Glossary Plant Breeding

barriers of several resistance to the pathogen population simultaneously. It should be
an effective strategy because a new race, to overcome multiple resistance genes, must
have two or more simultaneous changes towards the virulence, whereas a new race
needs only one change towards virulence to overcome a single gene for resistance. It
can be effective if the breeding is coordinated centrally, and the production area is
isolated from other areas where the system is not applied.
Multivalent. A pairing configuration of three or more completely or partially
homologous chromosomes observed during meiosis-I. Multivalent formation is a
characteristic feature of autopolyploids.
Mutagen. An agent (physical, chemical or even biological) that is capable of increasing
the mutation rate.
Mutagen Effectiveness. The number of induced mutations per unit dose of a mutagen.
Mutagen Efficiency. A ratio of specific desirable mutagenic change(s) to the undesired
effects such as plant damage, sterility, lethality, and the like.
Mutant. An organism or cell carrying a detectable mutation. The term is an adjective;
thus it must precede a noun (a mutant individual, for example).
Mutant Allele. An allele differing from the allele found in the standard or wild type.
Mutant Hunt. The process of collecting different mutants showing abnormalities in a
certain structure or in a certain function, as a preparation for mutational dissection of
that function.
Mutant Site. The damaged or altered area within a mutated gene.
Mutagenesis. Treatment of plants or plant parts with a mutagen to increase mutation
rates.
Mutation Breeding. A system of breeding in which plants/plant parts/seeds or any kinds
of propagules are treated with any kind of mutagen accompanied by selection for
desired types in succeeding generations.
Mutational Equilibrium. The product of frequency of mutations per individual per
generation and average number of generations during which mutated gene is
maintained in the population before it is eliminated.
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