16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
Plant-probiotic microorganisms for a sustainable buffer of input
reduction in organic and low-input tomato production systems
Baruffa, E.1, Picard, C.1,2, Sabbioni, F.3, Petrozza, A.4, Giovannetti, G.2, Bosco, M1.
Key words: Organic tomato; Input reduction; Plant-probiotic microorganisms;
Sustainable production; Farmer participation.
Abstract
A consortium of plant-probiotic microorganisms is under investigation in open field
conditions, at the ICEA-certified Organic Farm “La Carioncella”, for its ability to ensure
durable soil fertility while buffering nutritional inputs reduction. The primary objective of
our QLIF-WP333 three-years-long project is to produce scientific data to help farmers
in managing soil probiotics, as a way to reduce inputs, production costs, while keeping
quality and sustainability of organic and low-input tomato production systems.
Introduction
The root surface and the close rhizosphere are habitats where microbial activity is
maximum, due to several modification of soil environment: release of bioactive
compounds from the roots, soil aggregate formation, roots respiration, etc. Population
density and diversity of microorganisms that are in close relation with plant roots were
recently evidenced to be finely regulated by each plant genotype (Picard et al., 2008).
This finding is especially important for organic and low-input agriculture. In fact,
rhizospheric plant-growth-promoting prokaryotes and eukaryotes (now called PPM, for
Plant-Probiotic Microorganisms) do positively and directly affect plant production
through several mechanisms, such as biological nitrogen fixation, solubilization of
organic nitrogen, phosphorous, iron and oligoelements, enhanced water supply,
synthesis of plant hormones and plant hormone regulators (Picard and Bosco, 2008).
PPM can also indirectly promote plant growth by antagonizing the action of
phytopathogens, pests and weeds (Lugtenberg et al., 2002). As the diversity of
terrestrial plants is dependent from the diversity of their co-evolved soil probiotics (van
der Heijden et al., 1998), sustainable innovations in organic and low-input agriculture
will need to take into account the biological need of plants to co-operating with PPM.
Our present research aims to achieve a better understanding on how plant-probiotic
micro-flora management could buffer future reduction of external inputs, while keeping
tomato fruit quality and system sustainability.
Alma Mater Studiorum – Università di Bologna, 40127 Bologna, Italy, E-Mail
marco.bosco@unibo.it ; Internet: www.dista.unibo.it/person/bosco(e).php
1
2
Centro Colture Sperimentali Valle d’Aosta s.r.l., 11020 Quart, Italy
3
La Carioncella, ICEA-certified Organic Farm, 44012 Bondeno, Italy
4
Metapontum Agrobios s.r.l., 75010 Metaponto, Italy
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
Materials and methods
Plant materials consisted of tomato (Solanum lycopersicum L.) ‘Riogrande’, an
industrial processing cultivar, chosen by the organic farmer because it already
produced good yield, quality in his own farm during the past ten years. Microbial inputs
(M) consisted in an experimental consortium of PPM (Bosco et al., 2007), containing
the arbuscular mycorrhizal fungi (AMF) Glomus mosseae GP11, G. viscosum GC41,
G. intraradices GB67, as well as plant-growth-promoting-rhizobacteria (PGPR) like
Pseudomonas sp. PN01, P. fluorescens PA28, Bacillus subtilis BA41, Streptomyces
sp. SB14, three Italian strains of free-living nitrogen-fixing bacteria (BUSCoB Culture
Collection), and the antagonistic saprophytic fungus Trichoderma viride TH03.
Compost inputs consisted in a commercial green compost (1.8% total N, 30% total C)
produced by Nuova Geovis S.p.A. near Bologna.
Trials were performed with the active participation of the farmer at the Carioncella
organic farm, in northern Italy, which holds the AIAB-ICEA certificate since 1993. In
2007, tomato seedlings were re-planted into the same four replication blocks
established in 2006. Each block was randomly divided into main-plots and sub-plots
as summarized in Table 1.
Tab. 1: Experimental combinations of compost (C) and microbial (M) inputs
Main-plots
1
2
3
2006
C0M0(-)
C1M0(-)
C2M0(-)
2007
C0 (+)
C0 (-)
C1 (+)
C1 (-)
C2 (+)
C2 (-)
Sub-plots 2006
C0M1(-)
C1M1(-)
C2M1(-)
2007
C0 (+)
C0 (-)
C1 (+)
C1 (-)
C2 (+)
C2 (-)
2006
C0M2(-)
C1M2(-)
C2M2(-)
2007
C0 (+)
C0 (-)
C1 (+)
C1 (-)
C2 (+)
C2 (-)
C: compost inputs equivalent to zero (C0), 100 kg per ha (C1), 200 kg per ha (C2).
M: microbial inputs equivalent to zero (M0), 40 kg per ha (M1), 80 kg per ha (M2).
(+): nursery-inoculated tomato seedlings; (-) non inoculated seedlings.
Year
Evaluations
In 2007 growing season, tomato fruits representing 18 different treatments (Table 1)
were harvested from all the subplots and analyzed. Total and marketable fresh weight
(Kg) per subplot were recorded. Fruit average weight (g) and size (longitudinal and
transversal diameters) (mm) were determined. All yield data were subjected to oneway analysis of variance (ANOVA) to compare the different treatments. In order to
show whether the 2006 treatments had any continued effect on 2007 yield, all data of
2006 subplots (Bosco et al., 2007) were compared with those of 2007 non inoculated
subplots. A representative sample of marketable fruits (2 Kg) per subplot of the last
harvest was analysed for quality parameters such as soluble solids (°Brix), titratable
acidity (mEq 100 g-1), firmness (Kg cm2-1), and pH. Soluble solid concentration of the
clarified tomato juice was determined using a hand-held Atago PR1 refractometer
which provides values as Brix degrees (Brix range 0-32% at 20 °C). Acidity was
determined by titration with sodium hydroxide 0,1 mol l-1 and values were expressed in
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
mEq of citric acid per 100 g. The pH was determined using a Metrohm Model 654 pHmeter. Firmness was measured by using a pressure tester (Forge Gauge, Lutron FG5000-A) fitted with a cylindrical plunger of 6 mm in diameter. ANOVA was used to
compare quality parameters between treatments. Mycorrhizal colonisation of tomato
roots was monitored by a microscopic method (McGonigle et al., 1990;) on roots
sampled at two dates (8th and 10th weeks after planting), and analysed with ANOVA.
Results
Significant differences (p<0.05) according to the Duncan’s multiple range test were
detected between tomato fruit yields of 2007 non-inoculated subplots and 2006
inoculated ones. The medium amendment of compost in the 2007 growing season
more positively influenced yield than the high compost amendment of 2006 season.
The quality of marketable fruits was not significantly different between 2007
treatments. Mycorrhizal index was significantly different (p<0.05) between 2006 M
inputs in the roots corresponding to the first 2007 sampling. In particular, the low PPM
input (M1) positively influenced the mycorrhizal index in comparison to the control
(Fig. 1). In the same way, compost inputs enhanced mycorrhizal colonisation (non
significant). The mycorrhizal colonisation was significantly higher in the second
sampling, but the differences between treatments lost their significance (Fig. 1). It is
interesting to note that the mycorrhizal index of plants non-inoculated in 2007 wasn’t
significant different from the index of those sampled in 2006 PPM-inoculated subplots.
No. of arbuscules per cm of roots
8
7
6
5
4
c
c
3
2
1
0
a
M0
b
ab
c
c
c
M1
M2
M0
M1
M2
2006 inoculation treatments (see Table 1)
8 weeks after planting
10 weeks after planting
Figure 1: 2007 root mycorrhizal colonisation due to 2006 microbial (M) inputs:
the columns sharing the same letter(s) do not differ significantly.
Discussion
Plant-probiotic microorganisms are emerging as a sustainable production factor for
future agriculture. However, few experimental works have been done to assess their
actual impact on organic and low-input tomato fruit yield and quality. By comparing
results from our 2006 (Bosco et al., 2007) and 2007 field plots, we could evidence that
plants non treated in 2007 did produce significant higher yields than plants grown in
2006 treated plots, even if tomato was re-planted after tomato (experimental low-input
conditions) in an organic managed farm. In 2006-treated plots, the 2007 reduction of
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
compost input (C1) did not reduce yields, nor fruit quality, suggesting a long-lasting,
buffering effect by the first-year PPM treatment. This is in agreement with (and could
be explained by) the observed stability of mycorrhizal index between roots sampled in
2007 and 2006 growing seasons. However, a third experimental growing season is
desirable and already started to verify this explanation.
Concusions
As the moderate PPM input (M1) in 2006 had its positive impact on the second
growing season, and could buffer the 2007 reduction of compost inputs (C1), without
reducing tomato fruit yield and quality, we are now concerned with the actual cause of
such an effect. Further research into microbial parameters, such as community
diversity and structure evaluation, should help to understand the interactions of natural
soil microflora, external inputs of plant-probiotic microorganisms, reduced inputs of
fertilizers, and tomato fruit yield, quality, production costs, system sustainability.
Acknowledgments
We thank Nuova Geovis SpA for donation of green compost, Pedro Guzman, Linda
Zamariola, and the Sabbioni family for their help during the establishment and running
of field experiments. Authors from Bologna and Quart gratefully acknowledge funding
from the European Community financial participation under the Sixth Framework
Programme for Research, Technological Development and Demonstration Activities
for the Integrated Project QUALITYLOWINPUTFOOD, FP6-FOOD-CT-2003- 506358.
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