Accession No. 1 of Aegilops variabilis has complete resistance to the root knot nematode, Meloidogyne naasi. F2 segregation in a cross between this and two susceptible accessions showed that one dominant gene named Rkn-mnl prevented development of galls on the roots and consequently of female nematodes. The study of the numbers of females in galls on the F2 plants allowed detection of a recessive gene, Rkn-mnAv, suppressing development of 52 larvae into females. The presence of Rkn-mnAv also resulted in a decrease of the level of galling. Rkn-mnl has already been introduced into wheat. The interest in transferring also Rkn-mnAv is discussed in relation to extending durability of the nematode resistance.
Hybrids of Aegilops variabilis (2n = 28, UUS'Sŵ ith the low-pairing type lines of Ae. longissima, Ae. bicomis, Ae. searsii, Ae. speltoides and Ae. umbellulata were obtained. This is the first report of successful hybridization between Ae. variabilis and Ae. searsii. Meiotic analysis of these hybrids showed that the U genome of Ae. variabilis donated by Ae. umbellulata remained nearly unchanged and Ae. longissima is the possible donor species of the S genome to Ae. variabilis. But the S" genome and the S* genome of Ae. longissima are not completely homologous and are structurally differentiated by at least one interchange. According to their levels of homology with S'' through the means of chromosome associations, the four genomes of Sitopsis section species can be classified as follow: S^ -^ S* > S> S' > S. The meiotic behaviour of the hybrids between the wheat 'Chinese Spring' and the four Sitopsis section species studied has not supported the view that one of the four species is the donor of the B genome of wheat.
Root-knot nematode is a significant root-parasite of common wheat. A dominant gene Rkn-mnl for resistance was transferred into wheat from Aegilops variabilis. This gene was shown to be on chromosome 3B. Eurther analysis indicated that it is on the long arm of this chromosome and independent of the centromere.Key words: Triticum aestivum -monosomic analysis -telocentric mapping -genetic distanceThe cereal root-knot nematode, Meloidogyne naasi, can have a serious effect on the yield of wheat and barley crops (Goods and d'Herde 1977, Cook etal. 1986). Resistance to the nematode has not been identified in any true wheats. Sources of resistance to this parasite have been identified in related species belonging to the tribe Triticeae: Aegilops variabilis and Ae. umbellulata (Person-Dedryver and Jahier 1985), Hordeum chilense and H. jubatum (Cook and York 1981, Person-Dedryver et al. 1990). Yu et al. (1990) selected from the cross of wheat and an accession of Aegilops variabilis one line of wheat which displayed, like the Aegilops parent, complete monogenic resistance without gall formation (exceptionally with one to three galls). They also demonstrated that the alien chromosome segment carrying the gene for resistance was shorter than a normal chromosome arm, and seemed to have no negative effect on the regularity of meiotic behaviour and on chromosome stability. This paper reports the chromosomal location of the gene Rknmnl involved in the resistance of the recombinant line.To determine the chromosomal location of the gene, the Rkn-mnlhomozygous recombinant line X8, selected in the backcross progeny of cv. 'Lutin' with the hybrid 'Chinese Spring'/^£^ variabilis, was crossed with each of the 2! monosomics of cv. 'Cappelle-Desprez'. The monosomics were kindly provided by T. Worland. This set of monosomics was chosen because the recombinant line and 'Cappelle-Desprez' possess a similar overall chromosome structure.The monosomic plants of 'Cappelle-Desprez' used in the above crosses were tested for univalent shift according to the procedure of Law et al. (1973). The resistance in the E, monosomic famihes was compared to that of the Ej derived from disomic E, plants. To confirm the chromosomal location of Rkn-mnl and possibly to estimate its genetic distance from the centromere, the two ditelosomic lines for chromosome 3B of 'Chinese Spring' (CS) were crossed with a BC derivative of X8 known as Une E. The monotelodisomic E, plants were backcrossed as females to CS.Chromosome counting in root tips was carried out using a standard Eeulgen technique. Eor meiotic analysis, anthers at the first metaphase of meiosis were fixed in Carnoy's fixative (3:1), squashed in 1% acetocarmine and counterstained with carbol fuchsin. Tests of resistance were carried out in Petri dishes following the technique described by Person-Dedryver (1984). Galls developed on roots following an injection of about 70 juvenile larvae per Petri dish and a plant growth of 10 days at 21 C with a photoperiod of lOh.The results of the monosomic analy...
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