Agriculture Reference
In-Depth Information
tolerance at reproductive period has been associated with the
degree of panicle exsertion, which could be used as a selection
criterion. In fact, this trait was suggested as an indicative of
genotype adaptability to cool temperatures (Takahashi 1984).
During reproductive phase two types of spores, microspores
and megaspores are produced that give rise to male
gametophytes and female gametophytes, respectively. The
fusion of egg and sperm gives rise to the zygote, which is the
beginning of diploid sporophyte generation thereby completing
the lifecycle. The female gametophyte, also referred to as the
embryo sac or mega gametophyte, develops within the ovules,
which is formed within the carpel's ovary, consists of seven
cells and four different cell types; three anti podal cells, two
synergid cells, one egg cell and one central cell.
At panicle initiation stage microsporogenesis was
determined by the distance between the ligule of the fl ag leaf
and that of the penultimate leaf (Yoshida 1981) considering
an interval of -3 (Flag leaf ligule below the penultimate leaf
ligule) to +10cm (Flag leaf ligule above penultimate leaf ligule)
as indicative of this stage. Maximum microsporogenesis may
vary, however within their range, depending on the genotypes.
In some genotypes it may take place at -3 cm, in others at zero
and in others at +8 cm, indicating that genotype, reproductive
stage and duration of cold exposure differed for the percentage
of reduction in panicle exsertion and in spikelet sterility under
17ºC.
In all durations of cold exposure, reduction in panicle
exsertion was generally larger at anthesis (Anthesis was
considered as the beginning of panicle exposure) than at
microsporogenesis. There is no clear distinction between
cold tolerant and sensitive genotypes in regard to reduction
