ITEMS FROM FRANCE

INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE (INRA)

Station d'Amélioration des Plantes, BP 29, 35650 Le Rheu, France.

G. Doussinault, D. Barloy, N. Chantret, F. Dedryver, J. Jahier, B. Rolland, and M. Trottet.

Resistance to the cereal cyst nematode.

The Ae. ventricosa chromosome 6Mv carries partial resistance to CCN. Chromosome 6Mv has a translocation, the distal part of its long arm consists of a segment of the short arm of homoeologous group 2 (likely 2Mv). In order to define the part of 6Mv involved in the resistance, we evaluated addition lines with a 6M with either a deletion in the short arm or in the distal part of the long arm. The gene(s) are on the group 2 translocated segment. So far, the four CCN-resistance genes localized in wheat all are carried by group 2 chromosomes.

An Ae. variabilis accession previously used as a donor to wheat of resistance to the root knot nematode also displays complete resistance to the CCN. The progeny from a cross between the wild grass and wheat was tested for resistance to the CCN. Two different disomic addition lines and six lines with 42 chromosomes, likely translocation lines, were found partially resistant to CCN. Because the F1 interspecific hybrid was as resistant as the wild parent, we expect that combining the resistance genes of the two added chromosomes of the addition lines will lead to a wheat genotype with complete resistance. One of the genes involved in the resistance could be Rkn-mn1, which confers resistance to the root knot nematode.

Resistance to powdery mildew.

An original procedure leading to the early prediction of adult-plant reaction to powdery mildew infection at the seedling stage was defined. Seedlings of eight wheat lines were inoculated at the 2- and 5-leaf stages with various inocula (either clones or synthetic mildew populations) to overcome their major specific resistance genes. The mean mildew score and the mean time for first sporulation proved to be correlated strongly. For each line tested, the mildew reaction of adult plants was predicted closely by that of vernalized seedlings. We can predict the adult stage mildew reaction of a line where the specific resistance should be overcome. Using this method, it is possible to study genotypes, whose specific resistance is still effective in the field, thus preventing assessment of their possible nonspecific adult plant resistance in the field.

The winter wheat line RE714 (Ae. tauschii / T. dicoccon // ? /3/ VM4 /4/ Beauchamp; where ? = outcross and VM4 = Roazon sib) possesses two race-specific genes for resistance to powdery mildew: Pm4b, localized on chromosome 2A, and MlRE, recently identified and localized by monosomic analysis on the chromosome 7B. RE714 has a high level of adult-plant resistance in the field, even if the natural population of powdery mildew possesses the virulence genes matching MlRE and Pm4b.

Two progenies (44 DH and 140 F2­F3) between RE714 and the susceptible cultivar Hardi have been genotyped for race-specific genes in order to find a marker of MlRE. The same progenies were used to build a genetic map and assessed for their resistance at the adult plant stage in order to find QTL of resistance to powdery mildew (in collaboration with the Station d'Amélioration des Plantes, Gembloux, Belgium).

The third aspect deals with the relationships between race-specific genes and adult plant resistance. First results implicated the gene MlRE, but not of the gene Pm4b, in adult-plant resistance (to be published soon).

Resistance to barley yellow dwarf virus.

The transfer into adapted wheat lines of two genes of partial resistance for BYDV derived from Th. intermedium has been initiated. The first gene was derived from an addition line of chromosome 7Agi in a Vilmorin 27 background extracted from a backcross progeny of a partial amphiploid (TAF46, 2n = 56), created by Y. Cauderon. A translocation 7D-7Agi was produced by P. Banks (line TC14 in a Sunstar background). The second gene was found in the Agrotricum Zhong 5 from China, and the resistance was located on a homoeologous group 2 chromosome by P Banks (addition line Z6). We selected ditelosomic addition lines in the progeny of an F1 of the cross between Z6 and wheat.

With both sources of resistance, multiplication of the virus in the plants is slow, which has an effect on the proportion of plants that escape contamination. More than one-third of the plants of TC14 escape contamination, about 15 % of the plants with Zhong 5 are resistance, and less than 1 % of the plants are susceptible. In the contaminated plants, we observed a significantly lower multiplication of the virus in the plants derived from Zhong 5 than in plants derived from the ditelosomic addition. These data suggest a different mechanism of resistance for these two genes.

Molecular markers for both genes were found using RAPD markers. The data obtained from an F2 of the cross 'TC14 / Rendezvous' suggest that the fragment of the 7Agi chromosome could recombine with 7D, and will be verified from the study of the F3. The arm of the chromosome 2Agi carrying the resistance gene is characterized.

The introgression of these two resistance genes into an agronomic background adapted to France is in progress.

Resistance to the aphid Sitobion avenae.

A screening of accessions of T. monococcum by the Zoology Laboratory (INRA, Le Rheu) revealed a high level of resistance to S. avenae of some accessions. Amphiploids between 'T. monococcum x T. durum' were produced. The resistance was not expressed in these hexaploid amphiploids, but we hope to recover it in the tetraploid progenies of the backcrosses with T. durum wheats.

Publications.

Jahier J, Tanguy AM, Abelard P, and Rivoal R. 1996. Utilization of deletions to localize a gene for resistance to the cereal cyst nematode, Heterodera avenae, on an Aegilops ventricosa chromosome. Plant Breed 115:282-284.

Robe P, Pavoine MT, and Doussinault G. 1996. Early assessment of adult plant resistance of wheat (Triticum aestivum L) to powdery mildew (Erysiphe graminis f sp tritici) at the five-leaf seedling stage. Agronomie 16:441-451.

Dedryver F, Jubier M-F, Thouvenin J, and Goyeau H. 1996. Molecular marlers linked to the leaf rust resistance gene Lr24 in different wheat cultivars. Genome 39:830-835.