Threats

Calonectria leaf blight (CLB)

Calonectria leaf blight (CLB)
Calonectria De Not.

Cylindrocladium Morgan

Typical symptoms include damping off, root rot, discrete pale brown leaf spots, leaf blight, shoot blight, stem cankers and root disease of Eucalyptus (Crous 2002). Species in the Calonectria pteridis complex, which include important pathogens in South America, cause small (1-7 mm diam), round or elongated leaf spots, that are initially pale grey, becoming pale brown. Other species such as those in the Ca. candelabra complex, cause large, pale brown leaf botches (Alfenas et al. 2013). In China, South-East Asia and Australia, species in the Ca. retaudii complex are the most common causal agent of CLB. The disease first appears as greyish water-soaked spots on young leaves that coalesce and develop into extensive necrotic areas. Necrotic lesions cover the entire area of the leaf resulting in leaf and shoot blight symptoms (Old et al. 2003). Defoliation caused by CLB decreases timber volume due to the reduced photosynthetic area.

According to Crous et al. (2019), there are 37 species of Calonectria confirmed to cause CLB on Eucalyptus.

The sexual morphs of Calonectria are characterised by yellow to dark red ascomata, with scaly to warty walls, and clavate, 4–8-spored asci. They produce “Cylindrocladium” asexual morphs with branched conidiophores, cylindrical, septate conidia, and stipe extensions with terminal vesicles (Crous 2002; Lombard et al. 2010, 2016; Pham et al. 2019).

Life cycle of Ca. candelabrum (Crous et al. 1991).

1985 - Ca. candelabrum on Eucalyptus (Lundquist & Baxter 1985) as Cylindrocladium scoparium.
KwaZulu-Natal, Mpumalanga, Northern Province, Western Cape

Gallery

Life cycle of Ca. candelabrum
Calonectria leaf spot on E. urophylla x E. tereticornis hybrid
Calonectria symptoms on Eucalyptus leaves
Early infection of E. urophylla x E. grandis hybrid with Calonectria
Calonectria leaf blight in Eucalyptus plantation
Calonectria leaf blight in China

Alfenas RF, Pereira OL, Jorge VL, Crous PW, Alfenas AC. 2013. A new species of Calonectria causing leaf blight and cutting rot of three forest tree species in Brazil. Tropical Plant Pathology 38: 513-521.

Crous PW. 2002. Taxonomy and pathology of Cylindrocladium (Calonectria) and allied genera. American Phytopathological Society, Minnesota, USA.

Crous PW, Phillips AJL, Wingfield MJ. 1991. The genera Cylindrocladium and Cylindrocladiella in South Africa, with special reference to forest nurseries. South African Forestry Journal 157: 69-85.

Crous PW, Wingfield MJ, Cheewangkoon R, Carnegie AJ, Burgess TI, et al. 2019. Foliar pathogens of eucalypts. Studies in Mycology 94: 125-298.

Lombard L, Crous PW, Wingfield BD, Wingfield MJ. 2010. Species concepts in Calonectria (Cylindrocladium). Studies in Mycology 66: 1-13.

Lombard L, Wingfield MJ, Alfenas AC, Crous PW. 2016. The forgotten Calonectria collection: Pouring old wine into new bags. Studies in Mycology 85: 159-198.

Lundquist JE, Baxter AP. 1985. Fungi associated with Eucalyptus in South Africa. South African Forestry Journal 135: 9-19.

Old KM, Wingfield MJ, ZiQing Y. 2003. A manual of diseases of eucalypts in South-East Asia. Center for International Forestry Research, Indonesia.

Pham NQ, Barnes I, Chen S, Liu F, Dang QN, et al. 2019. Ten new species of Calonectria from Indonesia and Vietnam. Mycologia 111: 78-102.