Fusarium head blight in Argentina: an epidemiological study

CECILIA A. MOURELOS; ISMAEL MALBRÁN; PEDRO A. BALATTI; P.D. GHIRINGHELLI; GLADYS A. LORI

Florianópolis

Simposio; 5th International Symposium on Fusarium Head Blight, 2nd International Workshop on Wheat Blast; 2016

Universidade de Passo Fundo; Empresa Brasileira de Pesquisa Agropecuária - Embrapa Trigo; Universidade Federal de Viçosa

Fusarium Head Blight (FHB) is one of the most important diseases of wheat in Argentina. In the country, the disease is caused principally by Fusarium graminearum (teleomorph Gibberella zeae). The management of FHB is hindered by the capacity of G. zeae to survive saprophitically; by the prevalence of the inoculum and its dispersal to long distances; by the ample range of alternative hosts; and by the weather conditions that induce disease. As FHB is a monocyclic disease, the quantity of primary inoculum available at the time of anthesis is related to the occurrence of epidemics. This pathology affects yield and quality of the grain due to losses in the protein content and contamination with mycotoxins produced by the pathogen during the pathogenic process. The most frequent mycotoxins found on FHB-affected grains are deoxynivalenol (DON), nivalenol (NIV) and zearalenone, and they affect both human and animal health. Usually F. graminearum produces one of three chemotypes (15-ADON, 3-ADON or NIV chemotype). Genetic variation and variability in aggressiveness were observed in populations of F. graminearum and trichothecenes have been proposed to act as aggressiveness factors. To study the impact of different sources of inoculum on FHB, F. graminearum isolates were recovered from weeds and debris of several crops and identified by conventional mycology and PCR. Aggressiveness of a group of these isolates on wheat was evaluated by point inoculation under field conditions. In vivo capacity to produce mycotoxins (evaluated by ELISA); and genetic variability (using RFLP markers) were also analyzed. Additionally, pathogen dynamic on cereal and soybean residues naturally infected was evaluated through conventional methodologies and real-time PCR, by pre-optimizing a protocol for DNA extraction from crop residues. Fifty four weed species were identified as alternative hosts of the pathogen for the first time. Furthermore, inoculum presence along to the year and its viability were confirmed and quantified in these species. Fusarium graminearum inoculum was present in cereals and soybean residues by at least 18 and 14 postharvest months, respectively. All isolates induced FHB symptoms on inoculated spikes in pathogenicity tests. Even though differences in aggressiveness were found, no significant effect of the source of the isolate was identified. Genetic variability on F. graminearum DNA fragments of 2427 bp, showed that there were scarce genetic differences between isolates. Furthermore, no evident relationship between the RFLP profile and the source and/or aggressiveness was found. A positive correlation between symptom severity and in vivo DON production was observed. The information provided in this work could prove valuable to the understanding of the epidemiology of F. graminearum and for the development of practices aimed at reducing the FHB inoculum.