Items from the United Kingdom.

ITEMS FROM THE UNITED KINGDOM


JOHN INNES CENTRE

Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom.


The Watkins wheat collection.

T.E. Miller, S.M. Reader, and M.J. Ambrose.

This year the tetraploid section of the collection is being grown and will complete the regeneration of the living material.

The establishment of a current and historical archival database is well underway. Watkins' original collection contained over 7,400 accessions. He eventually selected over 2,750 of these for a permanent living collection. Unfortunately, the current living collection contains only 1,284 accessions. Much of the basic data have been entered, including species, country of origin, exact location where known, Watkins' type classification (based on ear characteristics), and his descriptive notes. In time, scanned images of the original letters that he received with the original samples in the 1920s and 1930s will be added. Cards of mounted, herbarium specimens of spikes also exist, and we plan to incorporate images of these into the database as well. New data will be added to the database as and when they are available. Eventually, we hope to make much of the data base available via the Internet.

 

Chromosome aberrations in wheat nullisomic-tetrasomic and ditelosomic lines.

K.M. Devos, M.E. Sorrells (Department of Plant Breeding and Biometry, Cornell University, Ithaca, NY, USA), J.A. Anderson (Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN, USA), T.E. Miller, S.M. Reader, A.J. Lukaszewski (Department of Botany and Plant Sciences, University of California, Riverside, CA, USA), J. Dubcovsky (Department of Agronomy and Range Science, University of California, Davis, CA, USA), P.J. Sharp (University of Sydney, Plant Breeding Institute, Cobbitty, Camden, NSW, Australia), J. Faris (Department of Plant Pathology, Kansas State University, Manhattan, USA), and M.D. Gale.

The ability of hexaploid bread wheat to tolerate the addition or loss of chromosomes or chromosome segments was first exploited by the late Prof. Ernie Sears, who constructed several series of aneuploid lines. Nearly half a century later, we know that the aneuploid stocks harbor a wealth of aberrations that can, and almost certainly have, confounded some experimental results arising from their use. The extensive use of aneuploid lines for mapping and tagging has led indirectly to their detailed characterization. Table 1 summarizes the cytological and molecular data available on polymorphism and aberrations for the CS NT and Dt lines. This information should be of value to researchers who use these genetic stocks in the future and may help resolve difficulties in interpretation of results already obtained.

 

Construction of a comparative genetic map between the genomes of wheat and Aegilops longissima.

H. Zhang, M.D. Gale, and K.M. Devos; and X. Liu and J.Z. Jia (Institute of Crop Germplasm Resources, Chinese Academy of Agricultural Sciences, Beijing, P. R. China).

Aegilops longissima is a diploid species belonging to the section Sitopsis of the genus Aegilops in the tribe Triticeae. The relationship between the genomes of Ae. longissima and wheat has been established using RFLP probes that have been mapped previously in hexaploid bread wheat. A high degree of conserved colinearity is observed between the two genomes. Chromosomes 1S^l^, 2S^l^, 3S^l^, 5S^l^, and 6S^l^ appear entirely homoeologous to the chromosomes of wheat groups 1, 2, 3, 5, and 6, respectively. The short arms and major part of the long arms of 4S^l^ and 7Sl are homoeologous to most of wheat 4 and 7, respectively. The presence of an unequal reciprocal translocation between the distal segments of the long arms of 4S^l^ and 7S^l^, previously observed using pairing studies (Naranjo 1995), has been confirmed using RFLP markers.

The amphiploid and seven disomic, single-chromosome, addition lines of CS/Ae. longissima, designated A-G, were analyzed using 41 RFLP probes. Lines A, C, D, F, and G have Ae. longissima chromosomes 2S^l^, 1S^l^, 4S^l^, 5S^l^, and 3S^l^, respectively, in addition to the 42 wheat chromosomes. In lines B and E, wheat chromosome 6B has been substituted with Ae. longissima chromosome 6S. Both lines have a further Ae. longissima chromosome, which is 1S^l^ in line B and a translocated T2S^l^S·7S^l^L chromosome in line E. These results are in agreement with the karyotypic data obtained by Friebe et al. (1993). The identification of the translocated chromosome in line E as T2S^l^S·7S^l^S by Friebe et al. (1993) and T2S^l^S·7S^l^L in our study may be explained by the fact that 7S^l^L is physically the smaller arm due to the unequal translocation between 7S^l^L and 4S^l^L (Naranjo 1995). The T2S^l^S·7S^l^L translocation is not present in the parents of the mapping population and is likely to have arisen during the production of the addition lines.

References.

 

'Hobbit 'sib' / Fiorello' intervarietal chromosome-substitution lines.

A.J. Worland and E. Sayers.

A set of single chromosome intervarietal substitution lines has been developed at the John Innes Centre to introduce individual chromosomes from the old Italian spring wheat cultivar Fiorello into the background of the UK-bred semi-dwarf winter wheat Hobbit 'sib'.

Analysis of the substitution lines grown as drilled plots from a replicated, autumn 1998 sowing shows that the earlier spike emergence of Fiorello by 21 days is determined by genes on chromosome 2D, 3B, and 5B. The largest effect on spike emergence time was promoted by chromosome 2D, due to the photoperiod insensitive gene Ppd1 present on this chromosome in Italian wheats. Chromosome 5B is known to have the vernalization-insensitive, spring-habit gene Vrn-B1 that promotes spring habit in many Italian wheats. The promotion of spike emergence time on chromosome 3B probably is due to earliness genes per se that affect flowering time independently of environmental stimuli and have been shown previously to be present on chromosomes of homoeologous group 3.

Eleven of the 21 Fiorello chromosome substitution lines were significantly different in height than the recipient cultivar demonstrating the complex nature of the genetical control of plant height. Although Fiorello is significantly taller than Hobbit 'sib', three substitution lines were even taller than Fiorello. These lines cotained chromosomes 4D, 5A, and a translocated chromosome T5BS·7BS. The increased height of chromosome 4D is because the gibberellic acid-insensitive, semidwarfing gene Rht-B1b on chromosome 4D of Hobbit 'sib' is missing. The increased height associated with chromosome T5BS·7BS is of interest, because other Italian cultivars have been shown to have a dwarfing gene Rht9 on this chromosome. The chromosomes of Fiorello that depress the height of Hobbit 'sib' are 1A, 1D, 2D, 3B, 4A, 6A, 7A, and 7D. The most pronounced effects were recorded for chromosome 3B and 2D, both of which significantly reduced the time to spike emergence and the life cycle of the plant. The 2D chromosome of Italian wheats is known to have Ppd1, which promotes photoperiod insensitivity and has pleiotropic effects in height reduction and also the GA-responsive, dwarfing gene Rht8.

Three Fiorello chromosomes significantly altered spikelet numbers, with chromosomes 1D and 7A increasing spikelet numbers and chromosome 2D reducing spikelet numbers. The effect of chromosome 2D is again due to Ppd1 on this chromosome. Number of grains/spikelet was increased significantly by chromosome 3B and reduced by chromosomes 2D, 4A, and 4D. The reduction in fertility on chromosome 4D was expected, because the substituted Fiorello chromosome removed the dwarfing gene Rht-B1b that is known to increase spikelet fertility. The introduction of Ppd1 on chromosome 2D of Fiorello also would normally be expected to increase spikelet fertility. The reverse effect recorded here suggests that other genes on Fiorello 2D are counteractive, thus reducing the fertility increase usually associated with Ppd1. Two chromosomes, 2D and 5A, increased 1,000-kernel weight. In the case of the 2D chromosome, this is probably a direct effect of the reduced grain numbers. Final plot yield was improved by chromosomes 1A, 1B, 3D, and 6B and reduced by chromosome 4A.

The substitution lines are now being used to develop single-chromosome, recombinant lines to map some of the agronomic effects located to chromosomes.

 

Targeted mutagenesis of disease resistance loci in wheat.

R.M.D. Koebner and J.E. Hadfield.

As part of a program to isolate major genes conferring resistance to yellow rust and powdery mildew in wheat, we have generated substantial numbers of mutants at defined loci. The race-specific nature of the genes precluded field screening for susceptible segregants in M2. Therefore, we devised a strategy to screen M1 seedlings by mutagenizing populations composed of a high proportion of individuals hemizygous for the chromosome carrying the target gene. To obtain such populations, we exploited the fact that the monosomic condition is transmitted to the majority of the selfed progeny of a hemizygote. The bulk of the remainder of these progeny is euploid and a small number is nullisomic. Mutagenization of euploid progeny is unlikely to deliver mutant phenotypes in M2, unless the mutation is dominant, whereas the majority of nullisomics, although showing the mutant phenotype, are generally nonviable or sterile, and so self-eliminate.

From 14,500 fast-neutron irradiated, hemizygous, Yr1 progeny, we were able to select 603 susceptible segregants, of which 32 were completely or almost completely self sterile; five lacked a copy of chromosome 2A, as assayed by microsatellite analysis; five gave no susceptible progeny; and the progeny of 24 segregated for resistance/susceptibility. This resulted in the stabilization of 561 putative mutants at Yr1 or at other unknown loci on 2A conferring race-specific resistance to yellow rust. Similar experiments delivered 71/8,500 M1 selections at Yr5, but half of these were thin leaved and failed to flower, resulting in a mutant panel of 35. At Yr10, we have a mutant panel of 240. At Pm3, we employed either gamma rays or EMS to generate approximately 300 putative mutants out of 4,000 seedlings following the same strategy. In a control (nonmutagenized) monosomic-derived population of approximately 750 individuals, we selected 45 susceptible seedlings; five of these still had microsatellite loci on chromosome 1A, whereas the remaining 40 were evidently nullisomic segregants.

The monosomic mutagenesis approach described here is applicable to any single-gene target where the chromosome location of the target is known. The primary advantage is that it allows the selection of the mutant phenotype in M1, representing a large saving in the number of individuals that need to be screened. Most importantly, this feature allows targets such as race-specific disease resistances to be targeted that are not readily amenable to conventional mutagenesis approaches, where the pathogen inoculum cannot be controlled.

 

Genetical analysis of animal-feed quality in wheat.

J.W. Snape, S.E. Orford, J.F. Wiseman (University of Nottingham, UK), W.J. Angus (Nickerson UK Ltd), and W. Wakeman (BOCM-Pauls, UK).

The animal feed market uses more of the UKs wheat crop than any other outlet. The poultry feed industry alone currently requires about two million tons of the UK crop to feed 300 million chickens every year. Wheat makes up about 65 % of a typical chicken feed diet and through its high starch and protein content, supplies much of the energy required by the birds. This characteristic has never been subject to genetical analysis. Therefore, genetical variation for this trait is unclear; plant breeders might be able to develop cultivars specifically designed for improved nutritional quality. We have started investigating whether this is the case by evaluating, in controlled chicken feed trials, precise genetic stocks containing genes that may have effects on feed quality because of their influence on grain characteristics. Genes investigated include those that affect grain texture, grain- storage proteins, starch composition, and grain color and alien segments such as the VPM Ae. ventricosa segment and the T1B·1R translocation.

The most significant of the effects investigated was due to the presence of the T1B·1R translocation. In a number of independent trials, in different genetic backgrounds, the presence of T1B·1R consistently reduced digestibility and, hence, had a negative feeding value. Whether this is due to the presence of undesirable rye genes on the 1RS segment or the absence of desirable wheat genes on the 1BL has yet to be determined. The effects of grain texture were significant but ambiguous, with hard being better than soft in some experiments, and vice versa in others. Several of the effects, such as the presence of the VPM segment, were neutral. These experiments have demonstrated that significant genetical variation for feed quality occurs in wheat, and that a breeding strategy for improved nutritional value should be possible.

 

Chromosomal location of Fusarium head blight-resistance genes and analysis of the relationship between resistance to head blight and brown foot rot.

A. Mentewab, H.N. Rezanoor, N. Gosman, A.J. Worland, and P. Nicholson.

In order to identify chromosomes involved in resistance to Fusarium head blight, a set of 21 substitution lines of T. macha (resistant) chromosomes in Hobbit 'sib' (susceptible) were evaluated in trials over 2 years. For the first year's trial, all plants were inoculated on the same day with a conidial suspension of F. culmorum. For the second trial, individual plants were inoculated precisely at midanthesis of each plant over a period of 2 weeks. The disease level was assessed by visual scoring, relative spike weight, and F. culmorum-specific quantitative PCR. The results showed that T. macha chromosomes 1B, 4A, and 7A conferred good overall resistance, suggesting that they have important genes for resistance. In two additional trials, T. macha and Hobbit 'sib' were evaluated for resistance to brown foot rot. The results showed that T. macha was more susceptible than Hobbit 'sib', indicating that response to stem base disease is not correlated with head blight resistance in these cultivars.

 

Publications.