Influence of Plant Root Exudates, Germ Tube Orientation and Passive Conidia Transport on Biological Control of Fusarium Wilt by Strains of Nonpathogenic Fusarium oxysporum |
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Authors: | Qaher A Mandeel |
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Institution: | (1) Department of Biology, College of Science, University of Bahrain, PO Box 32038, Isa Town Campus, Isa town, Kingdom of Bahrain |
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Abstract: | In earlier studies, biological control of Fusarium wilt of cucumber induced by Fusarium oxysporum f. sp. cucumerinum was demonstrated using nonpathogenic strains C5 and C14 of Fusarium oxysporum. Strain C14 induced resistance and competed for infection sites whether roots were wounded or intact, whereas strain C5 required
wounds to achieve biocontrol. In the current work, additional attributes involved in enhanced resistance by nonpathogenic
biocontrol agents strains to Fusarium wilt of cucumber and pea were further investigated. In pre-penetration assays, pathogenic
formae specials exhibited a significantly higher percentage of spore germination in 4-day-old root exudates of cucumber and
pea than nonpathogens. Also, strain C5 exhibited the lowest significant reduction in spore germination in contrast to strain
C14 or control. One-day-old cucumber roots injected with strain C14 resulted in significant reduction in germ tube orientation
towards the root surface, 48–96 h after inoculation with F. o. cucumerinum spores, whereas strain C5 induced significantly lower spore orientation of the pathogen and only at 72 and 96 h after inoculation.
In post-penetration tests, passive transport of microconidia of pathogenic and nonpathogens in stems from base to apex were
examined when severed plant roots were immersed in spore suspension. In repeated trials, strain C5, F. o. cucumerinum and F. o. pisi were consistently isolated from stem tissues of both cucumber and pea at increasing heights over a 17 days incubation period.
Strain C14 however, was recovered at a maximum translocation distance of 4.6 cm at day 6 and later height of isolation significantly
declined thereafter to 1.2 cm at day 17. In pea stem, the decline was even less. Significant induction of resistance to challenge
inoculation by the pathogen in cucumber occurred 72 and 96 h after pre-inoculation with biocontrol agents. Nonetheless, strain
C14 induced protection as early as 48 h and the maximum resistance was reached at 96 h. The presented data confirm the previous
findings that attributes important for nonpathogenic fusaria to induce resistant are: rapid spore germination and orientation
in response to root exudate; active root penetration and passive conidia transport in stem to initiate defence reaction without
pathogenicity and enough lag period between induction and challenge inoculation. Strain C14 possesses all these qualifications
and hence its ability to enhance host resistance is superior than strain C5. |
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Keywords: | biological control induced resistance nonpathogenic Fusarium oxysporum |
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