Relative Wilt‐Inducing Capacity of the Culture Filtrates of Isolates of Fusarium oxysporum f.sp. radicis‐lycopersici, the Tomato Crown and Root Rot Pathogen

Abstract

Cell‐free 30‐day‐old culture filtrates of 24 isolates of Fusarium oxysporum f.sp. radicis‐lycopersici (FORL) differed considerably in their capacity to induce wilting in 28‐day‐old tomato seedings and to inhibiting the germination of tomato seeds. The wilt effects ranged from mild on leaves and lateral stems, to total collapse of the seedlings in 24 h. Wilt, leaf curl and leaf chlorosis, appearing in this sequence, were the three symptoms clicited by the culture filtrates. Boiled and non‐boiled filtrates elicited similar sympotoms. The high wilt capacity filtrates were pH 7.2; the others were generally below pH 6. The high wilt capacity filtrates showed polyphenoloxidase activity but the overall pattern of this activity did not correlate consistently with wilt capacity. The majority of the lower wilt capacity filtrates showed a net inhibition of dihydroxy‐phenylalanine (DOPA) oxidation. The study suggests that the symptoms in the tomato seedlings were elicited by toxins in the culture filtrates. Further, it appears that the differences obtained in the wilt capacity of filtrates from the isolates were due, at least in part, to inherent differences in the concentration of the toxic factors. The rapidity of the onset of wilt, the total, collaps of filtrate‐treated seedlings and the absence of fungi in wilted seedlings suggest further that the operative mechanisms are physiological and biochemical and not impairment of the seedlings’ translocation system by physical blockage with mycelia.

Transforming a NEP1 toxin gene into two Fusarium spp. to enhance mycoherbicide activity on Orobanche—failure and success

“…The bioassay showed inhibition in the germination of tobacco seeds when the NEP 1‐like protein was applied (Fig. 6), similarly to previously reported results 26. This supports the hypothesis that it actually is a NEP 1 gene being expressed in the various formae speciales of F. oxysporum.…”

Rapid Tomato Seedling Assay for Virulent Isolates of Fusarium oxysporum F. sp. Radicis‐lycopersici (FORL), the Tomato Crown and Root Rot Pathogen

“…Table I shows that at 30 min the percetitages of plants wilted in each of the culture filtrates falls into three stalisticaliy different groups which correspond to three groups expressing differential disease capacity of the isolates in a 10-day assay 011 18-day seedhngs. These patterns of will and disease capacities among the isolates are similar 10 that obtained in a recent study with a filtrate will assay for 10 h under differetil conditions (Madhosingh, 1994). The 30-min assay appears suKstantive, therefore, for determining the relative will and disease virulence among FORL isolates.…”

“…Bonny Best is a relatively stisceptible variety of tomato which succumbs quickly to the wilt and disease. The data in this and the previous study (Madhosingh, 1994) suggest that wilt of seedlings is caused by toxic factors and lhat the rates of transpiration and quantitative to.«n uptake affects the rate of wilting for any one FORL isolate. The data imply further that wilting caused by the filtrates was due primarily to soluble toxins.…”

“…Six FORL isolates, selected from three groups based on differential wilt capacities (Madhosingh, 1994), were used in this study. The isolates were HRS-082, HRS-I52 (most virulent), HRS-043, HRS-081 (moderately virulent) and HRS-086, HRS-064 (least virulent).…”

“…These observations suggest that FORL, a virulent tomato pathogen, may cause significant problems in other crop species. Recent studies (Forsberg, 1989;Madhosingh, 1994) have demonstrated the range of differences in wilt capacity and pathogenicity which exist among FORL isolates. Further, periodic loss of pathogenicity or reduced pathogenicity occurs in isolates of FORL (Jarvis, Research Station, Agriculture and AgriFood Canada, Harrow, Ontario, pers.…”