When you’re scouring the pumpkin patch this autumn for the perfect pumpkin for your carving creations, you likely won’t come across Styrian pumpkins. These pumpkins are known as “naked-seeded pumpkins” because they possess seeds that are encased by just a thin membrane rather than a shell. The Styrian pumpkins were bred in the late 1800s for the production of a dark-green seed oil commonly used in Austria.
Despite their relatively short time of evolutionary existence, these pumpkins have acquired changes in their genomes so that some cultivars have a different microbiome than others. What’s more, the microbiome of pumpkin seeds can be passed down from generation to generation. (Details to both of these findings below.)
But, before getting into the nitty gritty of microbial pumpkin goodness, it’s important to understand why it matters. Scientists think that these microscopic partners associated with pumpkin seeds could guide the development of new cultivars that are enriched in beneficial microbes. This is especially important for Styrian pumpkins as they are prone to fungal and bacterial infections during germination. Already, some kind of chemical intervention or seed treatment is unavoidable. It’s possible that information about a pumpkin seed’s beneficial microbes could help design seed treatments that could replace antifungals and that breeding strategies could select for crops that are less susceptible to pathogens.
A pumpkin’s seed genome influences its microbiome
In 2016, a team of scientists from Gabriele Berg’s lab at Graz University of Technology examined 14 types of Styrian pumpkins and identified the microbes associated with them by sequencing their 16S rRNA gene, a gene often used for identifying and classifying microbes. They took samples from the seeds, the area around the plant roots (aka the rhizosphere), and the soil. Sure enough, the scientists found that different pumpkin cultivars possessed seeds with different microbiomes.
The seed microbiome was the least diverse compared to the rhizosphere and soil. Contrary to the previous thought that seeds carry only pathogens, the microbiologists found potentially beneficial bacteria such as Lysobacter, Paenibacillus, and Lactococcus in the seed samples. Some of these beneficial bacteria have already been used as seed treatments. However, pathogenic microbes, including Erwinia and Pectobacterium were also found in the seed microbiomes.
Some microbes were found only in the seeds or only in the rhizosphere, suggesting that the pumpkins have “enriched” for specific plant-associated microbes. Serratia, a biocontrol species, was found in low abundance in just a fraction of the seed samples and not in any of the soil samples. What’s more, species that help suppress disease, such as those within Gammaproteobacteria, Betaproteobacteria, and Firmicute were present in the rhizosphere, while other microbes like Thaumarchaeota, Acidobacteria, and Chloroflexi were found in the soil.
Passing down genes and microbiomes
Since that study was published, the team took it one step further and investigated the pumpkin’s microbiome throughout its lifecycle: from initial seed to plant to progeny seeds.
To compare the initial seeds to the progeny seeds, the team washed and soaked the seeds to eliminate microbes on the surface. Then they ground the seeds in a salt solution to obtain samples for sequencing. For the progeny seeds, the team opened up the grown pumpkins and extracted the seeds from the fruit. The seeds were then processed in the same way as the initial seeds.
They found that from sown seed to progeny seed, the bacterial signatures were linked. But, for fungal communities of the seeds, they were shaped by the soil and rhizosphere. Progeny seeds were enriched in bacteria beneficial to the plants including Bacillaceae, Burkholderiaceae, and Pseudomonadaceae species.
This wasn’t the only study to find that seed microbiomes are transferred to the next generation. Earlier in 2021, research from Stockholm university found that oak seedlings acquire their microbiomes from their acorns.
Studies such as these could make microbiome-driven breeding strategies for crops possible.
Want to hear more about fruit microbiomes?
Check out the blog post about the apple microbiome!
Further reading
