nish and Lymbery, 1987; Durr et al., 1992. Some other early-set characters may be limiting too. For
instance in spring barley, the earlier reproductive development in long daylength reduces the num-
ber of leaves Kirby and Appleyard, 1980. Also, wheat plants that begin tillering at the node of the
second true leaf bear shoots with lower growth capacity than plants with the first-leaf tiller
Masle-Meynard and Se´billotte, 1981a. At the same age, plants with delayed tillering start will
bear fewer tillers and, thus, they will be less competitive in the stand.
Distinguishing between the plant capacities in- duced during the early phase and later environ-
mental growth restrictions will improve analyses of crop growth and genotype – environment inter-
actions. The tiller number per plant is a result of competition for nitrogen or light Masle, 1985. In
fact, far-red signals from canopy closure Casal et al., 1986 or from neighbouring plants Casal et
al., 1990 stop the tillering before any actual reduction in individual growth becomes evident.
However, additional tillers produced by an artifi- cial red-light enrichment under the canopy will
not persist Casal et al., 1986: far-red signals adapt the plant morphogenesis to an imminent
shortage of carbon in naturally grown stands. The onset of competition can be back-dated to the
time the tillering stopped Kirby et al., 1985a.
Twenty years ago, cereal growing was more common in the highland farms of the French
Massif Central than it is at present Lafarge, 1983. In that time, spring barley crops in two
representative highland climates were compared to a lowland situation. The experimental locations
build a gradient of initial daylengths that can hasten the development and reduce the growth
capacities of the plants. This experiment was partly published Lafarge, 1991, 1992, but the
individual tillering measurements were not ex- ploited. We try to distinguish between initial
tillering characteristics defining phenotypes and characteristics indicating the cessation of tillering
and thus the onset of competition in the tillering patterns recorded on the plants. We also try to
link the cessation of tillering at the stand level to the distribution of phenotypes, and to link these
early phenotypes to the experimental conditions.
2. Material and methods
2
.
1
. Sites and experimental design The experimental design consisted of three sites
around Clermont-Ferrand, in the French Massif Central. One is at 320 m a.s.l., ‘Malintrat’, on the
commercial cereal-cropping plain, on an isohumic clay soil with a pH 8.2; it is the control lowland
site. The next is at 880 m a.s.l., ‘St Gene`s’; this site has a brown-acid soil pH 5.8 with a good
availability of P and K. The last site is at 1120 m a.s.l., ‘Landeyrat’, in a summer-pasture area
where combine-harvesting is risky; the andic soil pH 5.4 have some exchangeable aluminium 0.7
meq and low phosphorus availability, but the experimental field was cultivated and well sup-
plied with PK during the previous years.
The two-rowed variety ‘Berenice’ was the spring barley genotype used in this experiment. All sow-
ings were made from the same seed lot of the quality required for seed production. We drilled
at the end of the winter 1978 at each location: on Febraury 24th at Malintrat situation ME; on
April 3rd at St Gene`s situation SGE and on May 3rd at Landeyrat situation LE. At Malin-
trat, a later sowing was also carried out to provide a simultaneous stem elongation with the
last sowing in the highlands situation ML. This sowing was made on May 30th, with chemical
protection against Frit fly Oscinella frit L.. These four ‘situation treatments’ exposed the
genotype to environmental variation which acts on plant potential and competition: the initial
daylength influences the growth capacity and the risk of drought and the temperature influence the
resource availability Table 1.
At each treatment site, conditions which influ- ence competition were established with different
sowing densities and nitrogen fertilizations. A sowing density of 150 grains m
− 2
represented sparse stands. Dense stands were created from
sowing densities which were increased at each progressive sowing date, in order to equalize the
competition, considering the expected reductions in the plant growth capacities. These densities
were 300 grains m
− 2
at ME, 400 at SGE and 650 at LE and ML. Nitrogen fertilization was applied
at a rate that would yield 7 t ha
− 1
of grain, considering the resources available at each site.
These resources were set by the nitrate content of the soil at the end of the winter Re´my and
He´bert, 1977: 110 kg N ha
− 1
at Malintrat and St Gene`s, and 50 at Landeyrat. Thus, the rate of
fertilizer application was 100 kg N ha
− 1
for ME, SGE and ML, and 160 kg N ha
− 1
for LE. Half this fertilizer was applied at plant emergence and
the other half after the beginning of stem elonga- tion. As alternative treatment at all sites, no fertil-
ization was applied.
The following four conditions of competition were applied everywhere:
SO: sparse stand without nitrogen fertilizer;
SN: nitrogen-fertilized sparse stand;
DO: dense stand without nitrogen fertilizer;
DN: nitrogen-fertilized dense stand. There were six replicates of each condition in
each situation. The rows in each plot were spaced 25 cm apart in order to facilitate hoeing if chemi-
cal weed control was not effective. It was thought at the time of the experiment that spacing along
the rows did not effect plant development.
2
.
2
. Phenology and obser6ations The developmental stages of the apices were not
systematically recorded. The phenological scale was very simple: the beginning of the stem elonga-
tion ‘ear-at-1 cm’ — Kirby et al., 1985b, the ear emergence ‘heading’ and the beginning of the
grain ripening ‘pasty-ripe stage’. Samples of plant material were taken and measurements were
done at each of these three stages. After the beginning of stem elongation, the frequency of
Table 1 The situation treatments altitudes and sowing dates as modalities of two factors: the initial daylength and the availability of soil
resources
a
Initial daylength 12 h Initial daylength 14 h
Initial daylength \15 h Usual growth potential
Reduced growth potential Low growth potential
ME Low risk of drought during stand formation:
X LE
End-of-winter sowing End-of-winter sowing
Soil resources always available at 1120 m
at 320m Some dry periods during stand formation:
X SGE
X Occasional shortages of soil resources
End-of-winter sowing at 880 m
ML X
High initial temperatures and high risk of X
Late sowing at 320 m drought during stand formation:
Low sourcesink ratio and availability of resources depending on rains
a
According to the effect of the daylength Kirby and Appleyard, 1980, the growth potential is ‘usual’ when the plants emerge in the same daylength as in the areas of commercial cropping of spring barley, and ‘reduced’ when they emerge in longer days. The
‘low’ growth potential just refers to a greater reduction in even longer days. ME, SGE, LE and ML are the acronyms used in the next table and figures to refer to the situation treatments: end-of-winter sowings at Malintrat 320 m = ME, at Saint Gene`s 880
m = SGE, and at Landeyrat 1120 m = LE. ML refers to the late sowing May 30th at Malintrat. ‘X’ means the lack of the modality. The risks of drought were estimated according to the usual climates during the pre-anthesis phase of spring barley crops
at each location. At Malintrat and St Gene`s the rainfall is generally in excess in May. Afterwards, the drought is progressively rising. Spring barley crops sown at the end of the winter are usually at heading at the beginning of June that is before any drought at
Malintrat, but at the end of June at St Gene`s, inducing risks of drought during stem elongation. Spring barley sown at the end of May at Malintrat will continuously grow under drought. At Landeyrat, the rainfall is usually nearly equal to the evapotranspiration
throughout the spring and the summer.
young tillers was surveyed roughly in the stands. When this frequency seemed to be low, the tiller-
ing was supposed to be slowing down and a sampling was done to describe the tillering
pattern.
At each sampling stage in each treatment site, 0.35 m × 0.75 m = 0.26 m
2
of the stand was sam- pled from each plot. At the ‘ear-at-1 cm’ stage,
plants were counted and all above-ground parts were dried and weighed. Around the apparent end
of tillering, all the plants were counted and for 25 plants from each sample, the ‘tillering architec-
ture’ was described as below see Section 2.3. Next, at the ‘heading’ stage, all the ears were
counted and all the above-ground parts were dried and weighed. Finally, at the ‘pasty-ripe’
stage, plants and ears were counted and enough plants to get 60 ear-bearing shoots were sub-sam-
pled from each plot sample. In the sub-sample all the dead, ear-bearing and live non-ear-bearing
shoots were counted on each plant.
2
.
3
. Architecture and dynamics of the tillering On each plant of each ‘tillering architecture’
sub-sample, all emerged tillers were identified by the node which bore it Kirby et al., 1985a: TC
for the tiller on the coleoptile node, T1 for the tiller in the axil of the first leaf, and continuing
with this rule. On each shoot axis i.e. main stem or tillers, leaves were counted and the apex was
noted as growing or dead. Afterwards, plants were classified according to the lowest node bear-
ing a tiller, using the following codes: TC + for plants with a coleoptile tiller, T1 + , T2 + , T3 +
for plants with their first tiller in the axil of the leaf 1, 2, 3 and WT for plants without tiller. T1 +
is usually the most common type, but barley plants often bear TC Cannell, 1969; Kirby et al.,
1985a.
Observed plant architectures were compared with the tillering model by Masle-Meynard and
Se´billotte 1981b validated for barley by Kirby et al. 1985a and described on the Fig. 1 for each
tillering type. Tillering types have the same tim- ing; they differ by the node bearing the first
primary tiller and, therefore, by the number of secondary and tertiary tillers that the plant can
bear at a given age. A specified tiller emerges at a given age of its mother axis: during unfolding of
the ‘n’th leaf, the tiller in the axil of the ‘n − 3’th leaf emerges. For example, T2 appears with one
leaf when the main stem bears five leaves; T11 the secondary tiller in the axil of the first true leaf
of T1 appears when T1 bears four leaves, and so on the node of the coleoptile on the main stem
and the node of the prophyll on the tillers are numbered 0. All shoots of a plant have almost
the same phyllochron: all tillers in the same row on Fig. 1 emerge almost together: for example, in
a T1 + type, the five tillers in the last row emerge during unfolding of the eighth leaf on the main
stem. After the beginning of tillering, all succes- sive tillers must emerge until tillering stops. Tiller-
ing cessation occurs at almost the same time on all shoot axes of the same plant. If some tillers at
a given level in the hierarchy Fig. 1 are lacking on a plant, then no tiller of the next row can be
found.
The tillering is stopped at the row where all tillers are lacking, that is at the corresponding
phyllochron on the main stem Kirby et al., 1985a. For example, a T1 + plant with seven
leaves on its main stem at the sampling date but without T4, T11 nor T2p stopped its tillering at
the current phyllochron. If the tillering architec- ture of a plant agrees with the model i.e. the
numbers of leaves correspond to a point in Fig. 1 and there was no break in the succession of
tillers, it is possible to calculate the date tillering stopped for individual plants. Normally, after this
cessation the rapid increase in competition be- tween elongating shoots prevent resumption of
any tillering in cereal plants Masle, 1985, unlike the pasture grasses. Nevertheless, such a resump-
tion is sometimes observable on barley when there is a sharp increase in resources Aspinall, 1961.
In that case, the tillering leaves the model.
Leaves were counted with integer numbers; thus, a small difference in leaf unfolding rate
between tillers can make the observed plants dif- ferent from the model. Fortran-programmes were
written to compare the observed architecture of each sampled plant to the model, with a tolerance
of one leaf, to back date their cessation of tillering and to simulate additional tillering on plants,
which continue to tiller at the sampling date.
Fig. 1. Tillering models according to the node bearing the first tiller adapted from Masle-Meynard and Se´billotte, 1981b; Kirby et al., 1985a. The tillering can continue over eight leaves on the main stem with the same rule. MS, main stem; TC, tiller at the
coleoptile node; T1…T5, tillers in the axil of the first to the fifth true leaf of the main stem. TCp…T3p, secondary tillers in the axil of the prophyll of the specified primary tillers; TC…T2n, secondary tillers in the axil of the nth true leaf of the specified primary
tillers. TCp, TC1, T1pp…1, tertiary tillers in the axil of the prophyll or in the axil of the first true leaf of the specified secondary tillers.
2
.
4
. Growing conditions Soil temperatures during germination were
close to 6°C for the three end-of-winter sowings but much higher at ML 18°C. Crops emerged on
March 12th at ME, on April 23rd at SGE and on May 21st at LE. ML plants emerged in two
groups because they were sown in a dry seed bed.
In all plots one third emerged on June 4th and the other two thirds on June 12th after rain. During
the first days after plant emergence, the daylength was 12 h at ME, 14 h at SGE, 15 h 15 min at LE
and 15 h 30 min at ML. Fig. 2 summarizes the climatic conditions from emergence to the first
sampling date and between the successive sam- pling dates in each situation treatment. The
parameters shown were the air temperature, the daily mean balance between rainfall and maximal
evapotranspiration and the photothermal quo- tient. This quotient is the global radiation per
degree-day; it is an indicator for sourcesink ratio that can interact with daylength Rawson, 1993.
It was used by Fischer 1985 for comparisons between
crops grown
under very
different climates.
Light interceptions by the stands were not mea- sured. All time lengths are expressed in thermal
time with 0°C as base temperature Gallagher et al., 1983.
3. Results
