COLORADO
COLORADO STATE UNIVERSITY
Department of Agronomy, Ft. Collins, CO 85023, USA.
Molecular mapping of genes for resistance to Russian wheat
aphid in wheat.
Nora Lapitan, Cynthia Miller,
Garret Anderson, Zhengqiang Ma, Brad Erker, and James Quick.
The RWA is the most significant insect pest problem in Colorado.
This project's objectives were to develop DNA markers for tagging
two RWA resistance genes Dn2 and Dn4 and to evaluate
the use of these markers for pyramiding the genes in wheat. The
development of lines containing more than one resistance gene
may be an effective strategy for overcoming the appearance of
new biotypes. Combining two or more resistance genes is difficult
using conventional screening methods because of the absence of
RWA biotypes in the U.S. at present. However, at least seven biotypes
of the RWA are known to exist in different parts of the world;
hence, it is possible that new biotypes could appear in the U.S.
PI262660 and PI372129 are resistant, unadapted, wheat lines containing
genes Dn2 and Dn4, respectively. These lines were
crossed with susceptible wheat cultivars, and F2 populations were
produced for genetic mapping. Dn2 was linked to RFLP marker
pTtksuA1 at a genetic distance of 9.8 cM. Dn4 was linked
to RFLP markers pTtksuD14, ABC156, andpTt ksuE18 at distances
of 32.5 cM, 11.6 cM, and 16.6 cM, respectively (Ma et al. 1998).
Dn2 was localized to chromosome 7D and Dn4 to chromosome
1D using nullisomic-tetrasomic wheat lines. To find DNA markers
that are closer to the genes, AFLP and microsatellite markers
were tested on bulked segregants differing in the presence or
absence of the resistance genes. Microsatellite marker WMS 437-1
(Roder et al. 1998. Genetics 149:2007-2023) was linked
to Dn2 at a distance of 2.9 cM. This marker effectively
distinguishes PI262660 from susceptible cultivars and resistant
lines containing genes other than Dn2. WMS 437-1 is useful
for tagging Dn2 and for combining Dn2 with other
resistance genes into a single wheat background. Studies are underway
to find markers more tightly linked to Dn4 and to map genes
for Dn7, a resistance gene from rye (Marais et al. 1994.
Plant Breed 113:265-271).
Publications.
Erker B. 1998. Utility of molecular marker technology and
inheritance of resistance of PI 262660 in breeding Russian wheat
aphid resistant wheats. M. S. thesis. Colorado State University,
Fort Collins, CO. 53 pp.
Lapitan NLV. 1998. Using DNA markers to improve wheat and barley.
Agronomy News, Cooperative Extension, CSU. 18 (3): 2-3.
Ma Z-Q, Saidi A, Quick JS, and Lapitan NLV. 1998. Genetic mapping
of Russian wheat aphid resistance genes Dn2 and Dn4
in wheat. Genome 41:303-306.
Ma Z-Q, and Lapitan NLV. 1998. A comparison of amplified and restriction
fragment length polymorphism in wheat. Cereal Res Comm 26:7-13.
Rokka VM, Clark MS, Knudson DL, Pehu E, and Lapitan NL. 1998.
Cytological and molecular characterization of repetitive DNA sequences
of Solanum brevidens and Solanum tuberosum. Genome
41:487-494.
Rokka VM, Ishimaru CA, Lapitan NLV, and Pehu E. 1998. Production
of androgenic dihaploid lines of the disomic tetraploid potato
species Solanum acaule ssp. acaule. Plant Cell Rep
18: 89-93.
Rokka VM, Lapitan NLV, Knudson DL, and Pehu E. 1998. Fluorescence
in situ hybridization of potato somatohaploids and their somatic
hybrid donors using two Solanum brevidens specific sequences.
Agric and Food Sci in Finland 7:31-38.