Dynamic of production and maturation of Gibberella zeae perithecia on crop debris

Gibberella zeae (anamorph Fusarium graminearum) is a key species of Fusarium head blight and consequent mycotoxin accumulation in wheat grain. G. zeae produces inoculum on residues of the previous crops. The dynamic of perithecia production and maturation were studied in controlled conditions and in the field, to acquire information on ascospore dynamics during the season. Maize stalks inoculated with G. zeae were incubated at different temperatures (5 to 40°C) at 100% relative humidity (RH). Numbers and maturity class of perithecia were assessed once a week over 8 weeks. Perithecia were produced between 10 and 30°C. At optimum temperatures (20, 25°C), perithecia emerged after 7 days of incubation. Perithecia matured only at optimum temperatures, from 14 days of incubation onwards. Inoculated maize stalks were also incubated at 25°C between 62.5% and 100% RH, which correspond to 15 to 80% moisture of the stalks. Perithecia were produced at RH 75% and reached the maximum number at 100%. Perithecia matured only with RH85%. Studies were performed on different crops residues, inoculated and incubated at 20°C at 80% RH for 3 weeks. Perithecia were produced on all tested debris; emergence started after 9 days on rape, sugar beet and potato, which had the highest production, compared to wheat, maize, pea and sunflower. Infested stalks were exposed outside between March and July over two years, in three groups: i) always wet trough contact with a wet substrate, ii) kept dry by a protection from rain, iii) left in natural conditions. Perithecia dynamics were assessed twice a week. More perithecia and more rapid maturation occurred in the wet residues, while no perithecia were produced in the dry one. More perithecia were produced in the year with more rain. In conclusion, temperature, moisture and kind of residue influence the dynamic of perithecia production and maturation.