Biol Fertil Soils (1988) 7:53-57 Biology and F et3ili'ty °f So~S © Sprlnger-Verlag 1988 Bacteria and fungi on roots of different barley varieties (Hordeum vulgate L.) E. Liljeroth 1'* and E. Bfifith2 1 The Swedish University of Agricultural Sciences, Department of Crop Genetics and Breeding, S-26800 Sval~v, Sweden 2Microbial Ecology, Department of Ecology, University of Lund, Helgonav~gen 5, S-22362 Lund, Sweden Summary. We investigated the abundance of bacteria and fungi on roots of different barley varieties grown in soil and in a nutrient solution. Measurements were made on the rhizoplane and, for soil-grown plants, also in the rhizosphere soil. Further, the influence of plant age was investigated. Barley variety, had a signif- icant influence both for plants grown in soil and in the nutrient solution, and the effects were most pronounc- ed on the rhizoplane. There were no significant dif- ferences among varieties in fungal hyphal lengths on the roots. Bacterial abundance on the rhizoplane was significantly decreased with increasing plant age. Varietal differences were maintained over different plant ages. Key words: Bacterial abundance - Fungi - Rhizoplane - Plant age - Hordeum vulgare - Hydroponic cultivation Microbial proliferation in the rhizosphere and the rhizoplane occurs in response to the input of organic compounds exuded by the roots. Soil factors, par- ticularly moisture, physical structure and nutrient level, influence the amount of exudation and hence the colonization of the roots (Whipps and Lynch 1986). The plant itself may also influence colonization, because differences in total bacterial counts and in numbers of different physiological groups of bacteria have been found among wheat varieties (Neal et al. 1973). Other authors have also reported varietal dif- ferences, both in bacterial (Elkan 1962; Peterson and Rouatt 1967; Atkinson et al. 1975) and fungal col- onization (Timonin 1940, 1941; Hornby and Ullstrup * Present address and offprint requests to: ITAL, P.O. Box 48, 6700 AA Wageningen, The Netherlands 1967a, b; Rataj-Guranowska 1981). In some of these investigations the observed differences were small, or were only found at certain stages of the plant's devel- opment. Microorganisms growing on the plant roots can in- fluence plant growth positively or negatively and therefore the study of differences in microbial col- onization among varieties may have practical implica- tions. In the present study the bacterial abundance on roots of different barley varieties were compared both on the rhiz0plane and in the rhizosphere soil, using direct counts. Effects of plant age and root environ- ment were investigated. Fungal mycelium lengths on the root surface were also investigated. Materials and methods Plant material New commercial varieties and old varieties of barley (Hordeum vulgare L.) with different genetic background were selected. Further, two translocation lines and one line with a duplicated chromosome segment were used. All three of these lines, which were genetically identical except for the translocation and the duplicated segment, originated from the variety Bonus, and are characterized by a different phenotype; the line with the duplica- tion, for example, gives a higher yield in field trials. Finally, six ac- cessions of the wild progenitor of barley were used, viz. Hordeum vulgare ssp. spontaneum. Cultivation of plants. Three different soils were used, one sandy loam (soil 1), pH 7.0, 0.8°70 C and 0.07070 N, one sandy clay loams (soil 2), pH 6.7, 0.6o70 C and 0.070/0 N, and one clay loam (soil 3), pH 7.1, 1.6070 C and 0.08070 N. The soils were collected from fields in agricultural used and only the top layer (0-20 cm) was taken. The samples were stored in plastic sacks for up to 3 months at out- door temperatures. Before they were used in the experiments the soil samples were sieved (4 mm mesh). The soils had been routinely sup- plemented with a small amount of NPK (50 mg N, 44 rng P and 100 mg K per kg soil), so that the plants had adequate nutrients throughout the experiment. The plants were grown in test tubes (35x200mm), pots (80x200mm) or PVC plastic tubes (150x700mm, field experi- ments), depending on the length of the experiment, placed in a