Leptosphaeria maculans
| Leptosphaeria maculans | |
|---|---|
| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Dothideomycetes |
| Order: | Pleosporales |
| Family: | Leptosphaeriaceae |
| Genus: | Leptosphaeria |
| Species: | L. maculans |
| Binomial name | |
|
Leptosphaeria maculans (Sowerby) P.Karst. (1863) |
|
| Synonyms | |
|
Phyllosticta brassicae |
|
Phyllosticta brassicae
Sphaeria maculans Sowerby (1803)
Leptosphaeria maculans (anamorph Phoma lingam) is a fungal pathogen of the phylum Ascomycota that is the causal agent of blackleg disease on Brassica crops. Symptoms of blackleg generally include basal stem cankers, small grey lesions on leaves, and root rot. The major yield loss is due to stem canker. The fungus is dispersed by the wind as ascospores or rain splash in the case of the conidia. L. maculans grows best in wet conditions and a temperature range of 5–20 degrees Celsius. Rotation of crops, removal of stubble, application of fungicide, and crop resistance are all used to manage blackleg. The fungus is an important pathogen of Brassica napus (canola) crops.
L. maculans causes phoma stem canker or blackleg. Symptoms generally include basal stem cankers, small grey oval lesions on the leaf tissue and root rot (as the fungus can directly penetrate roots).L. maculans infects a wide variety of Brassicae crops including cabbage and oilseed rape. L. maculans is especially virulent on Brassica napus. The first dramatic epidemic of L. maculans occurred in Wisconsin on cabbage. The disease is diagnosed by the presence of small black pycnidia which occur on the edge of the leaf lesions. The presence of these pycnidia allow for this disease to be distinguished from Alternaria brassicae, another foliar pathogen with similar lesions, but no pycnidia.
L. maculans has a complicated life cycle. The pathogen begins as a saprophyte on stem residue and survives in the stubble. It then begins its necrotrophic cycle by producing leaf spots. Colonizing the plant tissue systematically, it begins its endophytic stage. When the growing season ends, the fungus causes cankers beginning another necrotrophic stage.
L. maculans has both a teliomorph phase (ascospores) and an anamorph phase (pycnidia). The disease spreads by wind born dispersal of ascospores and rain splash of conidia. In addition, phoma stem canker can also be spread by infected seeds when the fungus infects the seed pods of Brassica napus during the growing season, but this is far less frequent. The disease is polycyclic in nature even though the conidia are not as virulent as the ascospores. The disease cycle starts with airborne ascospores which are released from the pseudothecia in the spring. The ascospores enter through the stomata to infect the plant. Soon after the infection, gray lesions and black pycnidia form on the leaves.
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