Culturable endophytic fungi from tree peony Paeonia suffruticosa ‘Luoyang Hong’: diversity, identification, and biocontrol potential against plant pathogenic fungi

Imagine a hidden world living inside plants, a secret society of tiny fungi that don't make the plant sick but instead hang out in its roots, stems, and leaves like friendly roommates. These are called endophytes. Think of them as the plant's personal bodyguards and cheerleaders; they help the host grow stronger, fight off bad bugs, and even produce special chemicals. Scientists are always hunting for these microscopic allies because, in a world where we want to stop using harsh chemical sprays on our crops, these natural defenders could be the key to keeping plants healthy. The big question is: which plants are hiding the best bodyguards, and what superpowers do they have?

This study dives into the secret life of a very famous Chinese flower: the tree peony, specifically a red variety called 'Luoyang Hong'. The researchers wanted to see what kind of fungi were living inside this flower and if any of them could act as a superhero against plant diseases. They treated the peony like a treasure chest, opening up its roots, branches, and leaves to see what was inside. They found that the peony is home to a bustling community of 23 different fungal species. The roots were the most crowded neighborhood, hosting the most guests, while the seeds were surprisingly empty. But the real excitement came when they tested these fungi against dangerous plant pathogens. They discovered a standout champion: a fungus named Bartalinia robillardoides (strain T2-07). This little guy didn't just push the bad bacteria away; it attacked them on three different fronts, breaking their cell walls, confusing their internal energy systems, and stopping their antioxidant defenses. It's like finding a tiny soldier that can win a battle by smashing the enemy's shield, cutting their power supply, and poisoning their food all at the same time.

The Hidden Roommates of the Peony

Tree peonies are the rock stars of the plant world in China, famous for their stunning flowers and their medicinal roots. But like any celebrity, they have their share of troublemakers. Fungal diseases like black spot can ruin their beauty and health. For a long time, farmers have fought these diseases with chemical sprays, but everyone is looking for a greener, more natural solution. Enter the endophytes. These are fungi that live inside healthy plants without causing any harm. You can think of them as the plant's internal immune system, a secret network of allies that helps the host survive stress and fight off invaders.

The scientists behind this study decided to investigate the 'Luoyang Hong' peony to see what kind of allies it was hiding. They collected samples from roots, different ages of twigs (one-year-old, two-year-old, and three-year-old), leaves, and seeds. They carefully cleaned the outside of these plant parts to make sure they were only finding the fungi living inside, not the ones just sitting on the surface.

The Census: Who Lives Where?

After growing the fungi in the lab, the team counted their findings. Out of 480 tiny pieces of plant tissue they tested, they successfully grew 146 fungal strains. That's a colonization rate of about 25%, meaning one in four pieces of plant tissue was hosting a fungal roommate.

But not all rooms in the peony house were equal. The roots were the most popular address, hosting the highest number of fungi (56.25% colonization rate). The older, three-year-old twigs were the second most crowded, followed by the two-year-old twigs. The one-year-old twigs and leaves had fewer guests, and the seeds? They were completely empty. The researchers noted that this wasn't because the seeds were sterile, but likely because they were sampled too early in their development. The seeds were still tender and immature, so the fungi hadn't moved in yet. It's like trying to find a party in a house that hasn't been built yet.

The Neighborhood Map

Once they identified the fungi, the team mapped out who lived where. They found 23 different species belonging to 17 different genera (a group of related species). The community was dominated by four main families: Fusarium, Graphiopsis, Cephalosporium, and Paraconiothyrium.

The peony's fungal community was quite diverse, with a "Shannon diversity index" of 2.83, which is a fancy way of saying there was a healthy mix of different types of fungi, not just one or two dominant bullies. Interestingly, some fungi were very picky about their address. For example, Fusarium and Acrocalymma were only found in the roots, while Bartalinia and Cladosporium stuck strictly to the two-year-old twigs. It seems the peony has specific "neighborhoods" for different fungal species, just like a city has different districts for different types of businesses.

The Battle: Finding the Superheroes

The researchers didn't just want to know who lived there; they wanted to know who could fight. They set up a "dual-culture" test, which is like a boxing match in a petri dish. They put the peony fungi face-to-face with five different bad-guy pathogens that attack peonies and wheat.

Most of the peony fungi were weak fighters, but ten of them showed some serious punch.

• The Antibiotic Fighters: Eight strains produced chemicals that created a clear "inhibition zone"—a gap where the bad fungus couldn't grow. The star of the show was strain T2-07, a type of Bartalinia robillardoides. When it faced Gaeumannomyces graminis var. tritici (a nasty wheat pathogen called take-all), it created a massive 15 mm gap, completely stopping the enemy in its tracks.
• The Parasites: Two strains acted like biological ninjas, actually climbing onto and eating the bad fungi. One of these, Fusarium proliferatum, grew so fast it completely covered and consumed the bad fungus in just 15 days.

How the Champion Wins: A Three-Pronged Attack

The team decided to study the champion, strain T2-07, to figure out how it was so effective. They grew the fungus in a liquid broth, filtered out the fungus itself, and then added the remaining liquid (the "fermentation filtrate") to the bad wheat fungus. They watched what happened over time and discovered that T2-07 didn't use just one trick; it used a synergistic, three-part strategy to destroy the enemy:

1. Smashing the Shield: The liquid caused the bad fungus's cell membrane to become leaky. You can imagine this like popping a water balloon; the electrical conductivity of the solution went up, proving that the cell's contents were spilling out.
2. Disabling the Defense Team: The bad fungus usually has an antioxidant system (like SOD, POD, and CAT enzymes) to protect itself from damage. T2-07 shut these down, leaving the enemy defenseless against its own internal stress.
3. Cutting the Power: The liquid also blocked the bad fungus's energy factories. It stopped the enzymes that help the fungus eat and breathe (like HK, PK, and SDH), effectively cutting off its power supply and stopping it from growing.

The Takeaway

This study is a treasure map for the future of green agriculture. It shows us that the 'Luoyang Hong' peony is a goldmine of fungal diversity, hiding unique allies in its roots and stems. Most importantly, it identified strain T2-07 as a potential superhero biocontrol agent. By understanding that this fungus fights disease by breaking cell walls, disabling defenses, and cutting off energy, scientists now have a clear blueprint for how to use it. While this specific strain was found in a peony, its ability to fight wheat diseases suggests it could be a powerful tool for farmers looking to protect their crops without relying on chemical sprays. The peony, it turns out, is not just a beautiful flower; it's a guardian of its own health and a potential savior for other plants too.