Crop Protection 29 (2010) 744e750
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Crop Protection
journal homepage: www.elsevier.com/locate/cropro
Intercropping reduces Mycosphaerella pinodes severity and delays upward
progress on the pea plant
M. Fernández-Aparicio a, M. Amri b, M. Kharrat c, D. Rubiales a, *
a
Institute for Sustainable Agriculture, CSIC, Apdo. 4084, 14080 Córdoba, Spain
Agriculture experimental unit of Oued Béja, INRAT, Route de Tunis km 5, Béja, Tunisia
c
Field crop Lab., INRAT, Rue Hédi Karray, 2049, Ariana, Tunisia
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 September 2009
Received in revised form
4 February 2010
Accepted 14 February 2010
Mycosphaerella pinodes is a serious pea disease of worldwide distribution. The increasing interest of
sustainable tools for disease control, together with the lack of sufficient levels of genetic resistance has
brought our interest in the use of intercropping as a tool for management of this disease. Effect of
intercropping on M. pinodes severity was studied in field experiments performed in Spain and Tunisia, in
which a susceptible pea cultivar was grown as monocrop and as two species mixed intercrop with either
faba bean, barley, oat, triticale or wheat. Disease was significantly reduced in terms of both percent of
diseased tissue per plant and vertical progress of lesions when pea was intercropped. Faba bean and
triticale intercropped with pea showed the highest suppressive ability with above 60% of disease
reduction. Oat, barley and wheat showed low to moderate M. pinodes suppressive effects. Suppressive
effects can be ascribed to a combined reduction of host biomass, altered microclimate and physical
barrier to spore dispersal.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Cultivar mixtures effects
Mycosphaerella blight
Intercropping
Pisum sativum
1. Introduction
Field pea (Pisum sativum L.) is the most produced grain legume
in Europe and second-most in the world (FAOSTAT data, 2007;
http://faostat.fao.org/). Mycosphaerella blight incited by Mycosphaerella pinodes (Berk. and Blox.) Vestergr., the teleomorph of
Ascochyta pinodes Jones, is one of the most important pea diseases
(Moussart et al., 1998). M. pinodes can infect all above-ground
portions of the pea plant resulting in numerous lesions and
extended necrosis. Average yield losses have been estimated in 10%,
but losses of over 50% have been recorded (Xue et al., 1997). It is
severe on leaves and on internodes of the basal part of the plants,
causing a reduction in the number of seeds per stem and in seed
size, not affecting number and length of stems per plant (Tivoli
et al., 1996).
Breeding for resistance is the most environmentally friendly
method of control however only limited successful results have
been achieved until now, with only some intermediate levels of
resistance available in commercial cultivars (Fondevilla et al., 2008;
Schoeny et al., 2008). Fungicide use and agronomic practices, such
as burial or destruction of infected stubble, use of suitable crop
rotation schemes or spatial separation of fields from infected
* Corresponding author. Tel.: þ34 957 499215; fax: þ34 957 499252.
E-mail address: [email protected] (D. Rubiales).
0261-2194/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cropro.2010.02.013
stubble that remains from previous crops are the only available
control practices that may not be suitable for many farm situations
(Schoeny et al., 2008). Therefore, feasibility of control by alternative
practices such as intercropping should be explored.
Intercropping is the simultaneous cultivation of more than one
species in close association (Boudreau, 1993) to take advantage of
biodiversity, competition and complementarity between them.
It allows the simultaneous cultivation of grain legumes and cereals
increasing protein yields and forage nutritive value (Ofori and
Stern, 1987; Strydhorst et al., 2008). The beneficial effect of intercropping for disease control has often been acknowledged (Wolfe,
1985; Finckh et al., 2000; Mundt, 2002). The more obvious factor
reducing disease is the reduction of the number of host plants per
surface unit which is replaced by an associated immune crop
creating a physical barrier for inoculum spread. Other factors such
as modified plant structure induced by space and nutrient
competition between associated species and altered microclimate
inside the canopy of two mixed species might be of importance
modifying disease development in comparison with host monocrops (Burdon and Chilvers, 1982; Mundt and Browning, 1985;
Boudreau, 1993).
The aim of the present study was to discern the effects of species
mixtures in the development of M. pinodes in pea, identifying
optimal species mixtures with highest suppressive potential and to
discuss the mechanisms of suppression.
M. Fernández-Aparicio et al. / Crop Protection 29 (2010) 744e750
745
2. Material and methods
2.4. Crop harvest
2.1. Plant material and experimental set-up
All plants in a 0.5 m2 area for each plot were harvested cutting
above 2 cm from soil surface. It was done in two harvest times,at
Beja, Tunisia when plants were at vegetative stage (14 of March and
10 of April). In intercrop plots, the pea plants were separated from
the associated crop and the fresh weight determined separately.
Pea cv. Messire, a semi leafed winter field pea cultivar, was
grown as a monocrop at a sowing density of 100 plants per m2, and
as mixed intercrop with barley (Hordeum vulgare L., cv. Cory), faba
bean (Vicia faba var. minor L., cv. Prothabon), oat (Avena sativa L., cv.
Aspen), triticale (xTriticosecale Wittm., cv. Peñarroya), and durum
wheat (Triticum durum Desf., cv. Meridiano). The intercrop design
was based on the replacement principle. For that, the half of the pea
plants were substituted in each monocrop by the equivalent associated species. The two species were mechanically sown, mixed in
the same row in 50%: 50% ratios at the same time during December.
The experimental plots (8 1.4 m2) were laid out in a complete
randomised block design with three replicates. The experiments
were carried out in 2003e2004 and 2006e2007 field seasons at
Córdoba (37 51' N; 04 48'W; 117 m altitude), Spain.
During the 2006e2007 season, the same variety of pea was
cultivated in Beja (36 44'N; 913'E; 159 m altitude), Tunisia, both as
monocrop and in two species mixed intercrop with the same cereal
varieties used in the Spanish trials. In this country, faba bean was
not included in the experimentation. In order to isolate the effect of
host sowing density from other factors influencing disease reduction, an additional treatment was included by sowing pea at half
density without being replaced for another associated species.
Experimental plots of 8 1.7 m2 were laid out in a complete
randomised block design with four replications under organic
conditions. No inoculation was performed in any of the locations, as
high levels of natural infection were known to be common.
2.2. Disease assessment
In both countries disease severity (DS) was assessed by a visual
estimation of the percent of diseased tissue per plant. Measurements were made on 10 randomly chosen plants per plot. Plants
were assessed in Spain at 15 days interval during April 2004 and 9
days interval during AprileMay 2007. In Tunisia, data collection
was carried out twice in a 17 days interval during April 2007.
In addition, disease rating (DR) was visually assessed in Spanish
trials separately on both stems and leaves for each node of 10
randomly collected plants per plot. These measurements were also
made twice per year, from the bottom to the upper pea plant
using a 0e5 scale defined by Roger and Tivoli (1996) as follow:
(0, no lesions; 1 ¼ a few scattered flecks, 2 ¼ numerous flecks,
3 ¼ 10e15% of the leaf area necrotic and appearance of coalescent
necroses, 4 ¼ 50% of the leaf area dehydrated or necrotic,
5 ¼ 75e100% of the leaf area dehydrated or necrotic).
2.3. Assessment of effects on pea plant size and morphology
In order to estimate the competitive effect of each mixture on
the size and aerial structure of pea plants and its implication on
disease development, some measurements of structural plant
characteristics were performed. In Spanish trials, individual pea
weight (grams per plant) as well as pea main stem length and
number of nodes per main stem were assessed in 10 randomly
harvested plants at pod filling stage. This allowed calculation of the
mean internode length by dividing the pea length by the number of
pea nodes in each mean stem. In addition crop stature developed by
each plant species either in monocrop and each intercrop, was also
recorded as the distance from the soil surface to the youngest fully
emerged leaf in ten random plants per each associated crop. This
allowed the comparison of differences in height between both
crops.
2.5. Statistical analysis
Percentage of diseased tissue data were approximated to normal
frequency distribution by means of angular transformation. For
multiple comparisons, parametric ANOVA followed by Tukey test
were conducted on the data using SPSS 15.0.
3. Results
High disease severity (DS) occurred at Córdoba in both seasons
on pea cv. Messire (above 70 and 50%, for 2003e2004 and
2006e2007, respectively) but disease started earlier in 2003e2004
(Fig. 1). The earlier and highest fungal infection recorded in
2003e2004 season, might be explained by the milder and rainy
winter occurred during this season (Table 1, Fig. 1A and 1B).
Results in Fig. 1 show a general trend for disease reduction by all
intercrops in both seasons. However, the level of reduction varied
markedly with the crop used in the mixture and with the season.
M. pinodes severity on pea was reduced in all intercrops (Fig. 1A and
B) but with significant effect of the intercropped species
(p < 0.001). The most suppressive species were triticale and faba
bean, which, respectively reduced DS by 73.6 and 64.8% during
2003e2004 (p < 0.001) and 63.8 and 82.3% during 2006e2007
(p < 0.001). Oat and barley respectively reduced DS up to 14.1 and
10.2% during 2003e2004 (p < 0.001) and 45.2 and 41.1% during
2006e2007 (p < 0.001). Wheat was only tested during the second
season of experimentation, causing a 59.3% reduction of DS on the
intercropped pea (p < 0.001).
These results were confirmed in Beja, Tunisia during 2006e2007.
High DS (55% of diseased tissue per plant) occurred on monocropped
pea (Fig. 1C). This DS was significantly reduced by 43.1% in pea
intercropped with triticale, and by 23.9 and 27.3% in pea intercropped with wheat and barley (p < 0.001). Oat did not show
significant levels of suppressive ability, although some reduction
was observed in the early scoring time. Unfortunately faba bean was
not included as associated crop in the study. Growing pea monocrop
at half density showed that this reduced density by itself caused
a 30% disease reduction (Fig. 2).
The detailed observations per nodes of disease rating (DR)
performed at Córdoba showed that more and larger lesions were
formed in lower parts of pea plants (Figs. 3 and 4). These differences
in DR between lower and upper pea nodes decreased with the
epidemic progress due to vertical spread of the disease toward the
upper younger parts. Intercropping pea with nonhost species
resulted in a delayed vertical progress of the disease as seen by the
reduced DR in pea nodes already from the first scoring time.
Upward spread of the disease was delayed as shown by the lower
DR values in younger tissues in the second scoring time. This delay
in the spread of the disease was more marked in pea intercropped
with faba bean-pea or triticale. The reduction in DR values was
visible starting from the second and third node closer to the soil
surface (Figs. 3 and 4). Only isolated necrotic points were visible at
the second scoring time in the upper stipules and internodes of
peas intercropped with faba bean and triticale (DR ¼ 1e2) while
coalescent necrotic areas were observed in the same leaf layers in
monocropped pea plants. Although a reduction in the density of
lesions were observed in peas when intercropped with oats and
746
M. Fernández-Aparicio et al. / Crop Protection 29 (2010) 744e750
100
80
Disease severity (%)
A
a
b
b
60
a
40
b
b
c
c
20
c
c
0
6th April 2004
B
21t April 2004
21th
100
Disease severity (%)
80
60
a
40
b
b
c
c
20
ab
ab
d
a
b
c
c
0
28 April 2007
28th
C
7th May 2007
100
Disease severity (%)
80
60
a
a
b
40
b
c
a
20
b
bc
c
c
0
7t April 2007
7th
Pea monocrop
Barley 50%: Pea 50%
24th April 2007
Oat 50%: Pea 50%
Triticale 50%: Pea 50%
Wheat 50%: Pea 50%
Faba bean 50%: Pea 50%
Fig. 1. M. pinodes severity on pea when monocropped in full plant densities and when intercropped in replacement (50%:50%) with oat, barley, wheat, triticale and faba bean. Data
correspond to the mean values at each scoring times made at Córdoba, Spain 2004 (Fig. 1A.), and 2007 (Fig. 1B.) and at Beja, Tunisia 2007 (Fig. 1C). Treatments with the same letter
per scoring date are not statistically significant different (Tukey test, p < 0.05).
barley in comparison with pea monocropped, this reduction was
much smaller than that observed in faba bean and triticale
intercrops. Wheat was only tested in the second year of experimentation, showing an intermediate reduction in lesion evolution
smaller than faba bean and triticale but higher than oats and barley
(Figs. 3 and 4).
All intercrops lead to morphologic changes of pea plants. Pea
plants were taller when intercropped than when monocropped due
Table 1
Meteorological conditions at each growing season and site of experimentation.
Location
Córdoba, Sp
Beja, Tun
Season
2003e2004
2006e2007
2006e2007
Temperature average ( C)
Number of 4 mm rainy-days
November to April
Nov
Dec
Jan
Feb
Mar
Apr
Nov
Dec
Jan
Feb
Mar
Apr
Number of
rainy days
Total rain
(mm)
14.2
14.6
15.8
10.4
8.5
11.5
10.3
7.8
11.9
11.4
11.9
12.4
13.0
12.5
12.5
15.3
15.1
16.0
6
4
3
8
3
6
2
0
2
6
4
5
6
2
9
3
4
7
118
90
59
351.5
265.5
414.1
M. Fernández-Aparicio et al. / Crop Protection 29 (2010) 744e750
Accumulative biomass of pea plus associated crop was still lower
than that of pea monocrop. Reduction of pea biomass was however
lower at the second observation data, where accumulative biomass
of the intercrops (pea þ oat, pea þ triticale) was higher or similar to
that of pea monocrop.
100
80
a
4. Discussion
5
5
4
4
3
3
2
2
1
6th April 2004
leafs
n=30
1
0
5
0
5
4
4
3
3
2
2
Node 17
Node 15
Node 13
Node 11
Node 9
Node 7
1
Node 5
0
6th April 2004
internodal stem
n=30
Node 3
1
Node 1
(bottom)
Disease rating (DR) on internodal pea stems
Disease rating (DR) on pea leafs
to an increase in internode length (Table 2), with no difference in
number of nodes per pea plant (data not shown). Accordingly, pea
crop stature, was higher when intercropped than when monocropped (Table 2) due to the standing facility provided by the
associated crop and light competition. In Spanish trials pea plants
had lower biomass when intercropped with barley, oat or triticale
than when monocropped, but was not affected when intercropped
with faba bean or wheat (Table 2). When pea biomass was
measured in Tunisia, reduced biomass per unit area was observed
in all intercrops (Fig. 5), particularly in the early observation date.
0
21th April 2004
leafs
n=30
21th Apri l2 004
internodal stem
n=30
Node number from the soil
Pea monocrop
Node number from the soil
Barley 50%: Pea 50%
Oat 50%: Pea 50%
Node 17
Fig. 2. M. pinodes severity assessed at Tunisia 2007, on pea when monocropped in half
of plant densities in comparison with the pea monocrop full density. Treatments with
the same letter per scoring date are not statistically significant different (Tukey test,
p < 0.05).
Node 15
Pea 50% density
Node 13
24th April 2007
Pea monocrop full density
Node 11
7th April 2007
Node 9
b
0
The results of this work confirm that two species mixed intercrops can be an effective strategy for control M. pinodes in pea.
Similarly, reduction of M. pinodes severity in pea has been reported
late in the season in pea-barley and pea-wheat intercrops (Kinane
and Lyngkjær, 2002; Schoeny et al., 2007). We find here that this
beneficial effect varies with the associated species, being higher for
faba bean or triticale with up to 60% reduction of M. pinodes
severity on pea. Lower reductions were recorded in pea intercropped with oat, barley or wheat. These results were confirmed
along the time (in Spain 2004 and 2007) and in different experimental location (Spain and Tunisia in 2007) with different inoculum source but using the same plant species and cultivars.
M. pinodes infection starts early in the winter pea growing
season (Schoeny et al., 2007). The primarily inoculum is transmitted from the soil where spores survive on crop debris, being the
first cycles of the disease established in the tissues nearest to the
soil surface. Asexual spores of the fungus are produced by pycnidia
and these conidia are dispersed by rain-splash. They constitute the
secondary inoculum ensuring short distance disease progress from
primary lesions, upward the plant and to neighbouring plants,
spreading the disease to the youngest nodes (Roger and Tivoli,
1996). Later in the season, wind-borne ascospores produced by
Node 7
a
20
Node 5
b
40
Node 3
60
Node 1
(bottom)
Disease severity (%)
747
Faba bean 50%: Pea 50%
Triticale 50%: Pea 50%
Fig. 3. M. pinodes rating on leaves and stems at different nodes of pea monocropped or in various intercrops at two observation times at Córdoba, Spain, season 2003e2004. Data
are mean (N ¼ 30). Error bars represent s.e.
748
M. Fernández-Aparicio et al. / Crop Protection 29 (2010) 744e750
Fig. 4. M. pinodes rating on leaves and stems at different nodes of pea monocropped or in various intercrops at two observation times at Córdoba, Spain, season 2006e2007. Data
are mean (N ¼ 30). Error bars represent s.e.
perithecia on senescent organs may be dispersed over longer
distances (Roger and Tivoli, 1996).
Intercropping influences disease by means of changing the
architecture of the host plant in comparison with monocrops.
M. pinodes dynamics have been shown to be affected by plant
morphology (Le May et al., 2009a). Intercropped pea plants were
taller and thinner, with longer internodes, what is known to
reduce chance of splashed conidia to reach upper layers (Schoeny
et al., 2008; Le May et al., 2009a). Generally, cereals have much
greater rooting densities than legumes (Anil et al., 1998) what lead
to strong competition, in favour of cereals, for nutrients uptake.
The period of strong competition for soil N correspond to the
Table 2
Weight, plant length, mean internode length, and different in height with its associated crop species measured at pod setting in 10 randomly plants in monocrop and
in different intercrops. Data from trials at Córdoba, Spain, 2006e2007 season.
Pea monocrop 100%
Pea-oat IC
Pea-wheat IC
Pea-barley IC
Pea-triticale IC
Pea-faba bean IC
Pea
weight
(g/plant)
Pea crop
height
(cm)
Pea
internode
length
(cm)
Height difference
between the
associated crop and
pea in each intercrop
(cm)
10.6b
9.1c
11.2a
8.3d
9.5c
10.5b
47.3b
51.4a
50.4a
52.7a
53.5a
53.2a
2.54b
2.87a
2.95a
3.00a
2.98a
3.08a
e
19.4c
17.6c
21.8c
63.3a
35.3b
Treatments with the same letter per column are not statistically significant different
(Tukey test, p < 0.05).
period of fast growth in leaf area for both species (Corre-Hellou
et al., 2006) and as a result, genotypic unit area is reduced,
which is positively correlated with disease development. Similar
alteration of disease dispersal and development due to the varying
spatial arrangements of the associated crops was found previously
for Septoria tritici in a wheat clover intercrop (Bannon and Cooke,
1998). Shaw (1987) reported a fivefold reduction in the number of
spores of some cereal pathogens transported vertically by splash
for an increase in height of 10 cm. Although limited, this process is
likely to play a major role in the vertical spread of polycyclic
diseases such as ascochyta blight of pea, particularly since incubation and latency periods are short, i.e. there are many cycles
during the cropping season.
Schoeny et al. (2008) found that the probability for a M. pinodes
spore to remain on its source plant was nearly ninefold higher than
that of being splashed toward one specific neighbouring plant.
Accordingly, we observed in pea intercropped and monocropped,
a negative gradient in the development of the disease toward the
upper parts of the plant, being the bottom internodes and leaves
placed near the soil surface more heavily damaged. However, when
pea were intercropped, this gradient becomes more noticeable
which indicated that the vertical spread of the disease was delayed
due to the intercropping effects on pea architecture.
Reduced plant densities in intercrop can contribute to reduce
horizontal spore dispersal (Boudreau and Madden, 1995; Schoeny
et al., 2008). In the replacement intercrops, half of the pea plants
were replaced by a nonhost species. The decreased number of host
plants per unit area increases the distance between two neighbouring host plants. This was confirmed in Tunisian experiments by
M. Fernández-Aparicio et al. / Crop Protection 29 (2010) 744e750
14 March
pea
7000
Fresh shoot biomass per m2 (g)
749
cereal
6000
5000
4000
3000
2000
1000
0
10 April
Fresh shoot biomass per m2 (g)
7000
6000
5000
4000
3000
2000
1000
0
Pea
monocrop
100%
Pea
monocrop
50%
Oat 50%:
Pea 50%
Wheat 50%:
Pea 50%
Barley 50%: Triticale 50%:
Pea 50%
Pea 50%
Fig. 5. Aerial fresh weight accumulated by pea in monocrop full density and by pea and its associated crop in each intercrops. Data collection was made at two harvesting times at
Beja, Tunisia during 2006e2007 season. Data are mean (N ¼ 4). Error bars represent s.e.
reducing by half the number of pea plants per unit area without
being replaced by a nonhost. The reduction on disease although
significant, was smaller than the obtained by some species when
were intercropped at the same pea density, showing that not only
the reduction on pea density but a complex of factors are interacting in the reduction of the disease by intercrop.
In addition to the modified morphology and number of host
plants per unit area in intercrops, intercropping imposes a nonhost
barrier, and as a consequence, less conidia are successfully transported to new developing host tissue. Vertical disruption of splash
dispersal pathways by intercropping has been described by Newton
et al. (2009).
Intercropping also results in alteration of microclimate inside
canopy, as previously observed in corn-bean intercrops (Boudreau,
1993). Microclimate is known to influence M. pinodes development.
DS and the number of pycnidia formed on leaves increase with
temperature from 5 to 20 C, but decrease progressively when
temperatures are higher than 20 C (Roger et al., 1999). When peas
were intercropped, they grew straighten up, being their branches
supported by the associated species. In addition, there were
differences in the vertical distribution of successive foliar layers
across both associated crops (data not shown). As a consequence,
a more open canopy was established in intercrops than in pea
monocrops. This would improve air movement and light penetration, conditions that are less favourable for the disease (Bretag et al.,
1995).
Splash dispersal of conidia starts 14e45 days after emergency
in winter pea, depending on weather conditions (Schoeny et al.,
2007). In this case, the modified microclimate and the more
distance between pea plants can play in favour of disease
reductions. However, in spring peas M. pinodes usually starts later
in the cropping season when a fully canopy is developed. In this
case, canopy density and microclimate can play opposite roles in
the spread of the disease. A denser pea canopy present in late
M. pinodes development might hamper horizontal disease
dispersal being the barrier effects more important when the
canopy is denser (Schoeny et al., 2008; Le May et al., 2009a). But at
the same time, denser canopy could create more favourable
microclimatic conditions. Similarly, in mild climate such as the one
of southern Spain or Tunisia, if M. pinodes starts late in the season
in a winter sowing but when a full canopy is developed, then
splash dispersal of conidial secondary inoculum within the canopy
will be hampered. Subsequent disease progress will depend
mainly on the formation and wind dispersal of ascospore type
secondary inoculum (Schoeny et al., 2007). In the winter peas of
Spanish trials, disease onset varied largely across year of experimentation, depending on weather conditions. M. pinodes reductions by intercropping were more marked in 2006e2007 season in
which the disease started later. It could means that the physical
barrier imposed by a denser canopy could play a more important
role in reducing disease than the unfavourable microclimatic
conditions imposed by a denser canopy in a late disease onset.
The competition established early in the season between
intercropped cereal and pea forces the pea plant to establish an
enhanced symbiosis with Rhizobium in comparison with monocrops (Danso et al., 1987). The N2-fixation takes some time before
the benefits of this enhanced symbiosis are made available to the
pea plants, starting later than soil N uptake of pea and its very
competitive companion crop (Hauggaard-Nielsen et al., 2001).
Symbiosis does not completely restore the losses in the pea
component although maximise total dry matter and nitrogen
accumulation in the system. The competitive ability developed by
750
M. Fernández-Aparicio et al. / Crop Protection 29 (2010) 744e750
cereals in early growth leads to pea plants with lower foliar
biomass. The more advantaged cereal might impair the photosynthetic activity of pea by shading the pea foliage. In addition, the
established rhizobial symbiosis involves a considerable carbon sink,
in return of the N2-fixation benefits. Under these circumstances the
ratio of carbon to nitrogen content could be lower in intercropped
pea plants compared to monocropped ones, what could lead to an
increased allocation to nitrogen-based defences contributing to the
reduction of M. pinodes development (Dietrich et al., 2004).
Contrary to the competition exerted by cereals against pea
plants, in the faba bean-pea intercrop, individual pea weight was
not reduced. Despite the lack of reduction on pea genotypic unit
area due to its intercrop with faba bean-pea, mixture effects on this
system bring the maximum reduction on disease. Faba bean foliage
was observed as broader, less flexible and arranged in horizontal
layers in comparison with the thin, long flexible cereal leaves which
in addition were inclined downwards (data not shown). The
characteristics in roughness, flexibility and slope of the nonhost
leaf surface could contribute in a creation of a more efficient
physical barrier. Foliar roughness, flexibility, and inclination angle
could affect the splash process in a way that rain drops loaded with
conidia from an adjacent pea tissue, could be more efficiently
interfered its way to an adjacent pea plant by a less flexible, roughly
and horizontal nonhost leaf foliage (Stedman, 1979; Madden, 1992;
Huber et al., 1997). Faba bean architecture could form the more
efficient physical barrier against M. pinodes conidia spread.
In addition to faba bean, low competence was also exerted by
wheat to the pea plants in the sowing densities used in this work.
Low competence (data no shown) created by faba bean and wheat
for nutrients and water in comparison with oat and barley could
delay pea phenology. This retarded pea growth might have
additional influence on pea defences, as the phytoalexin pisatin
content on pea leaves have been described to decrease as the leaves
matured (Bailey, 1969). It might have direct implications limiting
disease progress by retarding ascospore release as a direct link
between formation of perithecia and host senescence has been
observed (Roger and Tivoli, 1996).
We cannot exclude induction of systemic acquired resistance on
pea by pathogens present on the intercropped species. It has
been demonstrated that co-inoculation with pathogens such as
Ascochyta fabae, Ascochyta pisi, Pseudomonas phaseolicola, Phoma
medicaginis var. pinodella or nonvirulent strains of M. pinodes
induce protection in pea against M. pinodes (Lepoivre, 1979; Le May
et al., 2009b)
Acknowledgements
This research was supported by EU FP6 integrated project Grain
Legumes and Spanish project AGL2008-01239.
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