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Wheat Information
Service
Number 71: 1-5 (1990)
Chromosomal
influences on spikelet number per ear in hexaploid wheat (Triticum
aestivum L.)
R. G. Flood and G. M. Halloran*
Victorian Crops Research Institute, Horsham 3400, Victoria,
Australia and *School of Agriculture and Forestry, The University of
Melbourne, Parkville 3052, Victoria, Australia
One option in breeding for increased yield in wheat is to select for
increased spikelet number per ear. This trait is strongly influenced
by photoperiod and temperature (Halse and Weir 1970; Rawson 1971;
Frank et al 1987) the interaction of which can cause variation in the
duration and/or rate of spikelet initiation (Rahman and Wilson 1977,
1978). Close positive relationships have been reported between
spikelet number per ear and the duration of the vegetative phase of
development (Pinthus 1967; Halse and Weir 1970; Lucas 1972) and
heading time in wheat (Pugsley 1971; Halloran 1977; Wall and
Cartwright 1974; Flood 1985). Success in breeding for increased
spikelet number per car for a particular environment may therefore be
limited if alteration in optimal heading time is not desirable for
that environment.
The presence of genetic variation in wheat for rate of spikelet
initiation independent of photoperiod effects (Rahman et al 1977)
provides a possible option for increasing spikelet number without a
concomitant delay in heading. More knowledge is required of the
genetic and physiological basis of developmental processes in wheat
to enable spikelet number per ear to be so manipulated. Of these
processes vernalization response has been shown to be associated with
spikelet number per ear. Artificial vernalization can cause
reductions in spikelet number (Evans et al 1970; Kushnir and Halloran
1982a; Flood and Halloran 1984a) and positive relationships have been
observed between spikelet number and levels of vernalization response
among different wheats (Flood 1985). While vernaIization response
genes do not appear to influence the development of wheat after
flower initiation (Flood and Halloran 1984b; Griffiths et al 1985) it
is possible that pleiotopic: effects of these genes, or closely
linked genes, influence spikelet number.
The present study used seven sets of intervarietal substitution lines
in Chinese Spring for chromosomes 5A, 5B and 5D, which are implicated
in influencing vernalization response, to evaluate their effects on
spikelet number per ear, with and without artificial
vernalization.
Materials and Methods
Substitution lines of homoeologous group 5 chromosomes of seven
cultivars viz., Hope, Thatcher, Kenya Farmer, Marquis, Red Egyptian,
Timstein and Capelle Desprez in Chinese Spring, were used in this
study. Seed of the substitution lines, the respective donor cultivars
and Chinese Spring were sown into a potting mix in plastic
containers, 40 mm square and 75 mm deep, which were supported in
polystyrene holders accommodating 84 plots. After sowing, the soil
mix was brought to field capacity and the seeds were allowed to
imbibe for 48 h at 20C and were then vernalized at 4C for six weeks
undera light regime, of 8 h per day provided by
fluorescent and incandescent lamps.
After vernalization the seedlings, plus an unvernalized set, were
transplanted into 15 cm diameter plastic pots containing potting mix,
as six replications of each line, per treatment. The plants from the
vernalized and unvernalized treatments were grown under a long
daylength (natural daylength extended to 18 h using a combination of
fluorescent and incandescent lamps which had a minimum irradiance at
soil level of 40 W m-2).
At ear emergence, the total number of spikelets on the ear on the
main stem of each plant was counted. Analyses of variance were
carried out on these data to determine significant differences
between the substitution lines and normal Chinese Spring.
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