Inheritance of russian wheat aphid resistance in spring barley germplasm
line STARS-9577B
D.W. Mornhinweg, D.R. Porter, and J.A. Webster
USDA-ARS, Stillwater, OK

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a devastating pest of barley grown in the intermountain regions of the western United States. All barley cultivars presently in commercial production are susceptible to RWA feeding damage. Typical RWA feeding damage to the leaf results in characteristic longitudinal white, yellow, or red chlorotic streaks with convolute rolling of the leaf. Rolling of leaves reduces photosynthetic area, provides an optimum environment for aphid reproduction, protects the aphids from contact insecticides and natural predators, reduces stand, and at the heading stage, can prevent spike extrusion, resulting in obstruction of flowering and decreased seed set.

A damage rating scale for wheat and barley seedlings has been developed by Webster et al. (5) based on visual rating of the amount of chlorotic leaf tissue, due to either leaf streaking or spotting, and on the amount of leaf rolling. On a scale of 1 to 9, resistant seedlings have a chlorosis rating of 1 to 3, moderately resistant to moderately susceptible seedlings have a chlorosis rating of 4 to 6, and susceptible seedlings a rating of 7 to 9. All available accessions of Hordeum vulgare in the USDA National Small Grains Collection have been screened as seedlings for RWA resistance using this scale. Forty-five lines have been identified as resistant and an additional 61 as moderately resistant to moderately susceptible (1).

Genetic diversity has been shown to exist for RWA resistance in wheat, where a total of 6 genes (Dn1 to Dn6) have been identified that confer some level of RWA resistance (4). Mornhinweg et al. (2) reported the high level of RWA resistance in barley germplasm line STARS-9301B to be under the control of two genes (Dnb1 and Dnb2). Analysis of data from the F2 and BC to both parents suggested recessive epistasis of a dominant gene (DNB2) on an incompletely dominant gene (DNB1). Robinson et al. (3) reported a single dominant gene that controlled a moderate level of RWA resistance in barley line S13. It has yet to be determined if Robinson's single dominant gene is the same as Dnb1 or Dnb2. The search for a barley germplasm line with a high level of RWA resistance and simple inheritance goes on, as does the search for genetic diversity.

Crosses were made between Morex, a susceptible malting barley cultivar, and STARS-9577B. Genetic analysis was performed on parents, F1, F2, and BC populations as well as 300 F2-derived F3 families. The number of homozygous resistant and homozygous susceptible F2-derived F3 families indicated multiple gene control. Chi-square analysis of the F2 and BC to either parent suggested RWA resistance in STARS-9577B to be under the control of two dominant genes with recessive epistasis.

RWA resistance in STARS-9577B, measured by chlorosis damage ratings following RWA infestation, appears to be under the control of two genes. Probable gene action is two dominant genes, with recessive epistatis. This inheritance differs from that of barley germplasm line STARS-9301B indicating that genetic diversity does exist for RWA resistance in barley.

References :

1. Mornhinweg, D.W., D.R. Porter, J.A. Webster, and R.A. Grossl. 1994. Germplasm enhancement for Russian wheat aphid resistance: 1994 update. Barley Newsl. 38:80-83.

2. Mornhinweg, D.W., D.R. Porter, and J.A. Webster. 1995. Inheritance of Russian wheat aphid resistance in spring barley. Crop Sci. 35:1368-1371.

3. Robinson, J., P.A. Burnett, H.E. Vivar, and F. Delgado. 1992. Russian wheat aphid in barley: Inheritance of resistance and yield loss, pp.94- 97. In W.P. Morrison (comp) Proceedings of the 5th Russian Wheat Aphid Conference. Great Plains Agric. Counc. Pub. 142.

4. Saidi, A., and J.S. Quick. 1994. Inheritance of Russian wheat aphid resistance in four winter wheats, pgs. 126-132. In F.B. Peairs, M.K. Kroening and C.L. Simmons (comps.) Proceedings of the Sixth Russian Wheat Aphid Workshop, Colorado State University, Ft. Collins, CO.

5. Webster, J.A., C.A. Baker, and D.R. Porter. 1991. Detection and mechanisms of Russian wheat aphid (Homoptera: Aphididae) resistance in barley. J. Econ. Entomol. 84:669-673.