Espécies de Fusarium associadas à Urochloa brizantha com sintomas de doença

Abstract

In Brazil, Marandu grass (Urochloa brizantha cv. Marandu) is cultivated throughout the Brazilian states, but mainly in the North and Central-West regions. However, starting in the 1990s, reports of sudden death disease that caused the degradation of pasture areas. This disease was related to water stress, compacted and/or poorly drained soils, and mainly to the attack of soil fungi that cause rot in the forage collector. Among the main fungi associated with marandu grass, Pythium perillum, Fusarium sp. and Rhizoctonia solani. In the North of Minas Gerais, there were reports of pasture deaths with symptoms similar to those occurring in the regions mentioned above. Thus, the objectives of the present work were (i.) to identify Fusarium species associated with the sudden death disease of Marandu grass, using molecular phylogeny and morphological markers and (ii.) to test pathogenicity in the Marandu and Xaraés cultivars. The 17 Fusarium isolates obtained from marandu grass with symptoms of sudden death were identified by morphological markers and grouped by morphotypes of species belonging to the FFSC (F. fujikuroi species complex), FIESC (F. incarnatum-equiseti species complex), FOSC (F. oxysporum species complex) and F. semitectum morphotype. The isolates found in the aerial mycelium, microconidia formed in long and short chains and false heads. Phylogenetic analysis was carried out based on the comparison of partial sequences of the elongation factor 1-α gene, (TEF-1-α), 07 isolated groups were grouped into four distinct clades of the F. fujikuroi species complex (FFSC) and were identified with F. proliferatum, F. verticillioides, F. caapi and a new phylogenetic lineage, belonging to the African clade, called Fusarium sp.4. The remaining isolates were compared by Blast tef with sequences from the F. oxysporum species complex (FOSC) and the F. incarnatum-equiseti species complex (FIESC). In the pathogenicity test, the isolates induced yellowing symptoms and the onset of rot in all of the Marandu and Xaraés cultivars. The Fusarium sp.4 lineage will be described and elevated to species level, representing a new phylogenetic species in the FFSC.