Verticillium wilt of chrysanthemum: anatomical observations on colonization of roots, stem, and leaves

Abstract

The morphology and distribution of Verticillium dahliae Kleb. within the ornamental chrysanthemum (Chrysanthemum morifolium Ramat) was determined at intervals after placement of rooted cuttings into infested potting mix. Most infection sites on the root system occurred on roots that developed after potting. Estimates of the number of infection courts per 100 cm of root ranged from 5.6 to 15.8. Root-cortex cells responded to invasion by producing lignitubers and a dark pigment. Microsclerotia had formed within root-cortex cells 8 days after potting. Hyphae, conidia, and conidiophores were observed throughout the vascular system. Hyphal widths ranged from 1.3 to 3.6 μm; conidial dimensions ranged from 1.8 × 3.6 to 2.6 × 5.8 μm. Colonization of vessels of stem and leaves was initially discontinuous and was therefore presumably initiated by conidia. Hyphae in root and stem vessels were generally narrow and there was rarely more than one strand per vessel. Occlusion of the lumen or pore plate of vessel elements in root and stem by hyphae, conidia, gums, gels, or tyloses was not observed. Conidia accumulated in petioles and basal portions of the midrib and lateral veins of leaves, often blocking pore plates. Initially, hyphae in leaf vessel elements were narrow but as wilt symptoms appeared, wide sinuous hyphae predominated, often coursing freely among adjacent vessel elements through pit-pairs and pore plates. Mycelium and conidia appeared to occur sufficiently abundantly in leaf vessels to significantly restrict water flow.

Towards a mechanistic model for the Verticillium dahliaepotato system

“…Ideally, also fungal components, like root and stem infection, should be included in the criterion value, but we have not quantified these parameters. Despite this simplification of reality, root and stem infection by V. dahliae were reasonably in line with data from Evans and Gleeson (1973), Alexander and Hall (1974), Nicot and Rouse (1987b) and Huisman (1988).…”

“…Each of the Y final parameter sets are considered as one of the optimal solutions of the model. For a detailed description and discussion of the optimization J Derived using data from Alexander and Hall (1974), Pollock and Drysdale (1976) and Perry and Evert (1983), who showed that once the root is penetrated, spread can be very fast, resulting at harvest time in completely colonised plants, and from Nicot and Rouse (1987b), who showed that at an inoculum deusity of 15 microsclerotia g J soil Russet Burbank potatoes mayor may not be completely colonised at harvest time. program, see Klepper and Rouse (1991).…”

“…Only a fraction of successful root infections reach the vascular system (Evert and Gleeson, 1973;Huisman, 1982). The intact endodermis seems to be resistant to infection by V. dahliae (Alexander and Hall, 1974;Bishop and Cooper, 1983;Perry and Evert, 1983). Key factors for the penetration of the vascular system are rate of fungal growth to reach the protoxylem (Bishop and Cooker, 1983) and root wounding.…”

“…Key factors for the penetration of the vascular system are rate of fungal growth to reach the protoxylem (Bishop and Cooker, 1983) and root wounding. In the xylem, the fungus produces conidia (Reinke and Berthold, 1879;Alexander and Hall, 1974;Ioannou et al, 1977) which ate transported passively. Conidia may stick to the perforation plates, where they may germinate.…”

Verticillium dahliaeand other pathogenic fungi inCirsium arvensefrom New Zealand pastures: occurrence, pathogenicity and biological control potential

“…dahliae has attributes that make it of particular interest with regard to its potential to colonize, and hence incapacitate, the creeping root system of C. arvense and the new shoots generated each year. It produces conidia within vessels of infected plants that enable it to develop systemically within below-ground and above-ground organs (Wright 1968;Alexander & Hall 1974). The fungus was extremely common in our survey, being found in C. arvense throughout New Zealand and throughout the growing season; 30% and 51% of sites sampled in spring and summer/autumn, respectively (Tables 3 and 6).…”