Potato growth is unexpectedly preserved during co-attack by the fall armyworm and a bacterial pathogen.

Jim Crocker
28th December, 2025

Potato growth is unexpectedly preserved during co-attack by the fall armyworm and a bacterial pathogen.

While potato tuber weight was reduced by either the bacterium Pseudomonas syringae pv. tomato (2) or the fall armyworm Spodoptera frugiperda (3) alone compared to the control (1), this negative effect was negated when both parasites were present (4), suggesting an antagonistic interaction.

Image adapted from: Maluleke et al. / CC BY (Source)

Key Findings

  • In South Africa, potato seedlings are vulnerable to fall armyworm (FAW) and Pseudomonas syringae pv. tomato (Pst) which reduce growth and yield
  • FAW individually reduced plant height, stem diameter, and tuber weight, but this negative impact was lessened when Pst was also present, suggesting a possible interaction
  • Both FAW and Pst altered the potato plants’ internal chemistry (metabolome), indicating a stress response, with the combination of both potentially reducing FAW’s effects
Potato crops are vital globally, but are susceptible to numerous pests and diseases that significantly reduce yield. Two major threats are the fall armyworm (FAW), a destructive insect pest, and Pseudomonas syringae pv. tomato (Pst), a bacterium causing bacterial speck disease. Managing these threats effectively requires understanding how they impact plants, and crucially, how they interact when present together. Researchers from the University of South Africa, University of Venda, Agricultural Research Council and United Arab Emirates University[1] recently investigated the combined effects of FAW and Pst on potato seedlings, aiming to identify how these parasites influence plant growth, function, and internal chemical processes. The study focused on measuring several key indicators of plant health. These included physical growth parameters like plant height, stem diameter, tuber number, and tuber weight. Equally important were physiological measurements – how well the plant was functioning, assessed by tracking photosynthesis rate (the process of converting light into energy), stomatal conductance (regulation of gas exchange), transpiration efficiency (water loss during photosynthesis), the ratio of CO2 inside the plant to the ambient air (Ci/Ca), and water use efficiency. Finally, the researchers analysed the plant’s metabolome – the complete set of chemicals present within the plant tissues, providing a snapshot of its internal state. The researchers subjected potato seedlings to four treatments: no infection (control), infection with FAW alone, infection with Pst alone, and simultaneous infection with both. The results showed that both parasites individually affected plant growth and physiology, but the combined effect wasn’t simply the sum of the individual impacts. While FAW significantly reduced plant height when acting alone, this reduction was less pronounced when Pst was also present. A similar pattern emerged with stem diameter and total tuber weight – FAW’s negative impact was diminished in the presence of the bacterium. These findings are particularly interesting because they suggest a potential antagonistic relationship between the FAW and Pst. This means the presence of one parasite somehow reduces the ability of the other to cause damage. This phenomenon isn't uncommon in ecological interactions, and understanding its underlying mechanisms could be crucial for developing more effective pest management strategies. Further investigation is needed to confirm this antagonism and identify the cause. The study also employed correlation analysis, which revealed connections between different growth and physiological parameters. This helped to understand how the parasites disrupted plant processes. Importantly, both parasites induced changes in the plant’s metabolome, indicating they altered the plant’s internal chemistry. This reprogramming of the metabolome is a common response to stress, and analysing these changes can provide clues about the plant’s defense mechanisms and the parasites’ strategies for overcoming them. The observed effects of FAW on corn, rice and potato plants, as outlined in earlier research[2], provide a useful context for understanding the current findings. The previous study highlighted that FAW’s reproductive rate was highest on corn, suggesting it’s a preferred host. However, FAW could successfully complete its life cycle on rice and potato, albeit with reduced reproductive success. This demonstrates FAW’s ability to adapt to different host plants, and potentially interact with other pathogens present on those hosts. The current study expands on this by showing how FAW’s impact on potato is altered in the presence of Pst. Similarly, research on Pseudomonas syringae pv. tomato[3][4] has revealed significant genetic diversity among isolates, with varying levels of virulence – the ability to cause disease. The use of molecular markers to differentiate strains is important for understanding disease outbreaks and developing effective control measures. This is relevant to the current study because the specific strain of Pst used could influence its interaction with FAW. The fact that Pst can survive on plant debris and is dispersed by aerosols[4] also highlights the importance of understanding its role in a multi-parasite context, as it’s likely to be present alongside FAW in many potato fields. The researchers acknowledge that some of their results were unexpected, particularly the lessened impact of FAW in the presence of Pst. This underscores the complexity of plant-parasite interactions and the need for further research to fully understand the mechanisms at play.

AgricultureEcologyPlant Science

References

Main Study

1) Pseudomonas syringae pv. tomato and the fall armyworm modulate the morpho-physiology and the metabolome of potato plants

Published 26th December, 2025

https://doi.org/10.1371/journal.pone.0324111

Related Studies

2) Impact of Rice and Potato Host Plants Is Higher on the Reproduction than Growth of Corn Strain Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae).

https://doi.org/10.3390/insects13030256

3) Isolation of Pseudomonas syringae pv. Tomato strains causing bacterial speck disease of tomato and marker-based monitoring for their virulence.

https://doi.org/10.1007/s11033-023-08302-x

4) Pseudomonas syringae pv. tomato: the right pathogen, of the right plant, at the right time.

https://doi.org/10.1046/j.1364-3703.2000.00036.x


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