| Fusarium head blight (FHB) is a devastating disease of wheat and barley worldwide and has been epidemic in South America's Southern cone for the past decade. This study examined the Fusarium species prevalent in wheat and barley in Uruguay, determined the survival and inoculum production of Gibberella zeae (Schwein.) Petch in the residues of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), corn (Zea maydis L.), sunflower ( Helianthus annus L.), and pasture and gramineous weed species common in Uruguayan cropping systems; and evaluated the effectiveness of applying Trichoderma harzianum and Bacillus subtilis to wheat residue as biological control agents. Gibberella zeae was the most prevalent species found in wheat grains, comprising 76% and 60% of all Fusarium species isolated in 2001 and 2002, respectively. Similarly G. zeae was the predominant species on barley grains (65%, 2001; 56%, 2002). Other species isolated from both crops included; F. avenaceum, F. equiseti, F. acuminatum, F. trincictum. F. culmorum (wheat only), F. sambucinum (barley only), F. semitectum (barley only) and F. chlamydosporum (barley only). All species recovered were pathogenic on wheat and barley, except F. semitectum which was not pathogenic on wheat. Gibberella zeae was recovered from residues of wheat, barley, corn, sunflower, fescue (Festuca arundinacea L.) and the gramineous weeds Digitaria sanguinalis, Setaria spp., Lolium multiflorum, and Cynodon dactylon but not from the other pasture species examined (birdsfoot trefoil-Lotus comiculatus L., white clover- Trifolium repens L.). Recovery of G. zeae declined over time in all residues examined. Wheat and barley residues are the major contributors to G. zeae inoculum in Uruguay. Interestingly, sunflower residue was the only residue not to support ascospore production. No-till production systems supported the colonization of residues by G. zeae for longer than reduced tillage systems. A slight reduction in the number of G. zeae perithecia occurred in some T. harzianum-treated wheat residues, however neither biocontrol agent effected the percentage of wheat nodes colonized by G. zeae. Bacillus subtilis did not have any effect on G. zeae inoculum production on wheat residues. Knowledge from this research will aid growers in implementing effective practices to manage FHB in Uruguay. |
