Effect of fludioxonil on morphological characteristics of Fusarium pseudograminearum and wheat crown rot control

In the past decade, due to straw incorporation and soil salinization, wheat crown rot (FCR) mainly caused by Fusarium pseudograminearum has become widespread in the Huang-Huai wheat-growing region of China. It poses a serious threat to the high and stable yield of wheat and has brought potential toxin pollution to animal feed made from wheat straw. The phenylpyrrole fungicide fludioxonil is widely used in seed dressing or coating. Previous studies of our research group have shown that fludioxonil has a strong inhibitory effect on the mycelial growth of F. pseudograminearum, but the mechanism of inhibition has remained unclear. In this paper, the inhibitory mechanism of fludioxonil on the mycelial growth of F. pseudograminearum was studied, and the inhibitory effect of fludioxonil on spore germination, germ tube elongation and sporulation were evaluated, and the field control efficacy of fludioxonil on FCR was determined. The results showed that fludioxonil made the mycelium of F. pseudograminearum malformed as follows: the top mycelium branches increased, the mycelium became dense, the mycelium spacing became shorter; mycelial cells in the colony became irregularly enlarged, branches increased but were short and uneven in thickness, had blunt round top or were enlarged. Compared with mycelial growth, the inhibitory effect of fludioxonil on conidial germination was weaker, and the EC₅₀ value to conidial germination was 7.2358–55.3856 μg/mL. However, fludioxonil delayed the germination time of conidia and increased the probability of conidia germination from intermediate cells. Fludioxonil also recorded a strong inhibitory effect on germ tube elongation, and the EC₅₀ to germ tube elongation was only 0.0078 μg/mL. Fludioxonil caused conidial cells enlargement, but the teratogenic effect on the germ tube was not obvious. Fludioxonil could also delay the formation time of conidia. In the mung bean soup liquid medium containing fludioxonil, it took 72 h to form conidia, while 0.8 μg/mL completely inhibited conidia formation. The EC₅₀ values of fludioxonil to sporulation ranged from 0.1439–0.2739 μg/mL. The control efficacies of fludioxonil against FCR at the jointing and filling stages of wheat were better than that of carbendazim, and it reduced the whiteheads rate at the milk stage, but decreased the control efficacy at the filling stage. Fludioxonil could be used as a seed dressing agent in the prevention and control of FCR.