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Taphrina pruni Infection Model

As the species name suggests, Taphrina pruni (german: Narren- oder Taschenkrankheit) infects Prunus domesticus (Plum) and Prunus spinosus (Blackthorn or Sloe) fruits to form pocket plums. It also infects the shoots of Blackthorn to cause stunted or swollen distortions.

The fungal pathogen T. pruni does not produce fruit bodies. The spore germinates on the plant surface (forms an appressorium) and penetrates the flesh seeking refuge for nutrition. Infected fruits tend to become elongated, often more  on one side than the other, which leads to  to  pocket-like shapes. The ascomycete fungi T. pruni produces its spores in tubes called asci (plural; singular = ascus). These asci penetrate through the surface of the fruit where the tip releases under pressure, shooting the spores out into the air (Ellis, M.B. and Ellis, J.P. (1997) Microfungi on land plants: An identification handbook. Richmond Publishing. 868pp.)

Sloe infected with Taphrina pruni (left) and uninfected (right)

Symptoms

The gall is usually known as 'pocket plum', however alternatives are 'starved plum'; 'bladder bullace; and 'mock plum'. The gall appears on the developing fruit, rendering it inedible and resulting in an elongated, flattened, hollow, stone-less gall of any colour from light green, through grey to light orange. The surface of the gall becomes corrugate and coated with the fungus, showing as a white bloom of ascospore producing hyphae. The totally inedible fruits shrivel and most fall. Some overwinter on the tree. Stems bearing deformed fruit may also thicken and grow with a deformation. The leaves are smaller and strap-like and shoots may be swollen, pale yellow and tinged with red. Cold and wet weather conditions promote the germination of spores, whilst warm and dry weather results in low infections. 

In fieldclimate we model the risk of a Taphrina pruni infection in dependence of the actual temperature. The temperature has to be below 16°C.

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Literature

REACTION OF SOME PLUM CULTIVARS TO NATURAL INFECTION WITH Taphrina pruni (Fuck.) Tul., Fusicladium Pruni DUCOMET AND Tranzschelia pruni-spinosae PERSOON DIETEL Mitre Ioana jr. 1) , V. Mitre1) , Erzsebet Buta1) , Ioana Mitre1) , Andreea Tripon1) , R. Sestras1)*