Mycocentrospora acerina   (R. Hartig) Deighton (1972)

Mycocentrospora leaf spot

- Distribution and damage

This fungus , which is quite widespread throughout the world, has rarely been reported on lettuce , mainly in England. In France , it has been sporadically found on this plant during February or March in the south, on lettuce produced in the open field.


- Symptoms

Small spots translucent at first, rather rounded, spreading quickly taking a tint brown to brown . Necrotic tissue dries out, becomes papery and falls off. Ultimately, many holes dot the leaf blade (figure 1). A black and deliquescent rot can be initiated and gradually spread to the apple.

The pivot, via the point of insertion of one or more rotten leaves, may be affected (Figure 2). In this case, the plant suddenly wilts, as in attacks on the crown of Botrytis cinerea or Sclerotinia spp.


- Elements of biology

Mycocentrospora acerina survives on plant debris thanks to its dense, brown mycelium with thick walls like those of chlamydospores (toruloid form) (figure 3). Its large polyphagia allows it to attack a large number of vegetable plants (parsley, parsnip, celery, carrot ...) and floral (primrose, cyclamen, pansy, petunia ...). The latter, like several sensitive weeds (capsella, nettle and stellate), ensure the multiplication of this fungus and play the role of reservoir plants. Contamination occurs during wet and cold periods, following splashing. Once in the tissues, the fungus quickly colonizes them and symptoms are visible after 5-6 days. It sporulates on altered tissues forming characteristic elongated, hyaline conidia. They have 5 to 11 septa and a thin, tapered lateral appendage (Figure 4). These spores are dispersed following rains and provide secondary contamination. In some plants, seeds also allow the fungus to spread over long distances.

Periods of humid and relatively cold weather ( 5 to 15 ° C ) favor the development and spread of this fungus.


- Protection

Several measures will be taken in the rare farms affected by this fungus:
- carry out crop rotations fairly long not involving sensitive crops;
- disinfect the soil with a fumigant; dazomet gives good results;
- use healthy seeds .

Fortunately, this fungus is rather rare because no fungicide is approved for this use in France.

Old diseased leaves will be removed at harvest time; they will in no case be left on the ground.

New plantings should be avoided near affected crops. The nursery floor as well as the structure of the shelters can be disinfected. No resistant variety is currently available.

NB: The legislation on pesticides evolving very quickly, we advise you to consult the e-phy site of the Ministry of Agriculture and Fisheries which is an online catalog of plant protection products and their uses, fertilizers and culture media approved in France. This also applies to all biological products based on microorganisms or natural substances.