SUSCEPTIBILITY OF POPULUS-DELTOIDES BARTR TO MELAMPSORA-LARICI-POPULINA AND M-ALLII-POPULINA

Qualitative susceptibility to Melampsora spp. was observed in a 6x6 P. deltoides factorial mating. For each of the 3 inocula tested, Melamps ora larici-populina races El and E2 and M. allii-populina, segregation s that occured in qualitative tests cannot be explained with less than 3 genes for susceptibility-resistance. Comparison with EL KARKOURY'S results (1991) suggest that race E1 would have another virulence gene which is not present in E2. However, the observed segregation pattern cannot be explained without another gene common to El and E2. Within 3 full sib families, qualitative resistance to both M. allii-populina a nd M. larici-populina may be genetically linked. Obviously, several un identified races of M. allii-populina were present in the nursery tria l.