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Rhytisma acerinum is the teleomorph of tar spot. In the spring, needle-shaped ascospores are released from overwintering apothecia in fallen leaf debris. [2] [7] These spores are disseminated by the wind and have a sticky coat to attach to new healthy leaves. [4] Once on the leaves, the spores germinate and penetrate through the stoma. [2]
Symptoms include needles developing yellow spots, horizontal brown bands around the needles, swelling of needles, and off-white fruiting bodies formed on infected needles. [ 2 ] [ 3 ] Because Cyclaneusma is an ascomycete it produces two spore types, an asexual ( conidiomata ) and sexual ( ascomycota ) spore.
The bands start yellow but turn brown/red and can become purple with spots on the upper or lower surface of the needle. [3] Signs of Rhabdocline pseudotsugae include apothecia that mature below epidermis where swelling is visible. These fruiting bodies are present on the underside of needles.
Leaf spots can vary in size, shape, and color depending on the age and type of the cause or pathogen. Plants, shrubs and trees are weakened by the spots on the leaves as they reduce available foliar space for photosynthesis. Other forms of leaf spot diseases include leaf rust, downy mildew and blights. [4]
This mycelial layer may quickly spread to cover all of the leaves. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.
The species is traditionally known as Meria laricis.Meria was first described by Jean Paul Vuillemin (Vuill.) in France in 1896. [1] DNA analysis in the 1990s indicated its closest ancestor was the Rhabdocline genus, with the similarity significant enough for the genera of Meria, Hartigiella, and Rhabdocline to be combined as synonyms, with Rhabdocline chosen as the name of the merged genus.
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A raspberry leaf spot infection initially causes dark green circular spots on the upper side of young leaves, which will eventually turn tan or gray. [3] These spots are typically 1–2 millimetres (0.039–0.079 in) in diameter, but can get as big as 4–6 millimetres (0.16–0.24 in). [4] These spots can also fall out, causing a shot effect.