The flowering time is the most susceptible period for primary infection of wheat heads by Fusarium spp. During this period spores can be deposited into the opened wheat florets where they may later cause infections. We quantitatively explored the relationship between variables related to the flowering process and the infection level by Fusarium graminearum in single spikelets. We imitated open (chasmogamous) and closed (cleistogamous) flowering by injecting well-defined amounts of spores into and between wheat florets. Applying the spores between the florets resulted in weaker disease symptoms and significantly lower amounts of Fusarium mycotoxins. With larger numbers of spores, the disease symptoms became more pronounced and the mycotoxin amounts per spikelet increased significantly.
Our results indicate that the probability of primary infection is approximately proportional to the number of spores reaching the open florets during the flowering process. The breeding of wheat lines which flower partially or completely cleistogamously might reduce the Fusarium susceptibility in wheat.