LAUSR

Simple Summary Aphids are vectors of plant viruses and can cause important yield losses in numerous crops. Rhopalosiphum padi is the main vector of Barley yellow dwarf virus PAV (BYDV-PAV). The yellow dwarf disease (YDD), present in all cereal growing regions in the world, caused by BYDV-PAV, can induce up to 80% of yield losses in barley. In a context of global warming, reduction of pesticide uses, and development of organic farming, new control methods for YDD incidence are needed. In this study, the association of a winter barley with clover was tested for its impact(s) on the R. padi/BYDV-PAV pathosystem. The effect of clover was different according to the morph of the aphid introduced in a multi-plant (i.e., arena) experimental design in laboratory. A spatial effect on aphid distribution (observed for alate founder morph) and a reduction of the size of aphid populations (observed for wingless founder morph) are described. However, the presence of clover did not modify, under our experimental conditions, the efficiency of BYDV-PAV infections and within arena spread of YDD. Thus, clover used by cereal growers for other services (weeds reduction, nitrogen supply, and soil cover), would participate to lower the risks associated to the presence of BYDV vectors through a bottom-up regulation of aphid populations within the field. Barley/clover intercropping should be considered as a promising method for a future management strategy against vectors of yellow dwarf disease, especially in an insecticide-free agriculture. Abstract Intercropping, i.e., association of two or more species, is promising to reduce insect populations in fields. The cereal aphid Rhopalosiphum padi, a vector of the Barley yellow dwarf virus PAV (BYDV-PAV), represents a major threat for cereal grain production. In this study, we tested the potential of winter barley intercropped with clover to reduce the size of R. padi populations and to lower the BYDV-PAV incidence in fields. We used arenas (i.e., sets of 36 barley plants) intercropped with or without clover plants (at different sown densities). In each arena, a single viruliferous founder, R. padi, (with an alate or a wingless morph) was deposited to introduce aphids and viruses in the experiment. Thirteen days later, the number of aphids in the arena, the percentage of plants hosting aphids and the infection rates were monitored. Data produced through this experimental design showed that clover alters the distribution of the aphid progeny (lower aphid spread) produced by an alate founder morph. Moreover, clover reduces the size of aphid populations produced by a wingless founder morph. However, despite the effects of clover on biological parameters of R. padi, the presence of clover in barley arena did not modify BYDV infections, suggesting complex mechanisms between partners of the BYDV pathosystem for plant-to-plant virus spread.