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A Scanning Electron Microscopic Study of the Infection of Water Oak (Quercus Nigra) by Taphrina Caerulescens

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A Scanning Electron Microscopic Study of the Infection of Water Oak (Quercus Nigra) by Taphrina Caerulescens View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by SFA ScholarWorks Stephen F. Austin State University SFA ScholarWorks Faculty Publications Biology 2000 A Scanning Electron Microscopic Study of the Infection of Water Oak (Quercus nigra) by Taphrina Caerulescens Josephine Taylor Stephen F Austin State University, Department of Biology, [email protected] Dale O. Birdwell Follow this and additional works at: http://scholarworks.sfasu.edu/biology Part of the Biology Commons, and the Plant Sciences Commons Tell us how this article helped you. Recommended Citation Taylor, Josephine and Birdwell, Dale O., "A Scanning Electron Microscopic Study of the Infection of Water Oak (Quercus nigra) by Taphrina Caerulescens" (2000). Faculty Publications. Paper 88. http://scholarworks.sfasu.edu/biology/88 This Article is brought to you for free and open access by the Biology at SFA ScholarWorks. It has been accepted for inclusion in Faculty Publications by an authorized administrator of SFA ScholarWorks. For more information, please contact [email protected]. Mycological Society of America A Scanning Electron Microscopic Study of the Infection of Water Oak (Quercus nigra) by Taphrina caerulescens Author(s): Josephine Taylor and Dale O. Birdwell Source: Mycologia, Vol. 92, No. 2 (Mar. - Apr., 2000), pp. 309-311 Published by: Mycological Society of America Stable URL: http://www.jstor.org/stable/3761566 Accessed: 07-10-2015 16:18 UTC Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://www.jstor.org/page/ info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Mycological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Mycologia. http://www.jstor.org This content downloaded from 144.96.121.100 on Wed, 07 Oct 2015 16:18:04 UTC All use subject to JSTOR Terms and Conditions Mycologia,92 (2), 2000, pp. 309-311. ( 2000 by The MycologicalSociety of America,Lawrence, KS 66044-8897 A scanning electron microscopic study of the infection of water oak (Quercusnigra) by Taphrina caerulescens Josephine Taylor1 ly inoculated bur oak (Quercus macrocarpaMichx.) Dale 0. Birdwell with cultured cells of T. caerulescensand used light Departmentof Biology, Stephen F Austin State microscopyto visualize cotton blue stained leaves at University,Nacogdoches, Texas 75962 approximately3 wk post inoculation. She observed hyphal strandsentering host stomata. Our research reports the use of scanning electron microscopy Abstract: The fungal pathogen Taphrina caerules- (SEM) to visualize infectionstructure development cens was isolated from leaves of water oak (Quercus by T caerulescensand documents the sequence of nigra) exhibiting symptoms of oak leaf blister. eventsinvolved in the transitionfrom saprophytic to Healthy leaves were inoculated with a suspension of parasiticgrowth in this species. cells from pure culture in order to examine the in- Pathogenisolation.-Leaf tissue of water oak (Quercusnigra fection process. Scanning electron microscopy was L.) bearingasci of T. caerulescenswas fastened to petridish used to monitor of T. caerulescenscells, for- budding lids overpotato dextrose (Martin 1925). Sporeswere dis- and of mation of germ tubes, indirect penetration chargedonto the agar within24 h and isolatedcolonies leaf tissue through stomata, which occurred within (blastosporesoriginating from single asci) thatformed were 48 h post-inoculation. Direct penetration was not ob- transferredto freshmedia and incubatedat 4 C. Cultures served. grewas yeast-likecells that exhibited frequent budding. No Key Words: conidia, indirect penetration, infec- mycelialgrowth was evident.Characteristics of theisolates tion process, oak leaf blister were consistentwith previous reports (Martin 1925, Mix 1924, 1949). Cell width(N = 20) from2-wk-old cultures was2.68 + 0.73 iLm.Colony diam at thistime was 9-13 mm. Colonieswere opaque and pale pinkin color,turning a Taphrina caerulescens (Mont. & Desm.) Tul. is a plant darkershade of pink with age. Theywere circular with en- pathogenic fungus that causes oak leaf blister disease. tiremargins and viscid in consistency,having a smooth,glis- Infected leaves develop raised, irregular lesions in teningappearance. early spring, with leaf tissue necrosing by midsum- Inoculation.-Culturedcells from a single2-wk-old isolate mer. Oak leaf blister results in defoliation and some- (approximately1.35 X 109 cells/mL)were suspended in times death of various oak species in the southern 0.01% Tween80 and atomizedonto the lowersurfaces of USA (Mix 1949, Horst 1978). leavesnewly emerged from buds on 2-mo-oldgreenhouse Taphrina caerulescens is an ascomycete with both grownwater oak seedlings(Martin 1925, Mix 1924). Inoc- parasitic and saprophytic phases that have varying ulatedseedlings were covered with plastic bags and main- morphologies (Sinclair et al 1987). In the parasitic tainedin a growthchamber (22 C). For microscopicex- phase, the pathogen infects leaves at the time they aminationsamples were taken at 24 and 48 h postinocu- emerge from buds. Infection stimulates hypertrophy lation.The experimentwas repeated three times. and hyperplasia in the host to produce a blisterlike Samplepreparation.-Inoculated leaf pieces were fixed over- overgrowth, and a layer of asci emerges on the leaf nightat 4 C in a 1:1 mixtureof 5% glutaraldehydeand 100 surface. Blastospores, often referred to as conidia, mM potassiumphosphate buffer, pH 6.8. The tissuethen bud directly from ascospores while they are still with- wasrinsed in 50 mMbuffer and postfixed in a 1:1 mixture in the ascus. These blastospores are discharged forc- of2% Os04 and 100mM buffer for 2 h at 4 C (Mims1981). ibly and can reinfect the host or give rise to the sap- Followingthorough rinsing in distilledwater, specimens were in a ethanolseries to rophytic phase, in which the fungus grows in a yeast- dehydrated graded 100% etha- nol. like form. Some of these somatic cells overwinter on Leaf pieceswere critical point dried with carbon di- oxide as the transitionfluid, mounted on specimenstubs, twigs or among bud scales and can cause new infec- and sputtercoated with gold-palladium. Samples were ex- tions in the Mix spring (Fitzpatrick 1934, 1935). aminedwith a HitachiS-405A scanning electron micro- The infection process in oak leaf blister disease has scopeoperating at 15 KV. not been characterized fully.Martin (1925) artificial- Observations.-SEM revealed that many T caerules- Accepted for publicationSeptember 23, 1999. censconidia on the host leaf surfaceexhibited bud- 1 Email:[email protected] ding withinthe first24 h followinginoculation (FIG. 309 This content downloaded from 144.96.121.100 on Wed, 07 Oct 2015 16:18:04 UTC All use subject to JSTOR Terms and Conditions 310 MYCOLOGIA FIGS. 1-6. Scanning electron micrographs of water oak leaf surfaces inoculated with T caerulescens. 1. At 24 h post inoculation.Budding conidia (C); buds indicated at arrowheads.2-6. At 48 h post inoculation.2. Earlystages in germ tube (G) formation.3, 4. Branched germ tubes (at arrowheads) and stomatalpenetration (S). Germ tube (G) thatgrew over a closed stoma is presentin upper leftof 3. 5, 6. Conidia (C), short,unbranched germ tubes (G), and stomatalpenetration (S). Bars = 5 p.m. This content downloaded from 144.96.121.100 on Wed, 07 Oct 2015 16:18:04 UTC All use subject to JSTOR Terms and Conditions TAYLORAND BIRDWELL:INFECTION BY T. CAERULESCENS 311 1). A bud formed at one end of the conidium, and indirectpenetration would be difficultto detect us- a constrictionwas prominentat the point of delimi- ing the techniques of Fitzpatrick(1934) and Mix tationbetween the parent cell and the newlyformed (1935). Clearing or sectioningeasily could displace spore. the longer, branching germ tubes observed in this Budding was observed infrequentlyin the 48 h study.Additionally, Mix (1935) inoculated emerging post inoculation samples. At this time period, ap- leaves before stomatalopenings had fullydifferenti- proximately20% of conidia present had formed ated. germ tubes (FIGS. 2-6). Germ tubes emerged from Although not observed in this investigation,it is the apical end of each conidium (FIG. 2), and had a probable that T caerulescensis capable of directly long, thinmorphology that was verydistinct from the penetratingan intact host leaf in the absence of a shape and size of immaturebuds. Germ tubes fre- naturalopening. This speculationis supportedby ob- quentlygrew to extensivelengths. Longer germtubes servationsof concave, ascus bearing depressionson were usuallybranched (FIGS. 3, 4), and theirgrowth both upper and lower leaf surfaces of water oak appeared random ratherthan directional.Germ tube (Birdwell 1996), with stomata present only on the tips were observed to extend over guard cells and lower surface.Hyphae of T caerulescensare subcutic- into stomatal openings (FIG. 3). Occasionally these ular and intercellularin the epidermis (Camp and hyphalstrands grew over closed stomata(FIG. 3). Tilt- Whittingham1974) and not known to traversethe ing of samples revealed that germ tubes were ap- mesophyll like those of T. deformans(Fitzpatrick pressed closelyto the host leaf surface,following
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