Twenty sunflower inbred lines were studied for their reactions to 7 Sclerotinia sclerotiorum tests on different plant parts. A principal component analysis (EC.A.) and t-tests on the means of resistant and susceptible groups indicated that reactions of inbred lines to infection of capitula by ascospores are independent from those to ascospore infections of terminal buds. They are even more contrasted with the results of any test measuring mycelial extension. However, for the last, there is a close association between the reactions of roots, leaves and capitula. Of the inbred lines, some showed good levels of resistance to most forms of attack, others were generally susceptible and there were some with good resistance to one particular form of attack. A EC.A. of 18 morphological and field characters showed no general association between these characters and Sclerotinia sclerotiorurn test results, although it was found that lines resistant to mycelial extension on capitula were generally earlier than those that were more susceptible. It is proposed that breeding programmes for general resistance to Sclerotinia sclerotiorum should include a combination of two or three tests.

-Sunflower was a crop of great importance in Argentina until 2002; it was ranked among the countries with the largest production, about 18% of the world total. Currently, it is in the fourth place, with only 7%. Several factors caused Argentina to lose its leadership, the most important being that farmers preferred the soybean crop because of its competitiveness pushing sunflower to areas where the former crop was not adapted. However, in 2016/2017 there was an increase in area and production of sunflower, probably associated with the reduction of state intervention in farmer's income because export duties were totally eliminated, while those for soybean remained high. International forecasts suggest that an increase in the demand for sunflower oil and by-products is expected. Argentinean farmers can make a significant contribution to meeting these needs. The whole sunflower chain of value, grouped in the association ASAGIR, makes continuous efforts to improve the sunflower product, by research programs and other activities which will render sunflower more attractive for farmer. It is likely that, in a short time, Argentina could regain its place on the podium of sunflower producing countries.Keywords: history / agronomy / breeding / production / perspectives Résumé -La culture du tournesol en Argentine : passé, présent et potentiel futur. En Argentine, le tournesol était une culture majeure jusqu'en 2002. À cette période, le pays assurait 18 % de la production mondiale. Quinze ans plus tard, cette contribution a chuté à 7 %. De multiples facteurs ont conduits l'Argentine à perdre cette position privilégiée. Parmi les plus importants, on peut mentionner le soja qui est devenue la culture préférée des agriculteurs argentins en raison de sa plus haute compétitivité, comparativement à toutes les cultures estivales. Par conséquent, la culture de tournesol a été repoussée dans les régions plus marginales où le soja n'était pas adapté. Durant la campagne agricole 2016/2017, la surface emblavée ainsi que la production de tournesol a cependant augmenté par rapport aux années précédentes. Un phénomène qui peut être associé à la réduction de l'intervention de l'État dans le revenu des agriculteurs. Ainsi, les droits à l'exportation ont été totalement supprimés pour le tournesol, alors que ceux du soja restent encore élevés. Selon des organismes mondiaux, une hausse de la demande globale d'huile de tournesol et de sous-produits pourrait être attendue à court terme. Pour les agriculteurs argentins, se dessine une très belle opportunité de répondre à ces besoins internationaux de manière significative. En Argentine, toute la chaîne de valeur est regroupée dans l'association nationale du tournesol, dite « ASAGIR ». Des efforts sont menés en vue d'améliorer le produit tournesol via différentes activités et programmes (mise en valeur, divulgation, recherche, etc.). L'objectif est clair : rendre cette culture oléagineuse beaucoup plus attractive pour les agriculteurs locaux. Ainsi, il est fort probable que, d'ici peu de...

Resistance of sunflower leaves to attack by Sclerotinia sclerotiorum was studied by infecting them, in the field, with agar disks containing Sclerotinia mycelium. Resistance levels were determined by the length of lesions after a given period. There were significant differences in reaction between both sunflower hybrids and inbred lines. Different Sclerotinia isolates gave the same classification of sunflower genotypes. The results of trials repeated in one year or different years were significantly correlated. The general combining ability variance/specific combining ability variance ratio was 1.35. Strict sense heritability was 0.61 + 0.03. The midparent-offspring correlation coefficient was significant, but the relation between per se values of the male parents used with the values of their hybrids was much closer than that for the female parents. Mean heterosis for resistance was 28.9%, compared with the midparent. The results of the leaf resistance test are frequently correlated with levels of resistance to root attack by Sclerotinia. Possible use of this test in breeding both directly for leaf resistance and indirectly for root resistance are discussed. H.P.L. Chromatography studies of the phenols present in healthy and infected leaves distinguished 19 compounds, all of the inhibitin type. There was a large increase in phenol content in leaves infected by Sclerotinia, for all genotypes. However, more especially in uninfected leaves, the contents of 3 chromatogram peaks, numbered 4, 6 and 9, showed a close relation with levels of Sclerotinia resistance. It is proposed that these compounds could be used as markers of certain types of resistance.

Sclerotinia sclerotiorum infections on sunflower capitula produce white rot, one of the most dangerous diseases sunflower bears in all humid areas. Therefore, disease quantification on developed genetic materials is a very important action in sunflower breeding. Given the horizontal type of resistance these evaluations should be made in different environments. Several hybrids obtained after crossing seven female × seven male sunflower inbred lines in a factorial mating design were evaluated for resistance to white rot in two locations in the southeast of the province of Buenos Aires, Argentina. Disease incidence and the symptom appearance index indicated significant genotypic effects and genotype × environment (G × E) interactions. Genotypic effects were a greater source of variance than the G × E interaction effects. The G × E interactions only represented changes in magnitude. These results were used to identify the best genotypes for both resistance factors. Four hybrids showed low disease incidence values under both artificial and natural infections, of which only two had high values of the symptom appearance index at both locations. These hybrids are considered to have adequate resistance attributes for the ascosporic penetration and the mycelium extension in the capitulum tissue and could therefore be sown in the province of Buenos Aires without increasing risks of S. sclerotiorum attacks.