Applied Soil Ecology 16 2001 169–177
Deleterious properties of certain rhizosphere bacteria on field pea Pisum sativum under gnotobiotic and non-sterile conditions
I. Berggren
a,∗
, S. Alström
b
, A.M. Mårtensson
a
a
Soil Science Department, Swedish University of Agricultural Sciences, P.O. Box 7014, SE-750 07 Uppsala, Sweden
b
Ecology and Crop Production Science Department, Swedish University of Agricultural Sciences, P.O. Box 7043, SE-750 07 Uppsala, Sweden Accepted 20 June 2000
Abstract
Three strains of Pseudomonas putida, one non-fluorescent and two fluorescent, were investigated in a series of complemen- tary experiments to characterise their inhibitory effects on peas under different environmental conditions. Firstly, a gnotobiotic
growth pouch system was developed to observe the deleterious effects of the strains on pea root development. A negative impact of the strains was observed on the development of the root morphology using these pouches which was accompanied
with a subsequent reduction in root biomass. By using this method it was concluded that the deleterious effect of one of the strains was dependent on the inoculum density. Secondly, two complementary studies in non-sterile growth systems where pea
seedsseedlings were inoculated with the bacteria, showed deleterious effects on plant biomass by two of the strains. Thirdly, by using a sterile plant growth system allowing microscopic observations on root hair development, all strains were found to
be able to induce root hair deformations on pea seedlings. The results showed that the mode of action for the deleterious effect differ between the strains. Based on our findings, we would like to emphasise the necessity to include a palette of different
sterile and non-sterile growth systems to be able to identify characteristics of importance for deleterious rhizosphere bacteria. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Pseudomonas putida ; Deleterious; Rhizosphere bacteria; DRB; Pseudomonads
1. Introduction
The rhizosphere accommodates a large number of saprophytic bacteria with stimulating, neutral or dele-
terious effects on crop plants. For instance, Åström 1990 has shown that 8–26 of the bacterial strains
from a rhizosphere soil had adverse effects on plants. However, although of great scientific and practical
interest, more information is needed on which fac- tors regulate the deleterious effects of the bacteria
∗
Corresponding author. Tel.: +46-18-67-3479; fax: +4618-67-2795.
E-mail address: ingela.berggrenmv.slu.se I. Berggren.
on the host plants. Changes in cropping practice Alström, 1992, nutrient status and microbial pop-
ulations Fredrickson and Elliott, 1985, soil tem- perature Davies and Whitbread, 1989 and plant
genotype Åström, 1991a; Sarathchandra et al., 1996 have for instance been shown to influence the capac-
ity of certain bacterial strains to express deleterious effects. When studying deleterious rhizosphere bac-
teria DRB, it is thus important to make a series of complementary studies under different conditions
before drawing any conclusions about the deleterious potential of a certain strain on a specific plant species.
In most of the studies carried out to date, con- clusions regarding the deleterious effects of an
0929-139301 – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 9 - 1 3 9 3 0 0 0 0 1 1 1 - 6
170 I. Berggren et al. Applied Soil Ecology 16 2001 169–177
individual strain have been based upon measurements of the length and weight of the plant root and shoot
Nehl et al., 1996. Studies seldom consider the de- velopment of the root system in the presence of DRB.
It is thus important to include morphological andor structural changes in the root system when classifying
DRB, since bacteria-induced alterations may finally have a great impact on plant health.
Detailed understanding of the inhibitory traits of bacteria would lead to the identification of mecha-
nisms underlying the competition and survival be- tween various groups of bacteria in the rhizosphere.
This information will be essential to create the con- ditions necessary to promote the legume-Rhizobium
symbiosis or to favour plant growth promoting rhi- zobacteria PGPR in cropping practices. With this
aim, we investigated whether three previously iso- lated and characterised DRB strains differed in their
deleterious activity on the model plant, pea, under different environmental conditions, before studying
their interrelation with Rhizobium establishment.
2. Materials and methods
