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Leguminous cover crop and living mulch species show not only great potential for providing multiple beneficial services to agro-ecosystems, but may also present pathological risks for other crops in rotations through shared pathogens, especially those of the genus Fusarium. Disease severity on roots of subterranean clover, white clover, winter and summer vetch grown as cover crop and living mulch species across five European sites as well as the frequency, distribution and aggressiveness to pea of Fusarium spp. recovered from the roots were assessed in 2013 and 2014. Disease symptoms were very low at all sites. Nevertheless, out of 1480 asymptomatic roots, 670 isolates of 14 Fusarium spp. were recovered. The most frequently isolated species in both years from all hosts were F. oxysporum and F. avenaceum accounting for 69% of total isolation percentage. They were common at the Swiss, Italian and German sites, whereas at the Swedish site F. oxysporum dominated and F. avenaceum occurred only rarely. The agressiveness and effect on pea biomass were tested in greenhouse assays for 72 isolates of six Fusarium species. Isolates of F. avenaceum caused severe root rot symptoms with mean severity index (DI) of 82 and 74% mean biomass reduction compared to the non-inoculated control. Fusarium oxysporum and F. solani isolates were higly variable in agressiveness and their impact on pea biomass. DI varied between 15 and 50 and biomass changes relative to the non-inoculated control -40% to +10%. Isolates of F. tricinctum, F. acuminatum and F. equiseti were non to weakly agressive often enhancing pea biomass. This study shows that some of the major pea pathogens are characterized by high ecological plasticity and have the ability to endophytically colonize the hosts studied that thus may serve as inoculum reservoir for susceptible main legume grain crops such as pea.

Early vigour traits of wheat composite cross populations (CCPs) based on high yielding (Y) or high quality (Q) or Y*Q varietal intercross evolving under organic or conventional conditions in parallel populations were studied hydroponically. To eliminate storage and year effects, frozen F 6 , F 10 , F 11 and F 15 seeds were multiplied in one field, resulting in the respective F x.1 generations. This eliminated generation and growing system effects on seed size for the F 6.1 F 10.1 and F 15.1. Due to a severe winter kill affecting the F 11 , the generation effect persisted, leading to larger seeds and markedly different seedling traits in the F 11.1 compared to the F 10.1 and F 15.1 . Seedling traits were similar among parallel populations. Shoot length and weight increased in both systems until the F 11.1 across farming systems and remained constant thereafter. Over time , seminal root length and root weight of organic CCPs increased and total- and specific- root length decreased significantly compared to the conventional CCPs. Rooting patterns under organic conditions suggests better ability to reach deeper soil nutrients. In both systems, Q and YQ CCPs were more vigorous than Y CCPs, confirming genetic differences among populations. Overall, heterogeneous populations appear very plastic and selection pressure was stronger in organic systems.

A winter wheat composite cross population (CCP), created in the UK in 2001, has been grown in Germany, Hungary, and the UK since 2005 (F5 generation). In 2008/09 (F8), a cycling pattern for the populations was developed between partners to test the effects of rapidly changing environments on agronomic performance and morphological characteristics. One CCP was grown by eight partners for one year and subsequently sent to the next partner, creating “cycling CCPs” with different histories. In 2013, all eight cycling CCPs and the three non-cycling CCPs (from Germany, Hungary, and the UK) were included in a two-year experiment in Germany with three line varieties as references. Differing seed weights of the F13 at sowing affected some agronomic parameters under drought conditions in 2014/15 but not under less stressful conditions in 2013/14. In both experimental years, the CCPs were comparable to the line varieties in terms of agronomic performance, with some CCPs yielding more than the varieties under the drought conditions of 2015. The results highlight the potential of CCPs to compete with line varieties, while the overall similarity of the CCPs based on their origin and cycling history for agronomic traits indicates a high buffering potential under highly variable environmental conditions.

Reducing soil tillage can lead to many benefits, but this practice often increases weed abundance and thus the need for herbicides, especially during the transition phase from inversion tillage to non-inversion tillage. We evaluated if subsidiary crops (SCs, e.g., cover crops) can mitigate the effects of non-inversion tillage on weed abundance. Two-year experiments studying SC use, tillage intensity, and nitrogen (N) fertilization level were carried out twice at six sites throughout northern and central Europe. SCs significantly reduced weed cover throughout the intercrop period (−55% to −1% depending on site), but only slightly during the main crops. Overall weed abundance and weed biomass were higher when using non-inversion tillage with SCs compared to inversion tillage without SCs. The effects differed due to site-specific weed pressure and management. With increasing weed pressure, the effect of SCs decreased, and the advantage of inversion over non-inversion tillage increased. N fertilization level did not affect weed abundance. The results suggest that SCs can contribute by controlling weeds but cannot fully compensate for reduced weed control of non-inversion tillage in the transition phase. Using non-inversion tillage together with SCs is primarily recommended in low weed pressure environments.

AbstractYields in organic farming have been stagnating, widening the gap with conventional systems. Thus, there is the need to reconsider traditional organic crop rotations and adopt innovative strategies that will maximize nutrient supply, weed suppression, and reduce disease risks. Overwintering legume cover crops offer potential solutions, but their role in nutrient cycling, weed management and pathogen dynamics needs to be clarified. In two multi-factorial field trials, we examined organic farming systems using no-till or minimal tillage with a 2-year rotation of winter-hardy legumes as cover crops, maize and a wheat/pea mixture. The risks of soil-borne pathogens and their transmission to subsequent crops were also assessed. The effects of the following factors were investigated: (a) cover crop type: winter vetch and crimson clover, (b) date of cover crop kill, (c) sowing technique: no-till or shallow tillage, and (d) use of cover crop biomass: green manure or mulch vs. harvest. The strong weed suppression of legumes allowed for herbicide-free implementation of minimum tillage and no-tillage systems, while their substantial nitrogen contributions supported the high maize yields. It was also possible to harvest the cover crop biomass before maize sowing instead of using it as mulch or green manure, without significantly affecting maize yields. Infestations with seed and root rot pathogens were generally low, and there was no risk of pathogen accumulation or transfer to subsequent crops. To our knowledge, this is the first systemic assessment of agronomic and phytopathological aspects in a rotation involving winter-hardy legumes, maize and a wheat/pea mixture under differential tillage practices. Taken together, our results demonstrate that, with proper management, legume-intensive rotations can maximize agronomic benefits, minimize phytopathological risks, and enhance productivity and sustainability in both organic and conventional farming, while contributing to a reduction of yield gap between systems.

The aim of this study was to investigate the potential of heterogeneous composite cross populations (CCPs) to increase sustainability and resilience of wheat cropping systems, a so far largely neglected approach. For this purpose, 10 CCPs originating from one CCP created in 2001 and having evolved under different environmental conditions since the F5, were compared in the F15 and F16 with 10 recently released cultivars and 10 inbred lines extracted randomly from the populations. Field trials were performed over 2 years at 2 organic and 2 conventional locations. Under organic conditions, yields of the CCPs were similar to those of recent commercial cultivars with comparable protein content, and considerably higher than that of the inbred lines. Under conventional conditions, conventionally-bred cultivars outyielded the other experimental entries. The organically-bred cultivars had the highest protein contents in both farming systems followed by the CCPs and the conventionally-bred cultivars. The yield stability and foliar disease resistances of CCPs was on average higher than that of the commercial cultivars and considerably higher than that of the inbred lines, indicating that the higher stability of the CCPs was due to their high genetic diversity, not to their genetic background. CCPs that had evolved in different environments differed in some morphological and phenological traits, indicating that adaptation to environmental conditions had taken place through natural selection. Greater tillering capacity and increased soil cover of CCPs in the juvenile stage compared to the inbred lines indicates niche complementarity in the CCPs, that may contribute to improved resource use and to an overall ecological intensification. We conclude, that the cultivation of CCPs or similar heterogeneous populations represents an important opportunity to increase the resilience of wheat cultivation, which should be given greater consideration in future research and breeding.

A total of 320 accessions of subterranean clover ( Trifolium subterranenum L.) were screened for adaptation to the environmental conditions in southern Germany, as well as their suitability as cover crops or living mulches. The accessions, derived from collections of the Department of Agriculture and Food Western Australia and the International Research Center for Agriculture in Dry Areas, were propagated in the greenhouse and grown in rows. Selected accessions were then tested in plots and as an intercrop in wheat, in order to test their suitability as living mulch. Moreover, a frost resistance screening was carried out in a climate chamber. Adaptation to southern German conditions and frost tolerance was generally better than expected, as most accessions survived winters with snow cover and transitory temperatures as low as - 10 ∘ C. Accessions with particularly high frost tolerance were identified and several accessions persisted over four generations of self-reseeding. Although there was a large range of morphological characteristics, no differences concerning their suitability as living mulch could be observed. The results suggest that subterranean clover is sufficiently winter hardy to be grown as an overwintering cover crop or living mulch in southern Germany. Commercially available cultivars appear suitable in the first instance, even though these have not been selected for cold winters. However, adaptation might be further improved by targeted selection among accessions.

Modern agriculture and conventional breeding and the liberal use of high inputs has resulted in the loss of genetic diversity and the stagnation of yields in cereals in less favourable areas. Increasingly landraces are being replaced by modern cultivars which are less resilient to pests, diseases and abiotic stresses and thereby losing a valuable source of germplasm for meeting the future needs of sustainable agriculture in the context of climate change. Where landraces persist there is concern that their potential is not fully realised. Much effort has gone into collecting, organising, studying and analysing landraces recently and we review the current status and potential for their improved deployment and exploitation, and incorporation of their positive qualities into new cultivars or populations for more sustainable agricultural production. In particular their potential as sources of novel disease and abiotic stress resistance genes or combination of genes if deployed appropriately, of phytonutrients accompanied with optimal micronutrient concentrations which can help alleviate aging-related and chronic diseases, and of nutrient use efficiency traits.We discuss the place of landraces in the origin of modern cereal crops and breeding of elite cereal cultivars, the importance of on-farm and ex situ diversity conservation; how modern genotyping approaches can help both conservation and exploitation; the importance of different phenotyping approaches; and whether legal issues associated with landrace marketing and utilisation need addressing. In this review of the current status and prospects for landraces of cereals in the context of sustainable agriculture, the major points are the following: (1) Landraces have very rich and complex ancestry representing variation in response to many diverse stresses and are vast resources for the development of future crops deriving many sustainable traits from their heritage. (2) There are many germplasm collections of landraces of the major cereals worldwide exhibiting much variation in valuable morphological, agronomic and biochemical traits. The germplasm has been characterised to variable degrees and in many different ways including molecular markers which can assist selection. (3) Much of this germplasm is being maintained both in long-term storage and on farm where it continues to evolve, both of which have their merits and problems. There is much concern about loss of variation, identification, description and accessibility of accessions despite international strategies for addressing these issues. (4) Developments in genotyping technologies are making the variation available in landraces ever more accessible. However, high quality, extensive and detailed, relevant and appropriate phenotyping needs to be associated with the genotyping to enable it to be exploited successfully. We also need to understand the complexity of the genetics of these desirable traits in order to develop new germplasm. (5) Nutrient use efficiency is a very important criterion for sustainability. Landrace material offers a potential source for crop improvement although these traits are highly interactive with their environment, particularly developmental stage, soil conditions and other organisms affecting roots and their environment. (6) Landraces are also a potential source of traits for improved nutrition of cereal crops, particularly antioxidants, phenolics in general, carotenoids and tocol in particular. They also have the potential to improve mineral content, particularly iron and zinc, if these traits can be successfully transferred to improved varieties. (7) Landraces have been shown to be valuable sources of resistance to pathogens and there is more to be gained from such sources. There is also potential, largely unrealised, for disease tolerance and resistance or tolerance of pest and various abiotic stresses too including to toxic environments. (8) Single gene traits are generally easily transferred from landrace germplasm to modern cultivars, but most of the desirable traits characteristic of landraces are complex and difficult to express in different genetic backgrounds. Maintaining these characteristics in heterogeneous landraces is also problematic. Breeding, selection and deployment methods appropriate to these objectives should be used rather than those used for high input intensive agriculture plant breeding. (9) Participatory plant breeding and variety selection has proven more successful than the approach used in high input breeding programmes for landrace improvement in stress-prone environments where sustainable approaches are a high priority. Despite being more complex to carry out, it not only delivers improved germplasm, but also aids uptake and communication between farmers, researchers and advisors for the benefit of all. (10) Previous seed trade legislation was designed primarily to protect trade and return royalty income to modern plant breeders with expensive programmes to fund. As the desirability of using landraces becomes more apparent to achieve greater sustainability, legislation changes are being made to facilitate this trade too. However, more changes are needed to promote the exploitation of diversity in landraces and encourage their use.