Search

Premature ripening (PR) is one of the most important fungal diseases in France, responsible for high yield losses in sunflower crop in the main regions of production. Previous results indicated that girdling canker of the stem base, caused by Phoma macdonaldii, was its primary cause. Previous studies have reported the influence of nitrogen and water supply on the incidence and severity of PR but an additional study was required to analyse the effect of plant density on the level of attack for a more comprehensive cultural control of PR. This study supplements the known effects of crop management on sunflower PR and emphasizes the key role of crop canopy in understanding the processes involved in the development of the disease. This morphology could be manipulated through crop management (plant density, N fertilization) and probably breeding.

International audience; Plant yield and oil content determine sunflower production. Those plant production determinants depend in turn on the plant–environment interaction. In the South West of France, there have been recent advances in soil tillage. To date, 35% ofthe soil surface dedicated to sunflower is cropped under a reduced tillage system. Major constraints to sunflower cropping are water stress and cryptogamic diseases. The second most important sunflower disease in the South West of France is premature ripening caused by Phoma macdonaldii. Aims of this work were to: 1) understand how these factors influence sunflower yield, and 2) quantify the fatty acid quality variation under reduced tillage and Phoma macdonaldii infection. Results showed that 1) soil tillage influences sunflower oil fatty acid composition, 2) Phoma macdonaldii-induced premature ripening impacts plant nutrition through its effects on organs (leaves, stems, roots), yield and yield components, and 3) thedisease influenced oil quality and the balance oleic-linoleic fatty acids.

National audience; Phoma macdonaldii is the causal agent of black stem disease of sunflower (Helianthus annuus L). In France, the incidence and severity of the disease increased dramatically in the early 90s and the entire sunflower cropping area is now affected. Premature ripening appeared in 1994: it is at the present time one of the most widespread and detrimental diseases of sunflower. Recent investigations confirmed that stem base girdling canker due to P. macdonaldii is the primary cause of this syndrome. Crop management and varietal susceptibility can influence significantly the incidence and severity of P. macdonaldii attacks and premature ripening. Partial resistance and presence of tissue-specific resistance genes have also been demonstrated.