Fusarium andiyazi species group: an application of the biological species concept

Abstract

Fusarium andiyazi is a member of the Fusarium fujikuroi species complex - FFSC, known to cause stem rot in sorghum in Africa and the United States. There are records of its association with other cultivated grasses and the natural vegetation as an endophyte. In association with different grasses from Brazil, the United States and African countries, a collection of 87 isolates of the morphotype F. andiyazi were obtained. The analysis of the barcode region TEF showed that these isolates represent F. andiyazi and two other, still undescribed phylogenetic species, morphologically indistinguishable. To date, the sexual phase of F. andiyazi is unknown, since the formation of fertile perithecia was not observed in laboratory crossings. The aims of this study were to evaluate the existence of the sexual reproduction of F. andiyazi and their sibling lineages through laboratory crossings, to report the species as possible new mating populations of the FFSC, to evaluate the morphological markers of the sexual phase as well as to verify the presence of a reproductive barrier with other FFSC mating populations. Strains deposited in the Coleção Micológica de Lavras - CML obtained from rice, sugarcane, sorghum, maize, Brachiaria and millet from Brazil, the United States and African countries, were included in the experiments. Amongst 87 strains, 19 represent F. andiyazi, 62 Fusarium sp.1 and six Fusarium sp.2. In the mating type PCR amplification for F. andiyazi, 12 strains were identified as MAT-1 and 7 as MAT-2, Fusarium sp.1 (21 MAT-1, 40 MAT-2), for Fusarium sp.2 two were identified as MAT-1 and four as MAT-2. Three fertile crossings were obtained between strains of F. andiyazi and 54 between Fusarium sp.1 strains. Therefore, F. andiyazi and Fusarium sp.1 represent new MPs within the FFSC. In crossings. of F. andiyazi and Fusarium sp.1 with the other MP of the FFSC, the production of fertile perithecia was not observed, showing that there is a reproductive barrier with the other biological species of the complex. A very few fertile crossings were observed between F. andiyazi and Fusarium sp.1, an indication that so far, no complete reproductive barrier between the two species has been established. Fusarium sp.2 did not produce any fertile crosses between its strains, with F. andiyazi, Fusarium sp.1 or with any other MP of the FFSC. In the morphological characterization of the sexual phase, the structures produced by F. andiyazi and Fusarium sp.1 were identical. The biological species concept applied to the study of these three species gives an insight into how important the use of this concept can be in determining a species, when the morphological markers are insufficient. The application of the biological species concept, besides consolidating the concept of species, can help in the identification of morphologically similar individuals.