Studies on the Colonization of Plant Roots by Verticillium dahliae Klebahn With Use of Immunofluorescent Staining

Abstract

The colonization of plant roots by Verticillium dahliae was studied with use of fluorescent antibodies to stain the fungus in soil and on plant roots. Microsclerotia were observed germinating in rhizosphere soil and in soil amended with nutrients. Germination occurred much earlier in soil amended with either a sugariamino acid solution or a solution of wheat root extract than in soil amended with distilled water. Usually only a single germ tube was observed, but some microsclerotia produced two, three or more initials. These grew into hyphal strands up to 100 μm long, but most began to lyse when the length exceeded 30 μm. Hyphae of V. dahliae were observed on the roots of both immune (wheat) and susceptible (common thorn-apple, cotton and Noogoora burr) plants growing in field soils infested with microsclerotia. These hyphae were sparse, up to 1500 μm in length and appeared to enter the cortex of the young roots directly, without the aid of specialized penetrating structures such as appressoria. Sporulating hyphae were observed on the rhizoplane of each of the four species examined. Conidial germination, however, was not observed on the rhizoplane. By cultural methods it was established that V . Dahliae colonized plant roots 2-3 cm back from the root tip, suggesting that microsclerotia are stimulated to germinate by the advancing root. Examination of the rhizosphere soil around the root cap and the zone prior to vascular differentiation failed to produce evidence of conidia or other structures that may have functioned as an intermediate stage in the colonization of plant roots by V. dahliae.

Effect of plant roots on the germination of microsclerotia ofVerticillum dahliae

“…In accordance with other authors [Emmatty and Green, 1969;Fitzell et al, 1980;Schnathorst, 1981;Schreiber and Green, 1963;Zilberstein et al, 1983b], we found that the stimulation of germination of MS of V. dahliae by plant roots is to some extent unspecific for crops. In accordance with other authors [Emmatty and Green, 1969;Fitzell et al, 1980;Schnathorst, 1981;Schreiber and Green, 1963;Zilberstein et al, 1983b], we found that the stimulation of germination of MS of V. dahliae by plant roots is to some extent unspecific for crops.…”

“…Fitzell et al [1980] found that the density of root colonisation by V. dahliae increased up to 20 mm from a growing root tip in wheat (Triticum aestivum) and thornapple (Datura stramonium), but Gerik and Huisman [1988] showed that in cotton the occurrence of colonies of V. dahliae did not increase beyond 5 mm from the root tip. Both these studies [Fitzell et al, 1980;Gerik and Huisman, 1988] give only an indication of the number of colonies at the root surface. Because of possible inter-actions between MS, root exudates, and rhizosphere microorganisms, the colonization of the root does not necessarily give a good indication of the effect of a root on the germination of MS in the soil.…”

Characterization of chitinase secreted by Bacillus cereus strain CH2 and evaluation of its efficacy against Verticillium wilt of eggplant

“…can cause vascular wilt, which is a serious disease of many plant species, including eggplant and cotton, in many areas of the world (Bhat and Subbarao 2001;Huang et al 2006), resulting in severe yield loss or even death (Levin et al 2003;Thanassoulopoulos et al 1979), because microsclerotia of V. dahliae primarily infect the region near root tips throughout the growing season without having to colonize the root surface extensively prior to the infection (Fitzell et al 1980;Gerik and Huisman 1988).…”

Diversity, Pathogenicity, and Management of Verticillium Species

“…In the absence of a host, microsclerotia can remain viable for up to 14 years (165), whereas the survival of melanized mycelium of V. albo-atrum is limited to 2-5 years (81,139). Upon germination, microsclerotia produce one to several hyphae that extend toward host roots (52). There is no evidence of any host-specific requirements or relationships that limit the initial colonization of roots during germination (47,52,90,101,136).…”

“…There is no evidence of any host-specific requirements or relationships that limit the initial colonization of roots during germination (47,52,90,101,136). Colonization of the root surface was often observed at or near root tips, or following root hairs to the root surface, with hyphae growing between epidermal cells (48,52,58,163,172).…”