Bacteria hitch a ride on raindrop spray (with implications for tackling kiwifruit Psa)

New research reveals how raindrops on soil create bioaerosols – tiny droplets of bacteria-laden water – which can help spread harmful microbes, including kiwifruit pathogen Psa.

Our attention was drawn to it by a Sciblog post (HERE).

Although soil bacteria are usually pretty slow at getting around, the post observes, wet weather has been suggested to give them a hand travelling large distances. But exactly how rain gets bacteria from the soil into the air has been something of a mystery – until now.

New research, published in Nature Communications, details the exact mechanism that allows bacteria to get airborne with the help of rain.

Using high-resolution imaging, Cullen Buie and colleagues from MIT’s Department of Mechanical Engineering tracked the fine mist released by a fizz of bubbles created when a drop of water hits soil. The researchers found that the tiny droplets in this mist carried up to several thousand bacteria from the soil and is some cases the bacteria remained alive for more than an hour afterward.

“Imagine you had a plant infected with a pathogen in a certain area, and that pathogen spread to the local soil,” Buie says. “We’ve now found that rain could further disperse it. Manmade droplets from sprinkler systems could also lead to this type of dispersal. So this [study] has implications for how you might contain a pathogen.”

The team calculated that precipitation around the world may be responsible for 1 to 25 percent of the total amount of bacteria emitted from land.

You can read more about the research on

The authors note that their research is important for studying the spread of all manner of bacteria that could harm humans, animals and plants.

The Sciblogs post notes that one of the sample bacteria they used in their research –Pseudomonas syringae – has direct relevance to New Zealand.

A variant of this bacteria, Pseudomonas syringae  pv actinidiae (Psa) is all too well known among NZ kiwifruit growers as the cause of kiwifruit vine disease.

A 2010 outbreak of the disease in the Bay of Plenty has been calculated to cost the NZ kiwifruit industry up to $885 million over 15 years.

Psa is known to spread more easily with the help of wet and wild weather and this new research offers a deeper understanding of exactly how Psa might be fizzed up into the air by raindrops and whisked away in bioaerosols. It will also offer further avenues for research on how to best predict and limit the spread of the costly disease.

Plant & Food Research has been working on using weather data to model the spread of the the disease in Bay of Plenty orchards.


Scholarship winner aims to prevent biosecurity disasters


Horticulture student Yvette Jones plans to put her studies to good use preventing biosecurity disasters like PSA affecting New Zealand growers.

The 19-year-old bachelor of agricultural science student at Massey University has just won a $2,500 horticultural scholarship from Agcarm to help her.

Growing up in the Bay of Plenty, Yvette was surrounded by large horticultural enterprises and experienced  first-hand the devastation of PSA – a bacterial kiwifruit vine disease first detected in 2010.

 “One of the reasons I’m so interested in maintaining New Zealand’s biosecurity is to prevent events like this affecting whole communities again. I think the horticulture industry definitely showed resilience in past years as the kiwifruit industry has grown and recovered. Some amazing new research and cultivars have been developed to help growers start over.

Her passion for horticulture developed while at school and when conducting research for the Manuka Research Group project which aims to grow the global potential of New Zealand’s honey industry. The experience gave her a taste for research and urged her to pursue a Masters or PhD.

Yvette is keen to promote horticulture as an option to prospective students. It is undervalued as a profession, she says.

Agcarm is an industry association of companies which manufacture, distribute and sell products that keep animals healthy and crops thriving.