Stemphylium botryosum f. lactucum  Padhi & Snyder (1954)

Stemphylium leaf spot

- Distribution and damage

Described many years ago in several countries, especially in Europe (Great Britain, Italy, the Netherlands, Spain and Portugal), in Israel, in South Africa and in the United States, this fungus is not currently considered as a major pathogen of lettuce, except possibly in Israel. A Stemphylium herbarum was reported on endive in Italy.


- Symptoms

At spots first small and moist , gradually taking on variable shapes : circular to oval, sometimes angular when limited by the veins. More or less dark concentric patterns are visible on these spots. Dark brown to black conidial felting covers them in wet periods (Figure 1). The central tissues, once necrotic and desiccated, can fall out; the leaves subsequently exhibit a number of perforations. Damage is mostly observed on old leaves.


- Elements of biology

This fungus has potential saprophytic significant . It is able to survive on plant debris , in its mycelial form, through its conidia or its perithecia (ensuring its sexual reproduction). It would also remain on seeds . The infections occur mainly during the cold and wet climate periods , through the stomata. Subsequently, the fungus quickly colonizes the tissues. If the conditions are favorable, symptoms are already visible a few days after the first contaminations. It sporulates profusely on injured tissue, producing large spores muriform . These are dispersed by the wind and splashing water following rain or irrigation. Morning dews also favor its development , as well as climatic periods humid and relatively cold . It develops from 4 ° C to 34 ° C . Its thermal optimum is between 22 and 28 ° C. Symptoms would still develop after harvest, during storage.


- Protection

be considered Crop rotations will . The control of this fungus also requires the use of healthy seeds . Treatments with fungicides can be carried out   in countries where it is authorized . No fungicide is registered for this use on salads in France .

This fungus is easily maintained on plant debris, it will be essential to eliminate the latter during or after harvest. Sprinkler irrigations should be avoided or they will be carried out during the day in order to allow the vegetation to dry quickly. Sources of resistance have been identified in Lactuca saligna : resistance controlled by a dominant gene ( Sm ) and a recessive gene ( sm ).