Fusarium head blight (FHB; scab), primarily caused by Fusarium graminearum, is a devastating disease of wheat worldwide. FHB causes yield reductions and contamination of grains with trichothecene mycotoxins such as deoxynivalenol (DON). The genetic variation in existing wheat germplasm pools for FHB resistance is low and may not provide sufficient resistance to develop cultivars through traditional breeding approaches. Thus, genetic engineering provides an additional approach to enhance FHB resistance. The objectives of this study were to develop transgenic wheat expressing a barley class II chitinase and to test the transgenic lines against F. graminearum infection under greenhouse and field conditions. A barley class II chitinase gene was introduced into the spring wheat cultivar, Bobwhite, by biolistic bombardment. Seven transgenic lines were identified that expressed the chitinase transgene and exhibited enhanced Type II resistance in the greenhouse evaluations. These seven transgenic lines were tested under field conditions for percentage FHB severity, percentage visually scabby kernels (VSK), and DON accumulation. Two lines (C8 and C17) that exhibited high chitinase protein levels also showed reduced FHB severity and VSK compared to Bobwhite. One of the lines (C8) also exhibited reduced DON concentration compared with Bobwhite. These results showed that transgenic wheat expressing a barley class II chitinase exhibited enhanced resistance against F. graminearum in greenhouse and field conditions.

Rates of haustorium formation by Erysiphe graminis f.sp. hordei were determined for epidermal tissues of primary leaves of a near-isogenic pair of barley (Hordeum vulgare) lines, AlgR and AlgS, which differed at the Mla locus for compatibility with the fungus. Epidermal cells were divided into two classes, namely shorter or longer than 450 μm. Cells near stomatal files were always short, whereas cells more distant from stomata were long on the abaxial surface, long on the adaxial surface over vascular bundles, but short on the adaxial surface when not over vascular bundles. At 24 h after inoculation, haustoria were formed in 70–80% of attacked short cells but in only 15–20% of attacked long cells. When haustoria were absent, papillae were present, so papilla-associated resistance was more frequent in long than in short cells. However, the percentage of attacked sites with papillae was the same in AlgR and AlgS, indicating that papilla-associated resistance was not related to Mla incompatibility. In AlgR, patterns of development showed that haustoria were produced before Mla incompatibility was expressed by hypersensitive cell death. Key words: papilla, hypersensitive, barley, epidermis, resistance, powdery mildew.

ZEYEN, R. J.. ;111d W. R. BUSHNELL. 1979. response of barley epidermal cells causecl by Et:~,.si/~hr gr~trri~irri.~: I-ate and method of deposition determined by rnicrocinemutogfi~phy and tr':~nsmission electron mic~'oscopy. Can. J. Bot. 57: 898-913. Papillae were cleposited in barley epitle~mal cells directly heneath appressoria of Et:vsiplrt, gt.o/irirli.c f. sp. Irordri anti appeal-ed as hemispherical, intel-nal wall appositions. The papilla {response began shortly after the formation of a ~.apitlly moving cytopl:~smic ;tggl.egate beneath the appressorium. As tlocumentetl in coleoptile tissue hy time-lapse light microcinematogl-aphy, the papillae grew ~xpitlly for 20-30min after becoming visible, their-I-atlii increasing by 0. I l~mlmin. For small papillae. tleposition continued for about 30rnin; for larger papillae, deposition continuetl for 120-180min. R e s~~l t s with tl'ansmission electron microscopy on leaf epidermal cells s~~ggested that papilla deposition by host cytoplasmic aggregates can be divided into ~O L I I .sequenti211 stages: (i) the tleposition of osrniophilic (lipidic) m:~te~.i:~ls. (ii) the deposition and partiill compaction of nonosmiophilic, amorphous material (probably insol~~ble polysaccharitles). (iii) compaction of nonosmiophilic, 21mo1-phous material, and (iv) the incorpo~.ation of osmiophilic material into the host wall and into the compacted nonosmiophilic, amorphous material. At maturity, the papillae are h:~rtlenecl, electron-opaque wall appositions that may be effective in preventing fungal penetration iuitl development. Failure of papillae to prevent fungal penetration and development may be related to the inability of the epidermal cells to complete the entire sequence of events in papilla deposition befol-e attempted fungal penetration. Z E Y E N ,R. J., et W. R. BUSHNELI.. 1979. Papilla response of barley epidermal cells caused by Ery.si/~l~e grtrrr~ir~is: rate and method of deposition determined by microcinematography and transmission electron microscopy. Can. J. Bot. 57: 898-913. Dans les cellules epidermiques de I'orge, les papilles se deposent dil-ectement SOLIS I'appressorium de I'B?;siphc grtrtni~~is f.sp. I~ortlri, et apparaissent SOLIS forme d'appositions parietales internes hemispheriq~~es. La reaction papillaire commence peu de temps aprts la formation d '~~n itgre~it cytoplasmique i mouvement rapide SOLIS I'appressorium. Sur des tiss~ls de coleoptiles e t~~d~e s par la microcinematoglaphie intermittente, on constate que les papilles croissent ~xpide-ment pendant 20-30 min apses l e~~r apparition alors que leur rayon augmente de 0. I pmlmin. La deposition continue pendant environ 30 min P O L I~ les petites papilles et 120-180 min pour les grosses. En microscopie electronique par t~xnsmission, I'observation de cellules epidermiques foliaires indique que la deposition de la papille par les agregats cytoplasmiques de I'hbte peut etre divisee en quatre stades successifs: (i) la deposition de materiaux osmiophiles (lipidiques), (ii) la tleposition et la compaction pa...

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Fusarium head blight (FHB) of wheat, caused by Fusarium graminearum and other Fusarium species, is a major disease problem for wheat production worldwide. To combat this problem, large-scale breeding efforts have been established. Although progress has been made through standard breeding approaches, the level of resistance attained is insufficient to withstand epidemic conditions. Genetic engineering provides an alternative approach to enhance the level of resistance. Many defense response genes are induced in wheat during F. graminearum infection and may play a role in reducing FHB. The objectives of this study were (1) to develop transgenic wheat overexpressing the defense response genes α-1-purothionin, thaumatin-like protein 1 (tlp-1), and β-1,3-glucanase; and (2) to test the resultant transgenic wheat lines against F. graminearum infection under greenhouse and field conditions. Using the wheat cultivar Bobwhite, we developed one, two, and four lines carrying the α-1-purothionin, tlp-1, and β-1,3-glucanase transgenes, respectively, that had statistically significant reductions in FHB severity in greenhouse evaluations. We tested these seven transgenic lines under field conditions for percent FHB disease severity, deoxynivalenol (DON) mycotoxin accumulation, and percent visually scabby kernels (VSK). Six of the seven lines differed from the nontransgenic parental Bobwhite line for at least one of the disease traits. A β-1,3-glucanase transgenic line had enhanced resistance, showing lower FHB severity, DON concentration, and percent VSK compared to Bobwhite. Taken together, the results showed that overexpression of defense response genes in wheat could enhance the FHB resistance in both greenhouse and field conditions.