Sphaerulina rubi
| Raspberry leaf spot | |
|---|---|
| Causal agents | Sphaerulina rubi |
| Hosts | Raspberry |
| EPPO code | SPHNRU |
| Sphaerulina rubi | |
|---|---|
| Scientific classification | |
| Kingdom: | Fungi |
| Phylum: | Ascomycota |
| Class: | Dothideomycetes |
| Subclass: | Dothideomycetidae |
| Order: | Capnodiales |
| Family: | Mycosphaerellaceae |
| Genus: | Sphaerulina |
| Species: | S. rubi |
| Binomial name | |
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Sphaerulina rubi Demaree & Wilcox, (1943) |
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Raspberry Leaf Spot is a plant disease caused by Sphaerulina rubi, an ascomycete fungus. Early symptoms of infection are dark green spots on young leaves. As the disease progresses, these spots turn tan or gray in color. Disease management strategies for Raspberry Leaf Spot include the use of genetically resistant raspberry plant varieties and chemical fungicide sprays.
Raspberries are an important fruit, mainly grown in Washington, Oregon and California. Although they are also grown in the Midwest and northeastern states, the output is not nearly as great due to the colder weathers and shorter growing seasons.S. rubi prefers warmer and wetter conditions, which can make raspberry production very difficult in California.
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. These spots are typically 1–2 mm in diameter, but can get as big as 4–6 mm. More severe infections can cause leaves to drop prematurely in the late summer and early fall. Due to the loss of leaves, infected raspberries are more susceptible to winter injury. As a result, Raspberry Leaf Spot may not only reduce yield in season, but cause lasting consequence into the next season.
The symptoms of Raspberry Leaf Spot are similar to the symptoms of Raspberry Anthracnose. The best way to differentiate between the two fungal diseases is to inspect the stems of the plant. Stem lesions are indicative of Raspberry Anthracnose.
In 1943, it was discovered that S. rubi only infects raspberry plants. Previously, the pathogen had also been blamed for leaf spot on blackberry and dewberry. However, Demaree and Wilcox demonstrated the raspberry pathogen could not cause leaf spots on blackberry or dewberry. The similar pathogens were also differentiated as perfect and imperfect, as the Blackberry Leaf Spot pathogen didn’t have a known sexual stage.
In spring, when conditions are favorable, ascospores are discharged from perithecia that have overwintered in fallen leaves and canes and disseminate to infect young leaves of raspberry plants. Once infected, the raspberry leaf serves as a nutrient source for the fungus to begin producing secondary inoculum, or conidia, within pycnidia, a survival structure that protects the spores. Conidia can undergo several repeating secondary cycles and re-infect other nearby plants. When the leaves of the raspberry plant begin to fall, perithecia form in the fallen tissue where asci and ascospores will be produced and protected until the following spring. The perithecia are black, found subepidermaly. The ascospores are characterized by a cylindrical, curved shape and are pointed at both ends with four septate usually.
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Wikipedia