Glossary Plant Breeding

describe stability. The mean yield of a variety is the most common description of its
performance. Multiline varieties, bulk populations, composites, or F 3 /F 4 derived lines
varieties are usually more stable than pure line varieties. Stable genotypes, however,
usually have below average yields. Several models have been used to study stability
of varieties. For example, Finley and Wilkinson (1963) used regression as a parameter
of stability. However, in the Eberhart and Russel (1966) model (the most commonly
used model), regression is termed response index and mean square deviations from
regression is referred to as the parameter of stability.
Stability Analysis. An analysis of consistency in performance of genotypes over a wide
range of environments based on certain statistical parameters. If a cultivar shows
consistent performance over a set of environments, it is released for wider cultivation.
For stability analysis, a number of stability models such as Finley and Wilkinson
model (1963), Eberhart and Russell model (1966), Perkins and Jinks model (1968),
Freeman and Perkins model (1971), and the like is available.
Stabilizing Selection (Van der Plank 1963, ’68). The reduction in the fitness of the
pathogen races that carry unnecessary virulence genes. Thus stabilizing selection
should favour simple races, that is, races with least number of unnecessary virulence
genes. In nature, however, there are many cases that contradict the concept of
stabilizing selection. For example, Flor (1971) reported several races of pathogens
(Puccinia sp.) carrying virulent genes not needed to parasitise the host crop. Overall,
stabilizing selection probably is not an important factor in preventing the
development of complex races.
Stable Feedback System. A system that promotes retention of a large number of
favourably interacting genotypes in a heavily inbreeding population. This system is
necessary in such a population as it leads to continuous release of genetic variability
through chance crossing (among the existing genotypes) followed by segregation and
recombination.
Staggered Cuts. The cleavage of two opposite strands of duplex DNA at points near one
another.
Stamen. The pollen-bearing organ in the flower composed of an anther and a filament.
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