Abstract
For sunflowers to be a profitable industrial-use crop, input costs must be as low as possible. Genetic resistance is therefore essential to control diseases without any spraying or seed treatment procedures. In France, Downy mildew is one of the most potentially important diseases. So far, complete, major gene resistance (Pl genes) has been used successfully, but with the appearance of seven new races since 2000, research on more durable resistance has been undertaken. Since 2003, methodologies for large-scale trials have been developed to study field reaction to Downy mildew attacks on genotypes which do not have Pl genes effective against the predominant races present. It has been shown that significant levels of partial resistance exist in cultivated sunflower lines (15% infection when susceptibles show 80-90% infection). This resistance appears independent of race (at least 710 and 703). Heredity is under additive control and the behaviour of hybrids can be quite well predicted from inbred lines. Present and future research programmes are discussed and suggestions are made for the use of partial resistance in breeding programmes.
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