A histological comparison of fungal colonization in tomato seedlings susceptible or resistant to Fusarium crown and root rot disease

Abstract

Root colonization of tomato cultivars susceptible or resistant to Fusarium crown and root rot disease, caused by the pathogen Fusarium oxysporum f.sp. radicis-lycopersici Jarvis & Shoemaker, was studied histologically. In seedlings of susceptible cultivars ('Ohio MR13', 'Bonny Best', and 'Vendor') held at 22 °C, direct penetration of epidermal cells occurred by 24 h after inoculation and colonization of suberized hypodermal cells and adjacent intercellular spaces by 72 h. The cortex was colonized between 72 and 96 h after inoculation and the stele was commonly colonized by 120 to 144 h. Colonization of the cortex and stele was associated with the breakdown of parenchymatous cell walls and middle lamellae near fungal hyphae. In cultivars resistant by a single dominant gene ('CR6', 'Larma', and 'B82-865') colonization was similar to that in susceptible cultivars until 72 h after inoculation. By this time, papillae were abundant within hypodermal cells. Successful colonization of hypodermal sites was associated with the incorporation of phenolic or lignin-like materials and suberin within cell walls of the underlying cortex. These cortical wall modifications were paralleled by the deposition of electron-opaque material into cortical cell walls and middle lamellae and the production of finely granular bands around the peripheries of colonized intercellular spaces. Phenolic-containing structural defensive barriers (i.e., papillae and modified cortical cell walls) appear to be important in limiting fungal colonization in cultivars possessing single dominant gene resistance to this disease.

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

“…The barrier was generally effective in limiting the extension of the non-pathogenic strain, which was restricted to the superficial layers of cells. This interpretation of our observations is in agreement with that of Brammall & Higgins (1988), who suggest that the hypodermis might be an important barrier to colonization of the inner cortex of tomato roots by F. oxysporum f. sp. radicis lycopersici.…”

“…lycopersici (Bishop & Cooper, 1983) and F. oxysporum f. sp. radicis lycopersici (Charest et al, 1984 ;Brammall & Higgins, 1988 ;Benhamou et al, 1990a,b), here we describe the colonization process under the same experimental conditions as those used for the nonpathogenic strain in order to compare the two patterns of colonization. The pathogenic F. oxysporum f. sp.…”

Colonization of tomato root by a non‐pathogenic strain of Fusarium oxysporum

“…The defence reactions observed in tomato colonized by this non-pathogenic strains of F. oxysporum did not differ from those described in tomato and other plant species infected by compatible or incompatible formae speciales of F. oxysporum (Charest et al, 1984;Brammall & Higgins. 1988;Teissier, Mueller & Morgham, 1990).…”

Microconidia germination of the tomato pathogenFusarium oxysporumin the presence of root exudates

“…lycopersici (Fol 007) in root exudates from tomato (host plant) and non-host plants. a decisive role in root exudation, similarly to plant species, cultivars, temperature or stress factors (Brammall & Higgins 1988, Hale et al 1978, Short & Lacy 1976. Compounds, such as root exudates sugars and organic acids, were shown to vary during individual growth stages of tomato (Kravchenko et al 2003, Lugtenberg et al 1999.…”

“…All stages are present in infected tissues or soil (Nelson 1981). Details of the colonization process of F. oxysporum within and outside the vascular system have been studied by several authors (Brammall & Higgins 1988, Charest et al 1984, Lagopodi et al 2002, Olivain & Alabouvette 1997, Rodriguez-Gálvez & Mendgen 1995 and the mycelial development in the vicinity of plant roots has been investigated by Steinberg et al (1999), but little is known about the germination of F. oxysporum propagules, a key step in plant-pathogen interactions (Nelson 1991). The purpose of our study was to assess the effect of root exudates of host (tomato) and non-host plants on spore germination of Fusarium oxysporum pathogenic on tomato.…”