Glossary Plant Breeding

Specific Resistance. Host plant resistance to specific race or biotype of a pathogen. Such
resistance reaction operates usually on a gene (for host resistance)-for-gene (pathogen
avirulence) basis.
Sperm. A male gamete. In animals and plants, it is called spermatozoon and
spermatozoid, respectively.
Spermatid. Any of the four haploid cells arising by meiosis from a single spermatocyte.
Each spermatid gives rise to a spermatozoon without further nuclear division.
Spermatocyte. Any of the sperm mother cells, derived from spermatogonium, which give
rise to spermatids.
Spike. An inflorescence with a more or less elongated axis, along which flowers are
sessile or nearly so.
Spikelet. A unit of inflorescence in the grasses, composed of the glumes, the rachilla, and
the florets.
Spindle. The set of microtubular fibres that seem to move eukaryotic chromosomes
through their attachment to centromere during cell division. Its main constituent is a
protein, called tubulin.
Spindle Poison. Any mitotic poison affecting the formation or function of the spindle and
blocking karyokinesis at metaphase. The prototype of spindle poison is colchicine.
Splicing. The reaction that removes introns and joins together exons to form functional
mRNA transcript in eukaryotes.
Split Plot Design. A design specifically suited for a two-factor experiment that has more
treatments than can be accommodated by a complete block design. In this design, a
factor whose precision of effect could be sacrificed is allotted to the main plot. Then
the main plot is sub-divided into sub-plots to which the second factor is assigned.
Thus each main plot becomes a block for the sub-plot treatments. Therefore,
measurement of the main effect of the sub-plot factor and its interaction with the
main-plot factor is more precise than that obtainable with a randomized complete
block design. Degree of precision, relative size of the main effects, and management
practices required by a factor are considered while assigning a factor to the main or
sub-plot.
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