16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
SOIL FUMIGATION WITH ALLIUM SULFUR VOLATILES AND
ALLIUM BY-PRODUCTS
Arnault I.1, Vey F. 2, Fleurance C.3, Nabil H.4, Auger J. 1
Key words: biofumigation, Allium spp., by-products
Abstract
Like Brassicaeae spp., Allium spp.have biofumigation properties attributed to sulfur
components, mainly three disulfides: dimethyl disulfide (DMDS), dipropyl disulfide
(DPDS); and diallyl disulfide (DADS), with an efficacy superior to that of DMDS. In this
study, the biofumigant activity of Allium (onion and leek) by-products was investigated
in vitro and in vivo. In vitro, the experimental model consisted of a host-pathogen
system: cucumber-Pythium ultimum. The results of the bioassay show that cucumber
plants in compost inoculated with the pathogen and containing onion or leek byproducts show better vegetative growth than the control. In vivo, soil biodisinfection
with onion by-products in asparagus leads to a yield intermediate between the
untreated soil and the methyl bromide treatment. Another aim of the present study
was to get more data about the nematicidal activity of disulfides. The activity of DMDS
and DADS was evaluated on two nematode species.
Introduction
The substances implicated in the beneficial effect of Allium spp. on human health are
mainly sulfur compounds, such as disulfides (DS) and thiosulfinates (Ti) (Agarwal,
1996). These chemicals are also responsible for the natural defences of these species
against herbivorous pests and pathogens. They are insecticidal, fungicidal, acaricidal,
nematicidal, and bactericidal (Auger et al, 2004).
When tissue of an Allium is crushed or degraded by micro-organisms, an enzyme,
alliinase, which is stored in the vacuoles, reacts with S-alk(en)yl-L-cysteine sulfoxides
(RCSO) (Lancaster et al, 1988) to give sulfenic acids (Ferary and Auger, 1996). In
onions and leeks, several RCSO (R= methyl, propyl, 1-propenyl) are present and a
complex rearrangement occurs to give mainly dipropyl disulfide, DPDS (Arnault et al,
2004) as the endproduct of biosynthesis. For some wild Allium spp., such as bear’s
garlic (A. ursinum), the major RCSO is methiin (S-methyl-L-cysteine sulfoxide); it gives
dimethyl thiosulfinate (DMTi), which gets rearranged into DMDS.
The nematicidal and fungicidal activity of Allium has been widely reported (Auger et al,
2004); this great pesticidal potential allows us to envisage the use of Allium spp. for
soil fumigation (Auger et al., 1994).
1
CRITT INNOPHYT, UFR Sciences et Techniques, Parc de Grandmont, 37200 Tours, France,
Email innophyt@univ-tours.fr
2
LNPV UFPS, 93 rue de Curembourg, 45404 Fleury Les Aubrais, France
3
SELT, le Riou, 41 250 Tour en Sologne
4
IRD, UMR 134 BIOSOL32, Avenue H. Varagnat, 93143 Bondy Cedex, France
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16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
In the Val of Loire, asparagus is a traditional crop representing an important economic
activity. However, the soils increasingly show the phenomenon of soil stress.
Therefore, in place of methyl bromide, which now is definitively banned, the
maintenance of these cultures requires the use of new fumigants. Among the
alternatives, biodesinfection with Allium spp. is an interesting method. In this study, we
evaluated the fungicidal activity of onion and leek by-products in vitro, with an
experimental model, and in vivo, with field experiments (asparagus). We also studied
the nematicidal effect of DMDS on other soil pests, especially two nematodes,
Meloidogyne graminicola and Heterodera sacchari
Materials and methods
Fungicidal test: Pythium ultimum type test
The compost used in glass jars was artificially infected with Pythium ultimum, with its
presence controlled to obtain a high level of infection and a homogenous inoculate.
The by-products were mixed, wetted, and homogenised with the compost and
transferred into the jars, just covered by an aluminium sheet that allows gas
exchange.
For each test, we used a sterile standard without P. ultimum inoculation, and an
infected standard inoculated with the fungus. We tested the activity of Allium byproducts at three different times: 15 days, and one and two months. After these
periods, we tested the capacity of the compost to be used for a culture. For this
purpose, seeds of cucumber, a plant very sensitive to P. Ultimum, were put in contact
with the compost. At the end of the growth period (13 days) the healthy, necrotic, and
dead plants were counted.
Two disulfides were tested, DMDS and DPDS, with two amounts of by-products in the
compost: 120 and 240 tonnes/ hectare (T/Ha).
Nematicide tests
Heterodera sacchari is a cyst nematode common in Africa and some Asian countries.
This cyst-forming nematode has sedentary endoparasitic habits (Nobbs et al., 1992).
Rice (Oryza sativa) and sugarcane (Saccharum officinarum) are the major field crops
infected by this nematode.
Meloidogyne graminicola (rice-root nematode) is a common species in the tropics and
subtropics, where it infects numerous grasses, including rice (Prot et al., 1993).
Because infesting larvae are the most sensitive to biofumigants at day 2 (d2), we
calculated the LC50 (lethal concentration for 50% of the population) with DMDS for the
two nematodes species at d2.
Field experiment
In 2002, the asparagus parcel was prepared and disinfected with Allium by-products
and methyl bromide, which constitutes the reference. An undisinfected parcel was also
used. An elementary parcel was composed of three ranks of asparagus (128 plants,
144 m²). The control was the central rank. The biodisinfection effect was evaluated by
incorporation of onion and leek by-products (75 T/ha).
Asparagus was planted in the parcel in April 2003; we measured productivity at the
harvests in April 2004 and 2005.
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16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
Results
Fungicidal tests
Compared to the infected standard, where the plants show necrosis, not only was the
sample with DMDS treatment healthy, but moreover a stimulant effect could be
observed. Furthermore, DMDS was more toxic than DPDS.
Figure 1 shows the results for 240 T/ha of Allium by-products in the soil. With onions
we can observe a Concentration-Time (CT) effect that is characteristic: 74% at 15
days and 94% at 1 month. Leek by-products were less efficient than the onion
treatment. The optimum disinfectant effect is reached sooner for the 240 T/ha dose (1
month) than with 120 T/ha (2 months).
D1
D2
100
%
80
94
74
60
40
20
0
%
Onion
Infected / uninfected
D1
D2
48
healthy
necrotic
dead
64
D1: 15 days
D2 : 1 month
Leek
Soil treatment
Figure 1: Percentage of healthy, necrotic and dead cucumbers after Allium byproducts were incorporated in the soil (240 T/ha).
Nematicide tests
The LC50 of d2 larvae (H. sacchari) is 0.79 µl/l. M. graminicola, for which LC50 = 1.6
µl/l, seems to be more sensitive to DMDS than H. sacchari.
Field experiments
Two years after planting, the parcels disinfected with Allium by-products had lower
productivity than the ones disinfected with methyl bromide. But the incorporation of
onions leads to an intermediate yield between the methyl bromide reference and the
undisinfected parcel (Figure 2).
12,0
P>95%
10,0
8,0
6,0
4,0
8.2
10.6
b
9.4
ab
a
8.3
a
2,0
0,0 undisinfected
MeBr
onion
leek
.
Figure 3: Yield (T/ha) of asparagus under four different disinfection conditions:
undisinfected, MeBr, onion, and leek.
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16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/view/projects/conference.html
Conclusion
This study shows in vitro and in vivo, with field experiments, the disinfection effect of
Allium spp., particularly onion by-products. The result can be explained by the kind of
by-product used. For onions, the by-products are unmarketable onions bulbs, while for
leeks they are the wastes from peeling, i.e. the green leaves, which are well known
to contain less sulfur compounds, in accordance with their lower dry matter content.
DPDS, the gas produced by onion and leek by-products in soil, persists for more than
one month (Arnault et al., 2004).
The results point to the ability of Allium by-products to disinfect a soil. The doses,
contact time, and characteristics of the by-products are very important.
Discussion
Allium spp. offer good potential for soil disinfection, but the practice in the field must
be improved. For this purpose, the choice of Allium spp. can be modified. As DMDS is
much more effective as a disinfectant and pesticide than DPDS, Allium spp. with high
potential levels of DMDS could be tested, so that the doses incorporated in the field
could be reduced. Some wild Allium species contain more DMDS than marketable
Allium. For example, A. vineale (wild garlic) and A. ursinum (bear's garlic), contain
more than 50% of methiin, the DMDS precursor (Keusgen et al, 2002).
Acknowledgments
We acknowledge the “Region centre” and “Delegation regionale à la recherche et à la
technologie” for their financial support.
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