Interactions in the Tomato Rhizosphere of Two Pseudomonas Biocontrol Strains with the Phytopathogenic Fungus Fusarium oxysporum f. sp. radicis-lycopersici

Abstract

The fungus Fusarium oxysporum f. sp. radicis-lycopersici causes foot and root rot of tomato plants, which can be controlled by the bacteria Pseudomonas fluorescens WCS365 and P. chlororaphis PCL1391. Induced systemic resistance is thought to be involved in biocontrol by P. fluorescens WCS365. The antifungal metabolite phenazine-1-carboxamide (PCN), as well as efficient root colonization, are essential in the mechanism of biocontrol by P. chlororaphis PCL1391. To understand the effects of bacterial strains WCS365 and PCL1391 on the fungus in the tomato rhizosphere, microscopic analyses were performed using different autofluorescent proteins as markers. Tomato seedlings were inoculated with biocontrol bacteria and planted in an F. oxysporum f. sp. radicis-lycopersici-infested gnotobiotic sand system. Confocal laser scanning microscope analyses of the interactions in the tomato rhizosphere revealed that i) the microbes effectively compete for the same niche, and presumably also for root exudate nutrients; ii) the presence of either of the two bacteria negatively affects infection of the tomato root by the fungus; iii) both biocontrol bacteria colonize the hyphae extensively, which may represent a new mechanism in biocontrol by these pseudomonads; and iv) the production of PCN by P. chlororaphis PCL1391 negatively affects hyphal growth and branching, which presumably affects the colonization and infecting ability of the fungus.

Antagonistic Gluconobacter sp. induces abnormal morphodifferentiation to Fusarium oxysporum f. sp. lycopersici hyphae

“…19) This possibly reduces the aggressive nature of Fusarium sp. 5) As shown in this study, rhizobacteria from alien plants may Vol. 33, No.…”

“…However, these new hyphae never reached normal thickness and were stunted in growth as a result of accelerated aging. 5) The creation of cytoplasmic vacuolation as a result of continual cytoplasmic extrusion further supports the phenomenon of acceleration in the aging process of hyphae. 19) This possibly reduces the aggressive nature of Fusarium sp.…”

“…5,6) Indeed, control of Fusarium sp., even with chemical fungicide combined with field management strategies, is difficult in practice; hence, the continual existence and high prevalence of several wilt diseases have prompted scientists to search for biological alternatives that are efficient, reliable and safe for the environment. 7,8) Therefore, we set up our experiment with a wider scope, to search for bacterial isolates that could inhibit the growth of Fusarium mycelia in vitro.…”

Red Pigment Production By Monascus Purpureus In Stirred-Drum Bioreactor

“…Otherwise the continuous mixing would most probably be necessary in order to aerate a relatively large volume of substrate, particularly in the central and at the bottom of the bed. Substrate capacity also strongly affects the fungal growth, as surface-mass ratio of the substrate was directly related to the surface area available for the growth to occur [21]. A method to determine the optimal loading capacity of a bioreactor has not been well established, especially in regard to this study.…”

Biocontrol of Fusarium wilt of banana: Key influence factors and strategies

“…The colonization of antagonistic microbes is hampered by several natural barriers. Obstacles to the initial colonization refers to the first set of natural barriers encountered by the antagonistic microbes after the application of BCAs, including the predation and phagocytosis from soil protozoa (Ekelund et al, 2001;Ronn et al, 2002), inhibition from the exudates of indigenous microbes (Bolwerk et al, 2003) or plant roots (Chao et al, 1986), the competition with indigenous microbes for ecological sites, nutrients and energy. Normally, influenced by these barriers, the population of most antagonistic microbes reduced drastically in the first 2 to 3 days after the application of the BCAs (Christoffersen et al, 1995).…”