Antracnose em meloeiro (Cucumis melo L.): caracterização molecular e morfológica de Colletotrichum brevisporum e controle utilizando compostos à base de silíco

Abstract

The melon (Cucumis melo L.) is among the top 20 vegetables grown in the world, being an important crop in the domestic market and export. Although the Northeast is the largest producer of the fruit in Brazil, the state of Alagoas has a small production of this vegetable, however, there is great potential for the production of melons, considering the great state portion inserted into the semi-arid and bathed by São Francisco River and therefore liable to irrigation. Post-harvest diseases account for losses ranging between 20 and 80%. Anthracnose, caused by Colletotrichum spp., is an important disease that attacks the melon crop. To control these and other diseases in post-harvest, it has been thought alternative methods based on silicon compounds as an alternative to the use of synthetic fungicides. In order to contribute to reducing the use of pesticides, were tested, in this work, the use of sodium silicate (NaSiO3) and silicon dioxide (SiO2), at doses of 100 and 200 mM in anthracnose control in melon variety Acclaim. For this purpose, first, an isolated Colletotrichum sp. anthracnose-causing in cucurbit, from the Embrapa Vegetables/DF, had its pathogenicity tested for melon fruits of variety Acclaim (Syngenta). With the result being positive, the pathogen were characterized in morphological and molecular level, based on genetic markers actin (ACT), β-tubulin (TUB2), calmodulin (CAL), chitin synthase (CHS I), glyceraldehyde 3-phosphate dehydrogenase (GPDH) and internal transcribed spacer rDNA (ITS). From the phylogenetic analysis it was possible to characterize the isolated as belonging to the species Colletotrichum brevisporum, being the first report of its occurrence colonizing melon in Brazil. For the control of anthracnose in melon fruit, it was tested the effect of SiO2 and NaSiO3 on the pathogen, by methods in vitro and in vivo. For the in vitro study, the mycelial growth of the pathogen on PDA medium was measured after addition of SiO2 and NaSiO3 compounds, at concentrations of 25, 50, 100 and 200 mM, included pH measurement. In vivo tests were carried out with concentrations of 100 and 200 mM, for the two sources of silicon. It was observed that NaSiO3, at concentrations of 100 and 200 mM, was capable of inhibiting the mycelial growth of the pathogen, in vitro conditions, and that the pH of the media plus sodium silicate rose sharply, reaching values of 12.36 (100 mM) and 12.96 (200 mM). NaSiO3, at 200 mM, reduced the severity of disease in Acclaim (Syngenta) melons, at 37.12%. Therefore, in this work it was established a host-pathogen relationship between Colletotrichum brevisporum and Cucumis melo, which is the first report of this pathogen colonizing that culture. Therefore, it was found that C. brevisporum growth inactivation occurred by the use of sodium silicate in concentrations above 100 mM, in vitro, and that decrease in the severity of anthracnose in Acclaim melon fruit was observed. Apparently, pH elevation had a direct effect on the pathogen, rather than the sodium silicate induced resistance in fruits.