| The Russian wheat aphid (RWA) is a serious economic pest of cereals. RWA infestation results in leaf rolling, leaf and head trapping, and death of susceptible plants. A RWA resistance gene Dn7 which was introduced into wheat from rye by 1BL.1RS translocation provides superior level of resistance against RWA biotypes 1 and 2. The objectives of this study were to: (1) Saturate the genetic map of a gene-rich region in rye chromosome arm 1RS, containing Dn7, (2) find out if there is synteny between the 1RS chromosome region containing Dn7 and rice, and (3) develop an in-vitro assay using RWA biotypes 1 & 2 to screen wheat genotypes. A saturated genetic map of 1RS region containing Dn7 with 26 DNA markers was generated on 98 recombinant inbred lines from a cross between wheat line '94M370' (resistant to RWA) and wheat cultivar 'Gamtoos' (susceptible). The markers flanking Dn7 are XHor1 and XIb267 which are 2.1 and 3.9cM from Dn7, respectively. PCR-based markers for Dn7 were developed for the first time. To ascertain synteny between 1RS region containing Dn7 and rice genome, DNA sequences of the markers linked to Dn7 were used to do BLAST homology searches with the rice databases. Three DNA markers linked to Dn7 were found to be homologous with rice BAC/PACs from rice chromosome 1. The rice BAC/PACs aligned in the same order as markers in Dn7 linkage map. For in vitro studies, cut etiolated seedlings of RWA resistant and susceptible cultivars were treated with crude extract, saliva, proteins, and non protein compounds of RWA biotypes 1 and 2. The data obtained from RWA crude extract, saliva, proteins and non protein compounds were generally uninformative as few significant differences were observed between treatments and control. |
