Pseudoidium neolycopersici

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tomato leaves infected with powdery mildew (click on image to enlarge it)
Source: Wikimedia Commons

Pseudoidium neolycopersici (L. Kiss) L. Kiss 2012 - (powdery mildew of tomato)

The origin of this fungus is unclear. It appeared in the 1980s as a disease of glasshouse tomatoes and is now common and widespread in many regions. It is also of increasing importance in field tomatoes. Significant yield losses occur on tomatoes if infections start early in the growth cycle. Although tomato is most susceptible, several other plants from the family Solanaceae, including pepper and tobacco, can become infected.

Infections start as white circular pustules, a few mm in diameter, on the upper side of the leaves which enlarge, can cover the whole leaf surface, cause defoliation and also spread to the petioles and stems. Only the asexual stage of the fungus is known. The conidia disperse through the wind and the fungus might persist on alternate hosts in the absence of tomatoes. For management, fungicides and cultural methods (removing infected plants) are used. Resistance is known from wild Solanum species. However, commercial tomato cultivars are mostly susceptible.

Vernacular names
• Deutsch: Echter Mehltau der Tomate
• English: tomato powdery mildew
• Français: oïdium de la tomate

The fungus is epiparasitic, in contrast to Leveillula taurica which also causes powdery mildew on tomato but grows endophytically. The conidia are elliptical to egg-shaped, about 25-45 x 10-20 µm large. The are formed singly, rarely in short chains of 2-6. Until 2001, this fungus has been often referred to as Oidium lycopersicum or Oidium lycopersici which are synonyms of Euoidium lycopersici, a tomato pathogen from Australia described in 1888.

Synonyms
Oidium neolycopersici