Early Detection of Alternaria alternata Infection in Fresh Peppers

Alternaria alternata (Ascomycota) is a fungus that causes leaf spots, rots, and blights on many parts of plants, as well as other diseases. It is an opportunistic pathogen affecting more than 380 species of host plants.

It typically spreads through airborne spores.

It is common in tomatoes, where symptoms begin with yellowing of the lower leaves. In addition to leaf and petiole necrosis, severe defoliation can be observed, leading to significant yield losses when it occurs before flowering. The fruits develop brown cankers that render them inedible.

Alternaria alternata is very common in warm and dry climates but can survive temperatures ranging from 1 to 35 °C.

Identification of Early Infections

Timely identification of A. alternata infection in postharvest green peppers is extremely important before more severe symptoms appear.

A recent study evaluated the appearance of chlorophyll, the fluorescence parameters of this compound, and the alteration of plasma membranes leading to leakage of cellular contents following infection by A. alternata.

Fatty acids in the thylakoid membranes (membranous structures located within the chloroplasts of plants and cyanobacteria, where the photochemical phase of photosynthesis takes place) in peppers were determined using gas chromatography–mass spectrometry (GC-MS).

Infected fruits show early size reduction, minimal chlorophyll fluorescence and electrical conductivity, as well as changes in nucleic acid absorbance at a wavelength of 260 nm—features that distinguish them from healthy controls.

In infected peppers, linoleic acid shows a significant correlation with cellular membrane destruction and altered chlorophyll fluorescence.

The degradation of unsaturated fatty acids causes significant changes in chlorophyll fluorescence parameters and the loss of cellular metabolites.

Sources

Zhao, C.; Niu, T.; Zhou, J.; Zhu, L.; Gu, S.; Wang, X. (2025).
Early Detection of Alternaria alternata Infection in Fresh Pepper Fruit Based on Chlorophyll Fluorescence Properties and Membrane Leakage.
Food Analytical Methods, (18):5.

https://en.wikipedia.org/wiki/Alternaria_alternata
Accessed on 05/31/2025.

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Accessed on 05/31/2025.