Fig' 5' Distribution of xylem at internode 3

1
Relationship between lodging, stem anatomy, and
reaction to Mycosphaerella blight in field pea
Parvaneh Hashemi, Sabine Banniza, ¹Art Davis,
Tom Warkentin, and Bert VandenbergCrop
Development Centre, ¹Biology Department,
University of Saskatchewan
Introduction Field pea production in Canada in
2002 is estimated to be 1,378,000 tonnes, down
from 2001 (AAFC statistics). The decrease in
production is due to a decrease in yield,
primarily due to drought. Lodging and
susceptibility to Mycosphaerella blight caused by
Mycosphaerella pinodes are two major constraints
to pea production. Peas have an inherently poor
standing ability. Most commercial varieties
lodge before maturity, resulting in decreased
seed quality and quantity and in increased
disease infection. Varieties with greater
resistance to stem lodging increase the
efficiency of combine harvesting (see Figs. 1 and
2). Mycosphaerella blight in field pea causes
yield reduction of up to 40 due to a reduction
in biomass production, seed number, and seed
weight (Garry et al. 1996) (Fig. 3). Resistance
to lodging and to infection with Mycosphaerella
blight are two major objectives in pea breeding
for Saskatchewan Objectives To determine the
correlation between lodging and susceptibility to
Mycosphaerella blight in field pea, To
investigate the effect of stem anatomy on
lodging and Mycosphaerella blight in field pea.
Materials and Methods During the summer of 2000
to 2002 commercial pea varieties (first year 10
varieties second and third year, 20 varieties)
were examined at Outlook (irrigated) and at
Saskatoon (rain fed). Varieties were selected to
cover a presumed range in response to lodging and
Mycosphaerella blight. The experimental design
was a randomized complete block with three
replications. During the growing season the
following measurements were recorded lodging
scores based on a 9 point scale, Mycosphaerella
blight severity on whole plants, stems and pods,
stem measurements including height of plant,
number of nodes, length and diameter of the
internodes. Stem sections were taken two weeks
before harvesting. Stem anatomy measurements were
compared on free hand sections of the internodes
3 and 9 from slide preparations and the
distribution and proportion of xylem were
quantified visually after staining (Fig. 4).
Results and Discussion Significant differences
in lodging and Mycosphaerella blight scores were
observed in all three years. Table 1 summarizes
the 2000 data from the Saskatoon experiment.
Correlation analysis between disease and yield
with lodging data showed that high lodging scores
were correlated with high Mycosphaerella blight
score on whole plants (2000-2002), stems
(2001-2002), and pods (2001-2002) (Table 2).
High lodging was correlated with low yields in
all three seasons, although the correlation was
only significant (0.05) in 2001 (Table 2).
Measurement of fiber, lignin and cellulose at
Saskatoon 2000 showed considerable variation
between varieties. The varieties Carneval, Keoma,
Integra, Nitouche and Espace had relatively more
lignin and fiber (Fig. 7). Microscopic analysis
of stem sections in 2000 and 2001 showed
significant differences in the proportion of of
xylem in stems at both internode 3 and 9 (Figs.
4-6). In 2000, varieties Carneval, Integra,
Nitouche and Keoma had a relatively higher
proportion of xylem at both internode 3 and 9
(Figs. 8 and 9). In 2001, varieties Carneval,
Integra, Nitouche, CDC Mozart, Eclipse, Miami,
CDC 0001, Espace, AC Melfort and Eiffel had a
relatively higher proportion of xylem at
internode 3 and 9 (Figs. 10 and 11). A higher
proportion of xylem at nodes 3 and 9 was
correlated with lower lodging in both 2000 and
2001 (Table 3). A higher proportion of xylem may
increase the strength and hardness of the stem,
and give more rigidity, enabling these varieties
to stay more upright. Conclusions More
lodging was correlated with higher severity of
Mycosphaerella blight. More lodging was also
correlated with lower yield. A higher
proportion of xylem in pea stem sections was
correlated with both reduced lodging and
reduced severity of Mycosphaerella blight. A
higher amount of lignin increased the strength
and stiffness of pea stems.      

Fig. 1. Lodging- resistant variety (Carneval)
Fig. 2. Lodging -susceptible variety ( Keoma)

Fig. 3. Mycosphaerella blight in field pea

Fig. 4. Stem anatomy sections at Internode 3 and 9
Fig. 5. Distribution of xylem at internode 3
References Agriculture and Agri -Food Canada.
2002. Specialty Crop. Statistics branch. Garry,
G., B. Tivoli, M. H. Jeuffroy, and Citharel,
J.1996. Effects of Ascochyta blight caused by
mycosphaerella pinodes on the translocation of
carbohydrates and nitrogen compounds from the
leaf and hull to the seed of dried- pea. Plant
Pathol. 45 469-479.
Miami
CDC Peko
AC Tamor

Fig. 6. Distribution of xylem at internode 9
Acknowledgments We gratefully
acknowledge funding of this research project from
the Saskatchewan Agricultural Development Fund.
We wish to thank the pulse crew for assisting
with the field work. We thank Monika Lulsdorf and
Tim Dament for permission to use the microscope
and camera. We thank Dennis Dyck for assistance
in the preparation of this poster.
PMR-16
Carneval
Courier