Co-inoculation timing affects the interspecific interactions between phoma stem canker pathogens Leptosphaeria maculans and Leptosphaeria biglobosa: Co-inoculation timing affects interspecific interactions

BACKGROUND: Phoma stem canker is an economically important disease of oilseed rape, caused by two co-existing fungalpathogen species,Leptosphaeria maculans(Plenodomus lingam) andLeptosphaeria biglobosa(Plenodomus biglobosus).Leptosphaeria maculansproduces a phytotoxin called sirodesmin PL. Our previous work showed thatL. biglobosahas an antag-onistic effect on the production of sirodesmin PL if it is simultaneously co-inoculated withL. maculans. However, the effects ofsequential co-inoculation on interspecific interactions between the two pathogens are not understood.RESULTS: The interactions betweenL. maculansandL. biglobosawere investigated in liquid culture by inoculation withL. maculansfirst, followed byL. biglobosasequentially at 1, 3, 5 or 7 days later and vice versa; the controls were inoculated withL. maculansonly,L. biglobosaonly, orL. maculansandL. biglobosasimultaneously. The results showed thatL. biglobosainhibited the growth ofL. maculans, the production of both sirodesmin PL and its precursors ifL. biglobosawas inoculatedbefore, or simultaneously with,L. maculans. However, the antagonistic effects ofL. biglobosawere lost if it was co-inoculated5 or 7 days afterL. maculans.CONCLUSION: For thefirst time, the results of this study provided evidence that the timing whenL. maculansandL. biglobosameet significantly influences the outcome of the interspecific competition between them.Leptosphaeria biglobosacan inhibitthe production of sirodesmin PL and the growth ofL. maculansif it is inoculated beforeL. maculansor less than 3 days afterL. maculansin liquid culture. There is a need to further investigate the timing of co-inoculation on interactions betweenL. maculansandL. biglobosain their host plants for improving the control of phoma stem canker.