Caracterização e teste de sensibilidade à fungicida dos agentes causais da podridão de Fusarium do melão no estado do Ceará

Abstract

Melon (Cucumis melo L.) is a fruit of great appreciation in the consumer market and represents an important source of income in Northeast Brazil, the main producing region. However, the lack of adequate management, such as crop rotation practices and fallow time, makes the incidence of pathogens relevant, affecting the production. Among the pathogens associated with the crop, the fungi, especially in genus Fusarium, have been reported to cause post-harvest damage, making the export of melon fruits unfeasible. In this sense, this study aimed to characterize Fusarium spp. associated with melon fruits in Ceará State. Thirty-three pure isolates were obtained for the working collection. Among the isolates obtained, one representative of each morphotype present in the collection was selected, resulting in six isolates (F. equiseti, F. incarnatum, F. oxysporum, F. solani, Neocosmospora sp. and F. chlamydosporum). In the isolates characterization were used: i) morphological characterization, with the evaluation of growth, color and morphological markers; ii) pathogenicity test; iii) molecular phylogeny of the isolates to confirm the morphological characterization; and iv) the in vitro test of the isolates sensitivity to a thiophanate methyl based fungicide. In the results of the morphotypes morphological characterization, the F. chlamydosporum isolate had the highest growth in a Petri dish after three days of incubation, with a diameter of 53.4 mm and the Neocosmospora sp. isolate had the smallest diameter, with 31.8 mm. Regarding the color, the tones varied between white in F. equiseti, cream in F. incarnatum, F. solani and Neocosmospora sp., purplish tones in F. oxysporum and pink in F. chlamydosporum. In the evaluation of morphological markers, typical structures were observed in all isolates, such as false heads in F. incarnatum, F. chlamydosporum and F. solani; short phialides in F. oxysporum; thin sporodochial conidia in F. equiseti and red perithecia in Neocosmospora sp. All isolates evaluated were pathogenic, especially the isolates of F. solani and F. incarnatum, which showed the highest rates of aggressiveness. The phylogeny confirmed the results of the morphological characterization, with the formation of well-defined clades, representing four Fusarium complexes. The in vitro sensitivity test of the thiophanate methyl fungicide showed medium efficiency in F. chlamydosporum and low in the other isolates evaluated.