DIFFERENTIAL DISEASE REACTIONS ON LUCERNE GENOTYPES INOCULATED WITH PHYTOPHTHORA-MEDICAGINIS ISOLATES FROM LUCERNE AND CHICKPEA

Stem inoculation of clonally propagated lucerne genotypes was used to assess levels of host species and genotype specialisation in Phytophth ora medicaginis. A quantitative assessment of pathogenic aggressivenes s of 29 P. medicaginis isolates (from lucerne and chickpea) on 9 diffe rent clonally propagated lucerne genotypes revealed no significant dif ference in aggressiveness between isolates from lucerne and those from chickpea on all of the lucerne genotypes. This supported previous stu dies which showed that P. medicaginis isolates from lucerne and chickp ea were indistinguishable using random amplified polymorphic DNA (RAPD ) analysis. Analysis of pathogenic aggressiveness towards individual l ucerne genotypes revealed, for the first time, specificity of individu al P. medicaginis isolates. This has implications for breeding for res istance to P. medicaginis in lucerne, where screening should be done u sing the widest range of pathogen specificity obtainable.