Resumen de Breeding for durable resistance to downy and powdery mildew in grapevine
D. Merdinoglu, P. Blasi, S. Wiedemann-Merdinoglu, P. Mestre, E. Peressotti, C. Schneider, E. Prado
The current strategy to control grapevine downy and powdery mildew relies on chemical treatments. An alternative solution to the use of chemicals is the development of varieties resistant to pathogens. Therefore a program to create new grapevine varieties with a durable resistance to downy and powdery mildew and with a berry quality suitable for high quality wine production was launched in 2000. The situation seemed very favourable to start up such a program: plenty of resistance sources were available, and several resistance QTLs with various effects had already been discovered. Nevertheless a first case of downy mildew resistance breakdown was described in the cultivar ?Bianca?. Even if resistance durability is a retrospective judgment, some principles can be considered to monitor the risk of resistance break-down: pyramiding resistance genes, taking into account the evolutionary potential of the pathogen or assessing the cost of virulence, from a practical point of view, a durable management of resistance meaning to reduce the selection pressure applied by the resistance genes on the pathogen population. Therefore we chose to use multiple sources of resistance as genitors. The genetic determinism of most of them was analysed and the molecular markers derived from these studies were quickly integrated to assist with selection. Concerning the shortening of the breeding process, we developed a greenhouse growing method allowing to go from seed to seed in one year and a resistance phenotyping platform to get the precise plant phenotype as early as possible in the process. Moreover all the field trials have been performed through an experimental network, which allows us to save time and to take into account the differences in environment conditions. The overall process of selection is organized into three steps and takes 16 years. We expect to propose our first varieties for registration in 2016.
