Inheritance of Russian Wheat Aphid Resistance in Spring Barley Germplasm Line STARS-9577B

A damage rating scale for wheat and barley seedlings was developed by Webster et al. (1991) based on visual The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), rating of leaf chlorosis, leaf streaking, and leaf spotting. has become a major pest of barley (Hordeum vulgare L.) in the This visual rating was on a scale of 1 to 9 (1 no western USA. STARS-9577B (PI 591617), a six-rowed, spring barley germplasm line with a high level of resistance to RWA, was recently damage, to 9 dead plant). The amount of leaf rolling released to barley breeders for barley improvement. Understanding (1 no rolling to 3 completely rolled) was also noted. the inheritance of RWA resistance in this germplasm line is necessary This scale was used to evaluate RWA resistance of all for breeders to develop an effective strategy for utilization of this available barley accessions (23 070) in the USDA Nagermplasm in their breeding programs. This greenhouse study was tional Small Grains Collection. One hundred-nine acconducted to determine the genetic control of RWA resistance in cessions, all originating from outside the USA, were STARS-9577B. Crosses were made between ‘Morex’, a susceptible, identified with some level of resistance at the seedling six-rowed, malting barley cultivar, and STARS-9577B. Genetic analystage. Homozygous pure lines selections were made ses were performed on reaction to RWA of parents, F1, reciprocal from each accession (Mornhinweg et al., 1996). F1, F2, backcrosses (BC1F1 ) to both parents, and F2-derived F3 families. Nkongolo et al. (1991) reported RWA resistance in Reaction was based on a visual rating scale of 1 to 9 (1 no damage, 9 dead plant). Segregation in the F2 and BC1F1 populations indicated wheat accession PI 372129 to be controlled by a single multiple gene control. Seventy-seven F3 families were found to be dominant gene. Baker et al. (1992) reported RWA resishomozygous resistant and 18 homozygous susceptible, indicating two tance in wheat accession PI 149898 to be under the gene control of RWA resistance in STARS-9577B. Analysis of data control of two genes (one dominant, one incompletely from F2 and BC1F1 populations suggested RWA resistance in STARSdominant). Robinson et al. (1992) reported a single 9577B is controlled by dominant alleles at two loci, with alleles at dominant gene for RWA resistance in barley line S13. one locus conferring a high level of resistance and alleles at the Nieto-Lopez and Blake (1994) analyzed the inheritance other locus conferring an intermediate level of resistance only when of RWA resistance in two barley accessions (PI 366444 recessive alleles are present at the first locus. and PI 366453) and determined there were at least two resistance genes in each accession. Genetic analysis of resistance in STARS-9301B (PI 573080), the first RWAI North America, the Russian wheat aphid, greenbug resistant barley germplasm line released (Mornhinweg [Schizaphis graminum (Rondani)], and the bird et al., 1995a), indicated control of RWA resistance by cherry-oat aphid [Rhopalosiphum padi (L.)] are considalleles at two loci, Rdn1 and Rdn2, originally designated ered the most serious aphid pests of small grains (Porter as Dnb1 and Dnb2 (Mornhinweg et al., 1995b). Specifiet al., 1999). RWA is a devastating pest on barley grown cally, expression of RWA resistance in STARS-9301B in the intermountain regions of the western USA. RWA, involves recessive epistasis of the dominant gene Rdn2 first found in the USA in West Texas in 1986, now on the incompletely dominant gene Rdn1 (Mornhinweg threatens wheat (Triticum aestivum L.) and barley proet al., 1995b). Although this resistance is excellent, mulduction throughout the western USA. Economic loss tiple gene inheritance in STARS-9301B would make the from RWA in the western USA for the period 1987 to utilization of this germplasm line in a barley breeding 1998 has been estimated over $1000 million (Porter et program somewhat complicated. The search continues al., 1999). For barley, in 1992 alone there were 0.7 milfor a barley germplasm line with a high level of resislion hectares infested with RWA, which resulted in a tance to RWA and a simple inheritance pattern, such loss of $18.5 million (Legg and Amosson, 1993). All a line would be preferred by breeders over this more barley cultivars presently in commercial production are complicated inheritance. A second barley germplasm susceptible to RWA feeding damage. Typical RWA line, STARS-9577B (PI 591617), has been released feeding damage to the leaf results in characteristic longi(Mornhinweg et al., 1999). STARS-9577B, a RWAtudinal white, yellow, or red streaks with convolute rollresistant selection from CIho 4165, is an excellent source ing of the leaf. Leaf rolling reduces photosynthetic area, of resistance to the RWA, but little is known of the provides an optimum environment for aphid reproducgenetic control of this resistance. The objective of our tion, protects aphids from contact insecticides and natustudy was to determine the inheritance of RWA resisral predators, and, at the heading stage, can prevent tance in STARS-9577B. spike extrusion and decrease seed set (Mornhinweg et