Mapping Cereal Aphid Resistance in Steptoe/Morex Doubled Haploid Population

Mapping Cereal Aphid Resistance in Steptoe/Morex Doubled Haploid Population

S. Moharramipour*., H. Yoshida, K. Sato, K. Takeda, T. Iida and H. Tsumuki

Research Institute for Bioresources, Okayama University, Kurashiki 710, Japan.
*Present address: Department of Entomology, Faculty of Agriculture, Tarbiat Modarres University, Tehran-Iran.

Using doubled haploid (DH) population of Harrington/TR306, we reported that principal QTL determining cereal aphid density was located on the distal region of the short arm of chromosome 1 (Moharramipour et al., 1997). The present study was conducted to detect other genetic factors controlling natural cereal aphid infestation in the DH population of Steptoe/Morex.

A set of 150 DH lines produced by the North American Barley Genome Mapping Project (NABGMP) (Kleinhofs et al., 1993) was used in this experiment. DH lines and parents were planted in the field at Kurashiki, Japan in mid November and harvested in early June. Each DH line and parent consisted a plot approximately 20 plants in a row with 100 cm length and 90 cm width.

The total number of aphids was counted weekly in each plot during April and May for three years from 1994 to 1996. The number of aphids per stem was calculated and determined as aphid density. Due to non-normal frequency distributions of the phenotypic data, Log10(x+1) transformation was performed for the number of aphids per stem. For QTL analysis, a 223 marker subset of the skeletal molecular marker map was generated by selecting loci to distribute markers evenly across the seven barley chromosomes (Mather, 1995). The phenotypic data sets were analyzed by simple interval mapping (SIM) and simplified composite interval mapping (sCIM) procedures of the software package MQTL (Tinker and Mather, 1995).

The density of natural aphid infestation was recorded weekly in each DH line and parent for nine weeks in 1994, five weeks in 1995, and six weeks in 1996. Aphid species at the time of maximum density was predominated by Rhopalosiphum maidis in 1994 and 1995, and R. padi in 1996. Schizaphis graminum and Sitobion akebiae were observed infrequently in small colonies throughout the study. The frequency distribution of aphids in the DH lines was continuous and skewed to low density at each sampling, because greater number of lines exhibited lower aphid densities. The maximum differences of aphid density on Steptoe and Morex were observed at the peak of aphid density. The mean value was 0.60 (1994), 1.72 (1995) and 0.16 (1996) in Steptoe and 1.36 (1994), 2.37 (1995) and 0.90 (1996) in Morex, indicating that Steptoe contributes to lower aphid density.

From the total of 20 observations in three years, two QTL were found using SIM. A QTL was located on the centromeric region of chromosome 2 close to the marker ABC167B, and the another QTL was located on the long arm of chromosome 5 close to the marker cMWG733 (Fig. 1). Both SIM and sCIM detected QTL x E interaction within the same marker interval of the QTL main effect on chromosome 2. However, no QTL x E interaction was detected for the QTL on chromosome 5. When we analyzed the phenotypic data sets separately for each year, QTL on chromosome 5 was only detected in 1994, and QTL on chromosome 2 was only detected in 1995. However, no QTL was detected in 1996. The significance of QTL on chromosome 2 was strongly expressed on April 17, 1995. It was accounted for 28% phenotypic variance, and was contributed by Morex. No QTL was detected in any observations scanned individually in 1994. It is lead to a conclusion that QTL on chromosome 5 may be of less importance.

Since the aphid populations at the maximum density was mainly predominated by R. maidis (more than 80%) in 1994 and 1995, the QTL on chromosome 2 and chromosome 5 may be contributed to the density of R. maidis. Nieto-Lopez and Blake (1994) identified the resistance genes for Russian wheat aphid (RWA) on chromosome 2 and 5. The symptom caused by the aphid species was severe and mainly scored by the degree of chlorosis on barley leaves, and different from the phenotype in the present study which was scored by the number of aphid per stem. As it may be difficult to do allelism test between the factors found in this study and the results found by Nieto-Lopez and Blake (1994), inoculation of RWA on Steptoe/Morex DH population may be effective to reveal the resistance spectrum of QTL on chromosome 2 found in this study.

References:

Kleinhofs, A., A. Kilian, M. A. Saghai Maroof, R. M. Biyashev, P. Hayes, F.Q. Chen, N. Lapitan, A. Fenwick, T. K. Blake, V. Kanazin, E. Ananiev, L. Dahleen, D. Kudrna, J. Bollinger, S. J. Knapp, B. Liu, M. Sorrells, M. Heun, J. D. Franckowiak, D. Hoffman, R. Skadsen and B. J. Steffenson (1993) A molecular, isozyme and morphological map of the barley (Hordeum vulgare) genome. Theor. Appl. Genet. 86: 705-712.

Mather, D. E. (1995) Base maps of NABGMP crosses. [on line] Available: World wide web: http://gnome.agrenv.mcgill.ca/info/basemaps.htm

Moharramipour, S., H. Tsumuki, K. Sato and H. Yoshida (1997) Mapping resistance to cereal aphids in barley. Theor. Appl. Genet. (in press)

Nieto-Lopez, R. M. and T. K. Blake (1994) Russian wheat aphid resistance in barley: inheritance and linked molecular markers. Crop Sci. 34: 655-659.

Tinker, N. A. and D. E. Mather (1995) Methods for QTL analysis with progeny replicated in multiple environments. JQTL 1: (1).