A critically endangered Hawaiian plant that can safely exist only within a heavily managed greenhouse environment has new hope for long-term survival thanks to a novel experiment conducted by botanists from the University of Hawaii.

Phyllostegia kaalaensis, part of the mint family, used to grow in the Waianae mountains but was driven to near-extinction by habitat loss, invasive animals and disease. Since 2002, the plants have existed in only two greenhouses on Oahu, one managed by the state and the other by the U.S. Army.

The plants are regularly treated with fungicide to protect them from a powdery mildew fungus that can cause significant damage to the plants. However, the monthly treatments also kill off the plants’ endophytes, beneficial microbes that live in the leaves, stems and roots that are a key component of the plant’s natural immune system.

Taking a cue from the use of probiotics to improve human health, researchers Anthony Amend and Geoff Zahn took leaves from a healthy plant closely related to P. kaalaensis, blended them and sprayed the mixture onto P. kaalaensis leaves to see if the endophytes from the healthy plant could be transplanted to the other.

Treated and untreated P. kaalaensis plants were then exposed to the powdery mildew. The treated plants successfully resisted the disease while the untreated plants succumbed and died.

Using DNA bar code sequencing, Amend and Zahn identified the yeast Pseudozyma aphidis as the endophyte most likely responsible for the positive result.

The treated plants have since been reintroduced to the wild.

“The power of this approach lies in its simplicity,” Zahn said. “There are quite a few plant species that only exist in the ‘purgatory’ of managed greenhouses, and quickly succumb to disease when they are taken to the wild and away from their regular fungicide treatments. Spraying these plants with a slurry of beneficial fungi once before outplanting could increase their chances of surviving in the wild.”

Their research was published in the Nov. 10 issue of the journal PeerJ.