The Michelmore lab at the University of California, Davis routinely monitors isolates of Bremia lactucae, the pathogen that causes lettuce downy mildew for their ability to overcome disease resistance genes and for insensitivity to fungicides. Isolates are currently being monitored for insensitivity to Revus, Forum, and Orondis. During 2021, 70 isolates were tested for growth on seedlings pretreated with 2 ppm Revus, 5 ppm Forum, or 0.5 ppm Orondis. Nearly all isolates were sensitive and showed no growth at these concentrations. However, two isolates were insensitive to Forum and when retested, grew on 4 ppm treated seedlings. Another isolate was insensitive to Revus and could grow on seedlings pretreated with 3 ppm Revus when retested. All three isolates were collected in Oceano. No isolates have been detected that are insensitive to Orondis. We are interested in receiving additional isolates from Oceano and other areas, particularly when there has been an apparent failure of control.
Please see the attached for instructions as to how to send samples.
Thank you for your help.
Richard Michelmore.
Distinguished Professor and Director
The Genome Center
Genome and Biomedical Sciences Facility
451 Health Sciences Drive
University of California
Davis, CA 95616
rwmichelmore@ucdavis.edu
http://genomecenter.ucdavis.edu
http://michelmorelab.ucdavis.edu
Please fill in as completely as possible. This will help entry into the database but do not worry if some/most of this information is not available.
Please include this datasheet when sending isolates.
Date Collected: ____/____/_____ Collector ID: _________________
Collector: _______________________________ (UC Lab ID: _________________)
Location: _____________________________________________________________________________________________
GPS coordinates if known: ____________________________
Disease Intensity / Level of infection (circle one):
Low (Few infected plants),
Intermediate (Infected plants scattered throughout field).
Severe (Many infected plants)
Please comment whether collected from a single plant or from several plants and whether from multiple locations in the field.
Comments: __________________________________________________________________________________________________________________________________________________________________________________________________________________
Fungicide treatment: Yes No Not known
If yes: Alliete Ridomil Revus Orondis Forum Other:__________________
Type: Crisphead Romaine Looseleaf Butterhead Babyleaf Other:______________
Cultivar/Variety: ____________________________________________________________________________
Approximate planting/water date ________________________________________________________
Other Comments: _________________________________________________________________________________________________________
_________________________________________________________________________________________________________Thank you for your help. Please address questions to Juliana Gill (giljuliana@gmail.com), and/or Richard Michelmore, rwmichelmore@ucdavis.edu.
Results will be available from http://bremia.ucdavis.edu/bremia_database.php.
Collection and Shipping Instructions:
Please send leaves with fresh sporulating lesions. These should be green or only slightly chlorotic:
Please not send leaves with dark necrotic lesions; it is difficult to rescue isolates from such samples because of bacterial contamination:
Please send overnight by Fed Ex (Account # 2630-4693-5) in a box rather than an envelope (to prevent samples being crushed) along with the datasheet and the words “Refrigerate upon arrival” on the outermost packaging to:
Attn: Juliana Gil
The Genome Center
Genome and Biomedical Sciences Facility
451 East Health Sciences Drive
University of California
Davis, CA 95616
Tel. 530-752-8889
Please notify Juliana Gil (giljuliana@gmail.com) with the tracking number when sent.
Please time the sending so that the isolate is not in the Fed Ex system over a weekend (i.e. do not send on a Friday). Isolates can be kept in a fridge at 5oC for a few days before sending if necessary, although sending samples immediately after collection is best.