Population genetic structure and mycotoxin potential of the wheat crown rot and head blight pathogen Fusarium culmorum in Algeria

Authors: LARABA, IMANE - National Higher School Of Agronomy; BOUREGHDA, HOUDA - National Higher School Of Agronomy; ABDALLAH, NORA - National Higher School Of Agronomy; BOUAICHA, OUSSAMA - National Higher School Of Agronomy; OBANOR, FRIDAY - Grains Research And Development Corporation; MORETTI, ANTONIA - National Research Council - Italy; GEISER, DAVID - Pennsylvania State University; Kim, Hye-Seon; McCormick, Susan; Proctor, Robert; Kelly, Amy; Ward, Todd; O Donnell, Kerry

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2017
Publication Date: 4/7/2017
Publication URL: https://handle.nal.usda.gov/10113/5667953
Citation: Laraba, I., Boureghda, H., Abdallah, N., Bouaicha, O., Obanor, F., Moretti, A., Geiser, D.M., Kim, H.-S., McCormick, S.P., Proctor, R.H., Kelly, A.C., Ward, T.J., O'Donnell, K. 2017. Population genetic structure and mycotoxin potential of the wheat crown rot and head blight pathogen Fusarium culmorum in Algeria. Fungal Genetics and Biology. 103:34-41.
DOI: https://doi.org/10.1016/j.fgb.2017.04.001

Interpretive Summary: Fusarium crown rot (FCR) and Fusarium head blight (FHB) of wheat and other small grain cereals are two of the most important plant diseases worldwide. These economically important diseases are responsible for multi-billion U.S. dollar losses annually to the world’s agricultural economy. In addition to reducing grain yield and quality, the molds responsible for FCR and FHB frequently contaminate grain with fungal toxins that pose a serious threat to food safety and the health of humans and other animals. Because Fusarium culmorum is one the most important FCR pathogens worldwide, the present study was conducted to characterize the genetic diversity, toxin potential, and population structure of this pathogen within Algeria and compare it with populations in other regions of the world (i.e., Australia, Italy, and the United States). Genetic tests and toxin analyses revealed that most strains of F. culmorum produce 3-acetyl-deoxynivalenol (3ADON) toxin, but some produce the toxin nivalenol (NIV). In addition, most of the strains tested also produced the toxin culmorin in liquid culture. Although sexual reproduction has not been discovered to date in F. culmorum, our population genetic data revealed a surprisingly high level of genetic diversity and the presence of both mating types in all populations sampled, consistent with a cryptic sexual cycle. Thus, results of the present study have raised important questions concerning what genetic mechanism(s) are responsible for generating the high levels of genetic variation we observed within a toxigenic cereal pathogen of importance to world agriculture. Results of this study should be of interest to plant disease specialists, mycotoxicologists, fungal biologists, and quarantine officials who are focused on minimizing the threat that these fungi pose to cereal production worldwide.

Technical Abstract: Surveys for crown rot (FCR) and head blight (FHB) of Algerian wheat conducted during 2014 and 2015 revealed that Fusarium culmorum strains producing 3-acetyl-deoxynivalenol (3ADON) or nivalenol (NIV) were the primary causal agents of these important diseases. Morphological identification of the isolates (n FCR = 91, n FHB = 15) was confirmed by sequencing a portion of TEF1. To assess mating type idiomorph, trichothecene chemotype potential and global population structure, the Algerian strains were compared with F. culmorum from Italy (n = 27), Australia (n = 30) and the United States (n = 28). A PCR assay for MAT idiomorph revealed that MAT1-1 and MAT1-2 strains were segregating in nearly equal proportions, except within Algeria where two-thirds of the strains were MAT1-2. An allele-specific PCR assay indicated that the 3ADON trichothecene genotype was predominant globally (83.8% 3ADON) and in each of the four countries sampled. While significant differences in trichothecene genotype frequencies were observed in Algeria, Australia and the United States, none were detected in Italy. Fusarium culmorum strains produced 3ADON (n = 65) or acetylated NIV (n = 14), and most strains produced culmorin (n = 79) in vitro; 9 strains failed to produce detectable levels of toxins. Global population genetic structure of 191 strains was assessed using nine microsatellite markers (SSRs). AMOVA of the clone corrected data indicated that 89% of the variation was within populations. Bayesian analysis of the SSR data identified two globally distributed, sympatric populations within which both trichothecene chemotypes and mating types were represented.