Threats

Diplodia shoot blight, Sphaeropsis die-back

Diplodia shoot blight, Sphaeropsis die-back
Diplodia sapinea (Fr.) Fuckel

Diplodia pinea (Desm.)

Shoot blight

In South Africa, D. sapinea has been found in association with bark weevils (Pissodes spp.),  the Mediterranean pine beetle (Orthotomicus erosus) (Zwolinski et al. 1995), black pine aphid (Cinara cronartii) and the pine bark beetle (Hylastes sp.) (Wingfield & Knox-Davies 1980a).

In the Mediterranean forests of Europe, the cone bug (Gastrodes grassipes), bark beetles (Ips pini) and western conifer seed bug (Leptoglossus occidentalis) are known to have an interactions with D. sapinea (Luchi et al. 2012).

Diplodia sapinea is an opportunistic pathogen that can cause disease to different Pinus species during all growth stages. It may be present as an endophyte in healthy, asymptomatic tissues (Smith et al. 1996; Burgess et al. 2001). Symptoms are often expressed soon after biotic or abiotic stresses such as hail, drought (Wingfield & Knox-Davies 1980b; Desprez-Loustau et al. 2006), infections of pruning wounds or material planted under stressed conditions. 

The symptoms include shoot blight or dieback, cankers on branches and stems sometimes with resin and blue staining of timber (Wingfield & Knox-Davies 1980b; Swart et al. 1985). After heavy infections, the tree is affected by stunted growth, twig deformation and death of terminal buds.

Dark blue radial lesions are observed in young roots that in advanced cases, can extend to the lateral roots and up the trunk of the tree. In the canopy of the tree, the needles become chlorotic and are shed (Wingfield & Knox-Davies 1980a). 

In nurseries, collar rot and root rot are the predominant symptoms in young seedlings with tissue discolouration, drops of resin and the development of pycnidia being observed (Wingfield & Knox-Davies 1980b; Swart et al. 1985).

Diplodia sapinea can subsist in dead plant material such as needles, twigs, cones and leaf sheaths were it forms fruiting structures known as pycnidia (Brookhouser & Peterson 1971). Once the environmental conditions are optimal, the pycnidia release spores that are transported by wind, rain, insects or equipment. These spores penetrate young needles through the stomata (or other natural openings) or through wounds caused by biotic or abiotic factors (Brookhouser & Peterson 1971, Wingfield & Knox-Davies 1980). After penetration, a lesion is formed on the needles, twigs or stems, where different symptoms will start to develop (Brookhouser & Peterson 1971). The dead tissue produced as a result of infection will be the source of inoculum for the new cycle of disease.  

A sexual state for this pathogen is not yet known.

1909 (Lundquist 1987)
Eastern Cape, Free State, Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga, Northern Cape, North West, Western Cape
The origin of D. sapinea is still unknown, however, it has been introduced to different areas as a consequence of the movement of infected plant material.

Gallery

Blue stain due to D. sapinea after hailstorm on P. patula
D. sapinea infections in branch whorl after pruning
Conidia of Diplodia sapinea
Diplodia shoot die-back and resin production
Advance damage of Diplodia sapinea on Pinus sp
Internal discolouration on branch
Diplodia tip blight on mature Pinus ponderosa
Diplodia tip blight on Pinus patula

Brookhouser LW, Peterson GW. 1971. Infection of Austrian, Scots and Ponderosa pines by Diplodia pinea. Phytopathology 61: 409-414.

Burgess T, Wingfield BD, Wingfield MJ. 2001. Comparison of genotypic diversity in native and introduced populations of Sphaeropsis sapinea isolated from Pinus radiata. Mycological Research 105: 1333-1339.

Desprez-Loustau ML, Marçais B, Nageleisen LM, Piou D, Vannini A. 2006. Interactive effects of drought and pathogens in forest trees. Annals of Forest Science 63: 597-612.

Luchi N, Mancini V, Feducci M, Santini A, Capretti P. 2012. Leptoglossus occidentalis and Diplodia pinea: a new insect‐fungus association in Mediterranean forests. Forest Pathology 42: 246-251.

Lundquist JE. 1987. A history of five forest diseases in South Africa. South African Forestry Journal 140: 51-59.

Smith H, Wingield MJ, Crous PW, Coutinho TA. 1996. Sphaeropsis sapinea and Botryosphaeria dothidea endophytic in Pinus spp. and Eucalyptus spp. in South Africa. South African Journal of Botany 62: 86-88.

Swart WJ, Wingfield MJ, Knox-Davies PS. 1985. Sphaeropsis sapinea, with special reference to its occurrence on Pinus spp. in South Africa. South African Forestry Journal 35: 1-8.

Wingfield MJ, Knox-Davies PS. 1980a. Observations on diseases in pine and eucalyptus plantations in South Africa. Phytophylactica 12: 57-63.

Wingfield MJ, Knox-Davies PS. 1980b. Association of Diplodia pinea with a root disease of pines in South Africa. Plant Disease 64: 221-222.

Zwolinski JB, Swart WJ, Wingfield MJ. 1995. Association of Sphaeropsis sapinea with insect infestation following hail damage of Pinus radiata. Forest Ecology and Management 72: 293-298.