Agriculture Reference
In-Depth Information
Chapter 3
The Flowering Pathway in Wheat
Liuling Yan
SUMMARY
three mapping populations. Several ortho-
logues of known fl owering genes in other
plant species have also been characterized
in wheat.
(5) New molecular information on wheat fl ow-
ering genes, combined with comparative
studies on fl owering pathways in other
species, has allowed the formation of a
fl owering pathway model in wheat.
(6) A better understanding of genetic and
molecular mechanisms for control of varia-
tion in vernalization requirement duration
among winter wheat cultivars, the improved
ability to control and design various lengths
of developmental phases, and the ability to
establish a gene network to regulate fl ow-
ering constitute key research areas for
revealing fl owering mechanisms and for
breeding novel cultivars of wheat.
(1) In international and industrial markets,
wheat cultivars are categorized into two
classes based on their growth habit: winter
wheat and spring wheat. Wheat cultivars
are also divided into sensitive and insensi-
tive types based on responses of their fl ow-
ering time to photoperiod.
(2) Flowering time may be regulated by plant
development factors independent of ver-
nalization requirement and photoperiod.
(3) Genetic studies have identifi ed internal
factors controlling fl owering time and have
determined their external environmental
cues.
(4)
Three major vernalization genes have been
cloned, based on unambiguous segregation
of growth habit by a single gene in each of
OVERVIEW OF FLOWERING
INDUCTION IN WHEAT
of wheat breeders and scientists, was that winter
wheat did not possess any of the dominant
Vrn
alleles (i.e., the current homoeologous series of
dominant vernalization genes,
Vrn-1
) and required
extended exposure to low temperature for fl ower-
ing when grown under nonvernalizing and long-
day conditions (Crofts 1989). Contemporary
understanding of the term winter wheat is that
fl owering is accelerated by a period of exposure to
low temperature, a process known as vernalization
(Law 1987; Amasino 2005). In contrast, the transi-
tion from vegetative to reproductive development
in spring wheat cannot be accelerated by vernal-
ization. Understanding of vernalization in wheat
has rapidly advanced to the molecular level since
the beginning of this century, promulgated by the
In international and industrial markets, wheat
(
Triticum aestivum
L.) cultivars are classifi ed into
two distinct types, spring wheat and winter wheat,
based on their growth habits. Understanding of
plant growth habit has evolved since it was
described by Klippart (1857), although the work
of Gassner (1918) is usually cited as the fi rst report
on different growth habits in plants (reviewed in
Chouard 1960). Wheat sown before winter was
originally defi ned as winter wheat, whereas wheat
sown during spring was originally defi ned as
spring wheat (Chouard 1960; Crofts 1989). An
original tenet, according to an international survey
