Inheritance and allelism for resistance to Russian wheat aphid in an Iranian spring wheat

Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is an important pes t of wheat (Triticum aestivum L.) in the United States of America. Developi ng adapted wheat cultivars with genetic resistance to RWA is an effective c ontrol strategy. Genetic studies were conducted to determine the mode of in heritance of gene(s) conferring resistance to RWA in an Iranian landrace wh eat line, G 5864. For the inheritance study, G 5864 was crossed with the su sceptible wheats 'Yecora Rojo' and ND 2375. Seedlings of F-1, reciprocal F- 1, F-2, BC1 to the susceptible parent (BCS), and BC1 to the resistant paren t (BCR) were screened for RWA reaction. Several phenotypic segregation rati os were tested in the F-2 populations for goodness of fit; the 9:3:3:1 rati o (resistant: rolled leaves: stunted plants: susceptible) was an acceptable fit in all cases. Thus, resistance in G 5864 seemed to be controlled by tw o independent dominant genes with additive gene effects. The allelic relati onships of gene(s) in this line with genes in other resistant lines, PI 137 739 (Dn1), PI 262660 (Dn2), PI 372129 (Dn4), PI 294994 (Dn5), and PI 243781 (Dn6), were also studied. Segregation patterns observed in G 5864 x resist ant (R x R) F-2 populations were inconclusive. However, no susceptible plan ts were observed in these F-2 populations. If previous reports concerning t he number of resistance genes present in the other resistant lines are corr ect, then given the high manifestation of resistance observed in G 5864, an d given the absence of susceptible plants in the R x R F-2 populations, it is indicated that RWA resistance in G 5864 is either controlled by differen t alleles at the same loci as the other resistance genes, or that G 5864 sh ares a resistance gene with each of the other resistant lines.