Penetration and colonization of resistant and susceptible Apium graveolens by Fusarium oxysporum f.sp. apii race 2: callose as a structural response

Abstract

Root apices of Apium graveolens L. resistant and susceptible to race 2 of Fusarium oxysporum f.sp. apii (R. Nels. & Sherb.) were studied at various times after inoculation, using light and electron microscopy to determine structural response(s) of the hosts during penetration and colonization by the pathogen. Penetration was intercellular and intracellular and involved mechanical and enzymatic mechanisms. At the onset of penetration, the host cell walls manifested fluorescence, induced with either aniline blue or sirofluor, at the point of penetration. The fluorescent area was more intense and larger in the resistant host. Fluorescence disappeared with time. After incubation with β-1,3 glucanase fluorescence disappeared, indicating β-1,3 polysaccharide (probably callose) presence. Callose deposits were 2 and 3 times greater in the epidermis and 4 and 9 times greater in the cortex of the resistant than in two susceptible hosts, respectively. Hyphal counts in the cortex of the resistant host were 50% fewer than in the susceptible hosts. Increased callose deposition on host cell walls was associated with reduced colonization. Callose formed in vascular tissue as the fungus colonized it. Callose detection with sirofluor was more sensitive; background fluorescence common with aniline blue without periodic acid – Schiff's reagent pretreatment was absent.

Process of tomato root colonization by a pathogenic strain of Fusarium oxysporum f. sp. lycopersici in comparison with a non‐pathogenic strain

“…The same but less intense and numerous defence reactions as described for the non-pathogenic strain have been observed in the root invaded by the pathogen : wall appositions and thickenings ; intracellular and intercellular deposits attached on hyphae ; and accumulation of granular plugs in the vessels. These defence reactions have been observed in other plant species infected by other formae speciales of F. oxysporum (Charest et al, 1984 ;Jordan et al, 1988 ;Tessier et al, 1990 ;Benhamou et al, 1990a). Based on our observations with F. oxysporum f. sp.…”

“…This leads to the conclusion that both possibilities exist, and that depending on the strain studied, on the forma specialis and on the experimental conditions, one or the other possibility is predominant. This might explain why the research published to date is so confusing (Alconero, 1968 ;Smith & Peterson, 1983 ;Jordan et al, 1988 ;Farquhar & Peterson, 1989 ;Bhalla et al, 1992). Finally, this study supports the hypothesis that the pathogenic and the non-pathogenic F. oxysporum might compete for colonization of the root surface and the root tissues.…”

Endophytic algae ofChondrus crispus(Rhodophyta). V. Fine structure of the infection byAcrochaete operculata(Chlorophyta)

“…In addition, mechanical penetration of the host has been reported in terrestrial associations, usually complementary to enzymatic penetration of the cuticle. An inward bending of the cuticle is characteristic of mechanical penetration (Politis & Wheeler, 1973;Jordan et al, 1988).…”

The infection process ofFusarium oxysporum in cotton root tips

“…Although no quantitative data were provided previously, it has been suggested that the penetration of F. oxysporum takes place in the root cap (Alconero 1968), in the meristematic zone (Bishop and Cooper 1983, Gerick and Huisman 1985, Farquhar and Peterson 1989, Smith and Peterson 1983 or in the elongation zone (Bhalla et al 1992, Jordan et al 1987. The root secretes exudates.…”