Young organisms, from toddlers in daycare to seedlings in forests, often exhibit a surprising tendency to fall ill more frequently than their adult counterparts. This intriguing phenomenon has long intrigued both parents and scientists. Recently, biologists from the University of Maryland (UMD) have shed light on this curiosity through a new study published in the prestigious journal Proceedings of the National Academy of Sciences on April 4, 2025.

The research specifically focused on juvenile plants, revealing that the struggle against disease during their early stages often comes with significant costs, adversely affecting their growth and future reproductive capabilities. As co-author Emily Bruns, an assistant professor of biology at UMD, pointed out, “It’s a mystery why young organisms don’t evolve stronger disease resistance because getting sick early in life can be deadly.” This study indicates that a hidden trade-off may prevent young organisms from developing robust defenses against diseases.

The researchers centered their investigation on a wild plant known as Silene latifolia, commonly referred to as white campion, and its interaction with a fungal disease called anther-smut. This particular affliction doesn’t result in the death of the plants; rather, it hinders their ability to produce pollen, rendering them incapable of reproduction— akin to what Bruns describes as a “plant STD.”

In a meticulously controlled setting, the team examined 45 different genetic variations of the Silene plant. Their findings revealed a concerning trend: seedlings exhibiting stronger disease resistance tended to produce significantly fewer flowers and seeds throughout their lifetime, particularly when nurtured in a disease-free environment. In sharp contrast, mature plants with enhanced resistance did not show such detrimental effects. Bruns elaborated, stating, “We found that young plants paid a higher 'cost' for fighting the disease compared with adult plants. Trying to fend off the fungus was far more challenging and resource-intensive for these juvenile plants. With limited energy reserves, if they allocate resources to disease defense, they are unable to channel that energy into future growth.”

Utilizing their findings, the research team developed a mathematical model illustrating that the costs associated with combating pathogens are substantial enough to hinder the evolution of stronger disease resistance in younger plants. In a hypothetical scenario where these costs were absent, plant families with heightened juvenile resistance could potentially eradicate the disease entirely. However, given the significant impact of developing resistance on young plants, they remain highly susceptible to infections.

Bruns explained, “Some young plants 'pay the cost' and manage to survive into adulthood, but the trade-off means they produce fewer flowers, making them less capable of reproducing. Meanwhile, the majority continue to be vulnerable during their juvenile stages, providing the disease a foothold.” Interestingly, the researchers were taken aback to find that these costs didn’t manifest immediately. Although plants that invested in disease resistance as seedlings appeared healthy initially, they produced significantly fewer flowers in their second year— typically when reproduction peaks.

Moreover, the study unveiled a surprising gender disparity: male plants bore a greater cost for disease resistance compared to their female counterparts. This discrepancy may stem from the fact that male plants generally produce a far greater number of flowers to maximize their pollen dispersion, making the diversion of resources to disease resistance particularly burdensome for them.

Bruns is optimistic about the broader implications of the team’s findings, suggesting that the juvenile susceptibility factor could have notable repercussions in managing diseases across various species. A deeper understanding of the evolutionary mechanisms driving this pattern could provide essential insights for disease management strategies in agriculture, conservation efforts, and public health initiatives.

Moving forward, Bruns and her team plan to explore whether introducing pathogens to plants later in life— after they have established their first true leaves and no longer depend on stored energy— could reduce the costs associated with disease resistance. They also aim to investigate if adult plants that exhibit higher disease resistance could offer protection to nearby seedlings by decreasing the overall disease presence in specific areas. “Nature is rife with infectious diseases,” Bruns remarked. “Understanding the various checks and balances between hosts and pathogens illuminates how evolution has shaped these relationships over millions of years.”

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