EXPRESSION OF THE PR-B(1)'' GENE IN ROOTS OF 2 NICOTIANA SPECIES AND THEIR AMPHIDIPLOID HYBRID INFECTED WITH VIRULENT AND AVIRULENT RACES OF CHALARA-ELEGANS

The expression levels of PR-b1'' gene coding for PR-b1'' protein (a PR -I group protein) were investigated in the roots of two Nicotiana spec ies and their amphidiploid hybrid in response to infection by virulent (84-1) or avirulent (85-26) races of black root rot fungus Chalara el egans. Nicotiana glutinosa is susceptible to C. elegans, while Nicotia na debneyi and the amphidiploid hybrid N. glutinosa x N. debneyi are h ighly resistant. The results showed that irrespective of whether the p lant is susceptible or resistant, and the fungal race virulent or avir ulent, low infection rates induce low levels of PR-b1'' mRNA, and high infection rates result in high production of PR-b1'' mRNA. The amphid iploid hybrid, which expresses the protein PR-b1'' constitutively, sho wed similar PR-b1'' mRNA levels with both races of C. elegans. At maxi mal levels of accumulation, PR-b1'' mRNA is quantitatively similar in the two Nicotiana species, and the amphidiploid hybrid, whatever the n ature of the inoculum.