Hurtin’ Hibiscus

The discovery of two new Viruses threaten Hawai’i’s Hibiscus plants

In 2020 a report published in a special issue of ‘Emerging Plant Viruses’ scientific journal detailed the presence of a viral pair. DNA Virus named Hibiscus Betacarmovirus (HBV) and RNA virus Hibiscus Soymovirus (HSV). 

Researchers from The University of Hawai'i’s Department of Plant and Environmental Protection Sciences who partook in the study noticed that during 2023 there was a significant decline in the health of the hibiscus on campus. 

The campus hibiscus showed symptoms such as ringspot (small yellow spots on the hibiscus leaves), mosaic (yellowing of veins), and curling of the leaves. 

Above: Infected hibiscus leaves (left and middle) next to a healthy hibiscus leaf (right) Photo courtesy: The University of Hawaii

Collecting 54 sample hibiscus from the campus as well as other locations researchers ruled out other common hibiscus viruses by comparing plants already infected with ringspot, foliar mosaic, and chlorotic spots to the samples collected containing HBV and HSV. 

Through a technique known as High-throughput sequencing or HTS, where both DNA and RNA are sequenced to generate an insight into the plant’s genomes and detect viruses, researchers compared the infected hibiscus sequences to known viruses before identifying Hibiscus Betacarmovirus and Hibiscus Soymovirus as two new viruses.    

Of the 54 collected samples, 12 of the plants were found to be infected. Nine were discovered to have tested positive for HSV, one positive for HBCV, and two hibiscuses tested positive for both HBV and HSV.  

Above: Various Hibiscus rosa-sinesis (Tropical) hibiscus on Oahu

DNA Viruses are uncommon for plants, DNA viruses work by penetrating the nucleus of the cell and delivering information before replicating whereas RNA viral infections - like coronavirus - bring their own pre-made RNA messengers ready to disrupt the host system. 

Vectors such as insects are the most popular way for plant viruses to spread with reports of 80% of plant viruses being insect transmitted. An insect will feed off an infected host plant, pick up the viral infection, and pass it on to the next plant it feeds on. 

Hawai’i has an abundance of non-native Heteroptera (True Bugs) such as aphids, coffee berry borers and coconut rhinoceros beetles - all of which wreak havoc on the local fauna and flora.   

Viral diseases, like the two newly discovered, can immensely impact agricultural resources, economic systems and even human health. 

Plants aren’t defenceless against infection, by using a technique known as Gene Silencing plants are able to block gene expression, meaning the gene will stop producing RNA and proteins. 

Genes are segments of DNA, therefore if the gene is silenced the information it was carrying is abruptly halted. 

Above: Hibiscus rosa-sinesis (Tropical Hibiscus)

Human intervention is another defence against viral plant infections, interrupting the transmission cycle before the infected insect can pass on the disease with the use of insecticides such as Neem oil spray, Castile soap spray or a homemade blend of garlic, vegetable oil and water. 

Other spread diseases can be combatted by cleaning your shoes after hiking/travelling to avoid cross-contamination, using mulch (either straw or plastic) to combat pathogens from spreading and making sure all garden tools and equipment are cleaned. 

Above: My personal propagated hibiscus (use Neem oil to deter insects)