Basil: improving knowledge and control of downy mildew in protected and outdoor crops (seed transmission and metalaxyl resistance)

Basil downy mildew, caused by the biotrophic oomycete Peronospora belbahrii, was first reported in sweet basil in the UK during the summer of 2010. Initially the disease was given quarantine status, with infected crops subject to statutory action; this status was lifted in 2012. The UK fresh basil industry is highly valuable, and the recurring problem of downy mildew is causing growers major issues.

Although new to the UK, the disease is endemic in many parts of Europe (including Switzerland (2001), Italy (2003), France (2005) and Hungary (2011)), North America, Africa, Asia and South America.

There has been a great deal of work published on basil downy mildew. However, knowledge gaps have been identified, particularly relating to sources of inoculum, role of alternate hosts, epidemiology and control. These gaps were primarily addressed in AHDB Project PE 024 however, on completion of the project, there were two areas where further work was required. These areas were covered in this extension project as follows:

1) Determine whether P. belbahrii infections can be transmitted to plants from P. belbahrii contaminated seed

2) Determine the level of metalaxyl-M resistance in P. belbahrii

Findings:

• Transmission of Peronospora belbahrii from basil seed to seedlings was demonstrated for two naturally infected seed lots, with 0.4% and 1.3% seedlings showing symptoms of downy mildew.
• Metalaxyl-M resistance was found in three out of the four Peronospora belbahrii isolates collected from the UK.

Additional information:

See related AHDB-funded research on basil downy mildew (PE 024)

1) Determine whether P. belbahrii infections can be transmitted to plants from P. belbahrii contaminated seed

2) Determine the level of metalaxyl-M resistance in P. belbahrii