Threats

Lophodermium needle cast

Lophodermium needle cast
Lophodermium seditiosum Minter, Staley & Millar (previously erroneously attributed to Lophodermium pinastri Schrad. ex Fr. Chev. (Minter et al. 1978)).

Leptostroma rostrupii Minter

All Lophodermium species have an endophytic lifestyle where the fungi colonise the living tissue of pine needles. Symptoms appear only after needles have died and are cast (Minter & Millar 1980). The exception is Lophodermium seditiosum, a pathogen that colonises the mesophyll cells and vascular system of the needles, which are killed leading to premature defoliation (Diwani & Millar 1986).

Lophodermium spp. can infect seedlings in nurseries or trees in young plantations. Initial symptoms include small yellow spots at the site of infection (Sinclair & Lyon 2005). These spots later coalesce, turn red-brown and are surrounded by a yellow halo. In advanced stages of disease, the needles turn brown, become dry and are cast. Under favourable conditions, shiny black oval-shaped fruiting structures (ascocarps), develop on the cast needles. Successive defoliation reduces tree vigour and growth. In severe cases, young seedlings may die (Ostry & Nicholls 1989).

On needles, pathogenic Lophodermium spp. are difficult to separate from non-pathogenic species in this genus. The shape of the ascocarp and depth at which it is embedded in the needle surface is characteristic for different Lophodermium species and may be used as a diagnostic feature. Ascocarps are oval shaped parallel to the needle and have a longitudinal slit down the middle. When immature, the flaps of the ascocarp appear grey but later turn shiny black as it develops. Occasionally, a black line can be seen around the ascocarp and wide brown lines adjacent to it (Minter et al. 1978; Gibson 1979).

The ascocarps of L. seditiosum are 800-1500 µm long and completely embedded in the epidermal tissue. The ascocarps can also be accompanied by brown stromatic lines crossing the needle. Ascospores released from the ascocarps are filiform (needle-like), colourless, 90-120 µm long and are surrounded by a gelatinous sheath.

There is limited understanding regarding the development of the ascocarps and many morphological features overlap between the different species of Lophodermium. Comparisons based on DNA sequence data are therefore used to accurately identify the species. A PCR-RFLP method has been developed to distinguish between different Lophodermium species and the pathogen, L. seditiosum (Johnston et al. 2003).

Lophodermium seditiosum affects the current years’ needles on the lower branches of trees. The fungus overwinters in dead needles still attached to the trees, needle litter and pine cones. Ascospores are liberated in summer at 100% relative humidity and temperatures between 20 - 30°C. Dissemination to lower branches is mainly by wind and rain. The spores germinate in the presence of water and optimal temperatures between 20 - 25°C (Gibson 1979). A germ tube is produced that later differentiates into an appressorium. The appressorium is a melanised structure that uses turgor pressure to directly penetrate the epidermal surface of the needle (Diwani & Millar 1986). The fungus incubates inside the needle for 2-3 weeks before the first symptoms are seen. The needles are killed and eventually cast early the following spring (Minter et al. 1978).

1984 (Roux & Lundguist, 1984)
Eastern Cape, KwaZulu-Natal

Gallery

Lophodermium sp. on P. contorta var. latifolia
Lophodermium sp. on Pinus radiata
Lophodermium symptoms
Lophodermium ascocarp
Lophodermium ascocarps

Diwani SA, Millar CS. 1986. Infection processes of three Lophodermium species on Pinus sylvestris. In: Recent Research on Conifer Needle Diseases. Proceedings of the IUFRO Working Party Conference on Needle Diseases, Gulfport, Mississippi. 14-18 October 1984. USA Washington DC: US Department of Agriculture Forest Services: 22-27.

Gibson IAS. 1979. Diseases of forest trees widely planted as exotics in the tropics and southern hemisphere. Part 2. The genus Pinus. C.M.I., Kew and Commonwealth Forestry Institute, Oxford.

Johnston PR, Park D, Dick MA, Ortiz-Garcia S, Gernandt DS. 2003. Identifying pine-inhabiting Lophodermium species using PCR-RFLP. New Zealand Journal of Forestry Sciences 33: 10-24.

Minter DW, Millar CS. 1980. Ecology and biology of three Lophodermium species on secondary needles of Pinus sylvestris. European Journal of Forest Pathology 10: 169-181.

Minter DW, Staley JM, Millar CS. 1978. Four species of Lophodermium on Pinus sylvestris. Transactions of the British Mycological Society 71: 295-301.

Ostry ME, Nicholls TH. 1989. Effect of Lophodermium seditiosum on growth of pine nursery seedlings in Wisconsin. Plant Disease 73: 798-800.

Roux C, Lundquist JE. 1984. Needle diseases found on pines in South Africa, caused by Lophodermium australe, L. seditiosum and L. indianum. Plant Disease 84: 628.

Sinclair WA, Lyon HH. 2005. Diseases of trees and shrubs. Comstock Publishing Associates.