Epidemiology of yellow Sigatoka, phenols quantification in banana varieties and phylogenetic analysis of Mycosphaerella musicola isolates using microsatellites / EPIDEMIOLOGIA DA SIGATOKA AMARELA, QUANTIFICAÃÃO DE FENÃIS EM VARIEDADES DE BANANEIRAS E ANÃLISE FILOGENÃTICA DE ISOLADOS DE Mycosphaerella musicola UTILIZANDO MICROSSATÃLITES

Herminio Souza Rocha

Due to the hetherothalic nature and sexual reproduction of the fungus Mycosphaerella musicola, the causal agent of yellow Sigatoka, and considering the climatic diversity of the Brazilian banana producing regions, a wide genetic variability is expected among the Brazilian isolates with distinct virulence and aggressiveness. For a better characterization of yellow Sigatoka (Mycosphaerella musicola) in Brazil, it is necessary that some aspects may be elucidated, mainly those related to the epidemiological analysis and to the genetic variability of the Brazilian isolates. Hence, studies concerning the temporal analysis and epidemiology of yellow Sigatoka were performed in a banana plantation localized in Coronel Pacheco- in the State of Minas Gerais, with the âSaquaremaâ (AAA) variety, having been evaluated the correlations between climatic variables with the alterations in the disease progress and also with the fluctuations of the fungus spores in the air. Two peaks of maximum severity of the disease were identified along the year, with the first occurring during the rainy season, and mainly associated to the high conidia concentration in the air, and the second having occurred in the middle of the draught season, being mainly produced by the high ascospore concentration. The best adjustment of the disease progress curve was verified for the monomolecular model. The climatic variables mostly associated to the disease progress were rain, relative humidity and leaf wetness. During the rainy season the disease progress followed the host vegetative development, having been observed the shortest lesion development periods for the new lesions. During the draught season, the lesions intensified the disease severity due to a lower vegetative development of the host. For a better characterization of the Coronel Pacheco â MG isolate, evaluations concerning the monocycle of yellow-Sigatoka were carried out, as well as the dynamics of lignin and the concentration of total phenolics in banana plantlets (âPacovanâ; âGrande Naineâ; âCaipiraâ and âPrata Zuluâ) artificially inoculated under controlled environment. The shortest incubation periods and disease development periods were obtained under 24o C, with no distinct behavior than the ones already related in literature. For the banana varieties tested, the constitutive total phenolic levels were not altered as a response to the infection by Mycosphaerella musicola. âCaipiraâ e âPrata Zuluâ presented the highest lignification of the cell wall after five days of inoculation, which denotes this biochemical mechanism, as being involved in resistance. The phylogenetic analysis was done with a group of 10 different microssatelite markers in 11 Mycosphaerella musicola isolates from a diversity of Brazilian banana producing regions along Brazil. Two major groups were generated in the dendrogram, with one being composed mostly by isolates from the South, South-East and Centre-West Regions, in which was localized the isolate from Coronel Pacheco â MG and the other mainly composed by the isolates from the North-East region of Brazil. One specific pair of primers Mm SSR 34 demonstrated high potential to differentiate both black and yellow Sigatokas, which may become powerful molecular marker to be used in phytossanitary official reports.

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