Abstract
The wilt caused by Fusarium oxysporum f.sp. vasinfectum in cotton is one of the main diseases of this crop. The pathogen is difficult to control because it produces chlamydospores, which allows it to survive in the soil for long periods without the presence of its main host. The control of this disease is based on varieties with some resistance, certified seeds, and fungicides used to treat seeds. Thus, the development of control alternatives is needed to increase the number of resources to manage this disease in the field. Bacillus are bioregulators and antagonists of several important phytopathogens. Therefore, the objective of this work was to select strains of Bacillus (Paenibacillus alvei, Bacillus thuringiensis, B. megaterium, and B. lentus), whose metabolites are toxic to F. oxysporum in laboratory and greenhouse conditions, in addition to adjusting in vitro methodologies to perform and evaluate selection tests. This work determined the best culture medium for the direct confrontation assays, proposed a grading scale to facilitate decisions about selection with the dual tests, identified among the strains selected in the confrontation assays those that produce volatile and non-volatile metabolites toxic to F. oxysporum, and tested these selected strains for disease control during seed germination in greenhouse trials. In last test, some strains of Bacillus had a potential protective effect during the germination of cotton seeds.
Highlights
Brazil is the fifth largest cotton (Gossypium hirsutum L.) producer with production areas in 15 states, but 85% of the planted area is concentrated in the states of Mato Grosso and Bahia (CONAB, 2021)
The productivity of cotton cultivation has increased due to genetic advances and improvements in the production system; this productivity could be even better if pests and diseases did not affect the crop
The best proportion of reagents for a neutral culture was potato dextrose agar (PDA) 100% + EM100%, which provided balanced growth without harming or favoring any organism. 3.2 Evaluation Scale for the Competition Assay the literature contains several grading scales, the proposed scale that we assembled for this assay was appropriate for our evaluations
Summary
Brazil is the fifth largest cotton (Gossypium hirsutum L.) producer with production areas in 15 states, but 85% of the planted area is concentrated in the states of Mato Grosso and Bahia (CONAB, 2021). This crucial national agricultural sector has undergone important transformations in the last 20 years and is today one of the most modern in agriculture (Borém & Freire, 2014). All cultivated cotton species host the fungus, but there may be variations in virulence, depending on the cultivar. Unlike most specialized forms, it may have alternative hosts, such as species belonging to the Malvaceae, Solanaceae, and Leguminosae families (Assigbetse et al, 1994)
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