on the island. Why P. kaalaensis is nearly
extinct is unclear, though both habitat loss
and powdery mildew are potential explanations. The fuzzy fungal disease attacks the
plants in greenhouses, and the researchers
presume it has killed all the plants they’ve
attempted to reintroduce to the wild.
Zahn had never encountered extinction
(or near to it) so directly before. He returned home overwhelmed and determined to help the little mint.
Just like humans and other animals, plants have their own
microbiomes, the bacteria, fungi and other microorganisms
living on and in the plants. Some, like the mildew, attack;
others are beneficial. A single leaf hosts millions of microbes,
sometimes hundreds of different types. The ones living within
the plant’s tissues are called endophytes. Plants acquire many
of these microbes from the soil and air; some are passed from
generation to generation through seeds.
The friendly microbes assist with growth and photosynthesis or help plants survive in the face of drought and other
stressors. Some protect plants from disease or from plant-munching animals. Scientists like Zahn are investigating how
these supportive communities might help endangered plants
One fine Hawaiian day in 2015, Geoff Zahn and Anthony Amend set off on an eight-hour hike. They climbed a jungle mountain on the island of Oahu, swattingmosquitoesandskirting wallowsof
wild pigs. The two headed to the site where a patch of critically
endangered Phyllostegia kaalaensis had been planted a few
months earlier. What they found was dispiriting.
“All the plants were gone,” recalls Zahn, then a postdoctoral fellow at the University of Hawaii at Manoa. The two
ecologists found only the red flags placed at the site of each
planting, plus a few dead stalks. “It was just like a graveyard,”
The plants, members of the mint family but without the menthol aroma, had most likely died of powdery mildew caused by
Neoerysiphe galeopsidis. Today the white-flowered plants, native
to Oahu, survive only in two government-managed greenhouses
on Oahu’s Koolau
until about 1970.
are looking to
microbes to help
the mint plant.
Scientists are tinkering with plant
microbiomes to feed the world
and save endangered species
By Amber Dance