Comparison of the influence of inoculum sources on the development of fusarium head blight and the deoxynivalenol content in spring wheat in a disease nursery

The screening for genetic resistance to fusarium head blight (FHB) in wheat has been challenged by the lack of efficacy of various artificial inoculation techniques in disease nurseries. In 2001-2003, we examined the influence of inoculum sources (conidial suspension, infested barley and corn kernels, or infested wheat debris) and inoculation frequency on the development of FHB and the deoxynivalenol (DON) content. The study was conducted on three spring wheat genotypes in a disease nursery of Ottawa, Ontario. The development of FHB was monitored by visually estimating disease severity on a scale of 0 to 9, six times during each growing season. Severity of FHB over time was summarized as the area under the disease-progress curve (AUDPC). Symptoms of FHB were also rated, at a critical developmental stage (soft dough), as critical-time disease severity (DS), percentage of infected spikelets (IS), and FHB index. The percentage of Fusarium-damaged kernels (FDK) and DON content in the wheat kernels were assessed after harvesting. All inoculation treatments had significantly greater AUDPC and DS in 2002, FHB index and IS in 2001 and 2002, and FDK in all three years than the noninoculated control. Regardless of inoculum source, two inoculations produced as much FHB, FDK, and DON as three inoculations. Among the inoculum sources, the conidial suspension or infested kernels yielded significantly greater AUDPC, DS, FHB index, IS, and DON content than the infested debris. Inoculation with conidial suspension resulted in greater FDK than inoculation with infested kernels or infested debris, between which there were no differences. The results of the present study confirm that conidial suspension and infested kernels are equally effective inoculants for FHB nurseries. Infested debris, though a natural source of inoculum, is less effective.