Interactions between French isolates of Phomopsis/Diaporthe helianthi Munt.-Cvet. et al. and sunflower (Helianthus annuus L.) genotypes

Three artificial infection tests measuring the rate of mycelial growth of 7 Phomopsis/Diaporthe helianthi isolates were used on leaves, stems and capi tula of 6 sunflower hybrids. Isolates and hybrids were chosen to cover the range of variability and resistance levels known at the present time. Signi ficant genotype and isolate effects and isolatexgenotype interactions were shown in all the tests, with some changes in order of hybrids according to the isolate used for infection. Consequences of interactions in breeding fo r stable resistance to P./D. helianthi are discussed.