Coevolution of Polystigma amygdalinum through a process of host tracking

The almond tree (Prunus dulcis) and its wild relative, the mountain almond tree (Amygdalus scoparia), grew up together in the province of Fars in Iran over decades. Red leaf blotch disease caused by Polystigma amygdalinum is one of the most important almond diseases in the world. This research was conducted with the aim of investigating the evolution of this pathogen on its wild and domestic hosts.

Ascospores suspension of P. amygdalinum isolates obtained from almond in Fars province was inoculated to almond and mountain almond seedlings in a greenhouse. The progress of the disease in the diseased leaves of mountain almond compared to almond was investigated by sectioning with a freezing microtome from the spots created on the leaves.

Red leaf blotch spots appeared on the leaves of both types of almonds. Statistical analysis of test data showed that P. amygdalinum isolates from almond are able to cause disease in mountain almond with significantly lower severity, and longer incubation period.

The results of this research show that P. amygdalinum, the cause of red leaf blotch disease, have coevolved on cultivated almond through a process of host tracking.