. Agro-ecosystems, however, are characterized by numerous insect species which are involved in complex interactions, forming food webs. In this study, we looked at transgenic disease-resistant wheat ( Triticum aestivum ) and its effect on aphid–parasitoid food webs. We hypothesized that the GM of the wheat lines directly or indirectly affect aphids and that these effects cascade up to change the structure of the associated food webs. Over 2 years, we studied different experimental wheat lines under semi-field conditions. We constructed quantitative food webs to compare their properties on GM lines with the properties on corresponding non-transgenic controls. We found significant effects of the different wheat lines on insect community structure up to the fourth trophic level. However, the observed effects were inconsistent between study years and the variation between wheat varieties was as big as between GM plants and their controls. This suggests that the impact of our powdery mildew-resistant GM wheat plants on food web structure may be negligible and potential ecological effects on non-target insects limited.