Taphrina padi

(1926) Taphrina padi is a fungal plant pathogen that induces the form of pocket plum gall that occurs on bird cherry (Prunus padus).

The gall is a chemically induced distortion of the fruits, which are swollen, hollow, curved and greatly elongated,[1] without a seed or stone, but retaining the style.

The surface of the gall eventually becomes corrugate and coated with the fungus, showing as a white bloom of ascospore producing hyphae.

[1] The fungus may also cause dense clusters of live and dead twig, called "witches' brooms".

[6] The fungus infects the ovaries causing a pseudo-pollination and an enhanced cell division, resulting in the infested fruit being larger than the healthy one.

Pocket plum galls on bird cherry at Dalgarven Mill in Ayrshire, Scotland
Distorted stem on bird cherry, possibly caused by T.padi
Corrugated pocket plums with ascospore bloom
Bird cherry ( Prunus padus ) with developing pocket plum galls
Detail of the closely related T. pruni structure
Maturing pocket plum galls