Fusarium head blight infection following point inoculation in the greenhouse compared with movement of Fusarium graminearum in seed and floral components

Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe can cause extensive losses in wheat (Triticum aestivum L.) seed quality and yield. Greenhouse studies were conducted in 2000 and 2001 to investigate the movement of F. graminearum into floral components of the wheat spike following point inoculation (PI) of a middle floret. The visual greenhouse rating of spikelet infection (severity) following PI for all genotypes in the Uniform Northern and Southern FHB Screening Nurseries with various levels of Type 11 resistance was also related to seed infection by F. graminearum in the same spikes and to field infection of all genotypes in 2001. Greenhouse ratings of FHB spikelet infection were poorly associated with E graminearum infection in seeds and other floral components from the same spikelets. Pathogen movement was primarily localized around the PI (resistant cultivars) or moved basally from the PI (susceptible cultivars). Greenhouse FHB spikelet infection ranged from 5 (resistant genotypes) to 100% (susceptible genotypes) with a wide but unrelated range in seed infection in the same spikes. Thus, Type II resistance to FHB (measured by spikelet severity) in the greenhouse was not a good indicator of E graminearum seed infection. Seed infection with F. graminearum exceeded 70% in all genotypes when grown under near epidemic conditions in the field nursery and was poorly related to visual measurements (spikelet severity and scabby seeds) of Type II resistance. It is proposed that a greenhouse rating of those spikes having < 30% spikelet FHB infection can be combined with a laboratory evaluation of the same spikes with < 30% F. graminearum seed infection to provide a more definitive method of selecting for Type II resistance.