Fusarium species associated with tropical grasses

Abstract

Many Fusarium species show an affinity with grass species, where they live in an endophytic association or cause disease. In this study, we analyzed Fusarium species recovered from a range of grasses, such as maize, rice, sorghum, sugarcane and forage grasses from Brazil, and also from African countries. Isolates were characterized using the morphological, biological and phylogenetic species concepts. Pathogenicity tests were conducted and for some of the species the potential to produce mycotoxins was evaluated. The grass species studied here are important for agriculture in Brazil and other countries, and have a wide spectrum of use, ranging from human and animal food, the use in the generation of secondary products, such as alcohol and sugar, or as biomass in no-tillage systems. The results of this study are presented in five chapters, each representing manuscripts of scientific papers. The first manuscript, “Fusarium species from tropical grasses in Brazil and description of two new taxa” is accepted for publication in Mycological Progress. Here we publish results about a set of Fusarium isolates obtained from forage grasses in Brazil, including Brachiaria and Panicum. These forage grasses are frequently used in consortia with important crop plants such as maize and sorghum. Surprisingly, despite of a somewhat reduced sampling, we identified nine known species of Fusarium from three different species complexes, and two novel phylogenetic species within the FFSC. These new species are described as F. caapi and F. brachiariae. This survey showed that wild and cultivated grasses harbor not only a high diversity of known species, which are pathogens of maize, sorghum, rice and sugar cane, but also novel Fusarium species. The second paper is under evaluation at Mycologia, with the title “Fusarium mirum sp. nov, intertwining Fusarium madaense and Fusarium andiyazi, pathogens of tropical grasses”. In this study we characterized a set of 138 Fusarium isolates from different grasses such as sorghum, maize, rice, sugarcane and Brachiaria from Brazil and African countries. In general, isolates share morphological markers of F. andiyazi, a well-known species within the Fusarium fukikuroi species complex (FFSC) and an important pathogen of sorghum. We emended the description of F. madaense, a recently described species, and contribute with information about host range and geographic distribution. An important fact is that this species is one of the main pathogens of sugar cane in Brazil, inducing pokkah boeng disease. We also describe Fusarium mirum, a new phylogenetic and biological species within the FFSC. This work is a result of an international collaborative project, with a group of distinct researchers, John F. Leslie from Kansas State University in USA and Brett A. Summerell from the Australian Institute of Botanical Science, specialists in Fusarium taxonomy and systematics, and some of their collaborators. In the third manuscript, which will be submitted to Plant Pathology, we present results from a study about the causal agents of red rot of sugar cane, one of the most important diseases of this crop. The relevant finding was that, in addition to Colletotrichum falcatum, which is the main pathogen, Fusarium species were also associated with symptomatic plants and these species induced red rot symptoms in pathogenicity tests. Fusarium sacchari, F. proliferatum and F. madaense cause red rot, but also induce symptoms of pokkah boeng. The results are important for the management of both diseases, because the etiology of red rot seems to be more complex. Our data will be support more accurate diagnosis and monitoring of the causal agents, but also breeding programs aiming at resistance to the disease. In the fourth manuscript, which will be submitted to International Journal of Food Microbiology, we report the diversity of species of the Fusarium chlamydosporum species complex (FCSC). Three species, F. chlamydosporum F. spinosum and F. atrovinosum were found in association with rice grains, and other hosts including cucurbits, maize, Pennisetum and Panicum. Isolates of the three species and reference isolates of F. sporodochiale and F. nelsonii, included in this study, produced detectable levels of nivalenol (NIV), deoxynivalenol (DON), beauvericin and enniatin in vitro. Part of the research was carried out during my sandwich doctorate under the supervision of Dr. Antonio Moretti, a specialist in studies on mycotoxins in the genus Fusarium. In another manuscript, the fifth, which is under preparation for submission to Fungal Biology, we describe a new phylogenetic and biological species, Fusarium claudionori, from the forage grass Brachiaria, based on the phylogeny of EF-1α, RPB2 and TUB dataset and laboratory crosses. When inoculated in important grass crops like maize and sorghum, strains of this species induced stalk rot. There is strong evidence that there is a much greater diversity of species than currently known in Brazilian agro-ecosystems. This Thesis represents a relevant contribution about the diversity of Fusarium species in agricultural and natural environments in Brazil. An astonishing diversity of species was found, and in this Thesis we made the first, but a very important step, to increase knowledge on their host range, geographic distribution and capacity to cause disease in crop plants. Knowing the range of hosts of supposedly pathogenic species is also relevant when proposing to work with consortia and crop rotations, including the grasses studied here.