Cytology of infection of apple leaves by Diplocarpon mali |
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Authors: | Hua Zhao Qingmei Han Jie Wang Xiaoning Gao Chang-Lin Xiao Jing Liu Lili Huang |
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Institution: | 1. State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, Yangling, Shaanxi, 712100, People’s Republic China 2. College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, 712100, People’s Republic China 3. Commodity Protection and Quality Research Unit, USDA-ARS San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA, 93648, USA
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Abstract: | Diplocarpon mali, the causal agent of Marssonina leaf blotch of apple, causes severe defoliation during the growing season. Little information is available on the mode of infection and the infection process. In this study, the infection strategies of D. mali in apple leaves were investigated using fluorescence and electron microscopy. Conidia attached to leaf surface apparently by mucilage and germinated on both sides of leaves 6 h post-inoculation (hpi). The pathogen penetrated the cuticle by infection pegs formed either in germ tubes or appressoria in 6 hpi, and then formed haustoria in host epidermal and mesophyll cells accompanied by extension of subcuticular and intercellular hyphae. Five days post-inoculation (dpi), the intracellular hyphae were observed. At the same time, the subcuticular hyphal strands (SHS) were produced as a means for fast expansion and reproduction. About 7 dpi, acervuli formed on inoculated leaves. This was the first observation that D. mali formed haustoria and SHS as infection strategies. Our results suggest that D. mali may behave like a hemibiotroph, which can use both biotrophic and necrotrophic strategies to establish infections on apple leaves. |
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