Glossary Plant Breeding

Reproductive Cell. Any of the germ cells (usually gametes) and their immediate
predecessors from which they arise by division.
Reproductive Isolation. Isolation by various genetically controlled mechanisms, which
prevent gene exchange between two populations and preserve differences in the gene
pools of populations previously attained by selection and other evolutionary factors.
Reproductive Potential. An organism’s ability to produce surviving offspring (up to the
stage of sexual maturity).
Reproductive System. Several variables (organs) of an individual orchestrated to
perform reproduction.
Repulsion Conformation. A type of linkage conformation in which one dominant and
one recessive gene are linked on one chromosome and their counterparts occur in
other homologous chromosome (Ab/aB).
Resistance Breeding. A system of breeding that involves selection of desired resistant
types from a genetically variable population under artificial epiphytotic condition in
the breeding nursery. It has assumed a very important position in plant breeding
because: (a) it plays a significant role in increasing and stabilizing supplies of food,
fibre, vegetable oils, etc., (b) it adds little or nothing to the cost of production, (c) it
does not create environmental or health hazards, and (d) it is an initial factor in
integrated disease management. Resistance breeding differs from any other
conventional methods for two reasons: (a) resistance can be assayed only by diseasing
plants, i.e., employing another living and variable organism, and (b) resistance may
appear elusive, that is, the resistance may break down.
Resistance Erosion. The gradual loss of resistance of the host against a particular
pathogen or pest. A variety may lose the resistance gene either due to mutation,
segregation or natural out crossing with a susceptible variety. It is interesting to note
that environment also plays an important role in the expression of resistance gene(s).
The same genotype that shows resistance to a particular race of the pathogen in one
season succumbs to the same race in other season. For instance, tomato varieties
carrying cf 1 gene show resistance to Cladosporium fulvum in summer but become
susceptible in winter.
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