View source for Blue Moulds of Oranges

By Georgy Pestsov (page moved here from http://phytopathology.net/Portal/Blue_Mould_of_Oranges )

Due to their superb taste and nutritional value, oranges figure prominently in the world’s production of citrus plants. Their refreshing taste is determined by a combination of sugar, organic acids, pectines, and vitamin C. However, when gathered, transported or stored, oranges can be infected by fungal diseases. When preserved under low temperatures, the disease symptoms usually don’t show. As soon as conditions grow favorable, phytopathogens reproduce intensively.

Infection of oranges by the Blue Mould (pathogen ''Penicillium italicum'' Wehmer) often occurs through the fruit’s peel lesion. Mycelium of the fungi start growing inside of the peel, and under room temperature quickly occupies new space (fig. 1). Initially small white colonies appear on the surface, rapidly growing larger. Within several hours they become grayish-green and in 24 hours grayish-blue. The color change is a result of the spore formation. The older the colony, the more spores are being produced and the more intensively it is thus colored (fig. 2).

In certain places, often at places of the peel injury, the peel is growing softer and acquires a watery consistence that is very distinct from the healthy one (fig. 3, 4). Tissue dissociation results from the fungi action. Gradually they insinuate in the inside of the fruit, changing its consistence, composition and coloring of the pulp.

Inside the fruit the fungi moves in the intercellular space and actively produces conidia inside the fruit (fig. 5). If an orange slice is kept under room temperature for 24 hours, mass sporification takes place in places already previously infected by the mycelium invisible to the naked eye (fig. 6). Sporulation occurs on asymmetrical conidiophores, bearing conidiogeneous cell producing billions of the rounded conidia in chains (fig. 7, 8, 9, 10, 11, 12). The conidia are dispersed and may damage other products. 

People, especially children, can suffer allergic reactions when inhaling or consuming the conidia.

The following images illustrate the development of blue mould on oranges.

{{Gallery
 | footer= All images by G. Pestsov.
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 | lines=4
 | File:Blue Mould of Oranges 1 - Overview.jpg | Figure 1. Orange infected with blue mould. (Image by G. Pestsov)
 | File:Blue Mould of Oranges 2 - Spreading Penicillium italicum.jpg |
Figure 2. Spreading of the colony of the fungus ''Penicillium italicum'' Wehmer. (Image by G. Pestsov)
 | File:Blue Mould of Oranges 3 - Surface details.jpg | Figure 3. Formation of the blue mould by the pathogen. (Image by G. Pestsov)
 | File:Blue Mould of Oranges 4 - Surface details.jpg | Figure 4. Formation of the blue mould by the pathogen. (Image by G. Pestsov)
 | File:Blue Mould of Oranges 5 - Inside.jpg | Figure 5. Development of the pathogen colony formation in the inside of the fruit. (Image by G. Pestsov)
 | File:Blue Mould of Oranges 6 - 24h incubated slice.jpg | Figure 6. Sporification of the fungus ''Penicillium italicum'' in 24 hours after the orange was cut. (Image by G. Pestsov)
 | File: Conidia chain on the conidiophore.jpg | Figure 7.Conidia chain on the conidiophore.jpg (Image by G. Pestsov)
 | File: Formation of conidia on the conidiophores with assymetrical penicillus.jpg | Figure 8.Formation of conidia on the conidiophores with assymetrical penicillus.jpg (Image by G. Pestsov)
 | File:Blue Mould of Oranges - Conidiophores.jpg | Figure 9.Conidiophores of the fungus ''Penicillium italicum''.jpg (Image by G. Pestsov)
 | File: Conidia formation on sterigma.jpg | Figure 10.Conidia formation on sterigma.jpg (Image by G. Pestsov)
 | File: 8. Formation of the conidiophores.jpg  | Figure 11. Formation of the conidiophores by the fungus ''Penicillium italicum''.jpg (Image by G. Pestsov)
 | File:Isolated conidiophore.jpg  | Figure 12.Isolated conidiophore.jpg (Image by G. Pestsov)
}}