Eggplant’s newest pathogenic fungus

Diseased fruit in the field at Bas-Boen Centre Rural de Développement Durable, Croix des Bouquets, Haiti
Diseased fruit in the field at Bas-Boën Centre Rural de Développement Durable, Croix des Bouquets, Haiti

A known pathogenic fungus, so far only reported to cause disease in two crops, has ensnared a third victim: eggplants. UF plant pathologists affiliated with both UF’s Institute of Food and Agricultural Sciences and the EPI, were the first to describe Lasiodiplodia hormozganensis’s jump to a new host.

Eggplant parmesan lovers needn’t panic yet, but plant pathologists with UF’s Emerging Pathogens Institute have discovered a fungus that is pathogenic to the famous purple fruit.

Lasiodiplodia hormozganensis is a microbe that, until recently, has been under the radar for crop health management. That is, until it was described infecting crop plants nine years ago. First it was found infecting mangos, then it showed up in castor beans. And in summer 2018, UF research associate Joubert Fayette, Ph.D., helped identify its latest victim: eggplants in Haiti.

Fayette’s work is supported by USAID’s AREA project (Appui à la Recherche et au Développement Agricole) which is led by Rose Koenig, Ph.D., of UF’s Institute for Food and Agricultural Sciences. The project spans from the plant pathology department in IFAS, to the Institute for Sustainable Food Systems and the EPI.

Several diseased eggplant fruits (yes, it’s technically a fruit) were observed and then collected from two research plots at the Centre Rural de Développement Durable de Bas-Boën in Croix-des-Bouquets, Haiti. Staff at the center, along with local partners, actively survey for and diagnose crop diseases. They were looking into a different disease affecting bananas when a few rotting eggplant orbs caught their eye.

Fayette then visited the farms to investigate reports of tan colored, water soaked lesions appearing on some of the island’s eggplant crops. The lesions extend to the entire egg-shaped fruit, which then take on a spongy texture and appear mummified. The affected fruits were then analyzed at an on-site plant disease lab.

Enlarged image of conidia, which are asexual and non-motile spores, of Lasiodiplodia hormozganensis. 

Researchers isolated and cultured the suspected fungal culprit in Haiti, and then evaluated samples at UF’s Plant Diagnostic Center using molecular tests. Using both morphology and sequencing of genetic markers, UF researchers — which included IFAS/EPI plant pathologists Carrie Lapaire Harmon and Karen Garrett — confirmed L. hormozganensis as the causative agent of the Haitian eggplant outbreak.

Eggplant is an important staple crop for Haiti, which produces more than 850 tons annually, most of which is consumed domestically. Researchers estimated that about 20 percent of two Haitian test plots used for study were affected by the rot.

Fruit rot has a few different microbial culprits; but until the researchers isolated L. hormozganensis from the affected Haitian fruit, it had a very short list of crops for which it was known to cause trouble. It was first described a mere nine years ago, infecting mangos. Last year, it was found to cause basal stem rot on castor beans. It is not yet known if the same pathogenic strain affects eggplant, mango and castor beans, according to Fayette, who led the study. (Harmon and Garrett  were coauthors on the study.)

“Other species of Lasiodiplodia are known to cause diseases in woody host plants and vegetable crops,” Fayette says. “For example, there have been previous reports of Lasiodiplodia theobroma on eggplant, but this is the first time we know of that L. hormozganensis has caused disease on eggplants.”

Strawberry, mango, papaya, banana, and grapevine are also affected by L. theobroma, he says.

“Since this is a new disease on eggplant, its epidemiology is not known,” Fayette says. “There is not yet a specific recommendation for its control. But general principles to control fungal disease include good sanitation, and cultural practices can be adopted to reduce potential infection from Lasiodiplodia.”

Cultural practices include avoiding injury of the plants, rotating the vulnerable crop with unrelated crops, removing diseased plants, and culling weeds, infected debris, and fruits. The investigators recently published a disease note about the fungus’s new host in the Plant Disease Journal.

By: DeLene Beeland