A harmful plant disease has been identified for the first time in North America. As reported in the journal Plant Health Progress, it is the first time this particular phytoplasma disease has been found in the continent and the first time it has been seen in this host plant, presenting a new threat to agricultural and ornamental crops.
In Florida, the parasite – Candidatus Phytoplasma brasiliense – has been detected in three samples of yellow nutsedge (Cyperus esculentus), a common and rapidly spreading weed.
“The host of the disease is known as one of the most widespread and problematic weeds found everywhere,” Brian Bahder, assistant professor of entomology at the University of Florida Institute of Food and Agricultural Sciences Fort Lauderdale Research and Education Center said in a statement.
“It is one of the most aggressive weeds that commonly grows in lawns, home landscapes, vegetable and flower gardens and agricultural systems.”
This could spell disaster for flowers, fruits, vegetables, and other crops, should the phytoplasma spread as rapidly as its host.
Phytoplasma are bacterial plant parasites, transmitted primarily by insects, which can reprogram the development of their hosts and induce massive changes in plant architecture. They can turn infected plants into “zombies” – if you think that sounds a bit “horror film”, you would be correct – taking over a host plant and rendering it sterile before converting it to a reservoir of phytoplasma pathogens and insect vectors.
For example, some phytoplasma can force a plant to grow leaves instead of flowers. This makes the plants more appealing to insects, who snack on the tasty leaves before moving on to the next (healthy) plant, taking the phytoplasma with them.
There are many species of phytoplasma each associated with different symptoms in plants ranging from stunted growth and petals turning green to excessive production of shoots and branches (witches' broom) and the aforementioned phyllody – development of leaves instead of flowers.
Ca. P. brasiliense is just one species of phytoplasma and was found (until now) mostly in South America and the Middle East. It has been known to harm hibiscus, papaya, and cauliflower in parts of Brazil and Peru, plus peaches in Azerbaijan.
Now, yellow nutsedge in Fort Pierce, Florida can be added to that list. While studying a different plant disease – lethal bronzing, also caused by a phytoplasma – Bahder and his team stumbled upon this new discovery.
Lethal bronzing affects palm trees and, like other phytoplasma diseases, is spread by insects. The team studied grasses that lethal bronzing-carrying insects are known to frequent in the hopes of finding a reservoir for lethal bronzing among them. Three species of weed were analyzed, including yellow nutsedge, which yielded a positive result for phytoplasma in three specimens.
"We thought we had found lethal bronzing in one of the grasses, so we proceeded to genetically sequence the sample," said Bahder. "The results confirmed it was not lethal bronzing but that it was another phytoplasma."
The team had discovered Ca. P. brasiliense for the first time in North America.
The discovery of a novel phytoplasma in one of the most noxious and widespread weeds in the US “presents a unique threat to ornamental and agricultural sectors in south Florida,” the authors write in their paper, recommending an “area-wide survey for the phytoplasma and potential vectors” be conducted.
"The next logical step is to find out which insect is spreading the disease,” Bahder concluded. “The good news is that we caught this early. We don't know if this is an isolated incident or if the insect is spreading in the grass, and if it will feed on the papaya, hibiscus or cauliflower – which are economically important in Florida. The point is that we don't know the extent of this disease in Florida or what threat it poses."