RA 00110.pdf - OAR@ICRISAT

Genetic Divergence in Landraces of Pearl Millet in Rajasthan
(Diversite genetique chez les races non ameliorees du mil au Rajasthan)
K.L. Vyas
Millet Breeder, Sukhadia University, Agricultural Research Station, Durgapura, Jaipur, Rajasthan 302 004,
India
About 300 local landraces of pearl millet were collected and evaluated in Rajasthan. The widest range of
variation was observed for plant height, grain yield, 1000 grain mass, head length, and grain density. Using a
cluster analysis, the landraces were classified into 23 genetically diverse cluster groups. Six of these were
clearly in the arid zone, three in the semi-arid zone, five in the adequate moisture zone, and two were common
to both semi-arid and adequate-moisture zones. Thus a meaningful distribution pattern of genetic clusters was
observed in relation to the pattern of agroclimatic variation. The maximum divergence between clusters was
created by time to flowering, plant height, and head length. However, out of the 12 characters studied, only
one, number of nodes per plant, was not effective in separating the landraces into groups.
Genetic Basis of Population Improvement in Pearl Millet
(Base genetique de l'amelioration des populations de mil)
V. Arunachalam
Professor of Quantitative Genetics, Indian Agricultural Research Institute Regional Station, Rajendranagar,
Hyderabad, Andhra Pradesh 500 030, India
Populations have multigenetic polymorphisms which from a plant breeding viewpoint are preferably "balanced".
They are maintained in stable equilibria in the population mainly through the selective advantage of
complex heterozygotes and they confer population homeostasis.
While composite populations cannot be regenerated, a synthetic can, in principle, be regenerated if its
parental lines are inbred and can be maintained without excessive inbreeding depression. It is not essential to
maintain the parental components of a composite. A number of alternatives to improve composites are
discussed.
One method depends on constructing a base gene pool from which a potential gene pool is derived by a few
cycles of large-scale intermating. It is important that low genotypes are not consciously eliminated during the
process, since high x low crosses may generate and sustain heterotic effects in successive cycles. Composites
can be derived from the potential gene pool by a process of intermating and mild selection in isolation. Since
the polymorphic equilibrium associated with composite populations can break down due to forces such as
small population size, various degrees of nonrandom mating, and natural selection (including biotic and
abiotic stresses), the yields of composites are, at most, only acceptable. Care in seed production is critical to
prevent the population from moving to another equilibrium associated with low yield, in which case
replacement will be needed. These genetic principles behind breeding populations and maintaining their yield
are highlighted with data on pearl millet composite populations.
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