Adaptation of the scab fungus Venturia inaequalis to different host plants and ecosystems
Venturia inaequalis is a species of biotrophic fungi best known for the disease it causes on apple, apple scab. However, V. inaequalis isolates have been categorised into two formae speciales, V. inaequalis f. sp. Pyracantha, that can infect Eriobotrya japonica (loquat) and Pyracantha sp. but not Malus ; and V. inaequalis f.sp. pomi that can infect Malus and E. japonica but not Pyracantha sp. Host range has been further categorised within V. inaequalis f.sp. pomi. In this group, seventeen races of V. inaequalis have been identified based on the corresponding resistance responses observed on a panel of differential hosts (Malus spp.). Furthermore, studies on the population genetics of V. inaequalis f.sp. pomi isolates from wild Malus species (Malus sieversii) in Central Asia, and those from modern domestic apple (M.× domestica) have revealed distinct population structures and differences in aggressiveness and host range depending on the populations from which they originate. Isolates from wild Malus sieversii Kazakh forests are less aggressive than those from domestic apple and while isolates from domestic apple are able to infect M. sieversii, isolates from M. sieversii are unable to infect domesticated apple. To understand the genic basis of these differences in host range and aggressiveness we have used traditional genetic analysis (crosses), comparative genomics and comparative transcriptomics of isolates from different populations and formae speciales. This approach has enabled us to identify candidate genes which may be involved in enabling or restricting growth of different isolates on specific hosts. More broadly, this analysis may help us to understand how pathogens can adapt to different host plants and from wild to domestic ecosystems.