Fusarium species dynamic and trichothecenes contamination in Argentinean soybean agroecosystem

BARROS G.G.; ABOD A.; OVIEDO M.S.; RAMIREZ M.L.; TORRES A. M.; CHULZE S.N.

Tull

Conferencia; ISM Conference, Worldwide Mycotoxin Reduction in Food and Feed Chains; 2009

International Society for Mycotoxicology

Soybean (Glycine max L. Merr.) production in Argentina reaches around 40.5 million tons per year. Around 70% of the soybean harvested is processed, providing 81% of the world´s exported soybean oil and 36% of soybean meal.  At present limited information about the natural occurrence of Fusarium mycotoxins in soybean and by-products is available. The aims of the present work were: i) to isolate and identify Fusarium species potentially toxigenic during different reproductive development stages of soybean. ii) to evaluate natural occurrence of deoxynivalenol (DON), nivalenol (NIV), T-2 and HT-2 toxins. iii) to determine the chemotype diversity among the Fusarium graminearum isolated. Samples were collected during 2007/2008 harvest season from an experimental field at the National University of Río Cuarto, Córdoba, Argentina. The mycoflora was dominated by two genera: Alternaria and Fusarium, at similar levels across all stages. Fusarium species (502 isolates) were identified from flowers (at pod formation), pods and seeds at R6 (full seed) and R8 (full maturity) growth stages. F. equiseti was recovered most frequently from flowers, pods and seeds (39.4% of isolates), followed by F. semitectum (27.0%) and F. graminearum (17.4%). Other species isolated were F. oxysporum, F. solani, F. sambucinum, F. proliferatum, F. subglutinans and F. verticillioides. Twenty soybean seed samples from each stage were evaluated for toxin presence. Two samples were contaminated with DON at levels of 1.6 mg kg-1 (in R6 stage) and 0.9 mg kg-1 (in R8 stage). This is the first report that showed DON contamination in soybean at the R6 growth stage. Only one sample in R8 stage was contamined with T-2 toxin at level of 0.28 mg kg-1. No NIV and HT-2 contamination was observed. The F. graminearum isolates evaluated showed as dominant DON/15 acetyl-DON chemotype, 20% of the isolates produced only DON and 8% were DON/NIV chemotype. The DON/3 acetyl-DON chemotype was not observed. Nearly all the isolates were zearalenone producers. The present study contributes with new information on the ecophysiology of Fusarium species in soybean at pre-harvest stages.