Drivers of Fusarium dispersion in Madeira Archipelago (Portugal)

Promotores da dispersão de Fusarium no Arquipélago da Madeira (Portugal)

Irene Camacho Rubina Leça Duarte Sardinha Mónica Fernandez Roberto Camacho About the authors

ABSTRACT

The present study aimed to analyze the possible routes of Fusarium spp. introduction in Madeira between 1990 and 2018 and to elucidate the factors that favored the introduction and settling of this fungus in the Island. Phytosanitary surveys were carried out in several crops and plants imported to Madeira. The isolates of Fusarium spp. were obtained from underground and aerial organs of the plants and cultured on differential media for species identification. Fungal colony and spore morphology were observed under a microscope and identified based on bibliography and dichotomous keys. The phytosanitary analysis for the incidence of Fusarium spp. in plants or crops indicated an increasing trend in the number of fungi, especially between 1990 and 2001. The greatest fungal contamination occurred in the municipalities located in the southern coast of the Island. Most of the contaminated samples were from Portugal (96.9%), while 0.1% to 1.6% samples derived from foreign countries, especially the Netherlands and France. Of 3,246 samples infected with Fusarium spp., 1,212 were from horticultural (37.3%), ornamental (36.9%), tropical and subtropical (16.9%), and temperate plants (9.9%). Fusarium wilt (Panama Disease) caused by F. oxysporum f. sp. cubense occurred in several products imported to Madeira. Other species like Fusarium oxysporum were also detected in several plants and agricultural products, along with Fusarium sp. and Fusarium equiseti. The geoclimatic conditions of Madeira can be suitable for the development and dispersion of these fungi. The trade of cultivars and plants from Portugal and from foreign countries has been an important route of Fusarium introduction in Madeira.

Keywords
Fusarium ; phytopathogen; phytosanitary control; invasion; Madeira

RESUMO

O trabalho teve como objetivo analisar as possíveis vias de introdução de Fusarium spp. na Madeira entre 1990 e 2018, para elucidar os fatores que favoreceram a sua introdução e fixação na ilha. Realizaram-se análises fitossanitárias em culturas e plantas importadas para a Madeira. Os isolados de Fusarium spp. foram obtidos de órgãos subterrâneos e aéreos das plantas e cultivados em meios diferenciais para identificação das espécies. A colônia de fungos e a morfologia dos esporos foram observadas ao microscópio e identificados com o auxílio de bibliografia e chaves dicotómicas. A análise fitossanitária revelou que a incidência de Fusarium spp. em plantas ou culturas apresentou uma tendência crescente no número de fungos, principalmente entre 1990 e 2001. A contaminação fúngica mais elevada ocorreu nos municípios localizados no litoral sul da ilha. A maioria das amostras contaminadas proveio de Portugal (96,9%) e 0,1% a 1,6% provieram do exterior, sobretudo da Holanda e França. De 3.246 amostras infectadas com Fusarium spp., 1212 eram hortícolas (37,3%), ornamentais (36,9%), tropicais e subtropicais (16,9%) e temperadas (9,9%). Fusarium Wilt (doença do Panamá) causada por F. oxysporum f. sp. cubense ocorreu em vários produtos importados para a Madeira. Outros como Fusarium oxysporum spp. foram detectados em várias plantas e produtos agrícolas, juntamente com Fusarium sp. e Fusarium equiseti. As condições geoclimáticas da Madeira podem ser adequadas para o desenvolvimento e dispersão destes fungos. O comércio de cultivares e plantas de Portugal e do estrangeiro tem sido uma importante via de introdução do Fusarium na Madeira.

Palavras-chave
Fusarium ; fitopatogénio; controle fitossanitário; invasões; Madeira

Fusarium species are among the most important soil-borne phytopathogenic fungi worldwide (1818 Okungbowa, F.I.; Shittu, H.O. Fusarium wilts: An overview. Environmental Research Journal, Reus, v.6, n.2, p.83-102, 2012.). They are common in fertile cultivated and rangeland soils, either as parasites, in association with plant roots, or as saprophytes, showing cosmopolitan distribution (1717 Nelson, P.E.; Dignani, M.C.; Anaisse, E.J. Taxonomy, biology, and clinical aspects of Fusarium species. Clinical Microbiology Reviews, Minnesota. v.7, n.4, p.479-504, 1994.). Several species constitute important plant pathogens, causing vascular wilts, collar rot, stalk and head rots, while other species are endophytic, leading to symptomless plant tissue infection (1212 Leslie, J.F.; Summerell, B.A. Fusarium Laboratory Manual. Iowa: Blackwell, 2006., 1414 Mezzomo, R.; Rolim, J.M.; Santos, A.F.; Poletto, T.; Walker, C.; Maciel, C.G.; Muniz, M.F.B. Aggressiveness of Fusarium oxysporum and F. solani isolates to yerba-mate and production of extracellular enzymes. Summa Phytopathologica, Botucatu, v.45, n.2, p.141-145, 2019.). Fusarium also represents a common cause of food spoilage and, together with Penicillium and Aspergillus, can lead to important stored-grain losses. Some species can produce mycotoxins and are often involved in mycotoxicoses in animals and occasionally in men (1212 Leslie, J.F.; Summerell, B.A. Fusarium Laboratory Manual. Iowa: Blackwell, 2006.).

Plant infections, caused by Fusarium or not, can occur at all developmental stages, from germinating seeds to mature vegetative tissues, depending on the host plant and the species involved (1515 Moretti, A.N. Taxonomy of Fusarium genus, a continuous fight between lumpers and splitters. Proceedings of the National Academy of Sciences, Matica Srpska Novi Sad, n.117, p.7-13, 2009.). Fungal growth and toxin production can be affected by factors such as crop variety, type of species and environmental conditions (2121 Pleadin, J.; Sokolović, M.; Perši, N.; Zadravec, M.; Jaki, V.; Vulić, A. Contamination of maize with deoxynivalenol and zearalenone in Croatia. Food Control, Wageningen, n.28, p.94-98, 2012.). Representatives of these fungi can be found in most bioclimatic regions of the world, including the tropical and temperate grasslands (1212 Leslie, J.F.; Summerell, B.A. Fusarium Laboratory Manual. Iowa: Blackwell, 2006.). Their distribution is influenced by environmental factors, such as rainfall, soil and vegetation type (2626 Summerell, B.A.; Leslie, J.F.; Liew, E.C.Y.; Laurence, M.H.; Bullock, S.; Petrovic, T.; Bentley, A.R.; Howard, C.G.; Peterson, S.A.; Walsh, J.L.; Burgess, L.W. Fusarium species associated with plants in Australia. Fungal Diversity, The Netherlands, v.46, p.1-27, 2011.), revealing a particular ability to survive at distinct temperature ranges, especially in drought periods (2626 Summerell, B.A.; Leslie, J.F.; Liew, E.C.Y.; Laurence, M.H.; Bullock, S.; Petrovic, T.; Bentley, A.R.; Howard, C.G.; Peterson, S.A.; Walsh, J.L.; Burgess, L.W. Fusarium species associated with plants in Australia. Fungal Diversity, The Netherlands, v.46, p.1-27, 2011.). In addition, Fusarium species show an efficient dispersion mechanism, dispersing spores under wet and hot weather or even under rainy conditions (1717 Nelson, P.E.; Dignani, M.C.; Anaisse, E.J. Taxonomy, biology, and clinical aspects of Fusarium species. Clinical Microbiology Reviews, Minnesota. v.7, n.4, p.479-504, 1994.).

The genus Fusarium currently comprises nearly 300 recognized species occurring worldwide in a diversity of habitats (88 Index Fungarum Partnership. Index Fungarum. Kew: CABI, 2015. Available at: http://www.indexfungorum.org/Names/names.asp. Accessed on: 07 Oct. 2019.
http://www.indexfungorum.org/Names/names...
, 1717 Nelson, P.E.; Dignani, M.C.; Anaisse, E.J. Taxonomy, biology, and clinical aspects of Fusarium species. Clinical Microbiology Reviews, Minnesota. v.7, n.4, p.479-504, 1994.); its species identification and classification is commonly based on morphological and cultural characters, fungus-specific region and gene sequencing (99 Karlsson, I.; Edel-Hermann, V.; Gautheron, N.; Durling, M.B.; Kolseth, A-K.; Steinberg, C.; Persson, P.; Friberg, H. Genus-specific primers for study of Fusarium communities in field samples. Applied and Environmental Microbiology, Michigan, v. 82, p.491-501, 2016.). Macroscopic and microscopic features are key features for Fusarium species differentiation (1515 Moretti, A.N. Taxonomy of Fusarium genus, a continuous fight between lumpers and splitters. Proceedings of the National Academy of Sciences, Matica Srpska Novi Sad, n.117, p.7-13, 2009.), which remains a rapid and less expensive technique to validate a primary alarm of foodstuff contamination.

Occurrence of this fungus, causing an array of diseases, has been described for several plant species that have economic importance, namely sweet potato (2727 Thilagam, R.; Kalaivani, G.; Hemalatha, N. Isolations and Identification of phytopathogenic fungi from infected plant parts. International Journal of Current Pharmaceutical Research, Bhopal, v.10, n.1, p.26-28, 2018.), passionfruit (1919 Ortiz, E.; Cruz, M.; Melgarejo, L.M.; Marquínez, X.; Hoyos-Carvajal, L. Características hispatologicas da infecção causada por Fusarium oxysporum e F. solani em maracujá-roxo (Passiflora edulis Sims). Summa Phytopathologica, Botucatu, v.40, n.2, p.134-140, 2014.), cereals (1111 Lee, T.; Paek, J-S.; Lee, K.A.; Lee, S.; Choi, J.H.; Ham, H.; Hong, S.K.; Ryu, J-G. Occurrence of toxigenic Fusarium vorosii among small Grain cereals in Korea. Plant Patholology Journal, London, v.32, n.5, p.407-413, 2016.) and other hosts, like ornamental plants.

In Madeira Island, occurrence of Fusarium spores in the atmosphere is common (2525 Sousa, L.; Camacho, I.; Grinn-Gofroń, A.; Camacho, R. Monitoring of anamorphic fungal spores in Madeira Region (Portugal), 2003-2008. Aerobiologia, Switzerland, v.31, n.2, p.1-13, 2015.), especially before the hottest period of the year (before June), and dispersion is usually favored by humid warm weather and rainfall. Nearly two-thirds of Madeira Archipelago territory are a national park with unique endemic flora and fauna. Its mild subtropical climate enables the coexistence of a noticeable variety of tropical and subtropical plants, representing a suitable substrate for fungal growth and reproduction (11 Borges, P.A.V.; Abreu, C.; Aguiar, A. M. F.; Carvalho, P.; Jardim, R.; Melo, I.; A list of the terrestrial fungi, flora and fauna of Madeira and Selvagens archipelagos. Funchal: Direcção Regional do Ambiente da Madeira e Universidade dos Açores, Funchal e Angra do Heroísmo, 2008.). Notwithstanding, descriptions of Fusarium in the Island are scarce. In 1973, an outbreak of fusariosis provoked by Fusarium oxysporum sp. cubense (Banana Fusarium wilt, also known as Panama disease) affected a plantation in Funchal Municipality. The infection affected the banana crop commonly named “Pequena Anã”, known until that moment as resistant to the disease. Since then, several infections were observed along the southern coast of the Island (in Câmara de Lobos and Ponta do Sol Municipalities), which varied according to the farming practices and the time of the year (2222 Ribeiro, L.; Silva, J.A.; Aguiar, A.M.F.; Pestana, M.; Rodrigues, M. Main Pests and diseases of bananas on Madeira Island. In: I Workshop de Fruticultura – Contributo para o seu desenvolvimento. n.1, 2009, Angra do Heroísmo. Livro de Actas do I Workshop de Fruticultura: Angra do Heroísmo, 2009. p.123-132,). In the study published by Moura & Rodrigues (1616 Moura, M.F.; Rodrigues, P.F. Fungal diseases on proteas identified in Madeira Island. Puerto de la Cruz, Tenerife, Spain, 2001. Available at: <https://www.actahort.org/books/545/>. Accessed on: 10 Oct. 2019.
https://www.actahort.org/books/545/...
), infections by Fusarium sp., Fusarium solani and Fusarium equiseti were described in a protea cultivation in Madeira Island, an outbreak that attacked the roots and crown and produced root rot.

Despite the growing body of published research on Fusarium invasions worldwide and their impacts on local ecosystems, there are no studies addressing Fusarium introductions in Portugal, namely in Madeira region. Therefore, the present study aimed to analyze the possible routes of Fusarium spp. introduction in Madeira in the three last decades and to elucidate the factors that favored the introduction and settling of this fungus in the Island.

MATERIALS AND METHODS

Site description

The study took place in Madeira (Portugal), between January 1990 and January 2018, at Agricultural Quality Laboratory (LQA) – “Direção Regional de Agricultura da Madeira” (DRA). Madeira is an archipelago composed of two inhabited islands (Madeira and Porto Santo) and two uninhabited islands that belong to the Natural Park of Madeira (“Desertas” and “Selvagens”). Madeira is a volcanic island, located 900 km south-west from Portugal and 600 km west from the western African coast. Its surface area is 739 km2 and 58 km by 23 km range. Madeira Island is within the Macaronesian biogeographical region (2323 Rivas-Martínez, S. Bioclimatic Map of Europe – Thermotypes. Léon: Cartographic Service of University of Léon, 2001.) and shows mild temperatures year-round (18.7°C on average), relative humidity varying between 55% and 75%, and rainfall ranging from 500 mm to 1000 mm.

Laboratory analysis

During the study period (1990-2018), phytosanitary surveys were carried out to evaluate the incidence of the phytopathogenic fungus Fusarium spp. in different crops and plants, in particular: temperate fruits, tropical and subtropical fruits, and horticultural and ornamental plants.

The analyzed samples consisted of symptomatic and asymptomatic plants from producers in mainland Portugal, autonomous region of the Azores, autonomous region of Madeira, and plants imported from France, Italy, the United Kingdom, Spain, the Netherlands, South Africa, Brazil, Australia and Thailand. Most of the analyzed samples were collected by different DRA Services from farms and cargo terminals at the airport and port.

The standard analysis for Fusarium spp. isolates currently performed at LQA-DRA laboratory is described below. Fusarium spp. isolates were obtained from tissue fragments of underground and aerial organs of the plants under analysis. After disinfection (10.0% sodium hypochlorite), they were washed in sterile distilled water, dried on filter paper, and placed in Petri dishes with different culture media: Corn Meal Agar (CMA), Corn Meal Agar + Antibiotics (CMA + A), Potato Carrot Agar (PCA), Potato Carrot Agar + Antibiotics (PCA + A) and Potato Dextrose Agar (PDA), followed by incubation at 21.5 ± 3.5°C. In each analysis, a blank test was also performed. Plates were periodically observed for growth. Fungal structures were stained with lactophenol cotton blue for further microscopic examination of spore structures under a binocular magnifying glass (Nikon SMZ-U) and an optical microscope (Nikon Model Eclipse E-600) at 10x, 20x, 40x and 100x magnifications. Species identification involved the use of morphological and cultural characteristics, a procedure broadly adopted in different studies and/or classification schemes of fungi (2929 Watanabe, M.; Yonezawa, T.; Lee, K-i.; Kumagai, S.; Sugita-Konishi, Y.; Keiichi Goto, K.; Hara-Kudo, Y. Molecular phylogeny of the higher and lower taxonomy of the Fusarium genus and differences in the evolutionary histories of multiple genes. BMC Evolutionary Biology, Wien, v.322, n.11, p.1-16, 2011.). Fungal elements were identified up to genus/species level. Pathogenicity test in the respective host was not carried out with the obtained Fusarium isolate.

Statistical analysis

Data were obtained from the samples submitted to LQA for fungal screening; thus, statistical inference may be hindered. The current study describes the evolution of detected Fusarium cases, their origin and the affected plant types.

To verify temporal evolution, moving-base indexes were calculated since they reflect the percentage variation in relation to the previous year. The frequency tables show the spatial and temporal evolution of Fusarium, as well as its incidence according to the types of colonized plants.

RESULTS AND DISCUSSION

The phytosanitary analysis carried out in Madeira considering the incidence of Fusarium spp. in plants or crops showed an increasing trend in the number of fungi between 1990 and 2001 (Figure 1A) and a downward trend thereafter. During the study period, the agricultural area was reduced, and the highest value was found in 1999 (Figure 1B).

Figure 1
Annual concentration of Fusarium spp. infections detected during the study period overall (A) and in Madeira Muncipality (B) (2222 Ribeiro, L.; Silva, J.A.; Aguiar, A.M.F.; Pestana, M.; Rodrigues, M. Main Pests and diseases of bananas on Madeira Island. In: I Workshop de Fruticultura – Contributo para o seu desenvolvimento. n.1, 2009, Angra do Heroísmo. Livro de Actas do I Workshop de Fruticultura: Angra do Heroísmo, 2009. p.123-132,, 3030 Wood, A.R. Fungi and invasions in South Africa. Bothalia - African Biodiversity & Conservation, Silverton, v.47, n.2, p.a2124, 2017.).

Contaminated samples were mostly from Portugal (96.9%), while 0.1% to 1.6% derived from foreign countries, especially the Netherlands, France and Spain. Among the Portuguese regions, Madeira revealed the highest rate of contaminated samples (91.4%), followed by Porto Santo (4.9%) and Ponta Delgada – Azores (0.3%) (Figure 2). Locally, the largest number of contaminated samples derived from the southern coast of Madeira (Funchal, Santa Cruz, Ponta do Sol and Câmara de Lobos) and from Santana (northern coast), municipalities that have an important agricultural area percentage.

Figure 2
Geographic origin of contaminated samples.

The plants or crops infected by Fusarium spp. were obtained from all municipalities in Madeira (Table 1). Most of the observed fungi were detected in samples from Funchal (20.8%) and Ponta do Sol (17.3%), followed by Santa Cruz (14.5%), Santana (13.3%) and Câmara de Lobos (11.2%). Of 3,246 samples infected with Fusarium spp., 1,212 were from horticultural plants (37.3%), followed by ornamental plants (38.8%), tropical and subtropical fruit trees (16.9%) and temperate fruit trees (9.9%). Considering the plants imported from the Netherlands, 70.6% infections caused by Fusarium spp. occurred in potatoes, and the remaining infections were observed in ornamental plants (Table 2). As regards the contaminated samples derived from France, the fungus was present in temperate fruit trees, showing the highest incidence in vine (17.9%) and apple trees (14.3%).

Table 1
Distribution of samples contaminated by Fusarium spp. among Madeira Municipalities and the corresponding agricultural area (3030 Wood, A.R. Fungi and invasions in South Africa. Bothalia - African Biodiversity & Conservation, Silverton, v.47, n.2, p.a2124, 2017.).
Table 2
Distribution of contaminated samples according to plant group and country of origin and Madeira Municipalities.

Analyzing the incidence of fungi among each plant group in Madeira, the municipalities showing higher rates of Fusarium spp. contamination were Funchal, Santa Cruz and Ponta do Sol. In vegetables, the infection rate was more pronounced in Santana (66.0%) and Câmara de Lobos (65.6%), whereas in ornamental plants contamination was mostly found in samples from Ponta do Sol (60.4%) and Funchal (41.1%). Infected samples from temperate fruit trees derived particularly from Santana (14.2%) and Funchal (8.9%), while those from tropical and subtropical fruit trees were primarily from Funchal (35.7%) and Ponta do Sol (15.3%). Overall, the vegetables and temperate plants most infected by Fusarium spp. were from municipalities in both coasts of Madeira (Table 3), whilst the ornamental plants from Porto Santo Island were particularly affected by the fungus.

Table 3
Plants or crops more frequently infected by Fusarium spp.

Mycological analysis allowed the identification of several fungi of the genus Fusarium. The horticultural products and the municipalities presenting the largest number of Fusarium infections were Câmara de Lobos and Santana, revealing Fusarium sp., Fusarium equiseti, Fusarium moniliforme, Fusarium oxysporum, Fusarium oxysporum f. sp. lycopersici, Fusarium oxysporum f. sp. phaseoli and Fusarium solani.

Considering ornamental plants, the most representative municipalities were Funchal and Ponta do Sol, and the most common fungi were: Fusarium sp., Fusarium equiseti, Fusarium moniliforme, Fusarium oxysporum, Fusarium oxysporum f. sp. dianthi, Fusarium poae, Fusarium roseum, Fusarium roseum var. graminearum and Fusarium solani.

For temperate fruits in Funchal and Santana, the most frequently identified fungi were: Fusarium sp., Fusarium equiseti, Fusarium solani and Fusarium avenaceaum.

As represented in Table 2, the group of tropical and subtropical fruits had Funchal and Ponta do Sol as the most prominent municipalities, and the most frequently identified fungi were: Fusarium sp., Fusarium equiseti, Fusarium moniliforme, Fusarium moniliforme var. subglutinans, Fusarium oxysporum, Fusarium oxysporum f. sp. cubense, Fusarium oxysporum f. sp. passiflorae and Fusarium solani.

Fusarium is considered one of the most remarkable genera of fungi, occurring in most bioclimatic regions of the world (2828 Walsh, J.L.; Laurence, M.H.; Liew, E.C.Y.; Sangalang, A.E.; Burgess, L.W.; Summerell, B.A.; Petrovic, T. Fusarium: two endophytic novel species from tropical grasses of northern Australia. Fungal Diversity, The Netherlands, v.44, p.149-159, 2010.). Madeira Island presents a temperate hyperoceanic submediterranean bioclimate and a mediterranean pluviseasonal oceanic bioclimate on the southern coast (2323 Rivas-Martínez, S. Bioclimatic Map of Europe – Thermotypes. Léon: Cartographic Service of University of Léon, 2001.). The temperate climate of Madeira region, showing mild temperatures and relative humidity levels, can promote the development and spread of common outdoor fungal spores, including these anamorphic fungi (2525 Sousa, L.; Camacho, I.; Grinn-Gofroń, A.; Camacho, R. Monitoring of anamorphic fungal spores in Madeira Region (Portugal), 2003-2008. Aerobiologia, Switzerland, v.31, n.2, p.1-13, 2015.).

The climatic conditions of Madeira, together with its mountainous relief, allow greatly diverse cultivation. As observed in the present survey, the product varieties are directly related to location and altitude: in lower areas, Mediterranean products are found (figs, vines and cereals). European fruit trees abound in the valleys, producing cherries, apples and plums. Near the seacoast, especially in the southern coast, tropical species prevail (bananas, sugar cane, custard apple and passion fruit). Such geoclimatic conditions are prone to soil-borne phytopathogens, such as Fusarium, known for posing serious constraints to plant growth and productivity. Therefore, Fusarium species are important pathogens of agricultural plants and livestock (1919 Ortiz, E.; Cruz, M.; Melgarejo, L.M.; Marquínez, X.; Hoyos-Carvajal, L. Características hispatologicas da infecção causada por Fusarium oxysporum e F. solani em maracujá-roxo (Passiflora edulis Sims). Summa Phytopathologica, Botucatu, v.40, n.2, p.134-140, 2014.).

The analyzed samples infected by Fusarium consisted of symptomatic and asymptomatic plants and/or horticultural plants from Portugal and several foreign countries. Diverse studies have reported that the trade of live plants is an important route of introduction and spread within countries and continents and that the human-assisted distribution of fungi around the world is the most important pathway of introduction (3030 Wood, A.R. Fungi and invasions in South Africa. Bothalia - African Biodiversity & Conservation, Silverton, v.47, n.2, p.a2124, 2017.). According to Burgess et al. (22 Burgess, T.I.; Crous, C.J.; Slippers, B.; Hantula, J.; Wingfield, M.J. Tree invasions and biosecurity: eco-evolutionary dynamics of hitchhiking fungi. AoB PLANTS, Oxford, v.8, n. plw076, 2016.), there are hidden microorganisms in seeds, plants themselves, or soil in which the plants were grown, which are largely ignored in the global transportation of plants. The above-mentioned authors stressed that those so-called hitchhikers may be beneficial or detrimental to their hosts, may become naturalized without causing harm, or may negatively affect native plants (66 Gladieux, P.; Feurtey, A.; Hood, M.E.; Snirc, A.; Clavel, J.; Dutech, C.; Row, M.; Giraus, T. The population biology of fungal invasions. Molecular Ecology, New Jersey, v.24, p.1969-1986, 2015.).

For our study period, an increase in agricultural products imported to Madeira was reported. On the other hand, the agricultural area was gradually reduced, especially in 2000-2002 (55 Direção Regional de Estatística da Madeira. Madeira em Números. Funchal: Direção Regional de Estatística da Madeira, 2018. Available at: <https://estatistica.madeira.gov.pt/download-now/multitematicas-pt/multitematicas-mn-pt/multitematicas-mn-publicacoes-pt/send/34-madeira-em-numeros-publicacoes/11888-madeira-em-numeros-2018.html>. Accessed on: 2 Jan. 2021.
https://estatistica.madeira.gov.pt/downl...
). During that period, Fusarium infections reached the highest peak in Madeira. In addition, lower production of banana crops was reported in 1999 due to the adverse weather conditions that affected the Island, which can explain the higher importation rates of agricultural products in 2000-2002 (77 Gramacho, A. Panorama da Agricultura em 1999. Revista de Política Agrícola, n.9, v.1, p.1-225, 2000.). According to Lockwood et al. (1313 Lockwood, J.L.; Cassey, P.; Blackburn, T. The role of propagule pressure in explaining species invasions. Trends in Ecology & Evolution, Maryland, n.20, p.23-28, 2005.), higher levels of imports are therefore likely to increase the probability of introduction of fungi and the propagule pressure, which is an important determinant of invasion success.

Our results are in line with previous studies showing that globalization, especially international trade, is a major driver of biological invasions across taxa and regions (44 Desprez-Loustau, M-L.; Courtecuisse, R.; Robin, C.; Husson, C.; Moreau, P.A.; Blancard, D.; Selosse, M-A.; Lung-Escarmant, B.; Piou, D.; Sache, I. Species diversity and drivers of spread of alien fungi (sensu lato) in Europe with a particular focus on France. Biol Invasions, Switzerland , n.12, p.157-172, 2010.). Increasing trade volume is probably an important factor contributing to increase the number of alien fungi in the studied region. Fusarium introductions in Madeira region, similarly to other fungal introductions worldwide, are considered an unintended consequence of human-mediated movement and trade (66 Gladieux, P.; Feurtey, A.; Hood, M.E.; Snirc, A.; Clavel, J.; Dutech, C.; Row, M.; Giraus, T. The population biology of fungal invasions. Molecular Ecology, New Jersey, v.24, p.1969-1986, 2015.).

Globally, crop losses due to plant diseases caused by such phytopathogens represent a major threat to food security worldwide (1010 Khan, N.; Maymon, M.; Hirsch, A.M. Combating Fusarium infection using Bacillus-based antimicrobials. Microorganisms, Switzerland, v.5, n.75, p.1-13, 2017.). As a result of several years of introducing crops and plants, it is likely that large numbers of fungi have been introduced in Madeira.

The widespread distribution of Fusarium species has been attributed to their ability to grow on a wide range of substrates and to their efficient mechanisms for spore dispersal (1919 Ortiz, E.; Cruz, M.; Melgarejo, L.M.; Marquínez, X.; Hoyos-Carvajal, L. Características hispatologicas da infecção causada por Fusarium oxysporum e F. solani em maracujá-roxo (Passiflora edulis Sims). Summa Phytopathologica, Botucatu, v.40, n.2, p.134-140, 2014.). Likewise, passive spore dispersal cannot be excluded across continents for fungi dispersed by airborne spores. Such dispersal is favored by some fungal features, including their inconspicuousness and production of numerous small propagules (66 Gladieux, P.; Feurtey, A.; Hood, M.E.; Snirc, A.; Clavel, J.; Dutech, C.; Row, M.; Giraus, T. The population biology of fungal invasions. Molecular Ecology, New Jersey, v.24, p.1969-1986, 2015.). Propagule characteristics are related to successful long-distance dispersal since it allows the rapid spread of fungi once they are introduced (2020 Philibert, A.; Desprez-Loustau, M-L.; Fabre, B.; Frey, P.; Halkett, F.; Husson, C.; Lung-Escarmant, B.; Marçais, B.; Robin, C.; Vacher, C.; Makowski, D. Predicting invasion success of forest pathogenic fungi from species traits. Journal of Applied Ecology, New Jersey, n.48, p.1381-1390, 2011.). Similarly to other regions across Europe, the influence of geographical, environmental (climate) and economic factors in Madeira region might be explanatory factors of the distribution and spread of such fungi (1313 Lockwood, J.L.; Cassey, P.; Blackburn, T. The role of propagule pressure in explaining species invasions. Trends in Ecology & Evolution, Maryland, n.20, p.23-28, 2005.).

The mycological analysis performed in the present study revealed several common Fusarium species described in the literature. Banana fusarium wilt (also known as Panama disease) caused by F. oxysporum f. sp. cubense occurred in several products imported to Madeira. This is the most important fungal species that attacks banana plants in Madeira Island, constituting more than 50% of the fungi identified in this crop (2828 Walsh, J.L.; Laurence, M.H.; Liew, E.C.Y.; Sangalang, A.E.; Burgess, L.W.; Summerell, B.A.; Petrovic, T. Fusarium: two endophytic novel species from tropical grasses of northern Australia. Fungal Diversity, The Netherlands, v.44, p.149-159, 2010.). Madeira has the major production area at national level considering banana plantations, and monitoring such fungal introductions in the region is very important.

Fusarium oxysporum is a ubiquitous species complex of fungi that includes soil-borne plant pathogenic lineages that are the causal agents of vascular wilt disease in a broad range of plant species, including cotton, tomatoes and vegetables (33 Carmona, S.L.; Burbano-David, D.; Gómez, M.R.; Lopez, W.; Ceballos, N.; Castaño-Zapata, J.; Simbaqueba, J.; Soto-Suárez, M. Characterization of pathogenic and nonpathogenic Fusarium oxysporum isolates associated with commercial tomato crops in the Andean Region of Colombia. Pathogens, Switzerland , v.9, n.70, p.1-23, 2020.).

Fusarium equiseti represented another frequent species in the present survey. It is a cosmopolitan soil inhabitant, common in drier areas and a frequent colonizer of senescent or damaged plant tissue. Although it is not an important plant pathogen, Fusarium equiseti has been implicated in a few diseases such as rots of cucurbit fruits in contact with the soil (2626 Summerell, B.A.; Leslie, J.F.; Liew, E.C.Y.; Laurence, M.H.; Bullock, S.; Petrovic, T.; Bentley, A.R.; Howard, C.G.; Peterson, S.A.; Walsh, J.L.; Burgess, L.W. Fusarium species associated with plants in Australia. Fungal Diversity, The Netherlands, v.46, p.1-27, 2011.). Infected soil and asymptomatic plants are the most probable pathways, easily escaping phytosanitary inspections (1313 Lockwood, J.L.; Cassey, P.; Blackburn, T. The role of propagule pressure in explaining species invasions. Trends in Ecology & Evolution, Maryland, n.20, p.23-28, 2005.). Notwithstanding, the phytosanitary monitoring carried out by local authorities has been crucial to detect and trace unintentional introduction processes of several phytopathogenic fungi, including Fusarium spp. in Madeira.

Finally, the adoption of a rotation system might reduce Fusarium wilt incidence and bring economic benefits to local farmers. Moreover, the early detection of outbreaks in small regions like Madeira can succeed with the eradication of host plants, limiting, if possible, the host range.

ACKNOWLEDGMENTS

he authors are grateful to the Agricultural Quality Laboratory – “Direção Regional de Agricultura da Madeira” for all laboratory support.

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Publication Dates

  • Publication in this collection
    06 June 2022
  • Date of issue
    Jan-Mar 2022

History

  • Received
    01 Mar 2021
  • Accepted
    09 Dec 2021
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