Effects of plant morphological traits on phoma black stem in sunflower

Abstract

Despite the importance of Phoma black stem of sunflower in France, no specific management tools are currently deployed to control this disease. The deployment of host plant resistance could be a cost-effective and sustainable way to manage the disease. Relationships between plant morphological traits and disease intensity may provide guidance towards the identification of sunflower morphological ideotypes associated with reduced disease intensity and therefore partial resistance. Such relationships were quantified in field experiments conducted over 2 years with a set of 21 sunflower genotypes, where several morphological attributes and several disease intensity variables were measured. Plant morphology was assessed prior to epidemic onset. Disease intensity was assessed at different scales of crop and plant hierarchy, using a nested sampling design, and implementing the concept of conditional disease intensity. The various analyses performed indicated that experimental plots grouped according to morphological attributes of sunflower at the flowering stage were associated with experimental plots grouped according to disease intensity variables, therefore indicating an association between morphological traits and disease intensity. Low disease intensity was associated with a morphological ideotype with large number of green leaves and tall stature. A sunflower plant morphological ideotype with more leaves and taller stature may represent an operational target in sunflower breeding when considering resistance to Phoma black stem.