Neopestalotiopsis (NeoP) has become a devastating disease in strawberries and a research team at North Carolina State University seeks to understand more about this disease and how the state’s growers can better understand and detect the pathogen. First identified in Florida commercial fields in 2017, the pathogen was discovered in North Carolina in 2022.
A Hidden Threat to the Bottom Line
The economic impacts of this disease in North Carolina have been significant, says Daisy Ahumada, an Extension field crop and strawberry pathologist at North Carolina State University. A survey of growers estimates an average of $10,000 a year in disease-related losses or about 10% of the crop. Ahumada is quick to point out, “That is an average level, which means that there are growers that are losing well over that amount.”
Mark Hoffmann, small fruit Extension specialist at NC State, says NeoP’s impact has been significant beyond the grower level: a major nursery in the state which was a suspected source of early infections closed because it did not know how to control the new pathogen.
Because roughly 50% of North Carolina’s strawberry growers also raise tobacco, Ahumada says interest in NeoP research has cross-commodity backing. Research into integrated pest management (IPM) and fungicide programs for NeoP is currently supported by the Tobacco Trust Fund Commission.
Ahumada says a significant challenge to managing NeoP is that it’s a relatively new pathogen and growers buying nursery plants that look healthy suffer losses and plant death later in the year to the disease.
“They look perfectly healthy and then all of a sudden during the season these plants start purpling and then dying and [growers] don’t know how to manage it,” she says.
Tracking a Stealth Pathogen
Diagnosis is complicated by regional variations. In Florida, NeoP often presents as a foliar leaf disease, whereas in North Carolina, it manifests as a crown disease that kills the strawberry plant at the base. Ahumada discovered the disease presents differently depending on how she inoculated the plants.
“It seems like if you start off the inoculation closer to the crown, then that’s where you get more of a crown disease,” she says. “But if you spray it over the top or if you sprinkle inoculum over the top, then you’re going to get more of that foliar disease.”
She says a major research project starting later this season and carrying into next season seeks to better understand transmission.
“The epidemiology or the actual source of where these infected plants are coming from is not well understood,” she says, noting her project, which was awarded a USDA grant, will look at how NeoP spreads from tissue culture plants to facilities and nurseries and then to growers.
Deploying AI and Genomics for Early Detection
Because the NeoP fungus can be present without visible symptoms, the NC State research team is developing qPCR, a high-tech DNA test for plants, and utilizing AI tools to detect low amounts of fungal DNA in seedlings and plugs before they reach the field.
Tika Adhikari, a principal research scholar and plant pathologist at NC State, and researcher Susmita Gaire are part of a team performing whole-genome sequencing to understand the genetic factors involved in NeoP. So far, the team has collected more than 100 different isolates of the fungus in North Carolina alone. The team has discovered there are pathogenic differences within the fungus itself, as well as variations in how the disease attacks different varieties.
Gaire, an NC State plant pathology researcher, says the research team grouped the different isolates with different lineages into three groups and inoculated 10 isolates into 15 commercially available cultivars.
“We found that there is a significant interaction between the pathogen and also the pathogen isolates and the varieties,” she says.
This research team has coordinated with Orlando Arguello-Miranda, an assistant professor in the Department of Plant and Microbial Biology at NC State, to learn more about the germination strategies of the pathogen. He says that with the help of an AI algorithm, germination has been detected in only some of the cells that are part of a NeoP spore.
“We have noticed very interesting things,” he says. “For example, not all the cells germinate. Not all the cells that compose the spore germinate, and we still don’t know why.”
As part of the research, the team authored a paper pending publication that compared NeoP to two common pathogens in strawberries: Colletotrichum, a foliar pathogen, and Verticillium, a soil-borne pathogen. Arguello-Miranda says what the team learned is that different strains of NeoP have different germination strategies and attack stressed plants differently.
“Neopestalotiopsis looks completely different,” he says. “[NeoP] seems to have a very specific way to deal with stress and it has very specific patterns of germination that we do not observe in [Verticillium] or [Colletotrichum] strains,” he says.
Arguello-Miranda says he plans to investigate more into how the fungus germinates and why the AI algorithm detects germination in certain cells.
Adhikari says through genomic data, the research team has identified mutation sites in the pathogen showing it can overcome common fungicides used by growers, which could severely exacerbate the issue. He says the research team seeks to understand if the fungus survives on alternative hosts in a dormant stage and then emerges later.
Bridging the Gap to Practical Solutions
As for moving forward, Hoffmann says nurseries are very aware of NeoP, and “do the best they can to manage it in their fields, but there’s also not a clean solution at the moment that would help to clean it up.”
Hoffmann says a goal for this research project is to bridge the gap between the biological discoveries and practical management recommendations. All the research at NC State, he says, is part of a larger multi-year project to better provide growers with data on susceptible cultivars, fungicide rotation programs and any potential interactions with pests.
“We can inform the growers a little bit better about what they should spray,” he says.
Hoffmann says North Carolina State University is working with four different breeding programs across the country to identify NeoP-resistant varieties. The goal is to breed NeoP resistance or higher tolerance in future releases.
“I think the bottom line of this is at the moment, it’s challenging for growers,” he says, pointing to all the different facets of research.
Hoffmann says a challenge for the research is that many of the varieties that have fared better against NeoP are not necessarily planted or favored by growers.
“Growers usually don’t change varieties because of diseases,” he says. “They usually stick with the varieties that sell. Unfortunately, a lot of the varieties that are grown in larger amounts are not very tolerant in North Carolina.”
Another challenge is that a lot of pick-your-own growers in the state have off-farm careers or jobs and part-time growing leaves operations highly vulnerable to severe NeoP outbreaks.
“For those [small operations], it’s very difficult in years where we have a lot of rain and a lot of non-favorable weather conditions because if they get plant material that is infected and then we get a lot of rain, then it spreads pretty fast and they often don’t have the manpower or equipment to stay on top of this,” he says. “The larger growers or growers that can manage this usually don’t have that big of a problem.”
