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Resistance to both barley yellow dwarf virus (BYDV) and cereal yellow dwarf virus (CYDV) has been demonstrated in wheat genetic stocks with Thinopyrum intennedium chromatin. A number of resistance-bearing translocations have been reported on chromosome arm 7DL from two independent Th. intermedium sources; one source is the addition line Ll and the other is the spontaneous substitution line P29. Another source of resistance in wheat cytogenetic stocks is available as a 2Ai(2D) substitution line. We used a set of 38 molecular markers and the available deletion stocks to compare the size of the 7DL translocations more comprehensively than has been done previously. We also compared the efficacy of BYDV resistance of the various genetic stocks both before and after transfer to a common genetic background. TC14 was confirmed as carrying the smallest translocation, replacing about 20% of the distal end of 7DL. TO and TC10 had 90% of the chromosome arm replaced by Th. intermedium chromatin; the proximal 10% corresponded to wheat chromatin. YW642 appeared to have the whole 7DL replaced by Th. intennedium chromatin, as confirmed by the co-dominant marker cfd68 mapping on the bin nearest the centromere. Translocation line P961341 had bins 3, 7, and 8 replaced by Th. intermedium chromatin, making this the second smallest translocation with BYDV and CYDV resistance. The translocation sizes reported here differ from some of the previous estimates. The translocated Th. intennedium segments appeared to be bigger than the replaced wheat 7DL fragments. All the resistances derived from the Ll and P29 group 7 chromosomes and the 2Ai#2 chromosome were effective in reducing the number of infected plants and the mean virus titre, regardless of the background. Some evidence is discussed suggesting the long arm of the Th. intermedium group 7 chromosome 7Ai#1 carries two resistances, the distal Bdv2 and a proximal second gene. Key words: Luteovirus, intermediate wheatgrass, CYDV, alien translocations, EST derived markers. La resistance au virus de la jaunisse nanisante de l'orge (BYDV) et au virus de la jaunisse nanisante des cereales (CYDV) a ete documentee chez des lignees de ble possedant de la chromatine provenant du Th. intennedium. Plusieurs translocations conferant la resistance ont ete rapportees sur le chromosome 7DL en provenance de deux sources independantes du Th. intennedium. L'une de celles-ci est la lignee d'addition Ll et l'autre est la substitution spontanee P29. Une autre source de resistance au sein des stocks genetiques du ble est disponible sous la forme d'une substitution 2Ai(2D). Les auteurs ont employe 38 marqueurs moleculaires et les deletions disponibles pour comparer la taille des translocations 7DL de maniere plus precise que cela n'avait ete fait anterieurement. Les auteurs ont egalement compare l'efficacite de la resistance au BYDV chez les diverses lignees avant et apres leur introduction dans un meme fond genetique. TC14 a ete confirmee comme etant la translocation la plus petite puisqu'elle remplace environ 20 % de l'extremite distale de 7DL. Chez TC5 et TC10, 90 % du bras chromosomique a ete remplace par la chromatine du Th. intermedium; le 10 % proximal etant constitue de chromatine du ble. Au sein de YW642, la totalite de 7DL semble avoir ete remplacee par la chromatine du Th. intermedium tel que confirme par le marqueur codominant cfd68, lequel est situe dans le segment le plus rapproche du centromere. Dans la translocation P961341, les intervalles (<< bins >>) 3, 7 et 8 etaient remplaces par la chromatine du Th. intermedium, ce qui en fait la seconde plus petite translocation conferant la resistance au BYDV et au CYDV. Les tailles des translocations rapportees dans ce travail different de certaines des estimations anterieures. Les segments provenant du Th. intermedium semblent plus grands que les regions remplacees au sein du bras 7DL du ble. Toutes les resistances examinees, derivees des chromosomes du groupe 7 chez Ll et P29 ainsi que du chromosome 2Ai#2, permettaient de reduire le nombre de plantes infectees et la charge virale moyenne sans egard au fond genetique. Les auteurs discutent certaines evidences suggerant que le bras long du chromosome de groupe 7 chez le Th. intennedium (7Ai#1) porterait deux resistances, le gene distal Bdv2 et un second gene proximal. Mots-cles : Luteovirus, agropyron intermediaire, CYDV, translocations interspecifiques, marqueurs derives d'EST. [Traduit par la Redaction], Introduction The cereal diseases caused by barley yellow dwarf viruses are now known to be caused by two related species, Barley yellow dwarf virus (BYDV, genus Luteovirus, family Luteoviridae) and [...]

Wheat streak mosaic virus (WSMV), vectored by Wheat curl mite, has been of great economic importance in the Great Plains of the United States and Canada. Recently, the virus has been identified in Australia, where it has spread quickly to all major wheat growing areas. The difficulties in finding adequate natural resistance in wheat prompted us to develop transgenic resistance based on RNA interference (RNAi). An RNAi construct was designed to target the nuclear inclusion protein 'a' (NIa) gene of WSMV. Wheat was stably cotransformed with two plasmids: pStargate-NIa expressing hairpin RNA (hpRNA) including WSMV sequence and pCMneoSTLS2 with the nptII selectable marker. When T(1) progeny were assayed against WSMV, ten of sixteen families showed complete resistance in transgenic segregants. The resistance was classified as immunity by four criteria: no disease symptoms were produced; ELISA readings were as in uninoculated plants; viral sequences could not be detected by RT-PCR from leaf extracts; and leaf extracts failed to give infections in susceptible plants when used in test-inoculation experiments. Southern blot hybridization analysis indicated hpRNA transgene integrated into the wheat genome. Moreover, accumulation of small RNAs derived from the hpRNA transgene sequence positively correlated with immunity. We also showed that the selectable marker gene nptII segregated independently of the hpRNA transgene in some transgenics, and therefore demonstrated that it is possible using these techniques, to produce marker-free WSMV immune transgenic plants. This is the first report of immunity in wheat to WSMV using a spliceable intron hpRNA strategy.

Thinopyrum intermedium translocations derived from the wheat (Triticum aestivum L.) substitution line P-29 were previously characterized by RFLP. We have further analyzed these lines and additional related germplasm with publicly available STS and SSRs. Primers which showed a polymorphism between wheat and P-29, were tested in all recombinant and nulli-tetrasomic lines confirming their position on chromosome 7D. The resulting 7D/7E chromosome maps appeared as a mosaic of wheat and Th. intermedium chromatin sections. To verify the composition of the translocation lines suggested by the RFLP-PCR map, F(2) progeny of two crosses (CS/216-1 and CS/260-1) were analyzed with molecular markers. Both populations gave an unexpectedly diverse number of recombinant individuals, suggesting that interstitial translocations occur more frequently than previously thought. This analysis also showed that there is a wide range in the number and position of the interstitial translocations within a given line such as the mosaic chromosome in recombinant line 260-1/CS-26, which has four Th. intermedium chromosome segments. Phenotypic data of the two populations suggested the presence of one gene which we have called Bdv3 to differentiate it from the previously reported orthologous gene Bdv2. Using the PCR-based molecular markers identified in this study, 5 out of 12 elite lines that showed good yields and no YDV symptoms contained Th. intermedium chromatin. Due to the multiple components involved in the YDV disease complex, combining selection for YDV resistance with the molecular markers and maps identified in this study will increase the efficiency of introgressing Th. intermedium chromatin containing YDV resistance or other beneficial traits into elite wheat germplasm.

Commelina yellow mottle virus (CoYMV) is the type member of the badnaviruses, a genus of plant pararetroviruses. The N-terminus of the polyprotein encoded by ORF III has limited similarity to known cell-to-cell movement proteins. To test the hypothesis that the N-terminus is required for viral movement, the phenotypes caused by mutations constructed in this region were determined. Similar to mutants affected in the reverse transcriptase, mutants affected in the putative movement protein were unable to cause a systemic infection. However, when the abilities of the mutated viral genomes to direct virion assembly and replication were tested using an in vitro stem-culture system, the mutants affected in the putative movement protein were found to assemble virions, whereas the reverse transcriptase mutants were unable to do so. Moreover, the putative movement protein mutants were shown to be replication competent by detection and mapping of one of the genomic discontinuities that are the hallmark of replication by reverse transcription. Thus the N-terminal region of ORF III is required for the systemic movement but not for the replication of CoYMV.