H. MOVIMIENTOS REPETITIVOS
2) Comparación del resultado de cada método de conteo de dinero
Fungi that produce mycotoxins are referred to as mycotoxigenic fungi which include a wide variety of diverse fungal species which, in general, are not aggressive pathogens. The most important mycotoxins are produced primarily by three genera, Aspergillus, Penicillium, and
Fusarium. Also, the genus Alternaria includes several mycotoxigenic species which play an
important role in plant pathogenesis.15 Many mycotoxins are produced by several species in one genus, but some toxins can be produced by species in phylogenetically different genera (Table 1). Whether the production of related mycotoxins in different genera is caused by horizontal gene transfer or by parallel evolution is not yet known.16 Curiously, some strains are also known to produce different compounds or even produce the same compounds by different biosynthetic pathways.17
Aspergillus genus is the main producer of aflatoxins, and it commonly affects corn, cotton,
peanuts, and certain tree nuts. Although the genus is not considered to be a major cause of plant diseases, it has a huge agricultural impact due to the high toxicity of the mycotoxins produced. Certain species in this genus produce not only harmful but also beneficial metabolites, such as drugs, and they are widely used in biotechnology, for example for the production of hydrolytic enzymes.15,18 Species of the genus Alternaria are ubiquitous and abundant in the atmosphere as well as in soil, seed, and agricultural commodities. The genus is widely distributed in the environment and can infect more than 4000 host plants. These species are not only pathogenic to plants, causing spoilage and significant economic losses, but they also produce a wide variety of toxic secondary metabolites, mainly phytotoxins.15,19 The genus
Penicillium has its claim to fame as the producer of the first antibiotics discovered nearly a
century ago, although some species of the genus are also renowned plant pathogens or mycotoxin producers. Penicillium fungi are typically associated with the storage of crops and the production of mycotoxins such as ochratoxin.10 This complex genus, in terms of the number of species and range of habitats, is of great economic importance primarily as a cause of food and feed spoilage.19
Genus Fusarium is an extensively studied and widely-spread fungi. This genus has been associated as endophytes or with plant diseases with virtually every plant family, and thus
Fusarium contamination can result in significant economic losses. Moreover, many Fusarium
species are known to directly incite diseases in plants, humans, and domesticated animals, and they are notorious producers of several mycotoxins.20 Variety of diseases caused by Fusarium in plants include root and stem rots, cankers, wilts, fruit or seed rots, and leaf diseases. In small grains, such as wheat and barley, Fusarium produces Fusarium head blight, a disease which is mainly associated with temperate regions and leads to serious reductions in the grain quality.21 While some Fusarium strains have a wide host range and can colonize a variety of different crops, others are more restricted, such as F. verticillioides which is associated only with maize that can be infected with Fusarium ear rot.17 Interestingly, Fusarium fungi can also grow as apparently symptomless endophytes under many conditions.20 Thus, although fungal infections in the field are primarily transmitted by airborne spores, also infected but asymptomatic seeds can spread the infection.22 Moreover, largely as a consequence of their ability to live without oxygen, species of Fusarium occur in almost every environment making them probably the most prevalent pathogen in maize and many other grains.14,23
Table 1. Examples of the most common mycotoxin-producing fungi and agricultural products commonly affected by these species.14–16,20,24
Fungi species Commodities affected Major mycotoxins produced
Aspergillus
A. flavus Ubiquitous in foods, mainly maize, peanut, and cottonseed AFBCyclopiazonic acid 1 and AFB2 Sterigmatocystin
A. parasiticus Peanut, maize, cotton, spices, walnut AFBAFG1 and AFB2
1 and AFG2
A. niger Grapes, maize, coffee, peanuts OTA FB
2, FB4,FB6
A. carbonarius Grapes, coffee, spices OTA
A. ochraceus Maize, peanuts, cottonseed, rice, cereal grains, coffee, spices OTA, ochratoxins B and C Penicillic acid
Penicillium
P. citrinum Cereals, foods, feedstuffs CIT
P. verrucosum Cereals, stored grains, cured meat, cheese OTA, CIT Cyclopiazonic acid Tenuazonic acid
P. expansum Fruits, especially apples Patulin Tenuazonic acid CIT
Fusarium
F. graminearum Maize, wheat, barley DON, nivalenol ZEA, zearalanone, zearalanol
F. culmorum Cereals DON, nivalenol HT-2 toxin ZEA, zearalanone
F. oxysporum Several crops, such as bean, cotton, potato, tomato, and banana FBEnniatins 1,FB2,FB3 F. proliferatum Maize, wheat, sorghum, mango, asparagus FBMoniliformin 1,FB2,FB3, FB4
Beauvericin
F. verticillioides Maize FBDON 1,FB2,FB3 Zearalanone
F. sporotrichioides Maize, small grains T-2 toxin HT-2 toxin Beauvericin Alternaria
A. alternata Tomato, pear, apple, strawberry Alternariols
A. tenuissima Tomato, grapevine, strawberry Alternariols Tenuazonic acid
Abbreviations: aflatoxin B1/B2, AFB1/2; aflatoxin G1/G2, AFG1/2; citrinin, CIT; deozynivalenol, DON; fumonisin B1–6,
As a genus, Fusarium lacks certain morphological characters that can be used to easily differentiate the species, which has led to a somewhat confusing nomenclature among this family.20 When the genus was first introduced in 1809, the primary character of Fusarium was the presence of a distinctive canoe- or banana-shaped conidia, but to date many Fusarium species have been poorly defined and characterized, and different biologies of morphologically similar strains have complicated the study of Fusarium.20 Among the Fusarium genus,
F. verticillioides and F. proliferatum, are among the most significant producers of toxic
mycotoxins.25 F. proliferatum is known to cause diseases worldwide in many crops, most important one being maize,20 and it has been reported to produce a wide variety of mycotoxins often at high levels. The wide host range of this fungus has resulted in recovering these toxins from seemingly unlikely sources, such as asparagus or garlic.20 The macroconidia of
F. proliferatum is similar to other species in Fusarium fujikuroi species complex (formerly known
as the Gibberella fujikuroi species complex), and in fact, F. proliferatum is easily confused with
F. fujikuroi, F. oxysporum, F. thapsinum, and F. verticillioides. Another important mycotoxin
producer, F. verticillioides, formerly known as F. moniliforme, is one of the most prevalent seed- borne fungi associated with maize worldwide,26 and it is known not only as a mycotoxin producer but also for being allergenic to human and capable of infecting cancer.20
Due to the wide diversity of mycotoxin-producing fungi in a wide variety of crops both before and after the harvest, it is difficult to make general statements about the occurrence of the mycotoxigenic fungi. Some toxigenic species, mainly from Fusarium and Alternaria genera, are often classified to as “field fungi” because they require very high moisture content, whereas “storage fungi,” such as Aspergillus and Penicillium, can also grow in low moisture environments.19 More commonly these species occur in temperate regions, and climate change due to global warming has been estimated to alter the incidence of toxigenic fungi and even modify host resistance and host–pathogen interactions.15 In addition to crops and plants, certain mycotoxigenic fungi, for example some species of Fusarium and Aspergillus, have been found in moisture-damaged buildings.27
Furthermore, the occurrence of mycotoxigenic fungi and subsequent mycotoxin contamination are affected by numerous external factors. Some are related to the susceptibility of crops, plant stress, harvesting practices, and storage of grains. First of all, fungal growth itself depends on favorable environmental conditions, and therefore, their occurrence varies among geographical areas and is strain-specific.28 For example, infection and ear rot by F. verticillioides and F. proliferatum, along with subsequent mycotoxin contamination, are more common in warm and dry weather, and, although not conclusive in all crops, high temperatures seem to play a role for example in aflatoxin contamination.10 Additionally, some microenvironmental factors are known to be a factor in mycotoxin production. For instance, the nitrogen and carbon sources that the fungi utilize as well as the pH of the environment are known to modulate mycotoxin production at the cellular level. Moreover, many epigenetic factors and environmentally activated genes have been identified to be relevant at the genomic level for certain mycotoxins. Production of mycotoxins also depends on when the infection occurs and on the host environment.29,30 For example, insect damage is known to play a large role in mycotoxin contamination in several species.15
Although it is widely acknowledged that mycotoxins are usually produced to protect the fungi against other organisms, it still remains partly unanswered when and how fungi produce these toxins.21 Proper harvesting practices and storage conditions are known to be a factor in
the initiation of fungal contamination and mycotoxin production.29 Fungal contamination can be prevented by correct harvesting techniques, such as harvesting at the appropriate time after maturation of plants and inspecting of the harvesting equipment and storage facilities before the harvest.29 Nevertheless, for the detection of a fungal infection and the potential for mycotoxin contamination, it is essential to develop methods to determine the presence of these mycotoxigenic species.