Threats

Dothistroma needle blight

Dothistroma needle blight
Dothistroma septosporum

Hypostomum flichianum Vuill., Cytosporina septospora Dorogin, Septoriella septospora (Dorogin) Sacc. apud Trotter, Dothistroma pini Hulbary, Dothistroma septospora (Dorogin) M. Morelet, among others. The sexual stage was known as Mycosphaerella pini.

The complete taxonomic revision and history for the genus Dothistroma can be found in Barnes et al. (2016).

 

The first symptoms develop on the current years’ needle tips as chlorotic yellow bands to tan spots (Gibson 1979). On older needles, the bands become more visible and change a red-brown colour caused by the accumulation of a mycotoxin called dothistromin. As the fungus proliferates inside the needle, the needle is killed and fruiting bodies resembling black stromata emerges from the necrotic tissue. Heavy infestations cause defoliation of older needles, “lion tail” appearance in branches and stunted growth in young established plantations and mature trees. In severe cases, it can cause tree death (Bulman et al. 2013).

Dothistroma septosporum is often confused with other needle pathogens and for this reason diagnostic molecular markers are used to differentiate them (Ioos et al. 2010). Morphologically, the main characteristic for identifying D. septosporum is the red bands occurring on the upper and lower needle surface. The fruiting structures are dark brown to black, sub-epidermal, erumpent and can be observed as individual structures or aggregated. The conidia are observed as slimy masses with a hyaline to cream colour, thin-wall, subcylindrical and with septa (1-5) (Barnes et al. 2004). 

Dothistroma septosporum is a hemibiotrophic fungus that can reproduce sexually and asexually. In the asexual life stage, the fungus reproduces by forming small black fruiting bodies within the red bands. Spores are released under optimal climatic conditions of high humidity and temperatures between 12-18ºC and are disseminated by wind, rain and mist clouds (Gibson et al. 1964; Gadgil 1967). The spore germinates on the needle surface, penetrates through the stomatal pores and colonizes the epistomatal chambers. During the colonization phase, the non-selective toxin, dothistromin, is produced and necrotic lesions form as result. Lesions are observed between 6 to 12 weeks after sporulation. Once the pathogen has established on the needle, new stromata develop and spores are released to continue the cycle (Kabir et al. 2015). The life cycle of the pathogen varies depending on the country where D. septosporum is found. For example, in tropical countries the life cycle is continuous which means that spores are able to infect at any time (Rodas et al. 2016); whereas in many countries of the Southern Hemisphere, the fungus overwinters in needles until favourable conditions are available. 

Dothistroma septosporum is also a heterothallic fungus, meaning individuals either carry the MAT1-1 or MAT1-2 gene and individuals of opposite mating types are required for sexual reproduction to occur (Groenewald et al. 2007). The sexual state of D. septosporum has rarely been observed in the Northern Hemisphere and no evidence of its presence in the Southern Hemisphere has been documented.

Planting of resistant varieties such as Pinus patula

1965 (Gibson 1972)
Limpopo, Eastern Cape
Pinus radiata very susceptible
Parts of Eurasia but there are also centers of diversity in Central America

Gallery

Dothistroma needle blight
Red bands on Pinus oocarpa

Barnes I, Crous PW, Wingfield BD, Wingfield MJ. 2004. Multigene phylogenies reveal that red band needle blight of Pinus is caused by two distinct species of Dothistroma, D. septosporum and D. pini. Studies in Mycology 50: 551-565.

Barnes I, van der Nest A, Mullett MS, Crous PW, Drenkhan R, et al. 2016. Neotypification of Dothistroma septosporum and epitypification of D. pini, causal agents of Dothistroma needle blight of pine. Forest Pathology 46(5): 388-407.

Bulman LS, Dick MA, Ganley RJ, McDougal RL, Schwelm A, et al. 2013. Dothistroma needle blight. In: Infectious Forest Diseases. Gonthier P, Nicolotti G (Eds.) Wallingford, Oxforshire, UK:CABI 436-457.

Gadgil P. 1967. Infection of Pinus radiata needles by Dothistroma pini. New Zealand Journal of Botany 5: 498-503.

Gibson IAS. 1972. Dothistroma blight of Pinus radiata. Annual Review of Phytopathology 10: 51-72.

Gibson IAS. 1979. Diseases of forest trees widely planted as exotics in the tropics and southern hemisphere. Part II. The genus Pinus. Commonwealth Forestry Institute, Kew, Surrey

Gibson IAS, Christensen PS, Munga FM. 1964. First observation in Kenya of a foliage disease of pines caused by Dothistroma pini Hulbary. Commonwealth Forestry Review 31-48.

Groenewald M, Barnes I, Bradshaw RE, Brown A V., Dale A, et al. 2007. Characterization and distribution of mating type genes in the Dothistroma needle blight pathogens. Phytopathology 97: 825-834.

Ioos R, Fabre B, Saurat C, Fourrier Ć, Frey P, et al. 2010. Development, comparison, and validation of real-time and conventional PCR tools for the detection of the fungal pathogens causing brown spot and red band needle blights of pine. Phytopathology 100: 105-114.

Kabir MS, Ganley RJ, Bradshaw RE. 2015. The hemibiotrophic lifestyle of the fungal pine pathogen Dothistroma septosporum. Forest Pathology 45: 190-202.

Rodas CA, Wingfield MJ, Granados GM, Barnes I. 2016. Dothistroma needle blight: An emerging epidemic caused by Dothistroma septosporum in Colombia. Plant Pathology 65: 53-63.