Principles of Plant Breeding (2+1)

Kinds Of Germplasm

• The sum total of all the hereditary material is referred as germplasm.In other words, gene pool refers to a whole library of different alleles of a species Germplasm or gene pool is the basic material with which a plant breeder has to initiate his breeding programme.

Kinds Of Germplasm
A. Land races
Land races are nothing but primitive cultivar which were selected and cultivated by the farmers for many generations.
• Land races were not deliberately bred like modem cultivars. They evolved under subsistence agriculture.
• Land races have high level of genetic diversity which provides them high degree of resistance to biotic and a biotic stresses. Biotic stress refers to hazards of diseases and insects, whereas a biotic stress means, drought, salinity, cold, frost, etc.
• Land races have broad genetic base which again provides them wider adaptability and protection from epidemic of diseases and insects.

B. Obsolete Cultivars
Improved varieties of recent past are known as obsolete cultivars. These are the varieties which were popular earlier and now have been replaced by new varieties.
For example, varieties K68, K65 and Pb 591 were most popular traditional tall varieties before introduction of high yielding dwarf Mexican wheat varieties.
These varieties are well known for their attractive grain colour and chapati making quality. Now these varieties are no more cultivated.

C. Modern Cultivars
The currently cultivated high yielding varieties are referred to as modern cultivars. These varieties have high yield potential and uniformity as compared to obsolete varieties and land races.
Modem cultivars constitute a major part of working collections and are extensively used as parents in the breeding programme.

D.Advanced Breeding lines
Pre-released plants which have been developed by plant breeders for use in modem scientific plant breeding are known as advanced lines, cultures and stocks.

E.Wild forms of Cultivated Species
Wild forms of cultivated species are available in crop plants. Such plants have generally high degree of resistance to biotic and a biotic stresses and are utilized in breeding programmes for genetic improvement of resistance to biotic and a biotic stresses.

F. Wild Relatives
Those naturally occurring plant species which have common ancestry with crops and can cross with crop species are referred to as wild relatives or wild species.
Wild relatives are important sources of resistance to biotic (diseases and insects) and a biotic (drought, cold, frost, salinity, etc.) stresses.

G. Mutants
Mutation breeding is used when the desired character is not found in the genetic stocks of cultivated species and their wild relatives. Mutations do occur in nature as well as can be induced through the use of physical and chemical mutagens.
For example, mutant genepool Dee-Geo-Woo-Gen in rice and Norin 10 in wheat proved to be valuable genetic resources in the development of high yielding and semi dwarf varieties in the respective crop species.