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Mycelia of Venturia inaquealis grown in cuticle of apple leaves of different age.
Host: Apple (MM.106 and Royal Gala) Malus x domestica Borkh. Disease name: Apple scab Pathogen name: Venturia inaquealis (Cooke) Wint.
Image A: Mycelium of Venturia inaequalis on the adaxial surface of a young leaf of MM.106. The leaf was unexpanded (the leaf just above the youngest unfolded leaf) when inoculated, and it was sampled one week after inoculation. The image shows that hyphae grow profusely on young susceptible leaf tissue at 20°C.
Image B: An inhibited mycelium on the adaxial surface of a leaf of MM.106. The leaf was inoculated about 10 days after it unfolded. (It was the fourth leaf from the youngest unfolded leaf when inoculated.) This photo, made three weeks after inoculation, shows that the growth of the hyphae was inhibited and few conidiophores (arrows) formed in the resistant leaf.
Images C and D: Restricted mycelia on the adaxial surface (C) and abaxial surface (D) of old cluster leaves of three-year-old trees of cv. Royal Gala. The leaves were sampled on October 20 from trees that had not received fungicide during the growing season and were heavily scabbed. The resistance of the old leaves did not prevent infection, however growth and sporulation of the pathogen were restricted.
For more information refer to B.Li and X. Xu 2002. Infection and development of apple scab (Venturia inaequalis) on old leaves J. Phytopathology 150: 687-691.
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