The newly designated resistance gene rym6 against Japanese strain II of barley yellow mosaic virus (BaYMV-II) is mapped on the long arm of chromosome 3H (3HL), distal from Est1 with the recombination value of 11.4% (Iida et al. 1999). It is noticeable that three BaYMV resistance loci, rym4, rym5 and rym6, are clustered around Est1 on chromosome 3HL (Graner and Bauer 1993; Konishi et al. 1997; Iida et al. 1999, respectively).

QTL analyses of disease resistance in barley have been conducted extensively. The single-locus regression underscored the importance of resistance QTLs to stripe rust on chromosomes 4H and 5H that were introgressed from BSR41 into the Steptoe back-ground. Another important resistance QTL is most likely on chromosome 3H, where BSR41 contributes the favorable allele. (Toojinda et al. 1998).

For scald severity, there were significant QTL peaks on chromosomes 3H, 4H and 6H, using field- scored data of disease severity under natural infestation of doubled haploid (DH) progeny of the two- row barley cross Harrington/TR306. The peak on chromosome 3H was at 124.8cM, on the minus (long) arm, with the resistance allele contributed by Harrington (Spaner et al. 1998).

Genetic variability for partial resistance to bacterial leaf streak in barley, caused by Xanthomonas campestris pv. hordei, was investigated in 119 DH lines developed by the Hordeum bulbosum method from the F1 progeny of the cross between Morex (resistant) and Steptoe (susceptible). At the two-leaf stage seedlings were inoculated with an Iranian strain of the pathogen in a controlled growth chamber. A QTL analysis of bacterial leaf streak resistance showed that two QTLs, about 60 cM apart, were detected on chromosome 3H and one QTL on chromosome 5H. Out of the QTLs on chromosome 3H, the resistance locus near ABG377 appears to be a major gene (Attari et al. 1998).

Three QTLs for plant height were found, using 103 recombinant inbred lines by single-seed descent from a cross between L94 and Vada. Two main plant height QTLs, Ph1 and Ph2, were mapped at the same positions as Dh1 and Dh2 for days to heading on chromosomes 7H and 2H respectively. Another QTL, Ph3, on chromosome 3H affected only plant height but not days to heading (Qi et al. 1998). This QTL (Ph3) is likely mapped at the same region (between Dor4A and ABG396, 6.4% recombination) of the plant height QTL detected in the Steptoe/Morex cross (Hayes et al. 1993).

The exposure of the caryopsis through lemma and palea is called "hull-cracked grain", which lowers the germinability and quality of malting in barley. QTL analysis for hull-cracked grain was conducted using 146 DH lines derived from Harrington/TR306. Interval mapping analysis revealed that two significant QTLs were present on chromosomes 3H and 7H. The QTL on chromosome 3H is mapped between ABG609B and MWG838, while the other QTL on chromosome 7H is located between MWG511 and MWG626. Their QTLs of Harrington contribute to increase the expression of hull-cracked grains (Kanatani et al. 1998).

Eight QTLs affecting predicted hot water extract were identified by a marker-regression approach, using 99 DH lines of a cross between Blenheim and Kym. The largest effects were found on chromosome 3HL, associated with the denso dwarfing gene which is present in Blenheim and conferred poorer predicted hot water extract quality, and 4HL. However, the denso gene had no detectable effect on grain nitrogen contents (Bezant et al. 1997).

Using 119 DH lines of the Steptoe/Morex cross, interval mapping of the crossability of barley with wheat identified four significant QTLs, which were mapped to the centromeric regions of chromosomes 2H, 3H and 5H and the short arm of chromosome 7H. Out of them, the QTLs on chromosomes 3H and 5H had larger effects compared with others. The QTL on chromosome 3H of Steptoe contributed more crossable with wheat, whereas other QTLs of Morex increased the crossability (Taketa et al. 1998).

Comparative genetic mapping among cereal genomes has demonstrated that homologous single-copy sequences or genes are collinear on the RFLP maps of wheat, barley, rye, oat, maize and rice. This has allowed the maps of several members of the Gramineae family to be compared and the synteny of these genomes to be defined. The Lr10 leaf rust resistance gene on wheat chromosome 1AS cosegregates with the Lrk10 receptor-like kinase gene. The rice gene corresponding to Lrk10 is mapped on rice chromosome 1. This region corresponds to the distal part of barley chromosome 3H and wheat chromosomes 3A and 3B, suggesting that the synteny is conserved between rice chromosome 1 and the Triticeae group 3S chromosomes up to the telomere of the chromosomes (Gallego et al. 1998).

References:

Attari, H.El, A. Rebai, P.M. Hayes, G. Barrault, G. Dechamp-Guillaume, and A. Sarrafi. 1998. Potential of doubled-haploid lines and location of quantitative trait loci (QTL) for partial resistance to bacterial leaf streak (Xanthomonas campestris pv. hordei) in barley. Theor. Appl. Genet. 96:95-100.

Bezant, J.H, D.A. Laurie, N. Pratchett, J. Chojecki, and M.J. Kearsey. 1997. Mapping of QTL controlling NIR predicted hot water extract and grain nitrogen content in a spring barley cross using marker-regression. Plant Breeding 116:141-145.

Gallego, F., C. Feuillet, M. Messmer, A. Penger, A. Graner, M. Yano, T. Sasaki, and B. Keller 1998. Comparative mapping of the two wheat leaf rust resistance loci Lr1 and Lr10 in rice and barley. Genome 41:328-336.

Graner, A. and E. Bauer. 1993. RFLP mapping of the ym4 virus resistance gene in barley. Theor. Appl. Genet. 86:689-693.

Hayes, P.M., B.H. Lui, S.J. Knapp, F. Chen, B. Jones, T. Blake, J. Franckowiak, D. Rasmusson, M. Sorrells, S.E. Ullrich, D. Wesenberg, and A. Kleinhofs. 1993. Quantitative trait locus effects and environmental interaction in a sample of North American barley germ plasm. Theor. Appl. Genet. 87:392-401.

Iida, Y., T. Ban, and T. Konishi. 1999. Linkage analysis of the rym6 resistance gene to Japaneses strain II of barley yellow mosaic virus (BaYMV-II) in barley. BGN 29: (this volume).

Kanatani, R., H. Takahashi, and K. Takeda. 1998. QTL analysis for expressivity of hull-cracked grain in two-rowed spring barley. Bull. Res. Inst. Bioresour. Okayama Univ. 5:183-191.

Konishi, T., T. Ban, Y. Iida, and R. Yoshimi. 1997. Genetic analysis of disease resistance to all strains of BaYMV in a Chinese barley landrace, Mokusekko 3. Theor. Appl. Genet. 94:871-877.

Qi, X., R.E. Niks, P. Stan, and P. Lindhout. 1998. Identification of QTLs for partial resistance to leaf rust (Puccinia hordei) in barley. Theor. Appl. Genet. 96:1205-1215.

Spaner, D., L.P. Shugar, T.M. Choo, I. Falak, K.G. Briggs, W.G. Legge, D.E. Falk, S.E. Ullrich, N.A. Tinker, B.J.

Steffenson, and D.E. Mather. 1998. Mapping of disease resistance loci in barley on the basis of visual assessment of naturally occurring symptoms. Crop Sci. 38:843-850.

Taketa, S., H. Takahashi, and K. Takeda. 1998. Genetic variation in barley of cross-ability with wheat and its quantitative trait loci analysis. Euphytica 103:187-193.

Toojinda, T., E. Baird, A. Booth, L. Broers, P. Hayes, W. Powell, W. Thomas, H. Vivar, and G. Young. 1998. Introgression of quantitative trait loci (QTLs) determining stripe rust resistance in barley: an example of marker-assisted line development. Theor. Appl. Genet. 96:123-131.