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Impact of Oxalic Acid Consumption and pH on the In Vitro Biological Control of Oxalogenic Phytopathogen Sclerotinia sclerotiorum

Summary

This research shows how bacteria can protect crops from a destructive fungus called Sclerotinia sclerotiorum. While scientists previously thought the bacteria worked by eating the toxic acid produced by the fungus, this study reveals that the bacteria also make the environment more alkaline (less acidic), which the fungus cannot tolerate. The combination of both effects—consuming the acid and changing the pH—is what actually stops the fungus from growing and damaging crops.

Background

Sclerotinia sclerotiorum is a destructive phytopathogenic fungus that causes significant economic losses in crops worldwide. This pathogen produces oxalic acid as a virulence factor. Oxalotrophic bacteria that degrade oxalic acid have been proposed as a biological control approach, but the mechanisms beyond oxalic acid consumption have not been fully investigated.

Objective

This study investigates whether biological control of S. sclerotiorum by oxalotrophic bacteria is mediated solely through oxalic acid consumption or if pH alkalinization plays a critical role. The research uses confrontation experiments with wild-type and oxalate-deficient mutant strains on different media to disentangle these mechanisms.

Results

Oxalotrophic bacteria controlled S. sclerotiorum only in media where oxalic acid was produced. However, the oxalate-deficient mutant was also controlled, indicating that oxalic acid consumption is not the sole biocontrol mechanism. Medium alkalinization, independent of oxotrophy, contributed significantly to fungal growth control, with dramatic effects on hyphal morphology in alkaline conditions.

Conclusion

While oxalic acid consumption was initially proposed as the basis for biocontrol, this study demonstrates that pH alkalinization is equally relevant for controlling S. sclerotiorum growth. The combined effects of oxalic acid degradation and bacterial metabolism-induced alkalinization, rather than oxalic acid consumption alone, drives the biocontrol effect.
  • Published in:Journal of Fungi,
  • Study Type:In Vitro Experimental Study,
  • Source: 10.3390/jof11030191, PMID: 40137229
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