Search

The presence of Fusarium spp. was examined in the residues of wheat, barley, corn, sunflower, pasture, and gramineous weed species common in wheat and barley cropping systems collected from no-tillage and reduced-tillage plots from February 2001 to March 2003 in Uruguay. Gibberella zeae was recovered from residues of wheat, barley, corn, sunflower, fescue, and the gramineous weeds Digitaria sanguinalis, Setaria spp., Lolium multifiorum, and Cynodon dactyIon, except from birdsfoot trefoil or white clover. Of the Fusarium spp. obtained, G. zeae was the most frequently recovered from wheat and barley residues, while other species were more common in other crops. G. zeae declined over time in all residues examined. Wheat and barley residues produced more ascospores of G. zeae than corn or other gramineous residues. Sunflower residue did not support ascospore production, indicating that it probably did not contribute to primary inoculum. Wheat and barley residues supported G. zeae colonization longer in no-till than in reduced-tillage production systems and, thus, may represent major contributors to Fusarium head blight (FHB) inoculum in Uruguay. The presence of C. zeae in the gramineous components of pastures, weed species, and sunflower should be considered when implementing control strategies for FHB. [ABSTRACT FROM AUTHOR]

Bacterial diseases affecting wheat production in Uruguay are an issue of growing concern yet remain largely uninvestigated in the region. Surveys of 61 wheat fields carried out from 2017 to 2019 yielded a regional collection of 63 strains identified by 16S rRNA gene analysis as Xanthomonas spp. A real-time PCR protocol with species-specific primers previously reported allowed the identification of 44 strains as X. translucens , the causal agent of bacterial leaf streak (BLS) in wheat and other cereal crops. Multilocus sequence analysis of four housekeeping genes ( dnaK , fyuA , gyrB , and rpoD ) revealed that these strains were most closely related to X. translucens pv. undulosa , the pathovar that is most commonly associated with BLS of wheat. Multilocus sequence typing was applied to examine the genetic diversity of X. translucens strains. Strains were assigned to four different sequence types, three of which were previously reported globally. Additionally, 17 Xanthomonas strains not belonging to X. translucens were obtained from diseased wheat leaves. Phylogenetic analysis showed that these strains are closely related to X. prunicola and clustered together with previously uncharacterized Xanthomonas strains isolated from wheat in Minnesota. In planta pathogenicity assays carried out on a BLS-susceptible wheat cultivar showed that X. translucens pv. undulosa strains caused brown necrosis symptoms typical of BLS, whereas non- translucens Xanthomonas sp. strains elicited an atypical symptom of dry necrosis. These findings suggest that local wheat fields are affected by X. translucens pv. undulosa and by a new wheat pathogen within the Xanthomonas genus.