When do which grass pollen fly?

New method could make prediction of tree pollen more accurate

Grass pollen is one of the most common allergy triggers, but only now researchers have developed a method to distinguish them. © Jeja / iStock
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Important progress for hay fever sufferers: The pollen prediction for grasses could soon become more accurate. Because a DNA-based method makes it possible for the first time to distinguish the grass pollen flying through the air into grass types - so far this was not possible. In the future, this could help to identify especially allergenic grass pollen and warn patients in good time of the pollen attacks.

Grass pollen is one of the major causes of hay fever and asthma worldwide - more people are allergic to it than any other type of pollen. But just about allergy triggers is hardly known. Because the pollen of the approximately 11, 000 grass species look extremely similar, researchers can hardly determine by microscopic analysis of which grass species pollen comes from. Therefore, one does not yet know when which grass pollen flies, nor which species are particularly allergenic. How far the grass pollen spread, was previously unknown.

DNA marker for grass pollen

An important breakthrough has now come from Georgina Brennan of Bangor University in Wales and her colleagues. After all, they have developed a method with which flying grasses can be determined precisely, down to the species. In this DNA barcoding, analyzing only two marker genes from the pollen is sufficient to identify its originator.

For their study, the researchers used this method to analyze pollen samples from across the UK during one season. Their hypothesis: Because grass pollen fly far, they would have to be relatively uniform, regardless of the local flowering time of the grasses. Instead of local and temporal peaks, the scientists therefore expected a rather homogeneous mixture throughout the season.

Surprisingly clear time frame

But the opposite is the case: The various grass species show both spatially and temporally clearly defined pollen peaks, as revealed by DNA barcoding. In the course of the pollen season, therefore, different types of grass alternate with their pollen. "The flying grass pollen of each genus took different time windows within the pollen season, " report Brennan and her colleagues. display

Accordingly, foxtailgrass (Alopecurus) and honeygrass (Holcus) dominate the early Groller season. "This coincides with the typical peaks of allergic hay fever, " say the researchers. On the other hand, the ryegrass (lolium), which is common in pastures and meadows, produces less sharply delimited pollen from about July. When exactly which pollen peak occurs, is also dependent on the geographical latitude.

More predictable pollen forecasts in sight

"These data are an important step towards a generic and in some cases even species-specific prediction of plant pollen, " the scientists emphasize. This may in future make it easier for hay fever and asthma patients to protect and prepare for their individual allergy risk. Because there are first indications that not every grass species carries the same and equally aggressive allergens on its pollen.

"I am suffering from hay fever myself, and I know that on some days, despite predictions of a high pollen load, I am less affected than on other days when less pollen is flying, " says Brennan's colleague Simon Creer. DNA barcoding could now allow researchers to link the relationship of certain pollen and their allergens to allergy pangs in patients.

"We hope to use this data to find out if certain grasses are more allergenic than others, " says co-author Nicholas Osborne of Exeter University. However, it may take a few more years for the different allergenic effects of different pollen to be resolved, the researchers explain. (Nature Ecology & Evolution, 2019; doi: 10.1038 / s41559-019-0849-7)

Source: Bangor University, University of Queensland

- Nadja Podbregar