In south-western France, sunflowers are usually grown in short rotations and after a long fallow period during which soils are left bare. This practice can favour diseases, caused by soilborne fungi, such as sunflower verticillium wilt (SVW), as well as nitrate leaching, both of which can decrease yields. Growing cover crops during a fallow period is an agroecological practice that could provide ecosystem services and mitigate SVW. A Brassicaceae cover crop that causes biofumigation produces glucosinolates and liberate biocidal compounds that might regulate SVW biologically. Moreover, the green manure effect of the Fabaceae might increase soil mineral nitrogen (SMN). To go further, mixtures of Brassicaceae and Fabaceae might mutualise the benefits that each cover crop has in sole crops. A four-year field study in south-western France tested Brassicaceae (brown mustard, turnip rape and fodder radish) and Fabaceae (purple vetch) in sole crops or a mixture with two or three species during the fallow period, followed by biofumigation, and sunflower crop. The cover crops were characterised, SMN was measured, the SVW and yield were assessed and compared to those of the crop grown on soils left bare during the fallow period. Purple vetch as a sole crop cover crop significantly increased SMN before sunflower sowing but only in 2019. Fodder radish as a sole crop reduced SVW severity significantly, overall, 80 days after sowing, except in 2019, when weather conditions were unfavourable to biofumigation. Purple vetch as a sole crop also reduced significantly SVW severity in 2017 and 2020. Finally, sunflower yields after cover crops were higher than those after bare soils, only after purple vetch as a sole crop in 2020, with a mean increase of 0.77 t ha⁻¹. Mixtures of Brassicaceae and Fabaceae sowed at these densities resulted in an intermediate SMN level between those in sole crops and the bare soil and they did not significantly decrease SVW or increase yields. Our results suggest that cover crops, especially fodder radish or purple vetch, and biofumigation can provide ecosystem services for sunflower, instead of leaving soils bare during the fallow period. However, the extent of ecosystem services is markedly affected by soil and climatic conditions as well as other management practices.

Sunflower (Helianthus annuus L.) is one of the three most productive oilseed crops worldwide. Soilborne diseases limit yields and are challenging to manage. The fungi Verticillium dahliae, Sclerotinia sclerotiorum and Macrophomina phaseolina can survive in the soil for many years and spread. Following the ban on fumigants, biofumigation, which consists of growing, chopping and incorporating a Brassicaceae cover crop to allow biocidal compounds production in the soil, may be an alternative. Biocidal effects of the hydrolysis of glucosinolate into active compounds, such as isothiocyanates, have been shown in laboratory studies, but the effectiveness of biofumigation varies more in the field. The present study reviews the main factors that determine effective biofumigation to protect sunflower. Since the toxicity of isothiocyanates to pathogens varies widely among the latter, we reviewed studies that assessed the suppressive effect of products of glucosinolate hydrolysis on V. dahliae, S. sclerotiorum and M. phaseolina. Farmers can use many mechanisms to increase isothiocyanate production, which may protect sunflower crop effectively. Increasing biomass production and chopping the cover crop during mild temperatures and before rainy periods could increase biofumigation effectiveness. Further field experiments are needed to confirm the potential of biofumigation to control soilborne diseases of sunflower and assess potential disservices to beneficial soil communities, given their potential key role in the control of soilborne pathogens.

Cover crops, sown between cash crops to provide ecosystem services, contribute to sustainability but present challenges related to the use of environmental resources out of the main cropping season. This dataset gathers the results of 37 field experiments related to cover crops, whether grown in sole crops or in mixtures, conducted in France over 19 years. It compiles quantitative data from field measurements and laboratory analyses on 33 species among five botanical families, along with information on technical management and climate conditions, providing a valuable resource for assessing cover crops performance.

Le dessèchement précoce du tournesol résulte d'une infection de bas de tige par Phoma macdonaldii qui provoque une nécrose encerclante et un rétrécissement du diamètre du collet. Cette attaque entraine une sénescence foliaire brutale occasionnant des pertes dommageables pour la culture. Des contaminations artificielles par des spores ou du mycélium de P. macdonaldii ont permis de reproduire artificiellement des pieds secs et confortent l'implication de ce champignon dans ce syndrome. Dans un contexte où la protection chimique et la résistance variétale sont limitées, la maîtrise de P. macdonaldii par le contrôle cultural pourrait constituer une alternative efficace. Des essais au champ et en serre menés de 2006 à 2009 à l'INRA et au Cetiom ont permis de mettre en évidence l'importance de la conduite de culture du tournesol sur la fréquence et la gravité du dessèchement précoce et de mieux comprendre l'étiologie de ce syndrome. Une alimentation azotée importante, un peuplement dense et à un régime hydrique limitant en post floraison forment trois facteurs particulièrement favorables au développement du syndrome de desséchement précoce attribué à P. macdonaldii. L'alimentation azotée, au travers de la fertilisation, est le principal facteur favorisant la maladie ; le régime hydrique limitant et la densité de peuplement amplifient la maladie. Le faible diamètre de bas de tige (sous de fortes densités) associé à la prolifération du champignon dans le xylème (azote), occasionnerait une réduction de la conductance hydraulique par obstruction des vaisseaux. Amplifiée lorsque la disponibilité en eau du sol est limitante, cet arrêt de la transpiration se traduit par une sénescence anticipée de 40 jours par rapport à la maturité physiologique de peuplement sains.