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Verticillium Wilt Of The Hop
Author(s) -
KEYWORTH W. G.
Publication year - 1953
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1953.tb01087.x
Subject(s) - biology , verticillium wilt , inoculation , pith , verticillium , fungus , virulence , root crops , botany , resistance (ecology) , verticillium dahliae , horticulture , cultivar , agronomy , gene , biochemistry
The two hop varieties Fuggle and OR 55 have respectively low and high resistance to wilt caused by virulent strains of Verticillium albo‐atrum. When the pathogen enters through the roots it grows vigorously in the stems of Fuggle plants and slightly in the stems of OR 55 plants. Leaf symptoms are correspondingly severe and mild. If Fuggle stems are grafted on to OR 55 roots and vice versa , and the fungus thus invades the stems from roots of the opposite resistance type, it now grows slightly in the Fuggle stems and vigorously in the OR 55 stems. Leaf symptoms are correspondingly mild and severe, and thus wilt intensity is related to the variety of root and not to the variety of stem. Evidence is available which shows that this is not due to the transfer of a ‘resistance factor’ generated in the resistant roots. The variety Fuggle has low resistance to virulent strains of V. albo‐atrum but high resistance to mild strains. As in the case of varietal type this resistance is expressed by vigorous or slight growth of the fungus in the stems (and corresponding leaf symptoms) when the fungi are introduced through Fuggle roots. When they are directly inoculated into the stems there is no differentiation of the strains. If a small inoculum is used both strains induce mild wilt. If a large inoculum is inserted into a pith cavity both strains induce severe wilt. The reaction of the Fuggle stem is thus governed by conditions relating to the type of invasion and not to the strain of pathogen. It is suggested that this also applies with root inoculations. Normal stems of both Fuggle and OR 55 varieties have a high resistance to invasion from a weak source of the pathogen (such as exists in a highly resistant root), and the fungus can invade the stems heavily only from a suitable inoculum source (i.e. a root of low resistance). Heavy invasion of the stem from a root may be due to1 A lowering of stem resistance by:(a) toxins diffused from the invaded root, (b) an impairment of normal root function.2 An increase in invasive power of the pathogen by:(a) the establishment of a ‘food base’ in the root, (b) the diffusion of a ‘fungal accelerator’.The main conclusions that the primary focus of the disease is in the root and that the normal stems of all varieties possess a similar (and possibly high) resistance is supported by other researches on Fusarium wilt of tomatoes and other wilt diseases and may be of general application.