Vitamin C and plant extracts show promise against guava root and stem diseases

Jenn Hoskins
14th October, 2025

Vitamin C and plant extracts show promise against guava root and stem diseases

The characteristic galls (yellow arrows) seen on these guava roots are caused by an infection of the microscopic root-knot nematode, Meloidogyne incognita.

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

Key Findings

  • In Egypt, guava crops are threatened by crown gall disease and root-knot nematodes, prompting a search for alternative control methods
  • Ascorbic acid (vitamin C) effectively inhibited the growth of both the crown gall bacterium Agrobacterium tumefaciens and the root-knot nematode Meloidogyne incognita in laboratory tests
  • Applying ascorbic acid to guava seedlings prevented tumor formation from A. tumefaciens and significantly reduced root damage from both pathogens, also boosting plant health
Crown gall disease, caused by the bacterium Agrobacterium tumefaciens, and root-knot disease, caused by nematodes like Meloidogyne incognita, are significant threats to agriculture, leading to substantial crop losses. Traditional control methods often rely on pesticides, but there’s a growing need for environmentally friendly alternatives. Researchers at the Central Agricultural Pesticides Laboratory (CAPL)[1] investigated the potential of organic acids – ascorbic acid (vitamin C) and citric acid – and a plant extract from Thevetia sp. to combat these pathogens. The study focused on two isolates of A. tumefaciens (Ag1 and Ag2) and M. incognita. Molecular analysis confirmed the identity of isolate Ag2 as A. tumefaciens through PCR analysis of its 16S rRNA gene, revealing a close genetic relationship to an Indian isolate. The Thevetia sp. extract was found to contain 35 different phytochemical compounds identified using GC-MS, suggesting a complex mixture of potentially active substances. Initial experiments were conducted in vitro – meaning in a laboratory setting, outside of a living organism – to assess the direct effects of the treatments on the pathogens. Ascorbic acid at a concentration of 6.4% proved most effective against A. tumefaciens Ag2, inhibiting its growth by 38.3 mm in a disc diffusion assay and completely blocking growth at a concentration of 1.00 g/l (minimum inhibitory concentration, or MIC). The Thevetia sp. extract was more potent against the nematode’s second-stage juveniles, with an LC50 (lethal concentration killing 50% of the population) of 0.478 g/l and an LC90 (lethal concentration killing 90% of the population) of 3.185 g/l. These promising in vitro results were followed by pot trials using guava seedlings. Seedlings were exposed to single or combined infections of A. tumefaciens and M. incognita. Ascorbic acid at 14.8 g/l completely prevented gall formation (tumors caused by A. tumefaciens) in infected seedlings. The Thevetia sp. extract at 6.4 g/l and ascorbic acid at 14.8 g/l significantly reduced root gall formation and the number of pathogens in the soil, with the combined infection showing the most substantial reduction – 81.67% for gall reduction with Thevetia sp. and 76.57% with ascorbic acid. Importantly, both treatments also boosted the health of the guava seedlings. Plants treated with either ascorbic acid or Thevetia sp. extract showed increased shoot height and root length, along with higher levels of total phenols and total soluble proteins. These compounds are often indicators of a plant's defense response. This research aligns with the broader trend of seeking biological alternatives to traditional pesticides[2]. The use of organic acids, such as citric and succinic acids, has been shown to promote plant growth and enhance resistance to pathogens. The study expands on this by demonstrating the efficacy of ascorbic acid and a Thevetia sp. extract against two specific, economically important plant pathogens. Interestingly, the finding that ascorbic acid suppresses virulence factors is consistent with research on Escherichia coli[3], suggesting a common mechanism by which this vitamin can reduce the impact of bacterial infections. Furthermore, the observation that Thevetia sp. extract contains a diverse array of phytochemicals echoes findings that complex mixtures of compounds can be more effective than single isolates[4], where trans-cinnamaldehyde derivatives were shown to inhibit biofilm formation and virulence in Agrobacterium tumefaciens. The CAPL study builds on this by identifying specific compounds within the Thevetia sp. extract that may contribute to its anti-nematode activity, although further research is needed to pinpoint the exact mechanisms involved.

AgricultureHealthPlant Science

References

Main Study

1) Efficacy of ascorbic acid, citric acid and Thevetia sp. extract against Agrobacterium tumefaciens and Meloidogyne incognita infecting guava

Published 10th October, 2025

https://doi.org/10.1038/s41598-025-21658-3

Related Studies

2) Application of organic acids for plant protection against phytopathogens.

https://doi.org/10.1007/s00253-016-8067-6

3) The Promising Effect of Ascorbic Acid and Paracetamol as Anti-Biofilm and Anti-Virulence Agents against Resistant Escherichia coli.

https://doi.org/10.3390/cimb46070406

4) Inhibition of growth, biofilm formation, virulence, and surface attachment of Agrobacterium tumefaciens by cinnamaldehyde derivatives.

https://doi.org/10.3389/fmicb.2022.1001865


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