Baseline and Temporal Changes in Sensitivity of Zymoseptoria tritici Isolates to Benzovindiflupyr in Oregon, U.S.A., and Cross-Sensitivity to Other SDHI Fungicides

Zymoseptoria tritici is the causal agent of Septoria tritici blotch (STB), a disease of wheat (Triticum aestivum) that results in significant yield loss worldwide. Z. tritici's life cycle, reproductive system, effective population size, and gene flow put it at high likelihood of developing fungicide resistance. Succinate dehydrogenase inhibitor (SDHI) fungicides (FRAC code 7) were not widely used to control STB in the Willamette Valley until 2016. Field isolates of Z. tritici collected in the Willamette Valley at dates spanning the introduction of SDHI (2015 to 2017) were screened for sensitivity to four SDHI active ingredients: benzovindiflupyr, penthiopyrad, fluxapyroxad, and fluindapyr. Fungicide sensitivity changes were determined by the fungicide concentration at which fungal growth is decreased by 50% (EC₅₀) values. The benzovindiflupyr EC₅₀ values increased significantly, indicating a reduction in sensitivity, following the adoption of SDHI fungicides in Oregon (P < 0.0001). Additionally, significant reduction in cross-sensitivity among SDHI active ingredients was also observed with a moderate and significant relationship between penthiopyrad and benzovindiflupyr (P = 0.0002) and a weak relationship between penthiopyrad and fluxapyroxad (P = 0.0482). No change in cross-sensitivity was observed with fluindapyr, which has not yet been labeled in the region. The results document a decrease in SDHI sensitivity in Z. tritici isolates following the introduction of the active ingredients to the Willamette Valley. The reduction in cross-sensitivity observed between SDHI active ingredients highlights the notion that careful consideration is required to manage fungicide resistance and suggests that within-group rotation is insufficient for resistance management.

Expression of iron binding proteins and hemin binding activity in the dental pathogen Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans was found to express a polypeptide immunologically related to the Neisseria gonorrhoeae FbpA iron binding protein. In addition, the expression of hitB and hitC homologs was detected by Northern blot analysis. This periodontal pathogen also expresses a polypeptide homologous to the 31-kDa Haemophilus influenzae protein, which shows amino acid sequence homology with the FimA and YfeA proteins from Streptococcus parasanguis and Yersinia pestis, respectively. Both A. actinomycetemcomitans protein homologs were located within the periplasmic space, and their synthesis was regulated by the iron and hemin concentration of the culture medium. Southern and Western blot analysis together with molecular cloning revealed the presence of a Fur-like repressor, which may control the iron regulation of gene expression in this bacterium. Cultivation in the presence of hemin or Congo red revealed the ability of this organism to bind hemin. This binding activity was further confirmed by isolating Escherichia coli DH5 alpha clones that produced red and brown colonies on agar plates containing Congo red and hemin, respectively, after transformation with an A. actinomycetemcomitans gene library.