Physiologic Specialization (Pathogenic Variability)

  • Govind Singh Saharan
  • Naresh Mehta
  • Prabhu Dayal Meena


Specificity in the downy mildew fungus on crucifers is very complex, since it occurs on a wide range of wild hosts as well as agricultural and horticultural species. However, there has been little sustained effort to introduce resistance to the disease; hence there has been less selection pressure exerted on the pathogen population than is the case with many other obligate parasites. Further impetus has been added by the exponential growth in research on the wild crucifer Arabidopsis thaliana, as a host for Hyaloperonospora parasitica and serving as a model system for genetic and molecular analysis. Discontinuities in the host range of isolates from different host genera and species suggest that the fungus may exist as a series of pathotypes adapted to each host of origin, although some cross infections may occur. There is also growing evidence that within host species, specificity may be determined by genotype-specific interactions consistent with a gene-for-gene recognition system. Specificity might therefore be expressed at several levels including family, genus, species, and cultivar or accession. In view of the close cytogenetic relationship between the major Brassica species, coupled with the strongly outbreeding nature of several of these crops, some overlap in the host range of species-adapted isolates is perhaps predictable. Physiologic specialization/pathogenic variability has long been recorded in H. parasitica infecting cruciferous plants all over the world.


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© Springer Nature Singapore Pte Ltd. 2017

Authors and Affiliations

  • Govind Singh Saharan
    • 1
  • Naresh Mehta
    • 1
  • Prabhu Dayal Meena
    • 2
  1. 1.Department of Plant PathologyCCS Haryana Agricultural UniversityHisarIndia
  2. 2.ICAR-Directorate of Rapeseed Mustard ResearchBharatpurIndia

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