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The absence of spikelets
occurs when certain genetic factors come together in F1
hybrid and the gene interaction affects the spikelet formation at
early stage of spike development. It will be premature to propound
any hypothesis but the assumption is that the suppression of
spikelets in the rachis is caused by the epistatic interaction of
genes in the hybrid. It is likely that the initial differentiation of
cells determining the development of rachis, spikelets and florets is
suppressed due to the interaction of certain genetic factors coming
together in F1 hybrid from different parents. Unequal
distribution of primordial cells to the developing spikelets may also
lead, to differential expression of spikelet suppression in the same
F1 plant.
The pentaploid (2n = 5x = 35, genome AABBD)
F1 hybrid had 13.52 + or - 0.21 mean bivalents and 7.78 +
or - 0.23 mean univalents. No other chromosome configurations were
observed, except in the hybrid involving Kalyansona where trivalents
and quadrivalents were recorded in low frequencies. A pentaplold
hybrid is an aneuploid hybrid chromosomally unstable but the absence
of spikelets on the rachis noticed in F1's and also in
F2 generation derived after selfing the pentaploid hybrid
seems to be genie and is not due to aneuploidy.
Production of abnormal spikes restrict the choice of parents to
produce desirable cross combinations. It will be worthwhile to
identify deleterious genes responsible for abnormal development of
spike.
Reference
Tomar SMS, Kochumadhavan M, Nambisan PNN and Joshi BC (1988) Proc
7th Int Wheat Genet Symp at Cambridge, England. Vol 1: 165-168.
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