Studying Light Behavior in Citrus Infected by Blue Mold

Jenn Hoskins
16th August, 2024

Studying Light Behavior in Citrus Infected by Blue Mold

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at Nanjing Agricultural University studied how light interacts with infected Nanfeng tangerines and Gannan navel oranges to detect early fungal infections
  • Infected fruits showed increased light absorption at 482 nm and decreased absorption at 675 nm, indicating changes in pigment levels
  • Monte-Carlo simulations revealed that light at 482 nm penetrated less in infected tangerines, suggesting higher sensitivity to infection
  • Models developed by the researchers accurately distinguished between healthy and infected fruits, with accuracy rates of 95.24% for tangerines and 98.67% for oranges
Understanding how light interacts with infected citrus fruits can greatly aid in the early detection and management of postharvest diseases. A recent study conducted by researchers at Nanjing Agricultural University has delved into this topic, focusing on the optical properties and Monte-Carlo (MC) based simulation of light propagation in the flavedo (the outermost layer) of Nanfeng tangerine (NF) and Gannan navel orange (GN) infected by the fungus Penicillium italicum[1]. Penicillium italicum is a common postharvest pathogen that causes blue mold disease, leading to significant economic losses in citrus production. Previous studies have shown that certain compounds, such as 7-demethoxytylophorine (DEM), can inhibit the growth of P. italicum by damaging the fungal cell membranes and disrupting energy production[2]. However, detecting early infection in citrus fruits remains a challenge. The research team observed that the absorption coefficient (μa) of light at around 482 nm increased, while it decreased at around 675 nm in infected NF and GN during storage. These changes indicate the accumulation of carotenoids (pigments that absorb light in the blue region) and the loss of chlorophyll (which absorbs light in the red region). Interestingly, the variation in μa was more pronounced in NF compared to GN, suggesting that NF might be more sensitive to infection. Despite these changes in absorption, the researchers found limited differences in the reduced scattering coefficient (μs') between infected and healthy fruits. This coefficient measures how much light is scattered by the fruit's internal structures. The minimal change in μs' suggests that the structural integrity of the fruit's flavedo remains relatively intact during early infection stages. To further understand these optical changes, the researchers used Monte-Carlo (MC) simulations to model light propagation within the fruit. MC simulations are computational methods that use random sampling to solve physical and mathematical problems, in this case, modeling how light travels through the fruit's tissues. The simulations revealed that the weight and penetration depth of photon packets at 482 nm were reduced more in NF than in GN, indicating that light at this wavelength is more absorbed by the infected NF flavedo. In contrast, there were almost no changes at 926 nm, a wavelength with relatively low absorption. These findings align with earlier research that demonstrated the utility of optical properties in detecting fruit diseases. For instance, a study on longan fruits infected by Phomopsis longanae Chi showed that changes in cell wall-degrading enzymes and cell wall components could be linked to disease progression[3]. Similarly, the current study suggests that monitoring specific wavelengths can provide early indicators of infection in citrus fruits. The team also developed Partial Least Squares Discriminant Analysis (PLS-DA) models to discriminate between healthy and infected fruits. These models achieved high accuracy rates of 95.24% for NF and 98.67% for GN, highlighting the potential of optical methods for disease detection. In summary, this study provides valuable insights into the optical changes in citrus fruits infected by P. italicum and demonstrates the effectiveness of MC simulations in modeling these changes. The findings could pave the way for developing non-invasive techniques for early disease detection, ultimately helping to reduce postharvest losses in citrus production.

FruitsBiochemPlant Science

References

Main Study

1) Assessment of optical properties and Monte-Carlo based simulation of light propagation in citrus infected by Penicillium italicum.

Published 15th August, 2024

https://doi.org/10.1016/j.foodres.2024.114787

Related Studies

2) Inhibitory Effect of 7-Demethoxytylophorine on Penicillium italicum and its Possible Mechanism.

https://doi.org/10.3390/microorganisms7020036

3) Phomopsis longanae Chi-Induced Changes in Activities of Cell Wall-Degrading Enzymes and Contents of Cell Wall Components in Pericarp of Harvested Longan Fruit and Its Relation to Disease Development.

https://doi.org/10.3389/fmicb.2018.01051


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