First Report of Fusarium poae Associated with Fusarium Head Blight in Wheat in Paraguay

Abstract

Fusarium head blight (FHB) is a devastating fungal disease of small grain cereals. In wheat, the disease is caused mainly by Fusarium graminearum, but other species may occur such as F. poae, which is able to produce dangerous mycotoxins such as HT-2 toxin, T-2 toxin, nivalenol, and deoxynivalenol (Stenglein et al. 2014). During the months of August and September, between 2013 and 2016, 10 random spikes (100% blighted and nonblighted) each were collected from two cultivars, Itapua 75 and E08075, grown in the Paraguayan Institute of Agricultural Research (IPTA) at Capitan Miranda, Itapua. Randomly selected kernels were surface-sterilized by immersion for 3 min in 50% ethanol and then for 3 min in hypochlorite (6%) and were subsequently washed with sterilized water. The kernels were deposited in Petri dishes containing potato dextrose agar (PDA) and incubated for 7 days at 22 ± 2°C under a 12-h photoperiod. Thirteen of over 450 isolates, representing less than 3%, emitted typical Fusarium poae odor. Of these, the two most representative monosporic strains, named as FP07 and FP013, originating from different spikes, developed a dense, whitish mycelium in PDA at 72 to 96 h. Microconidia were abundant, globose to piriform, zero to one septate, 4 to 10 × 4.5 to 7 μm, and formed on unbranched and branched monophialides. Cultures produced a fruity aroma, in accordance with Leslie and Summerell (2006). The identity of the fungus was confirmed by sequencing a portion of the EF1-α gene using the degenerate primers EF-1 (5′-ATGGGTAAGGAGGACAAGAC-3′) and EF-2 (5′-GGAAGTACCAGTGATCATGTT-3′) (O’Donnell et al. 1998). BLASTn searches of the obtained sequences FP07 (accession no. MG976797) and FP013 (accession no. MG976798) showed a 99% homology with gene sequences of F. poae Schw. in GenBank: accession EU744740 to FP07 and accession MG889924 to FP013. Koch’s postulates were completed for the two isolates under greenhouse conditions. Pathogenicity tests were conducted by drop-inoculating healthy spikelets with 5 ml of microconidia suspension (10⁶ spores/ml) (Stenglein et al. 2014). Control treatment consisted of heads inoculated only with water. After inoculation, plants were placed in a growth chamber with a 12-h photoperiod at 22 ± 2°C and covered with polyethylene bags that were removed after 3 days. Two weeks after inoculations, all spikes of the control treatment were healthy, but the spikes with FP07 and FP013 showed 20 to 30% spike infection; a lower infection rate than the one seen in spikes infected with F. graminearum strains. The fungus was reisolated from infected spikes according to the methods described above and appeared to be morphologically identical to the isolates used to inoculate the plants. This is the first report of F. poae associated with FHB symptoms in wheat in Paraguay, which is considered important owing to its association with nivalenol production.