Isolation of fluorescent pseudomonads from the rhizosphere of banana plants antagonistic towards root necrosing fungi

Abstract

Total aerobic bacteria and fluorescent pseudomonads were counted in bulk and rhizospheric soils of banana plants of 14 plantations in Martinique (French West Indies). Fluorescent Pseudomonas isolates were then identified and investigated for in vitro antagonism towards Cylindrocladium sp., a fungal pathogen of banana roots. Total aerobic bacteria and fluorescent pseudomonads were significantly more abundant in rhizospheric soils than in bulk soils. Among 58 fluorescent Pseudomonas isolates, 41 were identified as Pseudomonas fluorescens biovar V and 17 as Ps. putida biovar A. Six strains exhibited an antagonism towards Cylindrocladium isolates. Among them, Ps. putida strain 93.1 totally blocked fungal growth. No relationship was established between the antifungal effect and enzyme or hydrogen cyanide production by bacteria, suggesting that siderophores and other compounds were involved in fungal inhibition. Antagonistic fluorescent pseudomonads represent a potential for the biological control of banana root infections by Cylindrocladium sp.

Screening for fluorescent pseudomonades, isolated from the rhizosphere of tomato, for antagonistic activity toward Clavibacter michiganensis subsp. michiganensis

“…Bacterial counts in the rhizospheric soils of tomato plants reported here were lower than those previously observed by other authors with other plants (Sutra et al 2000) but the percentages of fluorescent pseudomonads among the aerobic bacteria isolated from the for the rhizosphere and the rhizoplane (7 and 20%, respectively) ( Fig. 1) were similar to those reported in banana plants by Sutra et al (2000). As previously reported by Boubyach et al (2001), fluorescent pseudomonads were predominantly isolated from the rhizoplane.…”

“…Numbers of aerobic bacteria were significantly superior to fluorescent pseudomonades for all samples. Bacterial counts in the rhizospheric soils of tomato plants reported here were lower than those previously observed by other authors with other plants (Sutra et al 2000) but the percentages of fluorescent pseudomonads among the aerobic bacteria isolated from the for the rhizosphere and the rhizoplane (7 and 20%, respectively) ( Fig. 1) were similar to those reported in banana plants by Sutra et al (2000).…”

“…In our investigation, from a total of 303 fluorescent pseudomonads isolated from all samples 44% (134 isolates) were isolated from the rhizoplane, 31% (93 isolates) from the rhizosphere and 25% (76 isolates) from the endorhizosphere (Table 1). However, results on the abundance of bacteria in soils must be interpreted with care; a high variability has been observed when counting fluorescent pseudomonads in several replicate samples of the same soils (Sutra et al 2000). This could be due to a heterogeneous distribution of bacteria in soil in relation with the agricultural practices and the use of chemicals products (Sutra et al 2000).…”

“…Counts of cultivable fast growing bacteria and fluorescent pseudomonads were compared using the Mann-Whitney test (Sutra et al 2000). Data of root colonization were analysed using Newman and Keuls test after transforming percentage to arcsin squares.…”

“…Fluorescent pseudomonads are ubiquitous bacteria that are common inhabitants of rhizosphere, and are the most studied group within the genus Pseudomonas (Weller 1988). They could prevent proliferation of phytopathogens and stimulate plant growth by facilitating either uptake of nutrients from soil or producing certain plant growth promoting substances (Weller 1988;Barnett et al 1999;Sutra et al 2000;Mercado-Blanco et al 2004;Dey et al 2004;Boudyach et al 2004;Ferrona and Deguine 2005;Verma et al 2007;Ahmad et al 2008;Trivedi et al 2008).…”