Survival of the rhizosphere-competent biocontrol strainPseudomonas fluorescensNBRI2650 in the soil and phytosphere

Abstract

Pseudomonas fluorescens NBRI2650 was isolated after screening 360 bacterial strains from the rhizosphere of chickpea (Cicer arietinum L.) grown in fungal-disease-suppressive field soil. The strain was selected because of its high rhizosphere competence and ability to inhibit the growth of Fusarium oxysporum f.sp. ciceri, Rhizoctonia bataticola, and Pythium sp. under in vitro conditions. Survival and colonization of NBRI2650 in the phytosphere of chickpea, cotton (Gossypium hirsutum L.), cucumber (Cucumis sativus L.), and tomato (Lycopersicon seculentum Mill.) were monitored using a chromosomally located rifampicin-marked mutant P. fluorescens NBRI2650R. The strain showed variable ability to invade and survive in the phytosphere of different plants. Chickpea was used as a tester plant for further work, as it was not invaded by NBRI2650R. The interaction between NBRI2650R and F. oxysporum f.sp. ciceri was studied by both light microscopy and scanning electron microscopy. The lysis of the fungal cell wall by NBRI2650R was clearly demonstrated. Treatment of the chickpea seeds with NBRI2650R in prerelease experiments in the greenhouse using disease-conducive field soils from Jhansi and Kanpur resulted in increased plant growth and did not result in any perturbation of the indigenous microbial community that inhabited the rhizosphere of chickpea compared with nonbacterized seeds. Direct fermentation of diluted NBRI2650R on vermiculite without the need of expensive fermentors offers a reliable process for manufacturing bacterial inoculants in developing countries. Under field conditions, the horizontal and vertical movement of NBRI2650R was restricted to 30 and 60 cm, respectively, and the strain could not survive in the field during the 7 months before the chickpea could be planted for next cropping season. Field trials conducted at Jhansi, Kanpur, and Pantnagar resulted in higher grain yield increase in the bacteria-treated seed compared with the nonbacterized control. Seed and furrow treatment of the two chickpeas ('Radhey' and 'H-208') at Pantnagar resulted in significantly (P = 0.05) greater seedling mortality in nonbacterized seedlings compared with bacterized ones. The seed dry weight and yield for each variety were also significantly higher in bacterized seedlings than in nonbacterized ones. The population of NBRI2650R persisted throughout the growing season of chickpea in the range of 5.4–6.4 log10CFU/g root.Key words: chickpea, competition, rhizosphere, biocontrol, survival.

Tripartite interactions among Paenibacillus lentimorbus NRRL B-30488, Piriformospora indica DSM 11827, and Cicer arietinum L.

“…The development of rhizosphere microbial communities is influenced by the plant, but in turn, microorganisms exert profound effects on plant growth. The rhizosphere of plants is therefore one of the most fascinating microbial habitats for basic and applied studies in the field of environmental microbiology, as it is shaped by the soil, the plant and the microorganisms (Nautiyal et al 2002(Nautiyal et al , 2008. Plant roots become quickly colonized by a diverse microflora of soil-borne bacteria and fungi that may have either beneficial or deleterious effects on the plant.…”

“…This rhizosphere effect is primarily due to the influx of mineral nutrients to the plant roots through mass flow and diffusion, alongside the efflux and accumulation of plant root exudates. Thus, most rhizosphere bacteria and fungi are highly dependent on associations with plants that are clearly regulated by root exudates (Nautiyal et al 2002;Bais et al 2004;Bonfante and Anca 2009;Hamer and Makeschin 2009;Schroeckh et al 2009;Zubek et al 2009). …”

Comparison of Effects of Compost Amendment and of Single-Strain Inoculation on Root Bacterial Communities of Young Cucumber Seedlings

“…Generally, the introduction of new microorganisms produces only restricted spatial and temporal effects on the soil, rhizosphere, and root microbial communities (4,29,35). Thus, the plant growth-promoting effect of such treatments may be related to microbial events occurring during the early stages of plant development.…”

Development of Integrated Disease Control Measures for the Valorisation of Traditional Crops in Southern Italy: The Case Study of Fagioli di Sarconi

“…Molecular studies leading to determine the occurrence of ISR in beanXapf pathosystem are in progress. However, a direct effect of rhizobacteria on the pathogen at the infection site cannot be excluded since it has been reported that bacteria applied to soil or on seeds colonise rhizosphere and then may move up to the phylloplane (Nautiyal et al 2002) or to behave as either facultative or opportunistic endophytes (Hardoim et al 2008). Some characters shown by rhizobacteria under study may be the responsible of the possible direct antagonism exerted on the pathogens.…”