Populations of Nonpathogenic Fusarium oxysporum Associated with Roots of Four Plant Species Compared to Soilborne Populations

Abstract

The effect of the plant on the diversity of soilborne populations of Fusarium oxysporum was assessed after successive cultures of flax, melon, tomato, and wheat in separate samples of the same soil. Forty soil-borne isolates of F. oxysporum and forty root-colonizing isolates of each plant species were sampled during the first (T0) and fourth (T1) cultures. The population structures were assessed by a genotypic method based on restriction fragment analysis of polymerase chain reaction-amplified ri-bosomal intergenic spacer (IGS) DNA. Sixteen IGS types were defined among the four hundred isolates analyzed. The distributions of soil isolates among IGS types were similar at both sampling times. The structure of F. oxysporum populations associated with the roots of flax or melon did not differ from the structure of soilborne populations. In contrast, the structure of F. oxysporum populations associated with roots of wheat or tomato differed from the structure of soilborne populations. High frequencies were found for IGS type 4 among wheat isolates at both T0 and T1 and for IGS type 11 among tomato isolates at T1. Moreover, a high level of genetic divergence was obtained between IGS types 4 and 11. Our results suggest that tomato and wheat have a selective effect on soilborne populations of F. oxysporum and that this effect seems to be plant specific.

Fungal Assemblages Associated with Roots of Halophytic and Non-halophytic Plant Species Vary Differentially Along a Salinity Gradient

“…In the first place, the great differences observed between the root fungal colonizers and those dwelling few centimeters apart in the rhizospheric soil would indicate specific adaptations either by certain fungi to enter and extend within plant tissues or by the host plant to trim among the soilborne-to-endophyte candidates. The latter capacity has been already observed in some plant species [32], and roots of Inula species (including the ones studied here) are known to produce antimicrobial metabolites that may affect their colonization by fungal endophytes (e.g., [33,34]). Fungi also differ broadly in their ability to invade plant tissues, and probably, the final selection of root colonizers is the result of both plant barriers and fungal capabilities.…”

Response of antioxidant enzymes and some metabolic activities in wheat to Fusarium spp. Infections

“…The latter can colonize the cortex of plant roots without causing disease symptoms (Appel and Gordon, 1994), surviving in live tissues. They may also cause antagonism between pathogenic forms in the soil (Edel et al, 1997). Fusarium species are common pathogens of wheat and barley, causing various diseases: foot and root rot, crown rot, and Fusarium head blight (FHB).…”

Highly Diverse Endophytic and Soil Fusarium oxysporum Populations Associated with Field-Grown Tomato Plants

“…These novel sequence types suggest that focusing only on plant-pathogenic F. oxysporum may underestimate the total species diversity. Other studies indicate that F. oxysporum populations from soil are geographically heterogeneous and greatly influenced by resident plant populations (19,20,21), suggesting that some plants may exert a selective effect on soil populations of F. oxysporum (22). Studies comparing pathogenic and nonpathogenic F. oxysporum populations associated with the same host have found much higher levels of diversity in the nonpathogenic populations than in the pathogens (11,14,23,24).…”

“…Also, different genotypes may interact with their host plants in different ways; for example, studies focusing on developing nonpathogenic F. oxysporum fungi as biocontrol agents have found particular isolates to be better biocontrol agents than others (26,27,28). A few studies have reported overrepresentation of a few genotypes within endophytic populations (12,22), suggesting a possible selective effect by the host on soil populations.…”