Stock Downy Mildew – an Update

Following the CFC organised meeting of stock growers at J A Collison and Son last week, the resistance testing trial is now underway with Dr Phil Jennings at FERA.  Downy mildew is an obligate parasite which means that it will only live on live tissue.  This means that testing can only be done on living plants rather than in test tubes or petri dishes.  The first stage of such testing is therefore to collect infected leaves from growers crops, wrap them up in moist tissue and post to FERA.  FERA then culture them overnight in their growth room to obtain a fresh flush of spores which are then washed of the old plant tissue and used to reinfect new seedling which will then act as the inoculum for infecting enough seedlings to start doing the resistance tests in due course.   This rather drawn out and complicated procedure for dealing with obligate parasites means that the results of the trial will not be available for another 6 to 8 weeks but the information will be available in good time for developing next years spray programme and hence give growers the confidence that we can successfully control this new aggressive strain of the disease.

So far FERA has been supplied with 4 different downy mildew samples and during  a visit on Friday the CFC Project Manager was shown the trial and it looks like 3 out of the 4 isolates has successfully infected the new seedling.  Fresh samples from the nursery that failed to take had in fact already been collected and were left with FERA on the day.

It has been agreed that 8 chemicals will be tested for resistance but the total number of isolates is still under discussion.   Florensis have very generously agreed to financially  contribute to this trial but discussions are under way with other propagators and seed houses to see if they will also contribute in order to enable more isolates to be tested.

We will updated the blog as the trial progresses.