GENETIC AND PHYSIOLOGICAL ANALYSIS OF DOUBLED-HAPLOID, ALUMINUM-RESISTANT LINES OF WHEAT PROVIDE EVIDENCE FOR THE INVOLVEMENT OF A 23 KD, ROOT EXUDATE POLYPEPTIDE IN MEDIATING RESISTANCE

We have made use of a genetic approach to develop homozygous, near-iso genic germplasm for investigating aluminium (Al) resistance in Triticu m aestivum L. A conventional backcross program was used to transfer Al resistance from the Al-resistant cultivar, Maringa, to a locally-adap ted, Al-sensitive cultivar, Katepwa. At the third backcross stage, a s ingle, resistant isoline (Alikat = Katepwa3/Maringa) was chosen on th e basis of superior root growth after 14 days of exposure to a broad r ange of Al concentrations (0 to 600 mu M). Genetic analysis of doubled -haploid lines (DH) developed from this isoline suggested that resista nce is controlled by a single dominant gene. Crosses between DH Alikat and DH Katepwa yielded an Al-resistant F1 population. Backcrossing th is F1 population to DH Katepwa produced a population which segregated 1:1 for Al resistance, while selfing produced a population segregating 3:1 for Al resistance. Under conditions of Al stress, Al-resistant F2 plants released a suite of novel low molecular weight polypeptides in to the rhizosphere. One of these polypeptides (23 kD) shows substantiv e Al-binding capacity and segregates with the resistant phenotype. Whi le the precise mechanisms that mediate Al resistance are still unknown , this research has provided support for a possible role of the 23 kD exudate polypeptide in mediating resistance to Al. To more fully under stand the role that this polypeptide plays in Al-resistance, we are at tempting to clone this gene from microsequence data obtained from puri fied protein.