Spongospora subterranea and Potato mop-top virus (PMTV) cause the economically important tuber blemish diseases powdery scab (PS) and spraing on potato tubers. Powdery scab causes significant losses because there is no effective means of chemical control, it is readily visible on tubers and is a major cause of rejection of exported seed.

Spraing induced by PMTV results in unsightly internal brown lines and raised external rings on the tubers of sensitive potato cultivars but can cause symptomless infection in other cultivars. No resistance genes to PMTV or S. subterranea have been identified in potato germplasm to date. PMTV-induced spraing has become more apparent in seed crops in recent years, which has led to crop failure in ware potatoes grown for the fresh (salad) market and rejection of seed crops for export.

Previous work at SCRI has produced molecular diagnostic tests for both PMTV and S. subterranea and has shown that PMTV is carried within vector zoospores. There is some evidence of genetic variation of S. subterranea and two types have been identified based on ribosomal DNA sequence analysis but there is little knowledge of the virulence or efficiency of virus transmission by the different types. It has been suggested that virus transmission may inhibit PS formation.

This project aims to investigate variation in S. subterranea populations for aggressiveness, genotypic character and efficiency of transmission of PMTV. In addition, PMTV encoded proteins that may be responsible for virus transmission will be investigated in order to elucidate the relationship between the virus, vector and disease incidence. Knowledge of the existence of pathotypes of S. subterranea is important for understanding survival in the environment and host resistance in potato, and together with information on virus transmission will be used to develop integrated disease control strategies for both PS and PMTV-induced spraing.