Cool Hawaiian science: blend up some healthy leaves, spray on sickly plants, and create healthy plants

We are not alone, and we can’t be.

Whether human or plant or other species, we all live by John Donne’s rule: “No man is an Island, entire of itself; every man is a piece of the Continent, a part of the main.”

(Image:  The native mint P. kaalaensis in flower, with fungal

infection (white spots on leaves). Credit: Geoff Zahn.)

University of Hawai`i researchers, in an elegant new piece of work, show that even plants in the garden depend on a community of other organisms to protect them. Some of these natural allies live in the soil and root, in the stems and leaves, and even on the stems and leaves.

In this case, working with a native mint called Phyllostegia kaalaensis, professor Anthony Amend and researcher Geoff Zahn found that they could transplant disease resistance into a plant that otherwise was a severe risk of fungal attack.

The mint, which was once thriving in the wild, has been extinct in the wild since 2015. The ones still living in nurseries were extremely weak--perhaps because they were sprayed regularly with fungicides to prevent fungus attack. The fungicide kept them alive but also kept them weak, said Zahn.

As long as the plants remained so vulnerable, there was little hope of restoring them to the wild, where they would immediately be killed off.

Healthy native mint in the wild. Credit: Vincent Costello.

All it took was to blend up (actually blend, in a blender) the leaves of a related wild plant, which presumably contained whatever protective organisms lived with the wild plant. The donor plant was a related endangered Hawaiian mint from Molokai, Phyllostegia hirsuta. 

They sprayed the blended stuff onto nursery plants. And the plants that had been given this “transplant” of beneficial organisms were suddenly able to fight off fungal attack. The beneficial organisms are called endophytes, which are forms of life like fungi and bacteria that live inside the plant. 

Here’s now the University of Hawai`i press release put it:

“They took leaves from a closely related wild that plant was healthy and contained a typical mix of endophytes, blended them into a smoothie and sprayed the mixture onto the leaves of (the native mint)  to see if beneficial microbes could be transplanted from one species to another. They then subjected these plants, along with a control group, to the deadly powdery mildew. The plants that received the microbial spray were able to resist disease, those that didn’t receive the spray soon died.”

The research is simply remarkable. Nursery plants, generally planted in sterile media, are “alone.” They don’t have their natural biological communities around them. And as a result they are severely vulnerable. 

In this case, Amend and Zahn weren’t sure which of the constituents of the blended spray did the anti-fungal work, so they tested for it.

“Using DNA barcode sequencing to identifying which species were inside leaves before, during, and after the disease, Amend and Zahn determined the beneficial fungus that was most likely responsible for protection from disease: the yeast Pseudozyma aphidis. Those treated plants did so well, that they have since been planted out in the wild, and now represent the only wild population of P. kaalaensis on the planet.”

Zahn said this yeast can live both on the leaf surface and inside the plant's tissues. When they prepared the leaves for blending, they cleaned the exterior, so the protective fungus came from inside the tissues of the hirsuta. 

The National Science Foundation and the Army funded the research. Anend and Zahn were associated with the University of Hawai‘i at Mānoa botany department and the O'ahu Army Natural Resources Program. Zahn has since moved on to Utah Valley University.

Amend continues the work in Hawai`i, and also works with University of Hawai`i researcher Nicole Hynson, who is studying, among other things, beneficial organisms in the roots of plants.

This remarkable research builds on a growing understanding of the relationship between diverse life forms. 

Some years ago, researchers were able to save an exceedingly rare native orchid on Molokai.

The orchid did poorly in captivity, and did poorly when planted out in the wild. But when it was planted in soil that had been inoculated with soil from places where it had once grown, it did fine.

Growing with the soil organisms on which it depended, it survived. Alone, it did not.

We’re not even going to go here into the relationships between humans and their gut organisms. But whether you go by “no man an island” or “it takes a village,” the message is clear.

 © Jan TenBruggencate 2017