Unravelling Pea–Ascochyta Blight Interaction and Its Implications for Pea Breeding

Pea (Pisum sativum L.) is an important temperate grain legume crop of high nutritional and agronomic value. Ascochyta blight, caused by a multi-species complex of necrotrophic fungi, remains a major constraint for pea production worldwide. This review synthesizes the available genetic, physiological and molecular knowledge on the pea–Ascochyta blight pathosystem, with emphasis on the genetic architecture of resistance, host defense mechanisms and the recent contributions from the omics disciplines. Current evidence indicates that genetic resistance to the various Ascochyta blight pathogens is incomplete and multicomponent, being associated with loci of small to moderate effect, with expression depending on organ, developmental stage and environment. Under field conditions, the observed phenotypes reflect the interaction between physiological resistance, plant architecture, phenology, canopy microenvironment and epidemic dynamics. Together, these factors bias phenotyping and limit the transferability of molecular markers. The practical value of these markers for use in marker-assisted selection (MAS) and genomic selection (GS) is presented and critically discussed. Future progress in breeding for Ascochyta blight resistance will depend on integrating molecular knowledge with a careful definition of ideotypes, well-calibrated phenotyping and multi-environment validation.