Spores of V. pirina.
Image credit: Cecilia Deng

Pear infected by V. pirina.
Image credit: Cecilia Deng

Venturia pirina (Aderh.)  (synonym, V. pyrina) is the causal agent of European pear scab disease and is the most important fungal disease of pears worldwide. It infects leaves, shoots, blossoms and fruit, and may result in major crop losses during particularly wet seasons. V. pirina belongs to the Ascomycota (Pezizomycotina; Dothidiomycete; Venturiaceae). It is closely related to the apple scab fungus, V. inaequalis, and has a very similar life cycle and mode of infection. The life cycle begins in early spring when ascospores, the primary inoculum, are released from pseudothecia and germinate on the surface of leaves or pear fruits, penetrating the cuticle and establishing infection in the sub-cuticular space.  During the growing season infections disrupt the cuticle to release asexual conidia that are dispersed by wind and rain, proliferating throughout spring and summer. In autumn, the fungus switches from its biotrophic lifestyle to a saprobic lifestyle, and fungal mating occurs on dead leaf litter between two isolates differing in mating type, prior to overwintering as developing pseudothecia. There are currently no commercial European pear cultivars available that are naturally resistant to the fungus and control measures involve multiple, timely applications of fungicide throughout spring through to summer and post-harvest. Asian pears such as Ya Li and Nashi are resistant to V. pirina.
V. pirina and V. nashicola  (S. Tanaka and S. Yamam.) have shared a co-evolutionary history with progenitor Pyrus hosts that has led to host specificity in these fungi.  This makes Venturia spp excellent candidates for further research into determinants of host-specificity and mechanisms of non-host resistance. In order to understand the genetic basis of specificity and pathogenicity determinants, the genome of V. pirina has been sequenced and comparisons between strains and other Venturia species will provide insights into the evolution of this and other pome-fruit infecting scab fungi.

• Bowen JK, et al. 2011. Venturia inaequalis: the causal agent of apple scab. Molecular Plant Pathology 12: 105-122.
• Bus VGM, et al. 2011. Revision of nomenclature of the differential host-pathogen interactions of Venturia inaequalis and Malus. In: VanAlfen NK, et al. eds. Annual Review of Phytopathology, Vol 49. Palo Alto, Annual Reviews. pp391-413.
• Cooke IR, et al. 2014. Proteogenomic Analysis of the Venturia pirina (Pear Scab Fungus) Secretome Reveals potential Effectors. Journal of Proteome Research, 13(8):3635-44. doi: 10.1021/pr500176c.
• Jones, D. PhD Thesis 2015  ‘Whole genome sequencing of Venturia pirina enables a comparison of effectomes of two fungal fruit pathogens’ La Trobe University, Melbourne Australia.