Glossary Plant Breeding

Genetic Male Sterility. A type of male sterility that is governed by the gene(s) carried
on the chromosomes. The male sterile condition is ordinarily monogenic recessive. Its
exploitation in hybrid seed production is rather difficult due to problems involved in
the maintenance of male-sterile line. Male-sterile stocks are maintained by crossing
with heterozygous male-fertile line (Ms ms). This necessitates identification of malesterile
(and male-fertile) plants since the progeny contains the two types in equal
proportions. To circumvent this problem, genetic markers such as tightly linked genes
or pleiotropic effects of male-sterile genes can be used.
Gene Pyramidying. A strategy for management of resistance that involves incorporation
of an increasing number of resistance genes into the same cultivars likely to be
released in succession. Thus, with the available number of genes, the resistance can
be used for a long time. However, there are several disadvantages that limit its use: (a)
considerable efforts are required to incorporate many a major gene into one
genotype, (b) the use of back cross method to incorporate the major genes into one
genotype restricts the agronomic characteristics of the new cultivar, and (c) resistance
of the cultivar may encourage evolution of new virulent races of the pathogen,
particularly if the same major genes are used singly in other varieties being grown in
the adjacent area.
Genetic Assortative Mating. Mating together of individuals more closely related (by
ancestry) than individuals mating at random. Genetic assortative mating at all loci is
called inbreeding. (Inbreeding deals with the entire genome whereas genetic
assortative mating is specific to a locus). It results in an increase in homozygosity.
Genetic Advance. The genetic superiority (and not phenotypic) of selected individuals /
lines/families over the base population. It measures the difference between mean
genotypic values of selected lines (As) and of the original lines (Ao). Thus, Gs = As –
Ao = k × σ P ×H 2 . Therefore, it depends on: k = standardized selection differential
and its value is fixed for a given proportion of lines saved from the base population
(2.06 at 5% selection intensity), σ P = phenotypic standard deviation of the original
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