UMD Researchers Find Evolutionary Explanation for Young Plants’ Disease Vulnerability

From toddlers in day care to seedlings in forests, young organisms tend to get sick more easily than adults—a phenomenon that has long puzzled parents and scientists alike.

University of Maryland biologists offer new insights into this mysteriously universal pattern in a new publication in the journal Proceedings of the National Academy of Sciences. The study on baby plants shows that fighting disease at a young age often comes at a steep cost to growth and future evolutionary fitness—or their ability to reproduce.

“It’s a mystery why young organisms don’t evolve stronger disease resistance because getting sick early in life can be deadly,” said study co-author Emily Bruns, an assistant professor of biology at UMD. “Our findings suggest that a hidden trade-off is involved, stopping them from being able to completely fight off a disease."

The researchers studied a wild plant called Silene latifolia (commonly known as white campion) and its relationship with a fungal disease called anther-smut that infects it. This disease doesn’t kill the plants but prevents them from producing pollen, making them unable to reproduce—much like a “plant STD,” as Bruns described it.

By testing 45 genetic variations of the Silene plant under controlled settings, the team discovered that plants with stronger disease resistance as seedlings produced significantly fewer flowers and seeds over their lifetime when grown in a disease-free field. Meanwhile, plants with stronger resistance as adults showed no such penalty.

Using their findings, the researchers created a mathematical model showing that these costs of fighting off pathogens are high enough to prevent the evolution of stronger disease resistance in younger plants. Without these costs, plant families with stronger juvenile resistance would theoretically be able to eliminate the disease entirely. But because developing resistance is so impactful for young plants, they remain vulnerable to infection.