Didymella lycopersici

Didymella lycopersici is a type of the order Pleosporales in the Department of ascomycetes ( Ascomycota ). It is the causative agent of Didymella - stem rot (also called Tomatenstängelfäule ) especially in tomato, but also in potato, eggplant and peppers.

Features

The pseudothecia are in the culture 120-200 microns, and host up to 300 microns in size, are round, light brown with a wart-like opening ( ostiole ). The asci are cylindrical to clavate bitunicate, short-stalked or sitting with eight spores and reach a size of 50-70 x 8-9 microns in culture or 70-95 x 6-10 microns on the host. The hyaline spores have oil droplets are irregular double row, elliptical and in the culture 12-15 x 5 microns, and host 16-18 x 5.5 microns in size. The Pseudoparaphysen threads are shaped, also hyaline and septate. The dark brown pycnidia appear on stems, leaves or fruits are available individually or sociable. They are first sunk in the tissue or then break out and reach a diameter of 140-200 microns in culture or 180-250 microns on the host. Their cell walls are slightly thicker from pseudoparenchymatischen cells at the outermost layer. The conidia are hyaline, elliptic to ovate, with no, or only a sept and 6-10 x 2-3 microns in size.

Morphology and life cycle

The fungus overwinters in plant residues by means of conidia. Transmissions by ascospores over the air or infected seeds seem less häuig occur. Spores are formed mainly on older infestation sites. Returning humidity gray to pink mycelium and spores growing form again. These are more common with splashes of water and mechanically tools and clothing. Using water splashes the spores over 100 and 75 cm up and down can spread to the plant. The fungus can also be spread via recirculating irrigation systems and lead to infection. Due to high moisture, light and temperature at 15 ° C Didymella is favored. Optimal growth takes place at 15-20 ° C.. About 20 ° C, the fungus develops better only under very favorable conditions. The secondary fruit shape occurs at the most, while the teleomorph, the perithecia, almost never contributes to the spread. The spread from the bottom is greater than the over the seed. On the seeds, the spores can hold a maximum of 9 months.

Symptoms

May be infested with tomato the whole plant. D. lycopersici usually occurs in the wild and only occasionally in the greenhouse. In general, the plant is attacked at the bottom and from the root of the neck up. Here, the stem is usually first settled by the formation of lesions. The lesions are brown to dark brown. In this case, the cortex tissue sinks and in a later stage to form black dots ( fruiting bodies ), the pycnidia. In case of heavy infestation of stem sap flow is interrupted and the plant dies above the point from infestation. Here also, the tissue is destroyed under the bark. The stem is soft and wet conditions is a pink fabric formed and an aqueous spore mass exits. If the infestation somewhat weaker withers the plant only, where the fruit comes to premature ripening. Especially infestation points higher on the plant caused by water splashes with spores. Also, leaves and fruit can be infested. The fruits are, however, affect almost only in the field. Infestation can occur there at all locations, but usually begins at the calyx and growing rapidly. This growth trend with concentric rings that only look aqueous- oily and later sunk blackish. Even at these points to form pycnidia. With complete infestation of the fruit is called mummification. The attack on the leaf looks similar to that of Alternaria. The spot, however, light brown to gray with pycnidia similar to Phoma lingam in cabbage plants. Later, the affected area may fall as shotgun. Sometimes doing the whole leaf is destroyed. And the infestation of the root neck down is known, however, the plant continues to grow and show wilting or yellowing of the older leaves. On sandier sites, the disease occurs less. The penetration of the pathogen but is promoted by injury of the plant. Very rarely, the roots are infested.

Dissemination

Didymella lycopersici is widespread. In Canada, it occasionally occurs in the area of British Columbia and Nova Scotia. Didymella - stem rot is quite common on tomato in Europe. It also occurs on potato and eggplant. Likewise, on plants and seeds from peppers.

Similar diseases

The disease can be caused by gray mold with Stängelfäulen (Botrytis cinerea) or late blight (Phytophthora infestans ) and early blight (Alternaria solani ) confused. The formation of pycnidia, however, are characteristic of Didymella lycopersici because they are seen with a magnifying glass with a 5 to 10 - fold magnification. Even the very rare root infestation is a sign of the disease. B. cinerea spore forms of lawn.

History

Klebahn described in 1921 for the first time perithecia of Didymella lycopersici and named the fungus. Only in 1944 succeeded in doing so also Hickman, who was able to confirm the finding of it. 2005 belongs Didymella - stem rot in Estonia the three most important fungal diseases in the culture of tomato in plastic greenhouse.

And synonyms

Didymella lycopersici one of the pleomorphic organisms, that is, it forms a major and a minor form of fruit. The anamorph (low fruit shape ) is called Phoma lycopersici. The following synonyms for Phoma lycopersici were described: Diplodina lycopersici, Phoma ferrarisii, Ascochyta lycopersici, Sphaeronaema lycopersici, Diplodina lycopersicola, Ascochyta socia.

Swell

MycoBank: Didymella lycopersici