European Journal of Agronomy 12 2000 211 – 223
Phenotypes and the onset of competition in spring barley stands of one genotype: daylength and density effects on
tillering
M. Lafarge
INRA, Station d
’
Agronomie,
234
A6enue du Bre´zet,
63039
Clermont-Ferrand, France Received 21 June 1999; received in revised form 21 November 1999; accepted 26 January 2000
Abstract
Understanding the genotype – environment interactions requires a distinction between two effects of the environ- ment on plants of a given genotype: the achievement of growth throughout their whole life and the prior
determination of their growth potentials. Spring barley seeds from the same seed lot were sown at the end of the winter at three altitudes: 320 m a.s.l. end of February, 880 m beginning of April and 1120 m beginning of May,
and at the end of May at the lowest site, in sparse and dense stands with and without nitrogen fertilization. This experimental design in natural conditions gave differences in initial daylengths 12, 14 and more than 15 h that must
modify the growth potentials, and different levels of competition, acting on growth achievement. The tillering patterns were measured on individual plants. The tillers in the axils of the first and the second leaf were lacking on many
plants growing in the long day treatments in the sparse stands, and this increased up to between 70 and 90 in the dense stands. This seems to be due to far-red signals on seedlings emerging in the conditions which induce the floral
development, before any competition can occur. Afterwards, the cessation of tillering as a result of the onset of competition, was delayed markedly during stem elongation in the stands established with long daylengths. Such
phenotypes showed strongly reduced growth potentials. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Spring barley; Phenotypes; Genotype – environment interactions; Tillering; Daylength; Neighbourhood; Competition www.elsevier.comlocateeuragr
1. Introduction
The growth potential of the plants proceeds from their genotype and its realization depends on
their environment, but with interactions Riggs, 1986 that reveal differences between growth ca-
pacities of genetically identical plants. Restricted growth capacities of the seedlings delay the onset
of competition and thus a good use of resources at the canopy level Boiffin et al., 1992. Low-po-
tential or high-potential phenotypes may come from the same genotype, according to the seed
quality Ellis, 1992 or the environmental condi- tions occurring around seedling emergence Cor-
Tel.: + 33-473-624421; fax: + 33-473-624457. E-mail address
:
michel.lafargeclermont.inra.fr M. La- farge
1161-030100 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 1 1 6 1 - 0 3 0 1 0 0 0 0 0 4 7 - 2
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
