Plant Pathology (1994) 43, 1031-1034

NEW OR UNUSUAL RECORDS

Canker and die-back of Eucalyptus in South Africa caused byBotryosphaeria dothidea

H. SMITH, G. H. J. KEMP andU. J. WINGFIELDDepartment of Microbiology and Biochemistry, University of the Orange Free State, Box 339,Bloemfontein 9300, South Africa

Die-back and canker of several Eucalyptus species and clones were observed during a survey of the mostimportant forestry areas of South Africa. Disease was often associated with extreme environmentalconditions such as drought, hot winds and frost. Botryosphaeria dothidea, which is well known as acause of canker and die-back of Eucalyptus in other countries, was consistently isolated fromsymptomatic trees. Artificial inoculations of Eucalyptus nitens resulted in lesion development,confirming the pathogenicity of .B. dothidea to Eucalyptus in South Africa. This is the first report of thisdisease in South Africa.

The forestry industry in South Africa dependslargely on species of Pinus and Eucalyptus fromwhich it produces pulp, paper and structuraltimber. Commercial plantations cover approxi-mately 1-2 million ha, and about half of this areais planted with Eucalyptus spp. (Anonymous,1990). Despite the importance of eucalypts inSouth Africa, very little attention has been givento the possibility that diseases might be affectingthe value of the crop or the success of establish-ing plantations. Concern has been expressedregarding the potential impact of diseases on theindustry in view of the extensive monoculturesystem practised (Wingfield et al, 1991).

In a survey of Eucalyptus plantations during1991 and 1992, twig die-back and stem cankerswere found to be widespread on variousEucalyptus spp. (E. grandis, E. nitens, E.macarthurii and E. smithii), clones of E. grandisand hybrids of E. grandis with E. camaldulensisand E. urophylla. Twig die-back was tbe mostcommon symptom and occurred on youngcurrent-year shoots and terminal leader shoots.Trees most commonly affected ranged in agefrom 1 to 2 years. Dead shoots were black, oftencurled and retained dead leaves (Fig. la). Visibledie-back was preceded by a dark discoloration ofthe pith and immediate surrounding sapwood inproximate stem portions (Fig. lb).

Cankers were commonly observed on twigs,branches and main stems. On young twigs andbranches they were often associated with haildamage. The first sign of canker formation was

the presence of reddish-brown necrotic lesions inthe bark of young shoots. With the extension oflesions to the wood, small irregular cankers wereproduced on the branches, causing deformity(Fig. lc), and often became sites of windbreakage. In severe cases, large deformedcankers developed which exceeded the diameterof the trunk. The cankers were also associatedwith a characteristic blackish discoloration of theheartwood and pith. These types of cankers weremost commonly associated with youngerbranches and main stems of up to 3 years of age.

Main stem cankers were evident as cracks inthe bark exuding kino. The location and degreeof canker formation appeared to vary betweentrees, especially in seedling populations, suggest-ing differences in host resistance. In trees thatappeared relatively resistant, cankers were smalland localized around the point of infection,causing irregular zones of cracks. Cankers weredistributed much more widely on the trunks ofapparently less resistant trees, often extending tothe apex of the tree. Extensive cankering wasassociated with general discoloration of theheartwood in mature trees (Fig. 2a).

The bark of severely infected trees appearedreddish in color due to the extensive productionof kino, which is water soluble and spreads downthe stems after rain. Cankers caused the forma-tion of kino pockets in the sapwood (Fig. 2b)which were sometimes sufficiently large andnumerous to form kino rings (Fig. 2c). Treesmost commonly affected ranged in age from

1032 H. Smith et al.

Fig. 1. Symptoms on Eiaalvpms associated with infection by Boiryosphaeria dothidea (a) Shoot die-back ofEuiahpius iiiicns (har .^Omm) (b) Dark discoloration of the pith and immediate surrounding sapwood (arrowlassociated with die-back of i niu'n (bar - 5mm) (c) Stem-deforming cankers (arrow) on an E grandis clone(bar 3(.)mm)

3 lo 12 years. Such cxlcnsi\c kino productionrenders the wood unacceptable to pulp mills, as iiwould necessitate extended periods ot bleaching.The kino rings also weaken the wood causing itlo spill when used as slruclural limber

In most cases where die-back due lo Botrya-\phiurui di'thuLa leads to mortality, there wasapparently an association with cn\ironmentalconditions stressful to the trees Winds asso-ciated with hot temperatures, hail, frost anddrought olten occur in certain areas andprobably served as predisposing laclors forinleclion by B dulhuka Therefore B dulhuUaintections on predisposed trees were ofteneonspicuous. leading to severe die-back, canker-ing and in some instances mortality, especially inthe case ol 1 2 year-old transplants There were,however, some clones and hybrids thai tended totoleralc damage by regenerating lerminal leadershoois. atid showed only reduced growth, fork-ing and slem delormalion

I'erithecM ol Ii Jmhuhu (Moug ) (. es el deNo( ( H nl'isi lude I , )(;rossenb iV Hugger)w e i c o i . c a s i ( i M , i l l \ o b s e r v e d o n d e , i d t w i g s I l i e s e

u e i e d a i k , i i u l s l u u l i i e c k e i l Xsci v s e r e b i t u n i c a l e

( " ' I l-''li - I ' l 24/ /111) .Mid e , K h c o i i u i i n e d e i g h t

ascospores. Ascospores (16 25 x 7 -10 ^m) wereunicellular, hyaline and ovoid. Corudiomatawere frequently observed on dead and dyingtissue These v\ere dark, ostiolate pycnidia.Conidiogenous cells developed from the innerwalls of pycnidia and the first conidia developedholoblastically Conidia e.xuded frotn thepycnidia in white masses during pienods of highrelative humidity Conidia ( P - 2 5 x 5-//im)were unicellular, hyaline and vaned fromellipsoidal lo fusiform vMth distinctU truncatebases. The conidia of some isolates becamedarker with ago and developed tv\o to threesepta prior lo germinaiion Gemiinatmg conidiahad one or two germ tubes ongmating eitherfrom or near the apices

Single-spore isolates vsere made on v̂ ater agartroni spore masses emerging from pentheciaand pycnidia fomied on dead shoots in thelield Cierminating ascospores and conidia weretransferred lo 2°u malt extract agar (Biolab)plates and incuhated at 20"C under continuouscool Huorescent light to stitiiulate sporulation.C oliniies were inilialh white and fluffy, becom-ing dark brown lo black with age. Conidiomatawere generally formed after 2 weeks but

New or unusual record.s 1033

Fig. 2. Symptoms on Eucalyptus associated with infection by Bdlryusphucnci doihuku (a) Exlensuc hca r tuooddiscoloration of a mature E. grandis clone (bar = .^5mm) (b) Kjno (resin) pockets formed in the sapwood (arrow)associated with cankers on E nitens (bar = 40 mm). (c) Ring of kino in the sapwood (arrows) of an H graiuhs clone(bar = 40 mm).

occasiotially colonies lost their pigmentation andfailed to sporulate, even after 30 daysof incubation. The teleomorph was neverobserved in culture and attempts to induceteleomorph formation by painng isolates wereunsuccessful.

Pathogenicity tests were conducted on 2-year-old E. nitens during February 1989 in the PietRetief area. South Africa, using an isolatefrom E. nitens growing in the same areaTwenty trees (approximately 50 mm in dia-meter) were inoculated by removing a single6-mm diameter piece of bark (I m above soillevel) on each tree with a cork-borer. The barkdiscs were replaced with discs of MEA from a1-week-old culture of B. dothidea. Twentycontrol trees were inoculated with sterile MEAdisks. Wounds were sealed with masking tape.After 3 months lesions had developed on all treesinoculated with B. duthidca, whereas all of thecontrol inoculation wounds had healed. Lesionswere in the range 32 64 mm long with a mean of42-3 mm. B. dothidea was re-isolated from alllesions resulting from inoculation.

In South Africa, B. dothidea has been

previously isolated from leaves of F.ucalvptusspecies (Crous et al.. 1989) but this is thefirst report of it being associated with twig die-back, cankers iind mortdluy of euciilypis. Thefungus has previousK been reported to causecanker and die-back diseases ot Eiaalvpiii.^species in Australia and the USA (Da\ ison &Tay. 19S3; Webb. 1983. Barnard cl al. 19X7.Shearer et al. 1987). Webb (1983) reported theabandonment of commercial seed production ofE cainalduknsis because ot the impact otdiseases caused b> B Jaihuha. but all otherreports were of isolated problems Shearer i i al(1987) reported the death ot h. raihaia inselection trails. DaMson & Ta> (l'JS3) reportedthe natural occurrence of B doihuica cankers in£. marginata forests and Barnard c7 al (I'^S^)reported B dothuka \o be invoKcd m a con-iple\of organisms that cause coppice t.iilurc otE grandi\ The damage in South M n c a iswidespread and may be more seNere. with moresigniticant mortality, than cNe\\ here

B. dothidea is ihe most economicalK importantand well-documented species in the genus andcauses diseases on various woods hosts (Snuth.

1034 H. Smith et al.

1934; Punithalingam & HoUiday, 1973). Stress isknown as a major factor contributing to diseasedevelopment caused by Botryosphaeria spp.Stresses that have been reported to predisposeplants to invasion by Botryosphaeria spp, andto subsequent disease development includedrought, freezing and defoliation (Crist &Schoeneweiss, 1975; Wene & Schoeneweiss,1980; Pusey, 1989). Indeed, Botryosphaeria spp.are, in general, considered to be opportunisticstress and wound related pathogens. As notedabove. South Africa has a harsh and extremeclimate, and these factors may play an importantrole in the epidemiology of B. dothidea oneucalypts.

B. dothidea may become one of the mostimportant pathogens of Eucalyptus in SouthAfrica. Strategies to avoid losses, includingscreening species, clones and hybrids for toler-ance of this disease, are therefore currently beingimplemented.

REFERENCESAnonymous, 1990. The South African forestry and

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Crist CR, Schoeneweiss DF, 1975. The influence ofcontrolled stresses on susceptibility of European

White Birch stems to attack by Botryosphaeriadothidea. Phytopathology 65,369-73.

Crous PW, Knox-Davies PS, Wingfield MJ, 1989.Newly-recorded foliage fungi of Eucalyptus spp. inSouth Africa. Phytophylactica 21, 85-8.

Davison EM, Tay CS, 1983. Twig, branch and uppertmak cankers of Eucalyptus marginata. PlantDisease 67, 1285-7.

Punithalingam E, HoUiday P, 1973. Botryosphaeriaribis. CMI Descriptions of Pathogenic Fungi andBacteria No. 395.

Pusey PL, 1989. Influence of water stress on suscep-tibility of non wounded peach bark to Botryosphaeriadothidea. Plant Disease 73,1000-3.

Shearer BL, Tippett JT, Bartle JR, 1987. Botryo-sphaeria ribis infection associated with death ofEucalyptus radiata in species selection trails. PlantDisease 71, 140-5.

Smith CO, 1934. Inoculation showing the wide hostrange of Botryosphaeria ribis. Journal of AgriculturalResearch 49,467-76.

Webb RS, 1983. Seed capsule abortion and twig die-back of Eucalyptus camaldulensis in South Floridainduced by Botryosphaeria ribis. Plartt Disease SI,108-9.

Wene EG, Schoeneweiss DF, 1980. Localized freezingpredisposition to Botryosphaeria canker in difleien-tially frozen woody stems. Canadian Journal ofBotany 58, 1455-8.

Wingfield MJ, Swart WJ, Kemp GHJ, 1991, Pathologyconsiderations in clonal propagation of Eucalyptuswith special reference to the South African situation.In: Proceedings of the 1991 WFRO Symposiian-Intensive-Forestry the Role of Eucalyptus, 811-20.