Directory UMM :Data Elmu:jurnal:A:Applied Soil Ecology:Vol15.Issue2.Oct2000:
Response of micropropagated potatoes transplanted to
peat media to post-vitro inoculation with arbuscular
mycorrhizal fungi and soil bacteria
Miroslav Vosátka
a,∗, Milan Gryndler
baInstitute of Botany, Academy of Sciences of the Czech Republic, 25243 Pruhonice, Czech Republic
bInstitute of Microbiology, Academy of Sciences of the Czech Republic, V´ıdenská 1083, 14220 Prague 4, Czech Republic Received 31 May 1999; received in revised form 13 January 2000; accepted 23 March 2000
Abstract
Positive effects of dual inoculation with some combinations of arbuscular mycorrhizal fungi (AMF) and bacteria on the growth of micropropagated potato (Solanum tuberosum) transplanted to a peat-based substrate were found in three different cultivation systems — pots, greenhouse or shadowhouse beds. Some inoculation treatments, e.g. with Glomus etunicatum,
Glomus fistulosum together with bacterial isolate B1 (Bacillus subtilis) in pots, or with Glomus fistulosum plus bacteria B1
in greenhouse beds or with a mixture of Glomus manihotis and two bacteria in shadowhouse beds resulted in higher number of minitubers (NT), higher weight per minituber or in higher total weight of minitubers per plant. However, the effects of mycorrhization varied for two different potato varieties and the synergistic effects of coinoculation with different bacteria isolated from rhizosphere or hyphosphere was not significant in most cases. There were no significant effects of Zeolite (clinoptinolite clay) amendment on the mycorrhization and aboveground growth of potato plants, while slight stimulation was observed for minituber weight. The inoculation into peat-based substrate might be successful regarding plant growth response; however, to increase the potential of the inoculation in practical production of potato minitubers, it is necessary to consider possible differences of various potato varieties and to select appropriate combination of bacteria and AMF symbionts. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Agrobacterium; Arbuscular mycorrhizal fungi (AMF); Bacillus; Dual inoculation; Potato minitubers; Rhizosphere bacteria; Zeolite
1. Introduction
Commercial importance of in vitro propagated potato plants for the production of minitubers is high enough to look for a way to reduce the cost of the final product by reducing the inputs of the large-scale cultivation systems. It could be possible to reduce the use of phosphate fertilizers and shorten the cultivation
∗Corresponding author. Tel./fax:+42-2-6775-0022.
E-mail address: vosatka@ibot.cas.cz (M. Vos´atka)
time to achieve valuable and marketable plant mate-rial by the introduction of beneficial microbial pop-ulation into the cultivation substrate. Regarding the plant mineral nutrition, arbuscular mycorrhizal fungi (AMF) represent one of the most important group of soil microflora which can be potentially used for practical inoculations in horticulture and agriculture (Holevas, 1966; Kiernan et al., 1984; Chang, 1994).
Inoculation of micropropagated potato plants with AMF during the transfer from in vitro conditions may improve the viability of potato and their physiological 0929-1393/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved.
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state (McArthur and Knowles, 1992, 1993; Niemira et al., 1995). Micropropagated plants form the rhizo-sphere during post-vitro establishment and there is a free niche and space for interaction with introduced soil microflora. During the step of post-vitro trans-plantation, there is a unique possibility to influence the composition of newly formed rhizosphere by preinoc-ulation of the cultivation substrate with selected mi-croorganisms (Vestberg, 1992). After dual inoculation with AMF and an appropriate bacterial partner, a syn-ergistic effect on plant growth and nutrition can be observed (Meyer and Lindermann, 1984; Barea and Azcón-Aguilar, 1986; Vosatka et al., 1992).
The aim of this study was to investigate the effects of dual inoculation with different AMF and bacteria on two varieties of micropropagated potatoes (Solanum tuberosum) transplanted to a peat-based substrate in three different cultivation systems. In addition, the ef-fect of Zeolite (clinoptinolite clay used as substrate conditioner) amendment on the mycorrhization and growth response of potato plants was tested.
2. Materials and methods
2.1. Experiment 1
Potato plants of two varieties — Karin and Krista were micropropagated and transplanted to multiple trays with 90 cell compartments, each 38 ml, filled with a peat-based substrate (mixture of peat and Per-lite 5:2). Each compartment was inoculated with 0.2 g of AMF inoculum consisting of Perlite-sand substrate, fragments of colonized roots, mycelium and spores from the AMF pot cultures grown for 4 months on maize. The fungal isolates used were Glomus etu-nicatum (isolate S 329 from University of Florida, Gainesville), Glomus fasciculatum (isolate from the Experimental Station Rothamsted), and Glomus fis-tulosum BEG23. Bacteria (B1 — isolate of Bacillus subtilis and M11 — isolate of Agrobacterium ra-diobacter, both from the rhizosphere of wheat) were inoculated as 1 ml suspension of bacterial culture cultivated for 48 h on Taylor media (Taylor, 1951). Factorial combination of two AMF and bacterized control with two bacteria and uninoculated control (12 treatments) involved six replicate blocks each with eight plants, in total 576 plants of each variety.
After 6 weeks of cultivation in the greenhouse, small seedlings of the potato were transplanted from mul-tiple trays to the 0.5 l plastic pots with the same peat substratum. Pots were randomly placed on the table in temperated greenhouse and grown for 12 weeks and irrigated daily as needed. Plants were harvested, the minitubers were counted, total fresh weight of minitubers (TFW) was measured and means of fresh weight of minitubers per plant and per eight plants in the experimental block (replicate) were calculated. Roots from eight plants in each replicate were sam-pled and stained according to Phillips and Hayman (1970) except that lactoglycerol was used instead of lactophenol. Mycorrhizal colonization (MC) was evaluated under a binocular microscope at the mag-nification of 120× by grid-line intersect method according to Giovannetti and Mosse (1980).
2.2. Experiment 2
Preinoculated plants of two varieties as in experi-ment 1 were transplanted to the greenhouse table beds (100 cm×40 cm) made from black plastic foil. The ex-perimental design, AMF isolates and bacterial strains were the same as in experiment 1, but 12 replicates were involved. One bed was a replicate and contained eight plants. Plants were cultivated for 12 weeks and the way of harvest and evaluation of growth parame-ters and MC were the same as in experiment 1. 2.3. Experiment 3
Potato plants of Karin variety were micropropa-gated and transplanted from tissue cultures directly to the 0.5 l pots with peat-based substrate. The ef-fects of microorganisms on plants in this experiment were studied using the factorial design involving three factors: amendment of Zeolite into the sub-strate, inoculation with AMF and inoculation with bacteria. In half of the treatments, the substrate was amended with clinoptinolite clay mineral Zeolite (peat substrate: Zeolite, 2:1, v:v) commonly used for the nutrient sorption and improvement of nutritional quality of growing media in horticulture, whereas other half of treatments remained with no substrate amendment. These two treatments represented two levels of first factor. These substrates were either left non-inoculated or they were inoculated with soil
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inoculum of six isolates of AMF (0.2 g per plant, seven levels of the second experimental factor): G. fis-tulosum isolate BEG23, Glomus manihotis BEG112, Glomus geosporum BEG11, Glomus deserticola BEG73, Glomus mosseae BEG25, Scutellospora het-erogama BEG35. Latter five isolates were obtained from The International Institute of Biotechnology, MIRCEN, Canterbury, Kent. As the third experimen-tal factor, the plants were either left non-inoculated or they were inoculated with two bacteria (three levels of the experimental factor): isolate B1 and iso-late M30 (the latter was isoiso-lated from hyphosphere under mycorrhizal culture of maize). Bacteria were propagated and applied the same way as in previous experiment. This factorial experiment thus involved 42 treatments (2×7×3) with eight replicates. All the 336 pots were placed randomly on a cultivation table in temperature-controlled greenhouse and the plants were irrigated daily with tap water as needed. Plants were harvested after 11 weeks, and dry biomass of the shoots, numbers and weight of minitubers were measured, and MC was evaluated as in experiment 1. 2.4. Experiment 4
Potato plants of Karin variety were either left non-inoculated or they were preinoculated in multi-ple trays in the same way as in experiment 1 with four isolates of AMF. All the inoculated treatments also received 1 ml of a mixture (1:1) of cultures of bacterial strains M30 and B1. AMF isolates used were G. manihotis BEG112, G. mosseae BEG25, G. deserticola BEG73, and G. etunicatum S329. The plants were transplanted to the shadowhouse beds (100 cm×40 cm). Each bed contained 30 plants. Each treatment involved nine replicates (beds). The plants were cultivated for 14 weeks and, after the harvest, the mean number of minitubers (NT), total weight of minitubers and number and weight of marketable size minitubers per plant were estimated, and the MC in each treatment was evaluated.
2.5. Statistical evaluation of the data
Data sets were checked for normal distribution and logarithmically transformed when necessary. One-, two- or three-way ANOVA was used for evaluation of effect of different factors and their interaction.
Duncan multiple range test was used to analyze sig-nificant differences between means. The statistical evaluation was performed using SOLO statistical package (BMDP Software, Los Angeles, CA, 1991). Control non-inoculated treatments were excluded in all experiments from statistical analysis of MC.
3. Results
3.1. Experiment 1
In the pot experiment, significant effects of exper-imental factors and significant interaction between both inoculations were observed for the Krista variety only, while no effects were found for Karin variety (Table 1). For the Krista variety, a significant de-crease in minitubers number per pot was observed as a response to inoculation with bacterial strain M11 compared to unbacterized treatment, and with AMF G. fasciculatum compared to uninoculated controls or to plants inoculated with G. fistulosum (Table 2). The opposite trend was observed for the mean weight of minituber. It was significantly increased in treatments
Table 1
F-values and significance of two-way ANOVA of number of mini-tubers (NT), total fresh weight of minimini-tubers (TFW), fresh weight of one minituber (FWO) and mycorrhizal colonization (MC) of potato plants of two varieties transplanted post-vitro to the pots and inoculated with two bacteria and three arbuscular mycorrhizal fungi (AMF) (experiment 1), d.f. represents degrees of freedom for the given factor
Factor d.f. NT TFW (g) FWO (g) MC (%) Variety Karin
Bacteria (A) 2 0.33 nsa 1.04 ns 0.04 ns 0.51 nsb AMF (B) 3 2.32 ns 0.57 ns 1.05 ns 0.12 ns A×B 6 0.53 ns 2.12 ns 0.63 ns 0.43 ns Error (mean square) 60 (1.12) 60 (8.11) 60 (0.387) 58 (0.67) Variety Krista
Bacteria (A) 2 17.32a,∗∗∗
2.10 ns 17.05∗∗∗
1.97 nsb AMF (B) 3 6.36∗
0.89 ns 6.30∗∗∗
0.96 ns A×B 6 2.08∗∗∗
2.16 ns 1.52 ns 0.38 ns Error (mean square) 60 (2.48) 60 (9.61) 60 (0.419) 58 (3.13)
ans — nonsignificant effect of the factor.
bNon-mycorrhizal treatments were not included into the sta-tistical treatment of MC.
∗Significant effect at p<0.05. ∗∗∗
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Table 2
The effect of inoculation with three AMF and two bacteria on NT, TFW, FWO and MC of potato plants of two varieties transplanted post-vitro to the pots (experiment 1)
Factor NT TFW (g) FWO (g) MC (%)
Variety Karin Bacteria
None 6.95 aa 24.22 a 3.52 a 12.3 ab Bacterial isolate B1 6.71 a 23.12 a 3.54 a 14.5 a Bacterial isolate M11 6.79 a 23.30 a 3.49 a 16.9 a AMF
None 6.39 aa 22.95 a 3.63 a 0b G. fistulosum 6.69 ab 23.87 a 3.65 a 15.7 a G. fasciculatum 6.89 ab 23.30 a 3.43 a 10.4 a G. etunicatum 7.30 b 24.05 b 3.35 a 18.9 a Variety Krista
Bacteria
None 9.70 ba 31.23 a 3.36 a 9.7 ab Bacterial isolate B1 9.22 b 32.88 a 3.71 a 11.9 a Bacterial isolate M11 7.18 a 31.35 a 4.42 b 8.9 a AMF
None 9.17 ba 31.00 a 3.51 a 0b G. fistulosum 9.79 b 32.68 b 3.49 a 10.7 a G. fasciculatum 7.80 a 31.86 ab 4.21 b 12.5 a G. etunicatum 8.06 ab 31.76 ab 4.11 ab 8.1 a aMeans of six replicates (each replicate as a mean from eight plants) within one parameter and one factor are not significantly different according to Duncan multiple range test, p<0.05.
bNon-mycorrhizal treatments were not included into the sta-tistical treatment of MC.
inoculated with all the three mentioned microorgan-isms. One-way ANOVA showed significant increase in minituber number in treatment inoculated with G. fistulosum together with bacteria B1, increase of mean weight of minituber in the treatments inocu-lated with bacteria B1 and all three AMF (according to AMF species the increase was 40, 57 and 60% compared to control uninoculated plants) (data of one-way ANOVA not shown).
3.2. Experiment 2
In greenhouse beds, bacterial inoculation signif-icantly affected the NT and the mean fresh weight of minitubers of both potato varieties (Table 3). The NT of Krista variety was further affected by AMF inoculation. MC of roots of both plant varieties was significantly affected by inoculation with different
Table 3
F-values and significance of two-way ANOVA of NT, TFW, FWO and MC of potatoes of two varieties post-vitro transplanted to the greenhouse beds, as influenced by inoculation with two bacteria and three AMF (experiment 2), d.f. represents degrees of freedom for the given factor
Factor d.f. NT TFW (g) FWO (g) MC (%) Variety Karin
Bacteria (A) 2 6.08a,∗∗
0.77 ns 4.54∗
1.15 nsb AMF (B) 3 0.82 ns 0.55 ns 0.22 ns 3.11∗
A×B 6 1.71 ns 0.73 ns 1.34 ns 0.33 ns Error (mean square) 36 (1.76) 36 (109.5) 36 (1.09) 32 (0.94) Variety Krista
Bacteria (A) 2 6.34a,∗∗
0.19 ns 3.51∗
0.78 nsb AMF (B) 3 4.22∗∗
1.13 ns 2.19 ns 4.53∗∗
A×B 6 5.18∗∗∗
0.55 ns 0.31 ns 0.74 ns Error (mean square) 36 (1.68) 36 (115.0) 36 (2.84) 32 (0.67)
ans — nonsignificant effect of the factor.
bNon-mycorrhizal treatments were not included into the sta-tistical treatment of MC.
∗Significant effect at p<0.05. ∗∗
Significant effect at p<0.01.
∗∗∗
Significant effect at p<0.001.
AMF species. Significant interaction between AMF and bacteria inoculation treatments was found for va-riety Krista for the NT. Inoculation of plants of vava-riety Karin with bacterial isolate B1 significantly increased the NT, compared to non-bacterized treatments (Table 4). For Krista variety, the bacterial inocula-tion increased only the mean weight of minituber. G. etunicatum caused the highest level of MC in roots of both plant varieties. The best combination of in-oculants was G. fistulosum and bacteria B1 but only for Krista variety. For this variety, an increased total yield of minitubers up to 24% was found compared to uninoculated control, whereas G. etunicatum itself without bacteria increased total NT up to 55% (data of one-way ANOVA not shown).
3.3. Experiment 3
The results of three-way ANOVA (Table 5) showed that Zeolite amendment of the substrate for Karin va-riety significantly affected shoot dry weight (SDW), TFW and the mean fresh weight of minituber (FWO). Bacterial treatments affected MC of roots. AMF in-oculation significantly affected SDW, TFW and MC. Significant interaction was found only between the
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Table 4
The effect of inoculation with three AMF and two bacteria on NT, TFW, FWO and MC of potatoes of two varieties post-vitro transplanted to the greenhouse beds (experiment 2)
Factor NT TFW (g) FWO (g) MC (%)
Variety Karin Bacteria
None 8.95 aa 50.78 a 5.72 a 16.9 ab Bacterial isolate B1 10.29 b 47.13 a 4.62 a 17.8 a Bacterial isolate M30 8.80 a 46.52 a 5.31 a 20.6 a AMF
None 9.63 aa 48.10 a 5.16 a 0b G. fistulosum 9.37 a 50.36 a 5.41 a 16.1 ab G. fasciculatum 9.53 a 49.01 a 5.21 a 11.8 a G. etunicatum 8.85 a 49.10 a 5.08 a 22.4 b Variety Krista
Bacteria
None 9.19 aa 64.45 a 7.37 a 9.7 ab Bacterial isolate B1 7.63 a 66.25 a 8.92 b 11.9 a Bacterial isolate M30 8.00 a 66.64 a 8.43 ab 8.9 a AMF
None 7.63 aa 62.08 a 8.45 a 0b G. fistulosum 8.04 a 70.00 b 8.95 a 11.9 a G. fasciculatum 8.03 a 66.15 ab 8.33 a 17.7 ab G. etunicatum 9.39 b 64.90 ab 7.24 a 19.4 b
aMeans of 12 replicates (each replicate as a mean from eight plants) within one parameter and one factor are not significantly different according to Duncan multiple range test, p<0.05.
bNon-mycorrhizal treatments were not included into the sta-tistical treatment of MC.
Table 5
F-values and significance of three-way ANOVA for shoot dry weight (SDW), NT, TFW, FWO and MC of potato plants of Karin variety inoculated with six AMF and two bacteria and grown in pots with peat-based substrate amended with Zeolite (experiment 3), d.f. represents degrees of freedom for the given factor
Factor d.f. SDW (g) NT TFW (g) FWO (g) MC (%)
Zeolite (A) 1 126.4a,∗∗∗ 0.7 ns 9.5∗∗ 7.6∗∗ 0.4 nsb
Bacteria (B) 2 1.0 ns 1.3 ns 1.4 ns 0.5 ns 7.7∗∗∗
AMF (C) 6 4.3∗∗∗
1.3 ns 2.3∗
2.2 ns 69.6∗∗∗
A×B 2 0.2 ns 0.5 ns 0.1 ns 7.1∗∗
4.2∗
A×C 6 1.1 ns 0.5 ns 0.9 ns 1.1 ns 1.5 ns
B×C 12 1.8 ns 1.4 ns 1.0 ns 0.8 ns 1.6 ns
A×B×C 12 0.8 ns 0.7 ns 1.1 ns 1.7 ns 1.7 ns
Error (mean square) 292 (0.03) 292 (0.6) 292 (17.5) 292 (20.5) 252 (101.9) ans — nonsignificant effect of the factor.
bNon-mycorrhizal treatments were not included into the statistical treatment of MC. ∗Significant effect at p<0.05.
∗∗
Significant effect at p<0.01.
∗∗∗
Significant effect at p<0.001.
type of substrate (Zeolite amendment) and bacte-rial inoculation for the mean weight of minitubers and for the MC. Inoculation with G. manihotis in-creased growth of shoots, total yield of minitubers and the mean FWO, compared to uninoculated plants (Table 6). At the same time, this fungus caused the highest colonization of potato roots. Inoculation with G. geosporum increased weight of minituber but no effect was found on the minitubers number. The only significant effect of bacterial inoculation was a decrease of MC in the treatments inoculated with bacteria B1. Amendment by Zeolite had negative effect on the growth of aboveground parts of the plants, nevertheless, it increased significantly the to-tal yield of minitubers and the mean fresh weight of minitubers.
3.4. Experiment 4
In shadowhouse, the dual inoculation of Karin va-riety affected significantly only the NT and MC of potato roots (Table 7). Total NT was increased by inoc-ulation with two AMF: G. mosseae and G. deserticola (Table 8). Similarly as in the previous experiment, G. manihotis was the inoculant causing the most extensive MC of potato. The number of marketable minitubers (NMT) and their fresh weight remained unaffected by the inoculation.
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Table 6
F-values and significance of ANOVA for SDW, NT, TFW, FWO and MC of potato plants of Karin variety inoculated with six AMF and two bacteria and grown in pots with peat-based substrate amended with Zeolite (experiment 3)
Factor SDW (g) NT TFW (g) FWO (g) MC (%)
Zeolite
Not added 0.91 ba 2.04 a 20.12 a 13.95 a 10.5 ab
Added 0.70 a 1.96 a 21.53 b 15.32 b 11.2 a
Bacteria
None 0.78 aa 1.93 a 20.3 a 14.4 a 12.6 bb
Bacterial isolate B1 0.81 a 2.10 a 21.1 a 14.3 a 7.6 a
Bacterial isolate M30 0.81 a 1.96 a 21.1 a 15.2 a 12.5 b
AMF
None 0.79 aba 2.02 a 20.22 a 13.64 a 0b
G. fistulosum 0.74 a 1.90 a 19.86 a 15.04 ab 5.4 a
G. manihotis 0.90 c 2.14 a 22.46 b 16.13 b 35.6 b
G. geosporum 0.83 bc 1.83 a 21.29 ab 16.08 b 6.5 a
G. deserticola 0.81 b 2.08 a 21.33 ab 14.01 a 4.3 a
G. mosseae 0.78 ab 1.87 a 20.14 a 13.89 a 8.0 a
S. heterogama 0.76 ab 2.14 a 20.46 a 13.66 a 5.6 a
aMeans of 12 replicates within one parameter and one factor are not significantly different according to Duncan multiple range test, p<0.05.
bNon-mycorrhizal treatments were not included into the statistical treatment of MC.
4. Discussion
Micropropagated potato plants can benefit from inoculation with AMF, as reported by McArthur and Knowles (1992, 1993) and these findings are also sup-ported by our recent observations. Our experiments have shown that there may be different responses in plant growth parameters of various plant varieties to microbial inoculants, as observed mainly in experi-ment 1 for Karin and Krista varieties. Increase in MC or efficiency caused by inoculation with bacteria was observed by, e.g., El-Shanshoury et al. (1989). But the extent of colonization of host roots by symbiotic
Table 7
F-values and significance of ANOVA for NT, TFW, number of marketable minitubers (NMT), fresh weight of marketable minitubers (FWMT) and for MC of potato variety Karin plants dually inoculated with mixture of two bacteria and with four different AMF and transplanted to the peat-based substrate in the shadowhouse (experiment 4), d.f. represents degrees of freedom for the given factor
Factor d.f. NT TFW (g) NMT FWMT (g) MC (%)
AMF 4 4.0a,∗∗
2.3 ns 0.3 ns 0.8 ns 2.6b,∗
Error (mean square) 40 (1.72) 40 (986) 40 (0.53) 40 (1286) 36 (3.1)
ans — nonsignificant effect of the factor.
bNon-mycorrhizal treatment was not included into the statistical treatment of MC. ∗Significant effect at p<0.05.
∗∗
Significant effect at p<0.01.
fungi does not necessarily correlate with benefits to the plant, as it was shown by Plenchette et al. (1982) in experiments with strawberry and some other plants in inert substrates. Nevertheless, in experiment 3, the best growth of potato plant as well as the production of minitubers were observed in treatments inoculated with G. manihotis. This AMF seems to be well com-patible with potato of the Karin variety. This may indi-cate a physiological specificity of this fungus to potato plants as a host. The compatibility of the mycorrhizal fungus with potato plants may be of particular impor-tance because they often form very weak root colo-nization under field conditions (Ocampo and Hayman,
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Table 8
Effect of dual inoculation with four AMF and two bacteria on NT, TFW, NMT, FWMT and for MC of potato variety Karin plants transplanted to the peat-based substrate beds in the shadowhouse (experiment 4)
AMF NT TFW (g) NMT FWMT (g) MC (%) None 7.4 aa 216 a 3.5 a 157 a 0b G. manihotis 8.6 a 256 a 3.8 a 185 a 37 b G. mosseae 9.2 b 249 a 3.7 a 173 a 23 a G. deserticola 9.7 b 252 a 3.7 a 166 a 18 a G. etunicatum 8.4 a 243 a 3.5 a 164 a 25 a
aMeans of nine replicates (mean from 30 plants) within one parameter and one factor are not significantly different according to Duncan multiple range test, p<0.05.
bNon-mycorrhizal treatment was not included into the statis-tical treatment of MC.
1980, our unpublished observations), and thus care-ful selection of the symbiotic fungus may improve the mycorrhizal growth response of inoculated plants. Moreover, some potato varieties may be almost resis-tant to colonization by AMF and no response to my-corrhizal inoculation can be expected (Bhattarai and Mishra, 1984).
Experiments 1 and 2 demonstrated the significant effect of inoculation (bacterial strains M11, B1 and AMF, particularly G. fasciculatum) on production of minitubers. Lower numbers of minitubers were found in inoculated treatments, but total minituber yield re-mained unaffected. This means that the produced mini-tubers were bigger which is supported by increased mean weight of minituber. This change in allocation of plant biomass may indicate a hormonal effect of intro-duced microorganisms. Plant growth regulating hor-mones are produced by bacterial cultures (e.g. Prikryl et al., 1985) and hence the introduction of bacteria may change the hormonal balance in potato rhizosphere. Similarly, the colonization of root cortex with myc-orrhizal fungi is accompanied by change in hormonal balance, e.g. by accumulation of cytokinins (Allen et al., 1980; Baas and Kuiper, 1989; Druge and Schon-beck, 1992) or abscisic acid (Danneberg et al., 1992). The bacterial inoculation would, in some cases, stimulate the extraradical mycelium of the AMF and consequently a positive plant growth response can be observed due to the increase of absorption surface of the roots. Possible positive effects of bacterial inoc-ulation on the development and activity of external mycelium was not a subject of this research but such
effects were previously reported (Azcón et al., 1978; Azcón, 1987; Gryndler and Vosátka, 1996; Vosatka and Gryndler, 1999).
The amendment of Zeolite could be of importance in nutritionally poor substrates with lower availabil-ity of essential nutrients, a positive effect of Zeolite amendment was found for mycorrhizal strawberry (Vosatka et al., 1992). We choose Zeolite as a compo-nent of the substrate to improve its physicochemical features (sorption) but no highly positive effects ex-pected on plant growth and MC were observed. The inoculation into peat-based substrate might be more successful as reported by Niemira et al. (1995). There were potentially effective AMF isolates among those tested, while bacteria themselves did not often stimu-late plant growth, nevertheless, bacterization can sup-port mycorrhization as was also previously resup-ported for potatoes or other plants (Gryndler and Vosátka, 1996; Vosatka and Gryndler, 1999). However, to in-crease the potential of the inoculation in practical production of potato minitubers, it is necessary to consider possible differences in potato varieties re-garding their growth response as well as appropriate combination of bacteria and AMF symbionts for a given cultivation system.
Acknowledgements
The authors are grateful to Dr. V. Horácková from the Institute of Potato Growing, Havlickuv Brod for cooperation during the project No. 502/94/0834 fi-nanced by the Grant Agency of the Czech Republic. The work on bacteria was financed by MSMT grant COST 8.38. The help of Dr. T. Frantik in statistical evaluation of the data is greatly acknowledged.
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Holevas, C.D., 1966. The effect of VA mycorrhiza on the uptake of soil phosphorus by strawberry (Fragaria sp., var. Cambridge Favourite). J. Hort. Sci. 41, 57–64.
Kiernan, J.M., Hendrix, J.W., Stolz, L.P., Maronek, D.M., 1984. Characterization of strawberry [Fragaria ananassa] plants produced by tissue culture and infected with specific mycorrhizal fungi. Hort. Sci. 19, 883–885.
McArthur, D.A.J., Knowles, N.R., 1992. Resistance responses of potato to vesicular-arbuscular mycorrhizal fungi under varying abiotic phosphorus levels. Plant Physiol. 100, 341– 351.
McArthur, D.A.J., Knowles, N.R., 1993. Influence of VAM fungi on the response of potato to phosphorus deficiency. Plant Physiol. 101, 147–160.
Meyer, J.R., Lindermann, R.G., 1984. Response of subterranean clover to dual inoculation with VAM fungi and a plant growth-promoting bacterium, Pseudomonas putida. Soil Biol. Biochem. 18, 185–190.
Niemira, B.A., Safir, G.R., Hammerschmidt, R., Bird, G., 1995. Production of prenuclear minitubers of potato with peat-based arbuscular mycorrhizal fungal inoculum. Agron. J. 87, 942– 946.
Ocampo, J.A., Hayman, D.S., 1980. Effects of pesticides on mycorrhiza in field-grown barley, maize and potatoes. Trans. Br. Mycol. Soc. 74, 413–416.
Phillips, J.M., Hayman, D.S., 1970. Improved procedure for clearing roots and staining parasitic and vesicular-arbuscular mycorrhizal fungi for rapid assessment of infection. Trans. Br. Mycol. Soc. 55, 158–161.
Plenchette, C., Furlan, V., Fortin, J.A., 1982. Effects of different endomycorrhizal fungi on five host plants grown on calcined montmorillonite clay. J. Am. Soc. Hort. Sci. 107, 535–538. Prikryl, Z., Vancura, V., Wurst, M., 1985. Auxin formation by
rhizosphere bacteria as a factor of root growth. Biol. Plant. 27, 159–163.
Taylor, C.B., 1951. The nutritional requirements of predominant flora of the soil. Proc. Soc. Appl. Bacteriol. 14, 11–111. Vestberg, M., 1992. Arbuscular mycorrhizal inoculation of
micropropagated strawberry and field observations in Finland. Agronomie 12, 865–867.
Vosatka, M., Gryndler, M., 1999. Treatment with culture fractions from Pseudomonas putida modifies the development of Glomus fistulosum mycorrhiza and the response of potato and maize plants to inoculation. Appl. Soil Ecol. 11, 245–251.
Vosatka, M., Gryndler, M., Prikryl, Z., 1992. Effect of the rhizosphere bacterium Pseudomonas putida, VAM fungi and substratum composition on the growth of strawberry. Agronomie 12, 859–863.
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inoculum of six isolates of AMF (0.2 g per plant,
seven levels of the second experimental factor): G.
fis-tulosum isolate BEG23, Glomus manihotis BEG112,
Glomus geosporum BEG11, Glomus deserticola
BEG73, Glomus mosseae BEG25, Scutellospora
het-erogama BEG35. Latter five isolates were obtained
from The International Institute of Biotechnology,
MIRCEN, Canterbury, Kent. As the third
experimen-tal factor, the plants were either left non-inoculated
or they were inoculated with two bacteria (three
levels of the experimental factor): isolate B1 and
iso-late M30 (the latter was isoiso-lated from hyphosphere
under mycorrhizal culture of maize). Bacteria were
propagated and applied the same way as in previous
experiment. This factorial experiment thus involved
42 treatments (2
×
7
×
3) with eight replicates. All the
336 pots were placed randomly on a cultivation table
in temperature-controlled greenhouse and the plants
were irrigated daily with tap water as needed. Plants
were harvested after 11 weeks, and dry biomass of
the shoots, numbers and weight of minitubers were
measured, and MC was evaluated as in experiment 1.
2.4. Experiment 4
Potato plants of Karin variety were either left
non-inoculated or they were preinoculated in
multi-ple trays in the same way as in experiment 1 with
four isolates of AMF. All the inoculated treatments
also received 1 ml of a mixture (1:1) of cultures of
bacterial strains M30 and B1. AMF isolates used
were G. manihotis BEG112, G. mosseae BEG25, G.
deserticola BEG73, and G. etunicatum S329. The
plants were transplanted to the shadowhouse beds
(100 cm
×
40 cm). Each bed contained 30 plants. Each
treatment involved nine replicates (beds). The plants
were cultivated for 14 weeks and, after the harvest,
the mean number of minitubers (NT), total weight of
minitubers and number and weight of marketable size
minitubers per plant were estimated, and the MC in
each treatment was evaluated.
2.5. Statistical evaluation of the data
Data sets were checked for normal distribution and
logarithmically transformed when necessary. One-,
two- or three-way ANOVA was used for evaluation
of effect of different factors and their interaction.
Duncan multiple range test was used to analyze
sig-nificant differences between means. The statistical
evaluation was performed using SOLO statistical
package (BMDP Software, Los Angeles, CA, 1991).
Control non-inoculated treatments were excluded in
all experiments from statistical analysis of MC.
3. Results
3.1. Experiment 1
In the pot experiment, significant effects of
exper-imental factors and significant interaction between
both inoculations were observed for the Krista variety
only, while no effects were found for Karin variety
(Table 1). For the Krista variety, a significant
de-crease in minitubers number per pot was observed as
a response to inoculation with bacterial strain M11
compared to unbacterized treatment, and with AMF
G. fasciculatum compared to uninoculated controls or
to plants inoculated with G. fistulosum (Table 2). The
opposite trend was observed for the mean weight of
minituber. It was significantly increased in treatments
Table 1
F-values and significance of two-way ANOVA of number of
mini-tubers (NT), total fresh weight of minimini-tubers (TFW), fresh weight of one minituber (FWO) and mycorrhizal colonization (MC) of potato plants of two varieties transplanted post-vitro to the pots and inoculated with two bacteria and three arbuscular mycorrhizal fungi (AMF) (experiment 1), d.f. represents degrees of freedom for the given factor
Factor d.f. NT TFW (g) FWO (g) MC (%)
Variety Karin
Bacteria (A) 2 0.33 nsa 1.04 ns 0.04 ns 0.51 nsb AMF (B) 3 2.32 ns 0.57 ns 1.05 ns 0.12 ns A×B 6 0.53 ns 2.12 ns 0.63 ns 0.43 ns Error (mean square) 60 (1.12) 60 (8.11) 60 (0.387) 58 (0.67)
Variety Krista
Bacteria (A) 2 17.32a,∗∗∗
2.10 ns 17.05∗∗∗
1.97 nsb AMF (B) 3 6.36∗
0.89 ns 6.30∗∗∗
0.96 ns A×B 6 2.08∗∗∗
2.16 ns 1.52 ns 0.38 ns Error (mean square) 60 (2.48) 60 (9.61) 60 (0.419) 58 (3.13)
ans — nonsignificant effect of the factor.
bNon-mycorrhizal treatments were not included into the
sta-tistical treatment of MC.
∗Significant effect at p<0.05. ∗∗∗
(2)
Table 2
The effect of inoculation with three AMF and two bacteria on NT, TFW, FWO and MC of potato plants of two varieties transplanted post-vitro to the pots (experiment 1)
Factor NT TFW (g) FWO (g) MC (%)
Variety Karin
Bacteria
None 6.95 aa 24.22 a 3.52 a 12.3 ab Bacterial isolate B1 6.71 a 23.12 a 3.54 a 14.5 a Bacterial isolate M11 6.79 a 23.30 a 3.49 a 16.9 a AMF
None 6.39 aa 22.95 a 3.63 a 0b
G. fistulosum 6.69 ab 23.87 a 3.65 a 15.7 a
G. fasciculatum 6.89 ab 23.30 a 3.43 a 10.4 a
G. etunicatum 7.30 b 24.05 b 3.35 a 18.9 a
Variety Krista
Bacteria
None 9.70 ba 31.23 a 3.36 a 9.7 ab
Bacterial isolate B1 9.22 b 32.88 a 3.71 a 11.9 a Bacterial isolate M11 7.18 a 31.35 a 4.42 b 8.9 a AMF
None 9.17 ba 31.00 a 3.51 a 0b
G. fistulosum 9.79 b 32.68 b 3.49 a 10.7 a
G. fasciculatum 7.80 a 31.86 ab 4.21 b 12.5 a
G. etunicatum 8.06 ab 31.76 ab 4.11 ab 8.1 a
aMeans of six replicates (each replicate as a mean from eight
plants) within one parameter and one factor are not significantly different according to Duncan multiple range test, p<0.05.
bNon-mycorrhizal treatments were not included into the
sta-tistical treatment of MC.
inoculated with all the three mentioned
microorgan-isms. One-way ANOVA showed significant increase
in minituber number in treatment inoculated with
G. fistulosum together with bacteria B1, increase of
mean weight of minituber in the treatments
inocu-lated with bacteria B1 and all three AMF (according
to AMF species the increase was 40, 57 and 60%
compared to control uninoculated plants) (data of
one-way ANOVA not shown).
3.2. Experiment 2
In greenhouse beds, bacterial inoculation
signif-icantly affected the NT and the mean fresh weight
of minitubers of both potato varieties (Table 3). The
NT of Krista variety was further affected by AMF
inoculation. MC of roots of both plant varieties was
significantly affected by inoculation with different
Table 3
F-values and significance of two-way ANOVA of NT, TFW, FWO
and MC of potatoes of two varieties post-vitro transplanted to the greenhouse beds, as influenced by inoculation with two bacteria and three AMF (experiment 2), d.f. represents degrees of freedom for the given factor
Factor d.f. NT TFW (g) FWO (g) MC (%)
Variety Karin
Bacteria (A) 2 6.08a,∗∗
0.77 ns 4.54∗
1.15 nsb AMF (B) 3 0.82 ns 0.55 ns 0.22 ns 3.11∗
A×B 6 1.71 ns 0.73 ns 1.34 ns 0.33 ns Error (mean square) 36 (1.76) 36 (109.5) 36 (1.09) 32 (0.94)
Variety Krista
Bacteria (A) 2 6.34a,∗∗
0.19 ns 3.51∗
0.78 nsb AMF (B) 3 4.22∗∗
1.13 ns 2.19 ns 4.53∗∗
A×B 6 5.18∗∗∗
0.55 ns 0.31 ns 0.74 ns Error (mean square) 36 (1.68) 36 (115.0) 36 (2.84) 32 (0.67)
ans — nonsignificant effect of the factor.
bNon-mycorrhizal treatments were not included into the
sta-tistical treatment of MC.
∗Significant effect at p<0.05. ∗∗
Significant effect at p<0.01.
∗∗∗
Significant effect at p<0.001.
AMF species. Significant interaction between AMF
and bacteria inoculation treatments was found for
va-riety Krista for the NT. Inoculation of plants of vava-riety
Karin with bacterial isolate B1 significantly increased
the NT, compared to non-bacterized treatments
(Table 4). For Krista variety, the bacterial
inocula-tion increased only the mean weight of minituber. G.
etunicatum caused the highest level of MC in roots
of both plant varieties. The best combination of
in-oculants was G. fistulosum and bacteria B1 but only
for Krista variety. For this variety, an increased total
yield of minitubers up to 24% was found compared
to uninoculated control, whereas G. etunicatum itself
without bacteria increased total NT up to 55% (data
of one-way ANOVA not shown).
3.3. Experiment 3
The results of three-way ANOVA (Table 5) showed
that Zeolite amendment of the substrate for Karin
va-riety significantly affected shoot dry weight (SDW),
TFW and the mean fresh weight of minituber (FWO).
Bacterial treatments affected MC of roots. AMF
in-oculation significantly affected SDW, TFW and MC.
Significant interaction was found only between the
(3)
Table 4
The effect of inoculation with three AMF and two bacteria on NT, TFW, FWO and MC of potatoes of two varieties post-vitro transplanted to the greenhouse beds (experiment 2)
Factor NT TFW (g) FWO (g) MC (%)
Variety Karin
Bacteria
None 8.95 aa 50.78 a 5.72 a 16.9 ab Bacterial isolate B1 10.29 b 47.13 a 4.62 a 17.8 a Bacterial isolate M30 8.80 a 46.52 a 5.31 a 20.6 a AMF
None 9.63 aa 48.10 a 5.16 a 0b
G. fistulosum 9.37 a 50.36 a 5.41 a 16.1 ab
G. fasciculatum 9.53 a 49.01 a 5.21 a 11.8 a
G. etunicatum 8.85 a 49.10 a 5.08 a 22.4 b
Variety Krista
Bacteria
None 9.19 aa 64.45 a 7.37 a 9.7 ab
Bacterial isolate B1 7.63 a 66.25 a 8.92 b 11.9 a Bacterial isolate M30 8.00 a 66.64 a 8.43 ab 8.9 a AMF
None 7.63 aa 62.08 a 8.45 a 0b
G. fistulosum 8.04 a 70.00 b 8.95 a 11.9 a
G. fasciculatum 8.03 a 66.15 ab 8.33 a 17.7 ab
G. etunicatum 9.39 b 64.90 ab 7.24 a 19.4 b
aMeans of 12 replicates (each replicate as a mean from eight
plants) within one parameter and one factor are not significantly different according to Duncan multiple range test, p<0.05.
bNon-mycorrhizal treatments were not included into the
sta-tistical treatment of MC.
Table 5
F-values and significance of three-way ANOVA for shoot dry weight (SDW), NT, TFW, FWO and MC of potato plants of Karin variety
inoculated with six AMF and two bacteria and grown in pots with peat-based substrate amended with Zeolite (experiment 3), d.f. represents degrees of freedom for the given factor
Factor d.f. SDW (g) NT TFW (g) FWO (g) MC (%)
Zeolite (A) 1 126.4a,∗∗∗ 0.7 ns 9.5∗∗ 7.6∗∗ 0.4 nsb
Bacteria (B) 2 1.0 ns 1.3 ns 1.4 ns 0.5 ns 7.7∗∗∗
AMF (C) 6 4.3∗∗∗
1.3 ns 2.3∗
2.2 ns 69.6∗∗∗
A×B 2 0.2 ns 0.5 ns 0.1 ns 7.1∗∗
4.2∗
A×C 6 1.1 ns 0.5 ns 0.9 ns 1.1 ns 1.5 ns
B×C 12 1.8 ns 1.4 ns 1.0 ns 0.8 ns 1.6 ns
A×B×C 12 0.8 ns 0.7 ns 1.1 ns 1.7 ns 1.7 ns
Error (mean square) 292 (0.03) 292 (0.6) 292 (17.5) 292 (20.5) 252 (101.9)
ans — nonsignificant effect of the factor.
bNon-mycorrhizal treatments were not included into the statistical treatment of MC. ∗Significant effect at p<0.05.
∗∗
Significant effect at p<0.01.
∗∗∗
Significant effect at p<0.001.
type of substrate (Zeolite amendment) and
bacte-rial inoculation for the mean weight of minitubers
and for the MC. Inoculation with G. manihotis
in-creased growth of shoots, total yield of minitubers
and the mean FWO, compared to uninoculated plants
(Table 6). At the same time, this fungus caused the
highest colonization of potato roots. Inoculation with
G. geosporum increased weight of minituber but
no effect was found on the minitubers number. The
only significant effect of bacterial inoculation was
a decrease of MC in the treatments inoculated with
bacteria B1. Amendment by Zeolite had negative
effect on the growth of aboveground parts of the
plants, nevertheless, it increased significantly the
to-tal yield of minitubers and the mean fresh weight of
minitubers.
3.4. Experiment 4
In shadowhouse, the dual inoculation of Karin
va-riety affected significantly only the NT and MC of
potato roots (Table 7). Total NT was increased by
inoc-ulation with two AMF: G. mosseae and G. deserticola
(Table 8). Similarly as in the previous experiment,
G. manihotis was the inoculant causing the most
extensive MC of potato. The number of marketable
minitubers (NMT) and their fresh weight remained
unaffected by the inoculation.
(4)
Table 6
F-values and significance of ANOVA for SDW, NT, TFW, FWO and MC of potato plants of Karin variety inoculated with six AMF and
two bacteria and grown in pots with peat-based substrate amended with Zeolite (experiment 3)
Factor SDW (g) NT TFW (g) FWO (g) MC (%)
Zeolite
Not added 0.91 ba 2.04 a 20.12 a 13.95 a 10.5 ab
Added 0.70 a 1.96 a 21.53 b 15.32 b 11.2 a
Bacteria
None 0.78 aa 1.93 a 20.3 a 14.4 a 12.6 bb
Bacterial isolate B1 0.81 a 2.10 a 21.1 a 14.3 a 7.6 a
Bacterial isolate M30 0.81 a 1.96 a 21.1 a 15.2 a 12.5 b
AMF
None 0.79 aba 2.02 a 20.22 a 13.64 a 0b
G. fistulosum 0.74 a 1.90 a 19.86 a 15.04 ab 5.4 a
G. manihotis 0.90 c 2.14 a 22.46 b 16.13 b 35.6 b
G. geosporum 0.83 bc 1.83 a 21.29 ab 16.08 b 6.5 a
G. deserticola 0.81 b 2.08 a 21.33 ab 14.01 a 4.3 a
G. mosseae 0.78 ab 1.87 a 20.14 a 13.89 a 8.0 a
S. heterogama 0.76 ab 2.14 a 20.46 a 13.66 a 5.6 a
aMeans of 12 replicates within one parameter and one factor are not significantly different according to Duncan multiple range test,
p<0.05.
bNon-mycorrhizal treatments were not included into the statistical treatment of MC.
4. Discussion
Micropropagated potato plants can benefit from
inoculation with AMF, as reported by McArthur and
Knowles (1992, 1993) and these findings are also
sup-ported by our recent observations. Our experiments
have shown that there may be different responses in
plant growth parameters of various plant varieties to
microbial inoculants, as observed mainly in
experi-ment 1 for Karin and Krista varieties. Increase in MC
or efficiency caused by inoculation with bacteria was
observed by, e.g., El-Shanshoury et al. (1989). But
the extent of colonization of host roots by symbiotic
Table 7
F-values and significance of ANOVA for NT, TFW, number of marketable minitubers (NMT), fresh weight of marketable minitubers
(FWMT) and for MC of potato variety Karin plants dually inoculated with mixture of two bacteria and with four different AMF and transplanted to the peat-based substrate in the shadowhouse (experiment 4), d.f. represents degrees of freedom for the given factor
Factor d.f. NT TFW (g) NMT FWMT (g) MC (%)
AMF 4 4.0a,∗∗
2.3 ns 0.3 ns 0.8 ns 2.6b,∗
Error (mean square) 40 (1.72) 40 (986) 40 (0.53) 40 (1286) 36 (3.1)
ans — nonsignificant effect of the factor.
bNon-mycorrhizal treatment was not included into the statistical treatment of MC. ∗Significant effect at p<0.05.
∗∗
Significant effect at p<0.01.
fungi does not necessarily correlate with benefits to
the plant, as it was shown by Plenchette et al. (1982)
in experiments with strawberry and some other plants
in inert substrates. Nevertheless, in experiment 3, the
best growth of potato plant as well as the production
of minitubers were observed in treatments inoculated
with G. manihotis. This AMF seems to be well
com-patible with potato of the Karin variety. This may
indi-cate a physiological specificity of this fungus to potato
plants as a host. The compatibility of the mycorrhizal
fungus with potato plants may be of particular
impor-tance because they often form very weak root
colo-nization under field conditions (Ocampo and Hayman,
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Table 8
Effect of dual inoculation with four AMF and two bacteria on NT, TFW, NMT, FWMT and for MC of potato variety Karin plants transplanted to the peat-based substrate beds in the shadowhouse (experiment 4)
AMF NT TFW (g) NMT FWMT (g) MC (%) None 7.4 aa 216 a 3.5 a 157 a 0b
G. manihotis 8.6 a 256 a 3.8 a 185 a 37 b
G. mosseae 9.2 b 249 a 3.7 a 173 a 23 a
G. deserticola 9.7 b 252 a 3.7 a 166 a 18 a
G. etunicatum 8.4 a 243 a 3.5 a 164 a 25 a
aMeans of nine replicates (mean from 30 plants) within one
parameter and one factor are not significantly different according to Duncan multiple range test, p<0.05.
bNon-mycorrhizal treatment was not included into the
statis-tical treatment of MC.
1980, our unpublished observations), and thus
care-ful selection of the symbiotic fungus may improve
the mycorrhizal growth response of inoculated plants.
Moreover, some potato varieties may be almost
resis-tant to colonization by AMF and no response to
my-corrhizal inoculation can be expected (Bhattarai and
Mishra, 1984).
Experiments 1 and 2 demonstrated the significant
effect of inoculation (bacterial strains M11, B1 and
AMF, particularly G. fasciculatum) on production of
minitubers. Lower numbers of minitubers were found
in inoculated treatments, but total minituber yield
re-mained unaffected. This means that the produced
mini-tubers were bigger which is supported by increased
mean weight of minituber. This change in allocation of
plant biomass may indicate a hormonal effect of
intro-duced microorganisms. Plant growth regulating
hor-mones are produced by bacterial cultures (e.g. Prikryl
et al., 1985) and hence the introduction of bacteria may
change the hormonal balance in potato rhizosphere.
Similarly, the colonization of root cortex with
myc-orrhizal fungi is accompanied by change in hormonal
balance, e.g. by accumulation of cytokinins (Allen et
al., 1980; Baas and Kuiper, 1989; Druge and
Schon-beck, 1992) or abscisic acid (Danneberg et al., 1992).
The bacterial inoculation would, in some cases,
stimulate the extraradical mycelium of the AMF and
consequently a positive plant growth response can be
observed due to the increase of absorption surface of
the roots. Possible positive effects of bacterial
inoc-ulation on the development and activity of external
mycelium was not a subject of this research but such
effects were previously reported (Azcón et al., 1978;
Azcón, 1987; Gryndler and Vosátka, 1996; Vosatka
and Gryndler, 1999).
The amendment of Zeolite could be of importance
in nutritionally poor substrates with lower
availabil-ity of essential nutrients, a positive effect of Zeolite
amendment was found for mycorrhizal strawberry
(Vosatka et al., 1992). We choose Zeolite as a
compo-nent of the substrate to improve its physicochemical
features (sorption) but no highly positive effects
ex-pected on plant growth and MC were observed. The
inoculation into peat-based substrate might be more
successful as reported by Niemira et al. (1995). There
were potentially effective AMF isolates among those
tested, while bacteria themselves did not often
stimu-late plant growth, nevertheless, bacterization can
sup-port mycorrhization as was also previously resup-ported
for potatoes or other plants (Gryndler and Vosátka,
1996; Vosatka and Gryndler, 1999). However, to
in-crease the potential of the inoculation in practical
production of potato minitubers, it is necessary to
consider possible differences in potato varieties
re-garding their growth response as well as appropriate
combination of bacteria and AMF symbionts for a
given cultivation system.
Acknowledgements
The authors are grateful to Dr. V. Horácková from
the Institute of Potato Growing, Havlickuv Brod for
cooperation during the project No. 502/94/0834
fi-nanced by the Grant Agency of the Czech Republic.
The work on bacteria was financed by MSMT grant
COST 8.38. The help of Dr. T. Frantik in statistical
evaluation of the data is greatly acknowledged.
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