M. gibsonii can be cultured on V8 juice + pine needle decoction agar, in natural light at 25°C (day), 0-10°C (night). Higher night temperatures (15°C) cause abnormal conidial formation (Suto, 1971). The fungus may also be cultured on PCA-UV at 25°C (Sullivan, 2010;Braun et al., 2013).
Stromata are dark-brown, tuberculated, filling the stomatal openings, 60-96 µm diameter. Conidiophores dense, dark-brown, straight or slightly curved, rarely septate and not branched;10-45 x 2.5 µm;conidiogenous loci unthickened. Conidia pale yellowish-olivaceous, long-obclavate, straight or slightly curved, 3-7 septate with a truncate or rounded unthickened base and obtuse tip;20-68 (mostly 40-50) x 2.5-4.5 µm (Ito, 1972). Asci bitunicate, clavate to cylindrical (33-) 35-38 x 5.5-7 µm, with thickened, bluntly rounded apex, rarely saccate and 32-36 x 6-8 µm, 8-spored, obliquely biseriate. Interthecial tissue present or absent (Evans, 1984). Ascospores hyaline, 1-septate, ellipsoidal to cuneate, (7.5-) 8.5 x 11 (-12.5) x 2 x 3 µm, guttulate (Evans, 1984).
Spermagonia are formed in discrete, unilocular stromata, or as locules in upper parts of large stromata (Ivory, 1987). They consist of a thin dark-brown wall enclosing white contents. The spermatia form on conidiogenous cells lining the inner wall of the locules, are hyaline, rod-shaped and 2-3 x 1 µm. They often become exuded in tiny hyaline droplets.
The fungus forms grey to grey-green or black, compact colonies which often become pulvinate and stromatic. They are mostly non-sporulating, although Asian isolates quite often produce brown, thin-walled spermagonia containing spermatia in a pale-grey slime when grown under black light. These isolates also produce conidia very occasionally in small fertile patches on stromatic colonies when exposed to black light. The African isolates grow more slowly, are more inhibited by black light, and are generally less spreading than Asian isolates (Ivory, 1987).
Related invasive species
- Mycosphaerella gibsonii
Related Farm Practice
- Light
- Incidence
Related location
- Philippines
- Japan
Mycosphaerella gibsonii is a fungal pathogen causing needle blight, primarily in Pinus species. It causes lesions on needles, first affecting lower needles and then spreading to the upper crown. The disease eventually causes needle necrosis and needle cast, leading to defoliation, stunted growth and host plant death;it is a major obstacle to the production of pine seedlings. M. gibsonii occurs in the tropics and subtropics of South and Central America, the Caribbean, sub-saharan Africa, India, South East Asia and East Asia;the native range is uncertain. Although natural dispersal by wind and water occur locally, international spread is largely due to movement of infected nursery stock. Phytosanitary control measures such as avoiding the planting of infected plants, removal and destruction of all infected pines in nurseries and cleaning between annual production cycles in nurseries can help to reduce the spread of the pathogen. It is listed as an A1 quarantine pest in the EPPO region, and is considered of quarantine significance in South America.
Lesions can occur at any point along infected primary and secondary needles (Ivory and Wingfield, 1986). However, they often appear towards the distal part of the needles, especially on 1- to 2-year-old seedlings (Suto, 1979;Ivory, 1987). Ivory and Wingfield (1986) suggest that foliage of the lower crown is usually the most affected due to the occurrence of more favourable conditions for the infection. Observations in the Philippines by Koboyashi et al. (1978) indicated that the disease tends to start in the lower needles and spread to the upper crown later on.
Lesions are usually 5-10 mm long (Diekmann et al., 2002);they tend to progress initially from pale-green spots or bands, to a yellowish to yellowish-brown colour, followed by greyish to blackish-brown colour;eventually they coalesce, resulting in complete needle necrosis and eventual needle cast (Ivory and Wingfield, 1986;Ivory, 1987;Braun et al., 2013). Lesions on needles often lead to defoliation and can be especially damaging on young saplings;defoliation often leads to stunted growth and host plant death (Smith et al., 1997). Resulting necrotic needles are always without the reddish tint that is often characteristic of other infections of needles in Pinus species (CABI/EPPO, undated).
Dark-brown stromata fill the stomatal cavities, and numerous fruiting bodies appear as sooty spots on the lesions and, depending on their abundance, give a grey or black discolouration to the bands on the needles (Ivory and Wingfield, 1986). In warm, damp weather, small, grey brush-like tufts of elongate conidia may be just visible on the erumpent stromata (Ivory and Wingfield, 1986). Spermatia may also be extruded in tiny, clear droplets from spermagonia (Ivory, 1987). The distal portions of affected needles die rapidly and become colonized by various saprophytic fungi, whereas the proximal portions remain alive for some time (Ivory, 1987). Ivory and Wingfield (1986) also note that dead foliage may remain on the tree for many months but can be shed during high wind or heavy rain.
M. gibsonii affects many species of Pinus. Additionally, it has recently been reported on Abies nobilis [ Abies procera ] in Japan (Farr and Rossman, 2018). It is particularly associated with old seedlings in tree nurseries, but is also quite common on older trees of highly susceptible species such as P. canariensis, P. radiata and P. roxburghii. Other susceptible species include P. halepensis, P. pinaster and P. sylvestris (EPPO, 2018). It also occurs on senescing foliage and leaf litter of many species at a much lower incidence level (Ivory, 1994).
During field surveys carried out by Ivory (1994) in Africa, Asia, Central America and Oceania, the fungus was found on Pinus ayacahuite, P. canariensis, P. caribaea, P. clausa, P. densiflora, P. elliottii, P. greggii, P. halepensis, P. kesiya, P. luchuensis, P. massoniana, P. merkusii, P. muricata, P. oocarpa, P. patula, P. pinaster, P. pseudostrobus, P. radiata, P. roxburghii, P. rudis [ P. hartwegii ], P. sylvestris, P. taeda, P. thunbergii and P. wallichiana. Other reported host species include P. cembra, P. contorta, P. echinata, P. flexilis, P. jeffreyi, P. lambertiana, P. mugo, P. nigra, P. parviflora, P. pinea, P. ponderosa, P. resinosa, P. rigida, P. strobus, P. taiwanensis, P. tabuliformis (Braun et al., 2013), P. maximinoi, P. morrisonicola, P. tecunumanii (Chen, 1965), P. armandii, Tsuga canadensis and Abies nobilis (Farr and Rossman, 2018).
It must also be noted that the following conifer species were found to be susceptible to the pathogen under artificial inoculation experiments: Abies veitchii, A. sachalinensis, Cedrus deodara, Picea glehnii, P. jezoensis, Pseudotsuga menziesii (Suto, 1979;Diekmann et al., 2002) and Larix kaempferi (Kobayashi et al., 1979;Suto, 1979;Diekmann et al., 2002).