Potato processors and growers seeking alternatives to conventional fungicides may soon have another tool available that combines disease control with a lower impact on the plant’s natural microbial ecosystem.

Researchers at the Swedish University of Agricultural Sciences (SLU), working with colleagues from The James Hutton Institute, have found that RNA-based sprays targeting potato late blight have only minimal effects on the microbial communities living on potato leaves. Their findings suggest that the disease itself causes far greater disruption to the potato microbiome than the treatment designed to control it.

The study, recently accepted for publication in npj Biofilms and Microbiomes, examined the impact of double-stranded RNA (dsRNA) sprays used in Spray-Induced Gene Silencing (SIGS), an emerging crop protection approach that targets specific genes required for pathogen development.

Researchers focused on Potato Late Blight, a disease caused by the pathogen Phytophthora infestans. Late blight remains one of the most economically damaging diseases affecting potato production worldwide, driving extensive fungicide applications and causing billions of euros in annual losses.

Using high-throughput sequencing techniques, the research team monitored bacterial and fungal communities inhabiting potato leaves after the application of dsRNA molecules designed to silence genes essential for pathogen growth and infection.

According to the study, the RNA treatments produced little change in the dominant microbial populations naturally present on potato foliage. Core bacterial and fungal communities remained largely stable following treatment. In contrast, infection by P. infestans caused substantially greater shifts in microbiome composition.

“One key question for RNA-based crop protection is whether it affects beneficial microorganisms. Here, we show that the potato microbiome remains remarkably stable after dsRNA treatment, while the pathogen itself drives much larger changes,” said Poorva Sundararajan.

The researchers also reported that several microbial groups associated with plant health and disease suppression remained present after treatment. Some potentially beneficial bacteria increased in abundance when plants were exposed to the pathogen.

Unlike conventional fungicides, SIGS employs naturally occurring RNA molecules to selectively silence genes needed by pathogens to infect plants. Because the technology can be designed to target specific organisms, it has attracted attention as a potentially more precise crop protection strategy with fewer unintended effects on non-target species.

“For any new crop protection technology, effectiveness alone is not enough. We also need to understand its environmental impact. Our findings show that SIGS can target the pathogen while largely preserving the beneficial microbial communities associated with the plant. This is an important step towards more precise and sustainable disease management,” said Samrat Ghosh.

While the results add to growing evidence supporting the environmental compatibility of RNA-based crop protection, the researchers caution that additional work remains necessary before broad conclusions can be drawn for commercial production environments.

“We still need more field studies across different potato varieties and growing conditions to confirm these results under field conditions. But overall, the study provides important evidence that RNA sprays can control the target disease without significantly disrupting the microbial communities that support plant health,” said Ramesh Vetukuri.

For the potato industry, the findings are particularly relevant as processors and growers face increasing pressure to reduce pesticide use while maintaining crop yields and tuber quality. Technologies such as SIGS could eventually become part of integrated disease management programmes that offer effective late blight control with a reduced environmental footprint.