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Penicillium italicum Wehmer is characterized as a widely distributed, destructive, blueish green post harvest mould on the fruits of Citrus spp. Post harvest fruits are susceptible to fungal infection through the transportation, storage life, and the ripening stages of the fruit. P. italicum is a necrotrophic wound pathogen that produces soft rots in citrus fruits through peel injuries and progressively reduces the fruit into a pulp. Transmission of disease can also occur through the contact diseased citrus fruits  to the healthy citrus fruits. Discovered in 1894 by Wehmer, P. italicum is an asexual pathogen which causes infection through the production of loosely synnematous conidiophores.

P. italicum is a mesophillic soil-borne fungus with a geographic distribution in temperate and subtropical zones. As a widespread citrus fruit pathogen responsible for economic losses of citrus crops, preventative treatment measures are currently developing for the pathogen.The efficacy of preventative treatment measures are improving from conventional fungicides such as imazalil (IMZ), and thiabendazole (TBZ) to botanical compounds such as Ageratun conzyodes.

History and taxonomy
Penicillium italicum belongs under the genus Penicillium of the Ascomycota division. Penicillium derived from the latin word penicillus meaning little brush, was identified by Link in the publication Observationes in Ordines plantarum naturales in 1809. P. italicum was discovered in 1894 by Wehmer through his investigation of infection in citrus fruits published in the journal Hedwigia titled Eine neue Sklerotien-bildende Penicillium-Species.  Further classification of P. italicum within Penicillium, is comprised within the section Cylindrosporum. Section Cylindrosporum includes species that characteristically produce terverticillate penicilli and form cylindrical conidia borne from philades. Section Cylindrosporum includes a single series; series Italica. Classified by Raper and Thom in 1949, the series Italica, comprises of four species: P. italicum Wehmer'',P. digitatum Persoon, P. resticulosum Birkinshaw et al. , and P. fennelliae'' Stolk with the first three species classified into different subdivisions.

Associated taxonomic names of P. italicum include Penicillium var.album C.T Wei (1940), and ''Penicillium italicum var. avellaneum Samson & Y. Gutter (1976). The species does not have associated homotypic synonyms however, heterotypic synonyms of the species include Oidium fasciculatum Berk (1836), Penicillium aeroginosum Dierck (1901), Penicillium digitatum var. latum Abe (1956), Penicillium italicum var. album C.T Wei (1940), Penicillium italicum var. avellaneum'' Samson & Y. Gutter (1976).

Growth and morphology
Penicillium italicum is an asexually reproducing pathogen which causes infection through the production of spore bearing structures called penicilli. The terverticillate penicilli in P. italicum are characterized as asymmetric with irregular branching of the metulae and sterigmata at different levels resulting in a the brush-like conformation. The conidiophore is a specialized branch that arises directly from the substratum or from the aerial hyphae. In P. italicum, the conidiophores are characterized as loosely synnematous and aggregate into coremia bundles following development. Conidiophores closely interact with rami that measures 15-25 μm by 3.5-4.5 μm. In P. italicum, conidiophores stalks are up to 100-250 x 3.5-5.0 μm stipes in size with each conidiophore tip bearing sterigmata or metulae at different levels. The sterigmata are few in number in the penicilli and occur in clusters of 3 to 6 in dimensions of 8-12 μm x 3.0 μm. The metulae is commonly measured in groups of 2 to 4 measuring 15-20 μm by 3.5-4.0 μm at different levels. Further branching from the metulae and sterigmata bears three to six flask shaped phialides that are 8-12 x 3.0 μm in size. The short neck of flask shaped phialides renders the formation of the cylindrical smooth-walled conidia from 3-5 x 2.0 to 3.0 μm in length. The chains of conidial fructification are loosely divergent and range up to 300 μm in length. During later stages of development, conidial morphology changes from cylindrical to elliptical in shape. External morphology indicates glassy, translucent conidiophores with green elliptical conidia with yellow to deep brown reverse colours. The sclerotia which is consists of hyphal threads are up to 300 μm diameter, and yellowish brown in pigment. Colonies of infected fruit also have white mycelium followed by bluish green to grayish green spores. ReDifferentiating P. italicum from related citrus rots species like P. digitatum can be elucidated through morphology''. P. italicum produces larger and more complexly branched penicilli whereas structural elements such as the metulae, sterigmata, and conidia are generally smaller than P. digitatum. Additionally in comparison to P. digitatum, P. italicum'' has a better developed terverticillate penicilli with greyish blue colonies. Analysis of reproduction in P. italicum indicate that the teleomorphic stage of reproduction is undefined. P. italicum will render the fruit into a slimy pulp whereas the P. digitatum shrivel and dry the fruits.

Physiology
The transmission and growth of moulds require important factors contributing to physiology such as pH, temperature, water activity, and nutrients. P. italicum has a pH range for growth from 1.9 to 9.8 with rapid growth occurring from 2.9 to 6.5. It is a mesophillic species as the maximal rapid growth occurs from 20-23 C and below 30 C. The rate of growth is slowed down at  temperatures below 5 C with a minimal temperature of 0 C. The minimum aw water activity for germination is 0.87, thus indicating  that the species thrives on a water-rich environment. Following infection by P. italicum, degreening of the fruit is stimulated by ethylene elevation of fruit at 17 C. As a natural plant hormone, increased ethylene elevation followed by stimulation by the pathogen,  contributes to the deterioration of the plant.

P. italicum is characterized as having a sweet, aromatic odour caused by metabolites such as ethyl acetate, isopentanol, linalool, isobutanol, 1-nonene. The scent is distinguished as lavender and lilac-like odour. As a pathogen that infects the citrus fruit through rind wounds, P. italicum mostly produces hydrolytic enzymes such as polygalacturonases and cellulases which account for tissues breakdown in infected fruits. The association of P. italicum as a cell wall wound pathogen is identified in the increase in expression of cell wall breakage enzymes polygalacturonase and β-glucosidase following infection in fruits. The pathogenicity of P. italicum has been is significantly impacted by the expression of volatiles emitted from wounded host tissues. Peel oil characterized as the essential oil that is produced in the rinds of the fruits and can significantly influence the germination of citrus fruit pathogens. In diseased fruits, P. italicum responded most strongly with myrcene stimulating germination and the formation of the germ tube.

Habitat and ecology
The primary habitat of P. italicum is established as a pathogen in the citrus spp. fruits and identified in soil debris of citrus plantations. Distributional data indicated a prevalence of P. italicum in regions of warmer climate and in soil of temperate and subtropical zones. Noted high incidence rate regions include Egypt, Libya, Israel, Ghana, Zambia, Rhodesia, South Africa, and New Zealand. Alternate hosts or substrates of P. italicum include avocado, mango, sweet potato, persimmon, melon, tomato, wheat and grapes. Isolations of P. italicum in different ecological conditions include presence in wet grasslands, rendzina, terra fusca, and salt-marshes. It is reported that the prevalence of P. italicum in alternate hosts and substrates are infrequent and hence the primary habitat of the species remains as a pathogen in citrus spp. fruits. Distinguishability of P. italicum from P. digitatum can be elucidated through the habitat of the pathogens as P. italicum abundantly occurs on oranges and grapefruit whereas the abundance of P. digitatum occurs on lemons.

Laboratory culturing methods
Under conditions of incubation and control, it is fundamental to understand the physiological growth mechanisms associated with different substrates. Substrate composition has a significant influence on the mycoflora in different foods even when the temperature and the water activity are accounted. Therefore, laboratory culturing methods are conducted to compare the growth of the P. italicum  on  different growth mediums. Colonies of P. italicum grown on Czapek yeast agar (CYA) at 25 &deg;C showed restricted growth development with a diameter of 30-40 mm within 7 days with a dense surface with a velvety to fasciculate texture. Morphological characteristics include irregular margins with white mycelium, greenish grey conidial development with heavy conidiogenesis, and small amounts of clear exudate. Colonies grown on Malt extract agar (MEA) displayed an increased growth with a diameters ranging from 40-50 mm in diameter within 7 days and under 25 &deg;C conditions. The surface texture of the colony is strictly velutinous with very small amounts of coremia development at the margin of the growth plate with moderate to heavy conidiogenesis. On glycerol nitrate (G25N), moderately dense colonies grow with a 12-17 mm diameter, with moderate conidiogenesis with brown pigmentation. Further analysis with colonies under 5 &deg;C with CYA exhibited micro colonies grown on CYA at 5 &deg;C displayed a 2-4 mm diameter increase within 7 days. At 37 &deg;C conditions on CYA,  P. italicum colonies exhibited no growth.

Human Pathogenicity
Mycotoxins are chemicals that induce a toxic response when ingested by humans and other animals. These chemicals can cause problems when ingested in low concentration over a relative time. Many species within Penicillium have noted negative influences on their hosts through the mycotoxins they make. Food mycotoxins are classified as secondary metabolite products of filamentous fungi. Although P. italicum is a common cause of post harvest fruit decay, the toxicity of many excreted toxins of the species are unknown. Previous research has noted the exhibition Deoxybrevianamide E a toxic compound of ducks, in biological assays. Although the compound is recognized as toxic to ducks, mammalian toxicity has not been tested. Another exhibited mycotoxin of P. italicum is 5,6-Dihydro-4-methoxy-2H-pyran-2-one however, toxicity of this compound has not been tested in mammals.

Fungi of the Ascomycota division are commonly found indoors and can grow on a wide range of surfaces. The asexual nature of fungi of the Penicillium genus stimulates the production of small fungal spores. The sporulation of P. italicum can produce spores that  be easily inhaled and thus be potentially allergenic. The allergenic response can thus be mediated through the inhalation of the mould spores and with the activity of the Immunoglobulin (Ig)  E specific antibody which interact with  mast cell tissues to promote the release of histamine. Through the release of histamine, allergic disease arises with nasal, and respiratory related symptoms.

Treatment
P. italicum is one of the most common cause of post harvest citrus fruit decay throughout the world. On an economic and commercial scale, difficulties in the preservation of citrus spp. fruits arise due to the long distance transport of the fruits. Disease by P. italicum occurs through skin tissue of the fruit and therefore control efficient treatment measures need to be elucidated to prevent costly economic damages in citrus crops. Currently, several treatment measures have been incorporated in reducing the incidence of P. italicum. Such treatment measures include the use of detergents, fungicides, and bioagents. Washes that are heated up to 40-50 &deg;C containing detergents and fungicides such as benomyl, thianemdazole, imazalil, guazantine or sodium-o-phenylphenate (SOPP) are currently used as treatment measures. After washing the fruit in detergents or fungicides, the fruit may be individually wrapped in waxed paper. Washing the fruits in weak boric acid and borax solution to prevent further rotting of the fruit in storage and in transit is an efficient preventive measure used today. As both boric acid and borax are low in toxicity, they reduce the incidence of P. italicum. In comparison to another prevalent citrus pathogen Penicillium digitatum, in response to fungicides imazalil (IMZ), and thiabendazole (TBZ), P. italicum showed less fungicidal resistance than P. digitatum.  An alternative to chemical pesticides are bioagents and in recent research studies, aspire, a product of the yeast Candida oleophila, was able to reduce the decay by P. italicum in the Citrus fruit. Additionally botanical compounds such as leaf extract from Ageratun conzyodes completely halted the production of P. italicum. Therefore, future preventive treatment measure plans for P. italicum  includes fungicide rotation, proper hygiene, proper harvesting without injury to fruit, and avoiding reprocessing of the fruit line.