Abstract
Agriculture suffers considerable losses in its production caused by plant diseases. In the citrus culture some problems were associated with citrus canker caused by Xanthomonas citri subsp. citri. That same way, sugarcane plantations are impaired to leaf scald disease caused by Xanthomonas albilineans. One of the measures used to contain citrus canker is the spray of cupric bactericides; however for scalding leaves there are no satisfactory control. Due to the phytosanitary problem caused by Xanthomonas (X. citri and X. albilineans) and by the difficulty of its control, the search for new forms of defense, less harmful to the environment, has become increasingly required. Thus, the aim of this work was to obtain crude organic extracts from filamentous fungi isolated from Antarctic soil samples and assess its bioactivity potential against X. citri and X. albilineans. One hundred and twenty-two extracts were tested, seven extracts inhibited the cell growth of X. citri, one was bioactive only against X. albilineans and one extract inhibited the cell growth of both bacteria. The bioactive extracts had a mean inhibition value of 96% against both bacteria. The values of MIC90 and MBC of bioactive extracts were also determined; for X. citri the isolate 3.1 Fe presented the lowest values of MIC90 (0.28 mg/mL) and MBC (1.0 mg/mL) and the two bioactive isolates for X. albilineans (1.1-Fe and B-Fe) presented the same values of MIC90 (1.4 mg/mL) and MBC (1.5 mg/mL). The filamentous fungi that produced positive extracts were identified as belonging to the genus Pseudogymnoascus (n=8) and Cladosporium (n=1). The filamentous fungi isolated from Antarctic soil produced compounds with bioactivity against phytopathogens from the Xanthomonas genus. Key words: Antarctic fungi; antibacterial action; citrus canker; leaf scald; natural extracts.
Highlights
Xanthomonas are rod-shaped Gram-negative and obligate aerobe bacteria, which have a polar flagellum (Tessmann, 2002)
Positive results of extracellular extracts may be associated with defense mechanism, since some microorganisms can produce substances that inhibit potential competitors (Smid and Lacroix, 2013; García et al, 2017)
The samples tested are crude extracts, a reduction in MIC90 value is expected after purification and isolation of the bioactive molecules
Summary
Xanthomonas are rod-shaped Gram-negative and obligate aerobe bacteria, which have a polar flagellum (Tessmann, 2002). This genus comprises 27 species that cause serious disease in about 400 plants hosts (Ryan et al, 2011) and affect at least 124 monocotyledonous and 268 dicotyledonous plant species (Leyns et al, 1984). Every year orchards around the world suffer losses due to citrus canker, mainly countries with favorable climates for the development of X. citri The control of this disease is accomplished by uses of less susceptible varieties, eradication of contaminated plants, decontamination of seeds and equipment, use of windbreakers and mostly use of antibiotics and copper sprays. This causes damage to the environment due to its accumulative potential in soil and trophic chain (Rocha and Azevedo, 2017)
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