Abstract
Alternaria brown spot (ABS), caused by the fungus Alternaria alternata pathotype tangerine, is one of the main phytosanitary problems for mandarin growers. About 15 applications per year of harmful fungicides are required for controlling ABS disease in citrus orchards. As chalcones seem to be less toxic to humans and environment than the commercial fungicides in use, this study initially aimed at synthesizing 137 chalcones through aldolic condensations between benzaldehydes and acetophenones. The resulting chalcones were screened for activity against A. altern ata through a fungal growth assay that was carried out in 96-cell polypropylene plates, using the same concentration to all studied substances. The four active chalcones underwent conidia germination and mycelial growth, which confirmed the antifungal activity of the compounds. These chalcones were then poured onto Murcott tangor fruit that had been inoculated with conidia of the fungus. All four chalcones reduced the ABS progress to values significantly smaller (P≤0.05) than that observed for the control. Statistical calculations showed that the best results were afforded by two compounds, bearing a 2,4,5-trimethoxyphenyl group at position 3 of prop-2-enal and a 3-nitro- or 3-hydroxyphenyl group at position 1 of the aldehyde. Such compounds reduced the incidence of the disease in Murcott tangor fruit to values that did not differ statistically from those obtained with a commercial fungicide.
Highlights
Mandarin became more valued by global consumers of fresh fruits, mainly because it is peeled
Mandarin growers face a number of phytosanitary problems, among which we can highlight the Alternaria brown spot (ABS), which is caused by the fungus Alternaria alternata pathotype tangerine.This disease has been a serious threat for the production of mandarin in Brazil since 2006, when it was detected in Citrus reticulata var
In Mycelial growth assay (MGA), chalcone L21 was similar to the fungicide Amistar®, inhibiting 36.2% of the mycelial growth of A. alternata (Table 1)
Summary
Mandarin became more valued by global consumers of fresh fruits, mainly because it is peeled. The production of mandarin increased within the citrus agribusiness (ZULIAN; DÖRR; ALMEIDA, 2013). Mandarin growers face a number of phytosanitary problems, among which we can highlight the Alternaria brown spot (ABS), which is caused by the fungus Alternaria alternata pathotype tangerine.This disease has been a serious threat for the production of mandarin in Brazil since 2006, when it was detected in Citrus reticulata var. Ponkan and hybrid tangor Murcott (Citrus reticulata x Citrus sinensis) (CARVALHO et al, 2008; STUART et al, 2009). In growing areas with high humidity and temperature, about 15 applications of fungicides are required per year to control this disease (TIMMER et al, 2003; BOSCH; BERG; PAVELEY, 2014), contaminating humans and the environment with substances of high toxicity (CARVALHO et al, 2007)
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