UH researchers discover 2 viruses infecting hibiscus

University of Hawaii researchers didn’t have to go far to discover two previously unidentified viruses infecting hibiscus plants in the islands.

“There’s a lot of hibiscus dying on campus,” said Michael Melzer, associate researcher with UH Manoa’s Department of Plant and Environmental Protection Sciences.

The viruses, identified through the use of genomic sequencing technology, are the latest threats to an ornamental that has grown in popularity here and on the mainland. The discoveries are described in a paper published in the journal Viruses in December.

“Do these viruses pose a threat to the survival of hibiscus?” professor John Hu asked the UH communications office. “That’s exactly the question we want to answer. Our early findings indicate it could; however, we don’t know the final answer yet. We plan to do more virus surveys including testing the mother plants at the propagation site.”

The pair of viruses, named hibiscus betacarmovirus and hibiscus soymovirus, cause infected hibiscus plants to show mosaic, ringspot and yellow spots on their leaves.

They were identified through analyzing 54 hibiscus samples collected in Hono­lulu — 34 from 18 locations on the UH Manoa campus and the remaining 20 from a variety of sites from Diamond Head to downtown.

Twelve of the 54 samples (22%) were positive for at least one of the viruses. One sample tested positive for hibiscus betacarmovirus, nine samples tested positive for hibiscus soymovirus and two samples tested positive for both viruses.

The same group of UH College of Tropical Agriculture and Human Resources researchers has identified a handful of viruses over the past dozen years or so, including hibiscus latent Fort Pierce virus and hibiscus latent Hawaii virus.

Melzer said a single virus is unlikely to kill a hibiscus bush. It’s more of a nuisance, like a cold that won’t go away. More risky is how multiple viruses and pests combine in the attack.

The hibiscus is particularly vulnerable to bugs and pathogens, the researcher said, and he seems to see a lot of ailing hibiscus on his travels around the state. On campus the hibiscus have been declining in health for years.

There may be help on the way, however. A University of Florida professor has gathered support from colleagues in Florida, Texas, California and Hawaii — the top hibiscus- producing states — and applied for U.S. Department of Agriculture grant money for research into the health challenges of the ornamental, among other things.

According to the proposal, although the hibiscus is a key U.S. specialty ornamental that generated $8.2 million in sales nationally in 2018, it remains an understudied plant susceptible to pests such as weevils, whiteflies, scales, mealybugs, flies, mites, fungi, bacteria and viruses.

“Despite its great economic and ecological importance, there are no concerted efforts to support and protect the hibiscus industry from multiple production challenges,” the proposal says.

Meanwhile, the hibiscus, with its spectacular daylong blooms, is experiencing new levels of popularity across the country, according to the proposal. Indeed, the growing admiration for hibiscus and its many colorful hybrids, especially among young people, was featured in New York Times Magazine in November.

In Hawaii the hibiscus bloom is an iconic symbol, its place in island gardens ubiquitous. While the tropical or Chinese hibiscus (rosa-sinensis) is the most widely planted hibiscus here, the native yellow hibiscus brackenridgei is the official state flower and one of only a handful of native hibiscus species.

Melzer said the main concern for researchers in the islands is how these viruses and pests infect and impact the native hibiscus, some of which are threatened and endangered.

Cleaning tools when pruning hedges will help prevent the spread of the viruses, he said, as will being sure to not propagate new plants from cuttings infected with virus.