|ZHAO, H - Northwest Agricultural & Forestry University|
|LIU, J - Northwest Agricultural & Forestry University|
|ZANG, R - Northwest Agricultural & Forestry University|
|GAO, X - Northwest Agricultural & Forestry University|
|HAN, Q - Northwest Agricultural & Forestry University|
|HUANG, L - Northwest Agricultural & Forestry University|
Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2014
Publication Date: N/A
Interpretive Summary: Marssonina leaf blotch is a serous fungal disease affecting apple production. The fungus Diplocarpon mali (anamorph Marssonina coronaria) is believed to be the cause of this disease. Fruiting bodies (conidia) of the fungus formed on diseased leaves serve as inoculum for infections of apple leaves during the growing season. Microconidia (small spores) are commonly associated with the fruiting bodies of D. mali, but the biological connection between the two are not well understood. In this study, we found that the small spores commonly associated with D. mali were microconidia of the fungus. Furthermore, we documented that these microconidia did not germinate on apple leaves and did not cause the disease on apple leaves inoculated with microconidia. Our results suggest that microconidia do not serve as inoculum for infections of apple leaves in the field.
Technical Abstract: Microconidia were observed in autumn to be commonly associated with acervuli of Diplocarpon mali (anamorph Marssonina coronaria) on diseased apple leaves exhibiting Marssonina leaf blotch symptoms. To clarify the connection with D. mali, cultures derived from single microconidium were obtained, and morphological and biological characteristics as well as ITS sequence of the cultures were compared with those derived from conidia of D. mali. Both conidia of D. mali and microconidia were observed in the fruiting bodies when the cultures derived from microconidia were incubated under the cycle consisting of 10 h at 24°C under light and 14 h at 10°C in the dark for 14 d. The morphology and ITS sequence analysis supported that this microconidium belonged to D. mali. Microconidia of D. mali were able to germinate on agar media but at a low rate. However, neither spore germination nor typical disease symptoms were observed on the apple leaves inoculated with either spore suspensions or agar plugs containing germinated microconidia within 10 days after inoculation. Our results suggest that microconidia do not serve as inoculum for infections of apple leaves and likely function as spermatia in the life cycle of D. mali.