Sustainable and efficient control of sunflower downy mildew by means of genetic resistance: a review.

The breeding of sunflower (Helianthus annuus L.) for resistance to downy mildew (caused by the oomycete Plasmopara halstedii Farl. Berl. & de Toni) is reviewed in this work under the scope of its sustainability and efficiency. When sunflower turned into an oilseed crop, resistance to the disease was included in its initial breeding strategies. Subsequent development of genomic tools allowed a significant expansion of the knowledge on the diversity of its genetic resistance and its application to the genetic control of the disease. Simultaneously to genetic improvements, and as a consequence of the close interaction between the pathogen and its host plant, an enormous variety of pathotypes has been described in all the sunflower-growing areas worldwide. Thus, the genetic control of sunflower downy mildew is an active research field subjected to continuous evolution and challenge. In practice, genetic resistance constitutes the base tier of Integrated Pest Management against sunflower downy mildew. The second tier is composed of elements related to crop management: rotation, removal of volunteer plants, sowing date, tillage. Biological control alternatives and resistance inducers could also provide additional restraint. Finally, the top tier includes chemical treatments that should only be used when necessary and if the more basal Integrated Pest Management elements fail to keep pathogen populations under the economic threshold.