MECHANISMS OF DISEASE RESISTANCE IN GOSSYPIUM SPECIES AND VARIATION IN VERTICILLIUM DAHLIAE
Mar 10, 2017

Breeding & Genetic improvement WCRC Breeding-NorthAmerica WCRC1
Introduction                                                                Back to Table of contents

Studies on Verticillium wilt of cotton have concentrated on host resistance to the pathogen and on genetic variation and mechanisms of virulence in Verticillium dahliae.  The resistance of cotton to V. dahliae depends on a number of anatomical and chemical characteristics that occur both constitutively and as active defense responses.  Terpenoid phytoalexins and condensed tannins appear to be especially important in defense reactions. Resistance in cultivars correlates with the concentration of tannin in leaves, the rate of phytoalexin synthesis in xylem vessels in response to infection, and the toxicity of the phytoalexins and tannins to V. dahliae.  Enzymes that appear to have critical roles in regulating terpenoid and tannin synthesis have been characterized, and partial genes coding for these enzymes have been cloned.  Strategies for manipulation of these genes and for introduction of foreign genes from other malvaceous plants to improve cotton resistance to wilt are being developed.  Vegetative compatibility (V-C) tests and isozyme analyses have been used to show that there are four genetically isolated populations (V-C groups) within the species V. dahliae, and that each V-C group has at least two subgroups.  The V-C groups and subgroups vary in geographical occurrence, virulence to cotton and other crops, and sensitivity to fungicides.  The severe defoliating form of Verticillium wilt found in the southwestern USA and in Peru is caused by isolates in the V-C 1A subgroup, whereas wilt in Europe and Asia is caused by isolates in the V-C 2 group.  Wilt in Australia is incited by isolates in the V-C 4B subgroup.  Isolates in the V-C 1A group show unique resistance to the antibiotic sanguinarine and have the ability to induce large accumulations of ammonium ions in cotton leaf tissues.  Identifying the specific V-C groups responsible for wilts in a given field and geographical area should allow better recommendations for disease control measures...

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