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The overall objectives were as follows:

1. Identify wheat root traits suitable for selection for mixed cropping and management (organic vs conventional) systems.
2. Document the effects of crop species mixtures on above ground diseases, pests and biotic ecosystem services: e.g. suppression of pests and diseases by natural antagonists.
3. Determine how diversity affects difficult to manage soil-borne pathogens.
4. Identify key criteria for efficient weed suppression in crop mixtures.

To identify wheat root traits suitable for selection for mixed cropping and management (organic vs conventional) systems, experiments under controlled conditions were conducted in Hungary (MTA ATK; mega pot experiment) and Germany (UNI KASSEL; hydroponic experiments).

In Hungary, wheat pure lines and diverse wheat populations were grown in monoculture or mixed with pea under well-watered and drought conditions. Diverse wheat populations performed well and were highly adaptable in species mixtures compared to wheat pure lines under both, well-watered and drought conditions. In parallel field experiments root colonization with arbuscular mycorrhizal fungi in all wheats was significantly higher when grown in mixtures with peas compared to the pure stands, and under organic vs conventional conditions. The work in Hungary shows that root reactions to intercropping can be measured in vivo and highlighted genotype specific reactions.

The hydroponic experiments in Germany documented farming system specific adaptations (organic vs conventional) of wheat populations and varieties in terms of root length and early soil cover. Selection for seminal root length could be done non-destructively and could thus be useful for population improvement.

Both, the work in Hungary and Germany have potential to become effective tools for breeders selecting for intercropping and management system. These results need to be validated in the field. Once validated they will add important methodology for breeding which should help to improve crop selection for species mixture (Figure 1).

The effects of species mixtures on pests, diseases, benefits and weeds was assessed in field experiments across a range of pedo-climatic conditions from southern to northern Europe. In Spain (INTIA), for example, broccoli-vetch intercropping helped suppress pests while floral strips in broccoli and fava bean-barley or fava bean- floral strips did not despite high numbers of natural enemies found in these treatments. In France (INRA-IGEPP), additional experiments under controlled conditions highlighted the importance of plant spatial arrangement on biological control of aphids in fava bean-oat mixtures. This study specifically showed dependencies of the aphid parasitoid on a food source in the near vicinity. In Germany (UNI KASSEL), cropping systems effects on earthworms and beneficial nematodes were also studied in a long-term organically managed experiment comparing plough vs minimum tillage systems. There, the minimum tillage system was more diversified as it received dead and living mulch treatments. After the excessive drought period in November 2018, the number of earthworms was very low with the large majority of animals in juvenile stage. This demonstrates the detrimental effect of the drought and that even in November no recovery of the population had occurred. Free living nematodes were significantly higher under minimum tillage compared to plough independent of the compost application. During a crop of grass-clover numbers were more than doubled. First results from the Netherlands (DLO) indicate that cover crop mixtures in light soils may favor nematode species such as Pratylenchus penetrans, and thus could result in yield reduction in susceptible cash crops in the rotation. However, taken together with the results from Germany, adding additional organic amendments might help shift the balance towards beneficial nematodes.

Cereal and legume diseases (foliar and foot and root rots) were low across the sites due to the dry conditions, but in general foliar diseases in mixed treatments tended to be lower than in the monocrops. More susceptible varieties often showed somewhat greater differences between pure and mixed treatments (Figure 2). With respect to foot and root rots, cereals generally had no or only low symptoms of foot rot. Foot and root rot on pea was also low in most sites (Hungary, Switzerland and Sweden) and moderate in Germany. With respect to pathogens isolated from the sampled plants, there were no clear effects of mixtures on frequency of any of the most frequent species isolated. However, different pathogens dominated on different hosts and in different pedo-climatic regions.

The differential effects of pea varieties and choice of mixing partner were shown to play an important role also in weed suppression. Field experiments in France (ACTA), for example, showed that the highest weed suppression was obtained when pea was intercropped with barley compared with pea monocrop and pea–wheat or pea-triticale intercrops. In Germany, weed pressure was generally low (8% cover and lower). A meta-analysis using the data from literature (performed by Wageningen University) showed that weed biomass in intercrops was between 8 and 58% lower than in pure stands depending on the plant species included in the mixture. The analysis included over 339 records from 76 field experiments. In addition, based on separate simulation experiments using FLORSYS conducted in France (INRAE), crop traits that contribute to weed suppression in mixed cropping systems were identified. This information will be used to specifically identify pea and wheat traits which contribute to weed suppression in intercropping and can then be used in breeding for species mixtures.