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American Association for the Advancement of Science

Are isolated plant populations more prone to disease?

Petri dish with powdery mildew infected leaves of Plantago lanceolata.
[Credit: Susanna Kekkonen]

Researchers have generally believed that diseases spread quicker among densely clustered populations and slower among populations that are spread out. However, a new study of the weed, Plantago lanceolata, and a fungal pathogen, known as powdery mildew, which infects the weed, shows that highly-connected plant populations—those that are growing close together—are more resistant to the powdery mildew than isolated populations of the plant.

Jussi Jousimo and colleagues spent 12 years studying 4,000 different populations of P. lanceolata as the weeds battled this fungal pathogen on the Åland Islands in the Baltic Sea. At the end of their study, the researchers concluded that closely-connected patches of plants exchange more genes—and also more resistance against the powdery mildew—with each other. Basically, their results show that well-connected plants are better at killing the powdery mildew and harder to infect with it compared to solitary plant populations.

Until now, most research has focused on understanding disease outbreaks, but this new approach demonstrates the value of studying how diseases hang out in populations for long periods of time. Future studies might tell researchers whether habitat fragmentation, which is currently widespread, increases the odds of disease outbreaks. But, for now, this work serves as a model of disease persistence in the wild.