Threats

Botryosphaeria canker and die-back

Botryosphaeria canker and die-back
Botryosphaeria dothidea (Mout. ex FR.) Ces. & De Not.
Canker

A wide range of symptoms have been associated with Botryosphaeriaceae species on Eucalyptus spp. A common manifestation of infection is the death of tree tops (Fig. 1). This leads to infection of the pith and a core of discoloured wood surrounded by a healthy sheath of outer wood (Fig. 2) that often extends throughout the entire length of the tree. These symptoms are common on E. grandis or clones of this species and often develops after tees have been exposed to hot winds. A similar symptom is known in E. nitens after growing tips of young (one or two year-old) trees have been damaged by late frost. 

One of the most serious symptoms associated with Botryosphaeriaceae species infection is the development of stem cankers. These cankers are more common on trees stressed by drought and are characterised by stem swelling, bark cracks and exudation of copious amount of black kino. In severe situations, similar symptoms are found on lateral branches and stems often break at the sites of cankers (Fig. 3).

Bot4. Fruiting structures with abundant mature dark conidia (Li et al. 2018)

Bot5. Neofusicoccum ursorum Pavlic, Maleme, Slippers & M.J. Wingf. (Crous et al. 2013)

Bot6. Neofusicoccum cryptoaustrale Pavlic, Maleme, Slippers & M.J. Wingf. (Crous et al. 2013)

The Botryosphaeriaceae are endophytes that penetrate plants, grow intercellularly and are transmitted horizontally. This group of fungi infect the plants via both natural apertures and wounds. The infection requires high humidity or free water. Conidia can be trapped among bud scales resulting in subsequent infection of the buds. The germ tubes emerge from conidia and grow inside tissues. The natural openings include stomata on leaves and shoots, and lenticels either on fruit or stems, as well as on the inflorescences, pedicels or peduncles of fruit trees which provide avenues for infection. Wounds result from human activities such as pruning, hand-picking of fruit, grafting, or via scars when scales, buds, petioles and fruit abscise. Large numbers of isolates have been obtained from graft unions, suggesting transmission by grafting tools. Other sources of wound infections include those attributed to branch splitting caused by wind, frost and hail damage or wounds naturally formed during root growth can be infected by the presence of inoculum on residual diseased plant material on the ground (Mehl et al. 2013).

1994 (Smith et al. 1994)
Eastern Cape, Free State, Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga, Northern Cape, North West, Western Cape
Unknown

Gallery

Dieback of tops of E. grandis after hot wind and cankers caused by Botryosphaeria

Crous P, Wingfield MJ, Guarro J, Cheewangkoon R, Van der Bank M, et al. 2013. Fungal Planet description sheets: 154-213. Persoonia: Molecular Phylogeny and Evolution of Fungi 31:270-271.

Li G, Liu F, Li J, Liu Q, Chen S. 2018. Botryosphaeriaceae from Eucalyptus plantations and adjacent plants in China. Persoonia 40:63-95.

Mehl JWM, Slippers B, Roux J, Wingfield MJ, Gonthier P, et al. 2013. Cankers and other diseases caused by the Botryosphaeriaceae. In: Gonthier P, Nicolotti G. (Eds.), Infectious forest diseases. CAB International, Oxon, UK 298-317.

Pavlic-Zupanc D, Maleme HM, Piškur B, Wingfield BD, Wingfield MJ, Slippers B. 2017. Diversity, phylogeny and pathogenicity of Botryosphaeriaceae on non-native Eucalyptus grown in an urban environment: A case study. Urban Forestry & Urban Greening 26: 139-148.

Pillay K, Slippers B, Wingfield MJ, Gryzenhout M. 2013. Diversity and distribution of co-infecting Botryosphaeriaceae from Eucalyptus grandis and Syzygium cordatum in South Africa. South African Journal of Botany 84: 38-43.

Slippers B, Fourie G, Crous PW, Coutinho TA, Wingfield BD, Carnegie AJ, Wingfield MJ. 2004. Speciation and distribution of Botryosphaeria spp. on native and introduced Eucalyptus trees in Australia and South Africa. Studies in Mycology, 343-358.

Slippers B, Wingfield MJ. 2007. Botryosphaeriaceae as endophytes and latent pathogens of woody plants: diversity, ecology and impact. Fungal Biology Reviews 21: 90-106.

Smith H, Crous PW, Wingfield MJ, Coutinho TA, Wingfield BD. 2001. Botryosphaeria eucalyptorum sp. nov., a New Species in the B. dothidea Complex on Eucalyptus in South Africa. Mycologia 93: 277-285.

Smith H, Kemp GHJ, Wingfield MJ. 1994. Canker and die-back of Eucalyptus in South Africa caused by Botryosphaeria dothidea. Plant Pathology 43: 1031-1034.