Indian Society of Genetics & Plant Breeding

Important

NATURE OF CHROMOSOME PAIRING IN THE GENUS SOLANUM SECTION TUBERARIUM

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BARRIERS to gene exchange are one of the prerequisites of species differentiation.
However, such barriers also make difficult the task of the plant breeder, who in most
programmes of plant improvement has to have recourse to wide interspecific and
even intergeneric crosses.
If such attempts to incorporate genes controlling desirable
characters into the genome of cultivated plants is to succeed, it is essential that we
have an adequate understanding of the nature of the species-isolating barrier
involved
ip each case. The barrier may be spatial or, even when the species
concerned grow in the same locality, they may be isolated by the fact that their
periods of flowerings do not coincide. Again, the barrier preventing gene flow may
be an incompatibility between the pollen and the style or the collapse of the hybrid
embryo and/or endosperm. Such external barriers may, in many cases, be overcome, 

by adopting suitable techniques like photoperiodic and vernalization treatments, 

provision of artificial stigma (Swaminathan, 1955) or even by artificial culture
of the hybrid embryo in suitable nutrient media (Brink, Cooper and Ausherman,
1944). However, even where hybrids between two species can be obtained, free
exchange can only occur if synapsis of the chromosomes derived from the two parents,
followed by fairly free crossing-over, occurs. This will be realised if speciation has
occurred, in the main, by gene substitution and accumulation of clusters of modifying
genes, as Harland (1936) postulated for cotton.
  

Info

Year: 1960
Volume: 20
Issue: 1
Article DOI: NA
Print ISSN: 0019-5200
Online ISSN: 0975-6906

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