Agriculture Reference
In-Depth Information
irrigated ecosystems and CNA-IRAT5 for upland and aerobic ecosystems,
were developed from recombination between elite lines of highly diverse
origin presenting a wide range of plant types (Taillebois and Guimarães
1988). From these two broad-based founder populations, numerous others
were developed from the introgression of new elite germplasm carrying
alleles of interest onto the male sterile plants from the base populations.
Training, capacity building, and germplasm exchange in the region
fostered the wide application of recurrent selection breeding in LAC.
This global effort at the level of an entire continent was made possible by
the support of FAO, CIAT, CIRAD, and Embrapa, whose alliance gave
birth to the Working Group on Advanced Rice Breeding (GRUMEGA, its
Spanish acronym) (Guimarães 2005).
Ten countries in LAC applied population improvement, targeting
both temperate and tropical zones, in upland and aerobic as well as
in lowland and irrigated ecosystems, focusing on grain yield potential
or adaptation to abiotic stresses or host plant resistance to pathogens
and pests, and mechanized or manual agriculture, from higher altitude
to coastal areas. Various populations were generated for different spe-
cial purposes and were exchanged within the GRUMEGA network. The
speci
c selection used for these populations created divergent popu-
lations with particular site adaptations. Numerous lines were selected
and cultivars released from various synthetic populations improved
through RS (Table 5.2). The application of population improvement in
rice holds important potential for promoting the use of genetic varia-
bility in rice breeding for LAC.
Recurrent selection has allowed exotic germplasm to be introduced into
populations before reaching the core of the breeding program. Donor
parents are evaluated for combining ability with a recipient population
to avoid negative changes in the population means. The concept is to retain
favorable genes from the exotic donor parents while eliminating
unfavorable genes through alternate cycles of selection and recombination
(Châtel and Guimarães 1997). Within a population, at the end of each cycle
of selection, the very best progenies are transferred to the outer-elite
breeding pool, where they are evaluated along with elite progenies forming
the
Depending on their performance in evaluation
trials, they are either discarded or admitted to the inner-elite breeding pool,
which means being used in crosses within the elite program.
“
outer-elite population.
”
B. New Advances in Rice Population Improvement
Recently, population improvement has been considered as a tool for
linking breeding with genetics. Indeed, synthetic populations present
