Recent
outbreaks of Fusarium head blight (FHB) in Georgia have negatively impacted
soft red winter wheat (SRWW) production; however, information on pathogen
population is lacking. To explore the distribution and diversity of Fusarium species, we collected 212
isolates from symptomatic wheat heads and corn stubble by sampling 46 wheat and
55 corn fields across 72 counties of Georgia in 2018 and 2019. Pure cultured
and single hyphal tipped isolates were subjected to genomic DNA extraction. The
sequencing date from translation elongation factor 1-alpha (TEF1) locus was used for species level identification
by querying publicly available sequence databases in NCBI GeneBank and Fusarium MLST. Trichothecene chemotypes
were determined using chemotype-specific primers designed from the TRI3 and TRI12 loci. We identified that the majority (nearly 84%) of
isolates from wheat were F. graminearum
of which 78.0% were 15ADON chemotype, 19% NIV chemotype, and few remaining
isolates of 3ADON chemotype. F. poae
was the second largest group of species recovered from wheat and were
distributed across six counties of Georgia. Interestingly, two-thirds of the
total isolates from corn were resolved under Fusarium incarnatum-equisetum species complex (FIESC) with a very
few (5%) presence of F. graminearum.
Additionally, several other species were identified including F. armeniacum, F. proliferatum, F.
verticillioides, F. fujikuroi, F. avenaceum, F. acuminatum, and F. chlamydosporum belonging to
different species complexes. Greenhouse pathogenicity tests were conducted on
five isolates of F. poae and one isolate
of F. graminearum in three hosts:
SRWW, durum wheat, and six-rowed barley, each consisting of two to three susceptible
and moderately resistant cultivars. Significant effects of isolates, cultivars,
and their interaction were observed on FHB traits with F. poae isolates causing up to 40% FHB severity (SEV) and 75% Fusarium-damaged kernel (FDK) and
producing type A trichothecene T-2/HT-2 as high as 45 ppb. On the other hand, F. graminearum isolate produced nearly
90% SEV and FDK and up to 40 ppm DON, while no disease was observed on the mock-inoculated
plants. Overall, our findings on the widespread distribution of FHB pathogens
and the ability of F. poae isolates to
cause disease in the greenhouse demonstrate that FHB outbreaks will likely continue
in Georgia whenever environmental conditions favor and thus growers should
consider integrated disease management strategies, whenever applicable.