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Published and distributed by the International Maize and Wheat Improvement Center (CIMMYT) with support of the Italian Government (DCAS). CIMMYT is an internationally funded, nonprofit
scientific research and training organization. Headquartered in Mexico, the Center works
with agricultural research institutions worldwide to improve the productivity and
sustainability of maize and wheat systems for poor farmers in developing countries. It is
one of 16 similar centers supported by the Consultative Group on International
Agricultural Research (CGIAR). The CGIAR comprises over 50 partner countries,
international and regional organizations, and private foundations. It is co-sponsored by
the Food and Agriculture Organization (FAO) of the United Nations, the International Bank
for Reconstruction and Development (World Bank), the United Nations Development Programme
(UNDP), and the United Nations Environment Programme (UNEP).
Germplasm Improvement and Genetic
Resources
I am very pleased to take over the edition of the BYD Newsletter from Lukas Bertschinger and put BYD-NL No. 6 together. The last edition, published in 1994, was a success judging by the number of contributions and their quality. The long silence that followed that issue is due to staff changes at CIMMYT. We hope to publish the Newsletter once a year and to get the next issue out in the first semester of 1998. The number of contributions (30) published in this issue is half what was included in the previous one (64). Very few country reports were received. Does that mean interest in this disease has decreased and that fewer people are studying BYDV? Or perhaps, information did not reach the interested people? Please give your views on the Newsletter by filling out the questionnaire included in this issue. As more and more people hook up to the internet, we hope to foster communication and reduce the cost of publications by including this issue of the Newsletter in the CIMMYT home page. BYD research has made exciting progress in the last few years. Many groups are now integrating alien derived resistance conferred by Thinopyrum intermedium into bread wheats and we hope that BYDV resistance will be soon available in many breeding programs and in the developing world. Good advances have been made in wheat transformation and some reports mention BYDV transgenic wheat. How long before we get them into the field? A lot of knowledge has been acquired on BYDV itself. We are starting to understand the mechanisms of vector transmission and specificity, as well as symptom expression. With the growing number of papers published on BYDV variability, the early classification method based on aphid transmission is becoming less clear. Moreover, BYDV might become two viruses, as was suggested at the last luteovirus meeting held in the UK in March 97. The BYD-NL was initiated at CIMMYT, and has always aimed to foster communication between developing and industrialized world scientists. This mandate will be maintained. Your subscription to the BYD-NL will help ensure that this communication tool will continue and reflects your interest and support. As we all know, funds for
agricultural research are being reduced by donors and BYDV is affected by these cuts.
Under these conditions, it is getting very important to focus our research and collaborate
with others working in the same areas. If any groups are interested in participating in
joint CIMMYT projects for BYD research and want to join us in presenting proposals, please
contact us at CIMMYT.
The BYD Newsletter consists of informal reports presented to foster communication and the exchange of ideas and information between developing and industrialized world BYD researchers. Responsibility for the views expressed in the article rests with each author. Research information distributed through the Newsletter is in the form of "notes" and not "published" in the sense of a refereed journal. It should NOT be cited in other publications without the authors' consent. Citations in refereed publications, whenever permitted, refer to the BYD Newsletter notes in the text, rather than in the bibliography. For example, specify "B. Yellow, BYD Newsletter 6: 95, 1997; unpublished data", or cite as "personal communication" (with the colleague's consent). BYD Newsletter No. 7, 1998 Contributions to BYD-Newsletter No. 7 should be received by M. Henry no later than December 31, 1997. Please send maximum one page per abstract. Abstracts should be written as narrative reports, including the most important progress made. A maximum of one figure and/or 2 tables can be accepted per abstract, if essential. Please follow the abstract header format and the citation format (e. g.: [Yellow and Dwarf, Gen. Res. Crop. Evol. 43:31-34 (1996)] and [Luteovirus et al., J. Gen. Virol. 65:222-229 (1995)]. To facilitate the edition of the
Newsletter, submission of abstracts via electronic mail (MHenry)
or on diskette (ASCII-, WordPerfect- or Word for Windows file) is strongly encouraged. Subscribe to the BYD Newsletter electronically The BYD Newsletter will be available on the Internet on the CIMMYT home page (http://www.cimmyt.mx/) or on CGIAR home page (http://www.cgiar.org). Subscription and submission of contributions can be done through the Internet. In 1997, the Newsletter will be mailed to all subscribing scientists. Principal authors of 1997 Newsletter articles will also receive it in recognition of their contribution, though some scientists from the industrialized world have not yet formally subscribed. THEY ARE ENCOURAGED TO SUBSCRIBE, AND TO SPONSOR A SUBSCRIPTION BY COLLEAGUES AND AGRICULTURAL RESEARCH INSTITUTIONS. The Newsletter will also be sent to all BYD researchers in developing countries who subscribed and/or who are on the 1994 mailing list, as long as they are still active in BYD research. In the future, the Newsletter will be sent only to principal authors of papers and to scientists or institutions that have completed their subscription form and showed interest in the Newsletter. The mailing list that I have used to advertise
this issue of the Newsletter dates from 1994. I have made some changes but to
update it thoroughly, I need your participation. PLEASE FILL AND RETURN THE SUBSCRIPTION
FORM included in this issue. Funding the BYD Newsletter Following a 1994 survey, it was decided that the
cost of a subscription to the Newsletter will be US$15 per year and that developing
countries scientists and institutions will receive the Newletter free of charge.
Interested parties may sponsor a developing country institution. We will maintain this
price for the next issue of the Newsletter but hope to reduce costs by introducing
the Internet version. C. J. D'Arcy1 and M. Mayo2 1University of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801, USA; 2Scottish Crop Research Institute, Invergowrie, Dundee, DD25DA, UK Introduction: At the recent Luteovirus conference in Cirenchester, UK an international group of 50 scientists discussed luteovirus taxonomy and nomenclature. The suggestions of that group for revisions to luteovirus taxonomy and nomenclature will be transmitted to the Luteovirus Study Group of the International Committee on Taxonomy of Viruses (ICTV) for consideration. Although there was a remarkable degree of agreement among the scientists present in Cirenchester, we believe that other opinions on luteovirus taxonomy and nomenclature exist within the scientific community. Therefore, we herein present a synopsis of the recommendations made by the group at the Luteovirus conference, and ask you for your comments and suggestions. Proposals on Luteovirus Taxonomy: 1. Luteoviruses will be placed in the family "Luteoviridae". 2. There will be three genera: a. Luteovirus - BYDV-MAV (type), BYDV-PAV b. Betaluteovirus (or Polerovirus or Potleavirus) - BWYV (type), BYDV-RPV, CRLV, PLRV c. Enamovirus - PEMV (type). 3. Some viruses currently assigned to the luteovirus subgroups will be classified as unassigned species in the family until sufficient information becomes available to allow their classification in a genus: e.g. BLRV, BYDV-RMV, BYDV-SGV, GRAV. 4. SDV will remain unassigned to a genus due to its recombinant nature. Other members may also have this nature (BLRV?), which may justify the creation of a fourth genus. 5. The list of tentative luteoviruses will be revised, with some members being deleted (e.g. milk vetch dwarf virus) and others added (e.g. sweet potato leaf speckling virus). 6. Isolates of viruses which belong to a genus will be considered distinct species if they meet most of the following criteria: differences in breadth and specificity of host range; failure of cross protection in either one-way or two-way relationships; differences in species of efficient aphid vectors; differences in serological specificity with discriminatory antibodies (polyclonal / monoclonal); differences of greater than 10% in amino acid sequences of any gene product. Proposals on Luteovirus Nomenclature: 1. The current nomenclature of BYDVs is confusing, since some viruses named "BYDV" are more closely related to other luteoviruses than they are to other BYDVs. It is proposed that the name "barley yellow dwarf virus" be reserved for MAV and PAV strains. Further, it is proposed that the name "cereal yellow dwarf virus" be used for RPV strains. BYDV or CYDV followed by a three letter acronym will be used to designate strains. 2. It is proposed that the differences in host range between BWYV and BMVY are sufficient for BMYV to be recognized as a distinct luteovirus, rather than as a strain of BWYV. Requested Response: The Luteovirus Study Group will be considering these and any other suggestions on luteovirus taxonomy and nomenclature, in preparation for a proposal to the ICTV. We would appreciate your input in the following areas: 1. Do you agree with the placement of these viruses within a family Luteoviridae? 2. Do you agree with the three proposed genera? 3. What viruses should be included in each of the genera? 4. What viruses should be deleted from/added to the list of tentative luteoviruses? 5.
Do you agree with the
nomenclature changes for BYDVs and BWYV/BMYV? Please send your responses by writing
to: Dr. Cleora J. D'Arcy, Chair, ICTV Luteovirus Study Group, Department
of Crop Sciences, University of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801 or by
sending email to c-darcy@uiuc.edu A. Comeau1, C.A. St-Pierre2, J. Collin2 and J.P. Dubuc1 1. Agriculture and Agrifoods Canada, Sainte-Foy G1V 2J3, Canada; 2. Université Laval, Dépt. Phytologie, Sainte-Foy, G1K 7P4, Canada BYDV resistance and tolerance has been an integral part of the breeding work effort in Ste-Foy and at Universite Laval in Quebec, for the last 25 years. Such research was undertaken for spring oats and barley, spring and winter wheat and triticale. The last oat cultivar from the BYDV testing program was AC Rigodon that was registered by Dubuc in 1992 (oat crossing had been stopped in 1987). The impact of the oat component of the program has been remarkable, since all sensitive cultivars have been replaced by a set of seven moderately tolerant oat cultivars (Marion, Nova, Sylva, Appalaches, Capital, Ultima, and AC Rigodon) and by one that is very tolerant (Donegal). They all come from AAC-Ste-Foy crosses and selections. These tolerant cultivars are grown on about 97% of surfaces. When the field performance of Ste-Foy cultivars is compared to that of neighboring provinces which did not devote similar effort against BYDV, we see that BYDV tolerance had a major positive impact. New cultivars from neighboring provinces have not outyielded Quebec BYDV tolerant cultivars since 1980; two cultivars, derived from Quebec lines have also been registered in Tasmania (Quamby and Cluan). A recent Quebec spring barley , ACCA, is the first BYDV tolerant cultivar registered in Canada. This line is a major breakthrough in overall disease resistance since it combines resistance to BYDV with resistance to scald, net blotch, surface-borne smuts, and perhaps even some resistance to root rot. Many of these tolerance genes are likely derived from CIMMYT line 8th IBON #32. We had previously complained of the difficulty of incorporating a BYDV resistance exempt from a series of agronomic defects, using various Ethiopian lines carrying resistance to BYDV. We now know that barley breeding for BYDV resistance was difficult because Yd2 is very close to the centromere, where recombination is uncommon and therefore renders linkage breakage difficult. Undesirable linkages present in the Ethiopian barleys were probably broken through the CIMMYT breeding work, and the goal of a good cultivar creation was facilitated using the CIMMYT BYDV-resistant germplasm. Interestingly, a scald resistance gene has just been mapped very close to Yd2 by Hayes at al., 1996, (see on internet http://probe.nalusda.gov:8000/otherdocs/jqtl/index.html). In wheat, besides offering testing services, we conducted research on various issues related to tolerance and resistance. The Quebec candidate wheat germplasm has been screened annually for BYDV reaction; this may have helped promote BYDV tolerance and avoid excess sensitivity. Most bread wheat cultivars grown in Quebec thus have some moderate BYDV tolerance, the best in this respect being AC Pollet and SS Blomidon. On the research side, academic aspects such as efforts at gene pyramiding were pursued, using conventional as well as interspecific crosses. Some of that work was done in collaboration with CIMMYT and ICARDA. The collaboration with Dr. Makkouk at ICARDA yielded progress in tissue-blot immunoassay systems, which facilitated the follow-up of epidemics. We also tried to understand and circumvent the special difficulties related to introgression of BYDV tolerance into shorter cultivars. This led to novel hypotheses which will set the stage for future BYDV research in Quebec. Thus a full overview of our research would necessitate discussion of the theoretical relationships between BYDV tolerance and other traits of broad adaptation, including biotic and abiotic stresses resistance. This will be discussed elsewhere in this Newsletter. Ongoing research in wheat resistance / immunity from alien sources : More recently, most of the work was related to
interspecific introgression and to understanding of tolerance. A 2n=56 line called
OK7211542 had near immunity (Comeau et al. 1994. Agronomie 2: 153-160). The
practical use of this resistance necessitates introgression into the ABD genome. We are
still pursuing this difficult work; Drs Mujeeb-Kazi and Makkouk are also investigating the
potential of OK7211542 and its derivatives. Dr. F. Ahmad (now at Lethbridge) isolated
2n=43 lines having a small alien telomere that contains the resistance. This may be an
important step in order to get the genes into wheat, as the amount of alien chromatin to
deal with is quite small by now. This strong resistance is just what is needed in winter
wheat, a crop that may suffer severe infestation in the fall. Research on barley yellow dwarf luteovirus in Ukraine L. I. Omelchenko and L. T. Babayants Phytopathology and Entomology Department,
Agricultural Sciences Plant Breeding and Genetics Institute, Ukraine In Ukraine barley yellow dwarf luteovirus (BYDV) was first described as infecting winter wheat and barley in 1972 (Geshele E.E., Dutko V.P., '¥«ì᪮¥ 宧ï©á⢮ § pã¡¥¦®¬. 6:56-68 (1972). Later the symptoms of this virus were observed on other cereal during the epidemics of 1975, 1980, 1982. Since then, it has become the most important virus pathogen of cereal crops in Ukraine. The average yield losses caused by BYDV in different years and varieties varied from 20 to 75% (Nickolenko M.P., Omelchenko L.I., '¥«ì᪮宧ï©áâ-¢¥-- ï ¡¨®«®£¨ïî 8: 63-68 (1985). The epidemics of 1982 and 1985 drew attention of virologists and plant breeders to BYDV, especially to the diagnosis and epidemiology of the disease. The aphid species infecting cereal and perennial grasses determined during a survey were Rhopalosiphum padi L., Sitobion avenae Fab., Rhopalosiphum maidis Fitch. R. padi and S. avenae were the main vectors of BYDV. The first species represented 60 % of the total vector population, especially in autumn. Other species were also present, but their role in virus transmission was less important (Omelchenko L.I. ãç-®-â¥å-¨ç¥áª¨© ¡î««¥â¥-ì ‚'ƒˆ. 2(64):56-63 (1987). While studying BYDV epidemiology, it was shown that the critical period for infection in Ukraine was usually September for winter crops, and April-May for spring crops when the vector activity was lighter. During 1990-1995, BYDV has been successfully detected from naturally infected barley and wheat leaves collected from many fields from the South of Ukraine. 750 samples of plant with symptoms of BYDV were tested by ELISA with PAV and MAV polyclonal antiserum produced in Germany (Institute of Virology and Phytopathology, Aschersleben). BYDV was detected in 87% of the samples tested. Differences were observed in symptoms, in the rate of disease spreading, and in the damages caused on wheat varieties. We investigated the possibility that BYDV could interact with other diseases during simultaneous infections. A research on the interaction between BYDV and stem rust (Puccinia graminis f. sp. tritici Pers), leaf brown rust (Puccinia recondita f. sp. tritici), and powdery mildew (Blumerta graminis (DC), Speer. f. sp. tritici) was carried out from 1989-1995. It also allowed us to assess the relative importance of those diseases. We observed an increase in BYDV incidence and a decrease in infection by powdery mildew when both pathogen were present together. In the interaction rust-BYDV, there was no change in the level of BYDV, but a decrease in rust and stem rust. Therefore, a field study on resistance of different wheat varieties to obligate fungi pathogens during mixed infections with BYDV is impossible. Phytopothological analysis of wheat cultivars,
incomplete - wheat - Elymus synthetics and their hybrids infected with BYDV have
shown a relation between sensitivity to virus infection and cultural practices,
environmental conditions and plant genotype. New potential sources of tolerance to BYDV
have been found (Omelchenko L.L., Simonenko V.K., Motsny I.I. ƒ¥-¥â¨ª ¨
æ¨â®«®£¨ï 2(30). „¥¯. ‚ˆˆ'ˆ 04.03.96 N
673-‚.96 (1996). A. Comeau1, C.A. St-Pierre2, J. Collin2 and J.P. Dubuc1 1. Agriculture and
Agrifoods Canada, Sainte-Foy G1V 2J3, Canada; 2. Université Laval, Dépt. Phytologie,
Sainte-Foy, G1K 7P4, Canada
In conventional and interspecific germplasm as well, it has been difficult to introduce BYDV tolerance into shorter genotypes. As a matter of fact, it has been difficult to transfer more than 50% of the tolerance of our tall, tolerant check Maringa into a moderate size genotype. The problem was observed as early as 1980, and has remained an obstacle. Understanding this problem has been a slow process. Many theories were tested and rejected. Another problem was that correlation between sites was generally a bit low for wheat. In comparing our data with that of S. Haber, the correlations between locations Winnipeg*Ste-Foy could reach 0.80 or 0.90 for oats and barley; for wheat, it would revolve around 0.50 or a bit higher. Therefore we suspected that BYDV tolerance had something to do with more rugged root systems, i.e. roots that would be more adapted to the "local" stresses than those of the common cultivars. Following this idea, the lower correlation between sites would reflect the fact that soil stresses differ between Ste-Foy and Winnipeg. We tested the root hypothesis first in barley and oats. In barley, our severe isolate (named "Cloutier") killed the meristem of barley plantlets in 4-5 days. Then, at ICARDA, during my sabbatical leave, it was observed that a relatively mild BYDV isolate used by K.M. Makkouk could produce more clear-cut symptoms on barley or wheat than what we could obtain in Quebec with the severe isolate "Cloutier". Definitely, a mild BYDV isolate in a drier area can be more damaging than a severe isolate in the humid climate of Quebec. This was interpreted as supporting our hypothesis that root related parameters relate closely to BYDV tolerance. In oats, C. Al Faiz (now at INRA, Morocco) proved that root damage was strongly correlated to yield losses and to symptoms. His ELISA data on the best genotypes showed that many of the tolerant genotypes had high ELISA values. Only two of them had relatively low ELISA values which are typical of true resistance, such as the resistance conferred by Yd2 in barley. However one must remember that the Yd2 resistance is a short-lived phenomenon, and that often the ELISA values of Yd2 lines become moderately high at some point in time. We suspect this resistance is accompanied by other phenomena more properly called tolerance. Exciting results were seen in interspecific crosses. For example, one line derived from T. durum x T. aestivum crosses has showed excellent tolerance levels in 1996. This line may perhaps contain a Thinopyrum (Agropyron) introgression. This tolerance was not obvious until mid-season, but assessment of BYDV effects on roots proved that this line maintains normal branching and near normal growth, whereas after mid-season, susceptible lines grow only a few feeble roots that extend downwards but lose capacity to branch when virus infected. This root health trait seems to bring durum wheat to a tolerance level that is close to a Yd2 barley. ELISA data was not done on this individual line yet, but all the parents had high virus levels in previous tests, and we cannot expect ELISA to show resistance. We also noted many sources of BYDV tolerance seem to do quite well in root rot situations, confirming Scott's Ph.D.(1968, Illinois) thesis conclusions on the predisposing effect of BYDV for root rot pathogens. A verification of Scott's conclusions is planned. BYDV tolerance and yield or yield stability parameters In general, the cultivars that have better BYDV tolerance are also cultivars which have better stability of yield over years and sites, which could fit both horizontal resistance and root health correlations. These tolerant cultivars also tend to yield more overall. The Web page http://www2.zone.ca/~pdubuc/bydv contains some of the current data on the relationship of BYDV tolerance with yield parameters (in French). We ran out of funds before we completed this web
page; eventually we hope it will be translated in English and moved to another server.
Essentially, BYDV tolerant lines had good yield potential in both sites (Winnipeg and
Quebec), and this yield advantage was more obvious under stress situations, especially if
a root stress was involved. The theory that general stress tolerance relates to BYDV
tolerance necessitates novel research approaches. We are now attempting to demonstrate a
unifying biochemical hypothesis according to which BYDV tolerance is truly a form of
horizontal resistance to most stresses. R. T. Plumb and C. Bass Crop and Disease
Management, IACR-Rothamsted, Harpenden, Herts, AL52JQ, UK
In the United Kingdom, recent mild winters seem to have contributed to an increased risk of BYDV infection in Spring-sown (February-April) crops and, in consequence, a renewed interest in resistance as insecticidal sprays are not economic [Mann et al., Crop Protection 16:81-87 (1997)]. Field trials over several years demonstrated that there were marked differences in BYDV incidence in spring barley cultivars but all showed symptoms of infection. Glasshouse tests with defined isolates also demonstrated that cultivars differed in the ease with which they were infected, but when infected all cultivars were severely damaged. As the Yd2 gene was not present in any of the cultivars tested the hypothesis was that the difference in the incidence of BYDV was due to an effect on aphid behaviour. In field trials the presence, side by side, of cultivars with different characters would accentuate any feeding preferences the aphid vectors might have. Electrophysiology tests proved inconclusive but the character is now present in several spring barley cultivars. The National Institute of Agricultural Botany, which is the independent cultivar testing station for the UK has now added BYDV resistance to the character set used to assess cultivars and on which recommendations are based. BYDV resistance, based on symptoms is rated from 1 (very susceptible and damaged) to 9 (little infection). One generally recommended cultivar (Optic) for 1997, is rated 8. A project involving the Arable Research Centres, FAR in New Zealand, New Farm Crops (a breeding company) and IACR-Rothamsted, and funded by the UK Home-Grown Cereals Authority, began in spring 1996 and seeks to investigate this resistance on a range of spring barley cultivars at 4 sites in England. The virus is scored and isolates identified. Inevitably, the winter of 1995/6 was relatively cold and there was very little BYDV infection at any of the sites. H. C. Sharma, H. W. Ohm and R. M. Lister Purdue University, 1155
Lily Hall of Life Sciences, West Lafayette, IN 47907-1155, USA
Resistance to BYDV has been found in the Agropyron complex, however, wheatgrasses are distantly related to wheat and gene transfer by natural recombination does not occur. Thus, it is tempting to find resistance in species that constitute the homologous gene pool (Triticum species, and Aegilops species containing A, B or D genomes) of cultivated wheat. Of the 39 accessions of Triticum species tested for PAV, 8 had ELISA values below twice the susceptible control [Makkouk & Ghulam, BYD Newsletter, No.4 (1991)]. Among a large number of accessions of Aegilops species screened for their reaction to a PAV serotype at ICARDA (Syria) and Sainte-Foy (Canada), seven accessions of biuncialis, caudata and triuncialis were resistant [Makkouk et al., Can. J. Pl. Sci. 74:631-634 (1994)] but when tested in France, none was resistant (Beuve & Lapierre 1994, BYD Newsletter). Furthermore, these species fall outside the homologous gene pool of wheat. Goletti et al. [BYD Newsletter, No.4 (1991)] found that out of 30 accessions of T. boeoticum, T. dicoccoides and T. spelta, only one accession of T. boeoticum appeared to be negative in dot blot hybridization using PAV-specific radioactive probe. Plants from four Aegilops species (ovata, triuncialis, cylindrica and juvenalis) were positive by ELISA for MAV, PAV as well as RPV isolates while Ae. ventricosa, which has D as one of the genomes, was positive to MAV but negative to PAV and RPV [Griesbach et al., Crop Sci. 30:1173-1177 (1990)]. We tested, by ELISA, 13, 8, 6, 3,1,1,1,1,1,1,1,1,9,1,1,1,1,2,4,1,2,2,1,1 and 1 accessions of T. monococcum, T. boeoticum, T. urartu, T. dicoccoides, T. araraticum, T. polonicum, T. spelta, T. compactum, T. vavilovii, T. macha, T. zhukovskyi, T. sphaerococcum, Ae. squarrosa, Ae. biuncialis, Ae. caudata, Ae. columnaris, Ae. crassa, Ae. kotschyi, Ae. ovata, Ae. umbellulata, Ae. speltoides, Ae. triuncialis, Ae. variabilis, Ae. cylindrica and Ae. longissima, respectively, against Purdue-PAV isolate of BYDV. ELISA values and hence the levels of resistance were not even close to those of Agropyrons. In some accessions, we found one of the several seedlings with low ELISA (<0.3, Agropyron=0.06) after 1h incubation but after 3h incubation, they were positive (susceptible) and in the second test with more seedlings, none was resistant. Furthermore, it may be noted that when genes from alien species are transferred into wheat, there may be a dilution effect. Comparing the ELISA values, Aegilops were the most susceptible, Agropyron were the most resistant and wild and primitive species of Triticum were intermediate for their reaction to BYDV. Out of the whole material tested, T. urartu accession G3248 appeared to be promising. The three plants of this accession tested had ELISA values for 1 h (3h) incubation as 0.113 (0.225), 0.012 (0.041) and 0.018 (0.091). In the second test, ELISA value was 0.181. This accession might be used in interspecific crosses with wheat for the introduction of resistance to BYDV but resistance of even this line should be established by testing a larger number of plants and performing progeny test. The present study as well as the works cited above underscore the significance of rigorous testing of the alien gene resources before embarking on an interspecific gene transfer. These results also confirm the general lack of resistance in near relatives of wheat. It appears that the best source known so far for BYDV resistance is Agropyron species and the lines developed from their crosses with wheat hold potential to breed for BYDV resistance [Mujeeb-Kazi et al., BYD Newsletter, No.6 (1994)], [Sharma et al., Genome 38:406-413 (1995)], [Banks et al., Genome 38:385-394 (1995)], [Hohmann et al., Genome 39:336-347 (1996)]. These species and their hybrids provide also less preference to aphid vectors [Tremblay et al., Environmental Entomology 18:921-932 (1989)], [Kieckhefer Environmental Entomology 12:442-445 (1983)], [Shukle et al., Phytopathology 77:725-729 (1987)] (We thank Giles Waines, Bik Gill, and K. Makkouk for seed. Research supported by PVI and PSTC/AID). M. Henry, CIMMYT Int., México D.F., México Seventeen derivatives of recombinant spring bread wheat lines with a translocation from Thinopyrum intermedium were obtained from CSIRO Australia. They belong to the five TC families (TC5, TC6, TC9, TC10 and TC14) [Banks et al., Genome 38:395-405 (1995)]. To select lines presenting the best BYDV resistance combined with agronomic characteristics, the material was tested in the field and in the greenhouse. Resistance to BYDV was assessed by inoculating the lines with three Mexican isolates, PAV-Mex, MAV-Mex and RPV-Mex. In the greenhouse, 10 plants per lines were
inoculated with 10 viruliferous aphids, three were kept as healthy controls. The last
emerging leaf minus one was collected 14, 28 and 43 days after inoculation. Virus titer
was assessed by ELISA using monoclonal antibodies (Mc91, Mc 92, Maff2) kindly given to us
by Ian Barker, CSL, UK. Table 1 : Glasshouse evaluation of the TC
translocation lines.
Nb. =
number infected as
determined by ELISA (* 9 inoculated, ** 8 inoculated). ELISA = Mean OD
value obtained for the infected samples (OD>3*healthy), 12 days after inoculation. In the field, a double 1 m row was inoculated with 5-10 viruliferous aphids, while the adjacent two rows were kept free of BYDV with regular insecticide treatments. Symptoms readings were taken after flowering as described by Bertschinger [BYDV Newsletter, 5, 14 (1994)]. Virus titer was assessed by ELISA two months after inoculation, using polyclonal antibodies from Purdue University (USA). Three samples were taken in the infected plot and one in the non inoculated one. Sampling was done as in the greenhouse experiment. In the greenhouse, ELISA values were lower for all TC lines compared to the susceptible (Bob White) and tolerant (Anza) controls (Table 1). The best lines were found in the TC14 families. The line CSIRO 293M (TC6) did not appear to be resistant to any of the isolates. Resistance was much stronger against the RPV isolate (group II). In many cases, inoculation failed and if it succeeded titers remained very low compared to the controls. In the field, no major differences were observed
in the ELISA titers with PAV and MAV isolates (Table 2). Success of infection was high for
both isolates. In most lines, symptoms in TCs were equivalent to symptoms observed in Anza
or Bob White. However, inoculation with RPV resulted in very low levels of infection and
attenuated symptoms. Table 2 : Field evaluation of the TC translocation lines.
Nb. = number of samples
infected as determined by ELISA (3 tested); ELISA = Mean OD value
obtained for the infected samples (OD>3*healthy); Symptoms = sum of
the 3 values (yellowing, tillering and dwarfing). N. Loi1, A. Casavola1, D. Vittori1, A. Loschi1, R. Osler1, E. Porceddu1 and C. De Pace2 1. Biol. Appl. Difesa
Piante, Univesità di Udine, Viale delle Scienze, P.O. Box 208, 33100 Udine, Italy; 2.
Agrobiology and Agrochemistry, University of Tuscia, via S. C. de Lell, Viterbo 01100,
Italy Sister lines from recombinant families TC5 through TC10 (except TC7) were received in 1995 by the CIMMYT International Wheat Nurseries. These lines were developed by cell culture of F1 immature embryos or F1 inflorescences obtained by crossing line L1 (=7Ai-1, a Thinopyrum intermedium chromosome group 7, probably 7X, disomic addition to the hexaploid wheat nuclear genome background of cv "Vilmorin 27") with the Australian wheat cultivars "Sunstar" or "Millewa", followed by backcrossing of the regenerated plants to the wheat parents or crossing to the lines "Vulcan.cms" and "R35733" fertility restorer, selfing, backcross to commercial wheat cultivars (i.e. cv "Hartog"), and selection for BYDV resistance [Banks et al., Genome 38:395-405 (1995)]. Thirty-one out of 43 lines belonging to five families were rated BYDV resistant after ELISA test at CIMMYT and were expected to have 2n=42 and carry one or two copies of the 7DL/7Ai-1L recombinant chromosome; therefore they could be either hemyzigous or homozygous for the gene located on the 7Ai-1L chromosome arm which confers resistance to BYDV in line 7Ai-1. The rest of the lines were rated BYDV susceptible, and probably they lost both the recombinant chromosome and the gene for resistance. In February 1995, the lines were planted at the University of Tuscia's experimental station at Viterbo for seed increase and preliminary evaluation of plant morphology and grain yield components. Seed germination was above 90% and seedling emergence was uniform. At maturity three to four plants from each sister line were evaluated for culm height, number of spikes and grain yield. The plants (one or two) that for each line showed the highest grain yield were used for progeny test (Table 1). In March 1995, seeds from the same lines were
sown in pots in the greenhouse at University of Udine, in order to check their behaviour
when inoculated with the Italian strain M-PAV of BYDV (an isolate from maize). The
seedlings were inoculated at the one leaf stage, using 5-8 viruliferous Rhopalosiphum
padi aphids, that had acquired the virus during a 48 hs feeding on BYDV infected oat
plants. After 3 days the aphids were killed with an insecticide. ELISA test was carried
out one month after inoculation. Table 1.
Behavior of Thinopyrum
intermedium recombinant lines inoculated with BYDV M-PAV
Considering the virus titer detected in the inoculated plants as well as the number of virus-free plants within the same line, the results obtained by ELISA confirmed substantially the evaluation about resistance (R) and susceptibility (S) to BYDV observed in the tests carried out by the CIMMYT researchers. Only in two cases of the 43 lines graded R in the Mexican trials all the plants tested in Udine had a virus content of the order of the S plants. At the end of October 1995, the progeny-test was set on at the University of Tuscia experimental station using seeds from the plants selected from the R lines of all the five families and from the S lines of the TC8 family. Each progeny-test included plots of six 1m long rows in two replicates. The final plant density was six plants per row. Seedlings of one replicated plot were artificially infected with M-PAV, as described above and the other plot served as healthy check. The experimental plots were covered with aphid-proof tissue. After seven days, the inoculated plants were sprayed with insecticide. The treated and the untreated plots were kept free of natural aphid infestations by insecticide sprayings. Three months after inoculation (plants at tillering stage; evident yellowing symptoms on progenies from S lines), 0.5 g leaf sample was taken from all the inoculated plants and from three plants of the healthy checks of each tested progeny. The BYDV visual scoring system used for individual wheat plants [Qualset, Barley Yellow Dwarf, CIMMYT, pp.72-80 (1984)] was used to evaluate symptoms in the field. The scale was modified as follows: score "0" was given for no visible symptoms; "1" for extensive yellowing, no dwarfing, moderate to good plant vigor; "3" for high level of yellowing, moderate dwarfing, poor plant appearance; "4" for dwarfing, rosette appearance, few spikes with some sterility. All the tested progenies from the R lines showed plants whose symptoms fall in the four score categories. The proportions of plants with no symptoms (score 0) varied from 16% (progenies from R lines of the TC 8 family) to 27% (progenies from the R lines of the TC5, TC9 and TC10 families), and the proportion of plants showing the most severe symptoms (score 4) varies from 34% (progenies from the R lines of the TC9 family) to 61% (progenies from the TC8 family). The average of the OD405 values from ELISA was calculated for each group of plants showing the same field score in each progenies. Symptom scores correlated closely with the average OD405 (Table1), indicating that the suppression of the virus multiplication is greater in plants showing score "0" and "1". In the progenies from the R lines of all the families, the average grain yield of the group of plants showing score "4" was 85-96% less than those with score "0", and the average plant height of the plants with score "4" was 16-37% less than those with score "0". None of the individuals in the tested progenies
from the S lines showed score "0"; those showing score "4" had 86%
grain yield reduction and 20% culm height reduction compared to the healthy control. The
presence of individuals showing score "0" only in the progenies from R lines
indicate that those individuals must possess the BYDV resistance gene from the 7Ai-1L
chromosome fragment. Since that gene show additive action (Banks, loc. cit.), the plants
with score "0" should have two copies of the resistance gene, and the plants
with higher score should have either 1 copy (score "1") or none (score
"3" and "4"). This implies that all the parental plants from the R
lines included in the progeny test were hemizygous for the BYDV resistance gene (only one
copy of the 7DL/7Ai-1L translocated chromosome should be present). The observed proportion
of plants with score "0" (16-27%) is compatible with the proportion of 25%
expected for the progenies having two copies of the translocated chromosome in the
segregating progenies. Although this seems the most reasonable explanation to the obtained
results, it is very hard to explain why all the parental plants should have been
hemizygous and not homozygous for the BYDV resistance gene despite their pedigree showing
a long history of selfing and BYDV resistance. A further progeny test of the plants
showing score "0", "1","3" and "4" is in progress
in the field at Viterbo. The artificial inoculation has been performed in November 1996. A
first verification of symptoms on plants at tillering stage in February 1997 indicates
that susceptible plants are appearing in the progenies from parental plants that had score
"0". To solve this puzzling behavior of the tested progenies we should verify
the number of copies of the 7DL/7Ai-1L translocated chromosome using the molecular markers
psr 129 and pEleAcc2. L. Ayala1, M. Henry1, D. González-de-León1, M. van Ginkel1 and and B. Keller2 1. CIMMYT Int., México
D.F., México; 2. FAL-Rechenholz, Switzerland
No major genes for tolerance or resistance to BYDV have been identified in bread wheat. Resistance to the virus has been reported in several grasses of the Triticeae. Using Thinopyrum intermedium as the source of resistance to the virus, [Banks et al. Genome 38:395-405 (1995)] developed a series of translocation lines called 'TC'. The alien chromatin of the translocation lines replaces a portion of chromosome 7D of wheat. Depending on the TC family involved, it is a small terminal translocation (TC14) or a large portion (TC5-TC10) of chromosome 7D of wheat [Banks, loc.cit.; Hohmann et al., Genome 39:336-347 (1996)]. Tolerance to BYDV has been identified in wheat and is present in several CIMMYT lines. Singh et al. [Crop Science 33:231-234 (1993)] showed that tolerance present in the variety Anza was due to one gene, Bdv1, which was closely linked to Lr34 and Yr18 genes for resistance to leaf rust and stripe rust, respectively, and to the marker leaf tip necrosis. Because those genes are known to be located on chromosome 7DS of bread wheat, Singh and his colleagues proposed that Bdv1 is also located on 7DS. Tolerance and resistance to BYDV are two desirable characteristics in bread wheat. Tolerance has been incorporated into CIMMYT germplasm, but the varieties having the Bdv1 gene show high virus titers. Field and glasshouse studies conducted in Mexico showed that even if there is a reduction in virus titer in the TC lines, symptoms can be severe in the field [Henry, BYD Newsletter No.6 (1997)]. We believe that by combining tolerance with resistance it will be possible to obtain plants with reduced virus titer and no symptoms. Three populations of recombinant inbred lines (RILs) are being developed using the translocation line TC-14, which has the smallest portion of Th. intermedium heterochromatin, the tolerant variety Anza and the susceptible variety Bagula. RIL populations will be tested under field conditions with artificial inoculation to evaluate tolerance (symptom expression) and resistance (ELISA titer). The presence of the Thinopyrum introgression and the Bdv1 gene will be assessed with the appropriate molecular markers. This will allow us to study the behavior, interaction, and inheritance of the Th. intermedium translocation and the Bdv1 gene. TC14 has been crossed with five
elite bread wheat varieties, four of them having the Bdv1 gene, to study the effect
of wheat background on the expression of alien-derived resistance. In each backcross, the
individuals that have the translocation will be selected using the molecular markers for
TC and backcrossed to the bread wheat. Populations in BC2F3 will be analyzed in field
trials and molecular studies. Y. T. Qian, X. P. Sun, Y. Liu, Y. P. Liang and G. G. Zhou Institute of Plant
Protection, CAAS, Chinese Society of Plant Pathology, Western yuan ming yuan road, Beijing
100094, China
Barley Yellow Dwarf Luteovirus (BYDV) is an important cereal virus with significant economic losses in some of the major wheat producing areas in China. The major isolates of BYDV in China were GPV, GAV and PAV. GPV was unique in China. Breeding for resistant cultivars is the only positive and economical approach to reduce yield losses. Since 1989, 1773 translocation lines of wheat - Thinopyrum intermedium, derived from L1 by crossing to common wheat and using tissue culture techniques, were screened by artificial inoculation with BYDV-GPV isolate in the field. 54 lines were resistant to GPV, some lines were also resistant to GAV but susceptible or segregating for resistance to BYDV-PAV as assessed by ELISA (enzyme-linked immunosorbent assay) or inoculation in the field. The results suggested that differences existed in the translocation lines' resistances to 3 isolates of BYDV. Nearly ten years ago, octoploid Zhong 5 (Zhong4
awnless), derived by crossing wheat with Th. intermedium, showed stable and high
resistance to BYDV-GPV, GAV and PAV isolates as measured by ELISA following artificial
inoculation in the field. The addition lines Z1-1 (Zhong5 / Zhong7902) showed good
resistance to GPV. Z1-1 and Zhong 7902 were analyzed by RAPD with 104 random primers.
Primer OPS-16 amplified a DNA fragment which existed in Z1-1 but not in Zhong7902. Th.
intermedium, Zhong5, Z1-1 and Zhong7902 were amplified by OPS-16. Amplification of Th.
intermedium, Zhong5 and Z1-1 by OPS-16 gave a product that did not exist in Zhong7902.
After 3 repeated amplifications, the product was named OPS-161766. The progenies of 5
resistant and 4 susceptible individuals were amplified by primer OPS-16. OPS-161766
existed in progenies of resistant individuals, but did not exist in progenies of
susceptible individuals. OPS-161766 may be used as a marker to identify the BYDV
resistance in wheat breeding program. L. Ayala1, M. Henry1, D. González-de-León1, M. van Ginkel1 and B. Keller2 1. CIMMYT Int., México
D.F., México; 2. FAL-Rechenholz, Switzerland
Resistance to BYDV is a desirable characteristic not found in bread wheat, but alien-derived resistance from Thinopyrum intermedium has been incorporated into translocation lines developed in Australia (Banks et al., Genome 38:395-405 (1995)]. Tolerance to the virus due to gene Bdv1 has been widely used in the CIMMYT bread wheat breeding program and characterized at the field level [Singh et al., Crop Science 33:231-234 (1993)]. To combine both characteristics, we need a screening method that is reliable, fast and environmentally independent. The traditional screening method for BYDV tolerance and resistance has been a time-consuming procedure that requires maintenance of large aphid populations and virus cultures, field and/or greenhouse inoculations, measurement of virus titers, and large field trials. This complicated testing system is also strongly influenced by the environment. With the use of molecular markers, screening for tolerance and resistance to BYDV and incorporating both tolerance due to Bdv1 and resistance due to Th. intermedium into the same genotype will be facilitated. To develop markers for the Bdv1 gene for tolerance, we will first map its position. Three RIL populations (Altar84/AE. SQ.//Opata, Frontana/INIA, Parula/7Cerros) will be used in field trials. These populations were developed to map the position of the Lr34 complex for adult plant leaf rust resistance in wheat. Because those genes are related to Bdv1 (Singh et al. loc. cit.), these populations can also be used to map Bdv1. Several laboratories have collected molecular data on those populations, and phenotypic symptoms will be assessed in the field according to [Bertschinger, BYD Newsletter, No.5 (1994)]. Field data will be correlated with available molecular data to draw a map indicating the identified position of the viral tolerance genes, if present. In addition, 5 near isogenic lines (NILs) developed at CIMMYT, also for Lr34 studies, will be used to map the Bdv1 gene. The low frequency of polymorphisms found in wheat moved us to use AFLP analysis to map the position of Bdv1. This technique combines the specificity of restriction analysis with PCR amplification, which improves our chances of mapping the gene for tolerance. In a second part, we are searching for specific markers to tag the position of the alien chromatin in wheat, because of the size of the Th. intermedium segment carrying BYDV resistance the use RFLPs and microsatellites are suitable. Four RFLP polymorphic probes and two microsatellites have been identified to tag the presence and putative position of the alien chromatin in TC-14. The polymorphic probes are being sequenced to develop allele specific amplicons (ASA) to facilitate the testing of large numbers of samples. Top N. Paltridge, C. Ford, N. Collins and B. Symons Department of Plant Science,
Waite Campus, University of Adelaide, Glen Osmond, SA 5064, Australia The use of resistant germplasm is generally regarded as the most effective means of controlling damage caused by barley yellow dwarf luteovirus (BYDV). In barley, the Yd2 gene of several Ethiopian accessions is the only effective BYDV resistance gene to have been identified. The gene has so far been incorporated into at least 17 barley cultivars and has provided useful levels of protection for over 20 years. A major constraint to the breeding of BYDV resistant barley, however, has always been the inconvenience of the biological assay for resistance, which is difficult to score and requires the use of viruliferous aphids. A molecular marker linked to Yd2 is therefore of paramount importance for the efficient selection of Yd2-carrying lines in breeding programs. RFLP markers are the most commonly used genetic markers in barley and several such markers linked to Yd2 have been identified [Collins et al., Theor. Appl. Genet. 92:858-864 (1996)]. These markers, however, are time-consuming and expensive to work with, and impractical for routine use in breeding programs. Molecular markers based on the polymerase chain reaction (PCR) offer a favorable alternative; genotype analysis is fast and economical and can be conducted at the single leaf stage, as only small amounts of genomic DNA are required. We have now developed two PCR markers for use in Yd2 breeding programs. The first of these (designated YLM1) was developed as a result of our final characterization of a Yd2 linked protein (YLP), which varies in isoelectric point between barleys with and without Yd2 [Holloway & Heath, Theor. Appl. Genet. 85:346-352 (1992)]. Two assays were developed for genotype analysis at this locus [Ford et al., (1997), submitted]; one employs post-amplification restriction digestion to distinguish resistance and susceptibility associated alleles of the Ylp gene; the other uses allele-specific amplification to identify directly the resistance-associated allele of the gene. The second PCR marker developed to Yd2 (designated YLM2) is a codominant, PCR-amplifiable polymorphism which can be visualized immediately upon amplification, and was identified using AFLP analysis on Shannon (Yd2+) and Proctor (Yd2-) barley [Paltridge et al., 1997, manuscript in preparation]. Both markers map to within 1 cM of the Yd2 gene. To determine the suitability of the two PCR markers for broad application in the marker-assisted breeding of BYDV-resistant lines, it was necessary to check that each was polymorphic between a majority of different Yd2 and non-Yd2 barleys. Consequently, test amplifications were conducted on over 100 different Yd2 and non-Yd2 lines. All 12 Yd2-carrying lines displayed the Shannon allele of both markers, and at the YLM 1 locus all 96 non-Yd2 lines were shown to carry the Proctor allele. Of 96 non-Yd2 lines tested at the YLM2 locus, 90 displayed the Proctor allele and 6 the Shannon allele. Both markers were therefore considered to have widespread utility in breeding programs, and now provide invaluable tools for the selection of Yd2-carrying lines. © CIMMYT October 1997 |
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