Agriculture Reference
In-Depth Information
lines for population improvement or classic crossing schemes (Châtel
et al. 2008). Promising lines were identi
ed for the savanna conditions
of the Llanos of Colombia, which combine tolerance of acid soils, high
yield under low nitrogen fertility, yield stability across various envi-
ronments, and resistance to the biotic stresses predominant in this
environment.
Breeding for drought tolerance started in 2004 at Embrapa with
screening for sources of tolerance. Nowadays, besides an RS population,
speci
c crosses are made for heat and drought tolerance, for which
the segregating populations are evaluated under stress conditions. In
April 2013, Embrapa released its
first upland rice variety with drought
tolerance, BRS Esmeralda. Recently, CIAT has started an RS program
for tolerance of drought through IR thermographic screening. This
population is under development, completing a second RS cycle.
For improving tolerance of low P, Embrapa proceeds with popula-
tion improvement, in which selection of the best families is made
under stress conditions such that S
0:1
plants and S
0:2
progenies are
evaluated under low P conditions. For the S
0:2
generation, evaluation
in a multilocation trial is conducted at three different locations under
low P. One population (CNA9) is in its fourth cycle of RS conducted in
a low P environment.
Breeding for cold tolerance is performed from population improvement
activities as well as from classic crossing schemes. At Embrapa, pedigree
breeding for cold tolerance is closely associatedwith population improve-
ment either as a source of rawmaterial for line development or as parental
lines to generate new crosses. Variety BRS Firmeza, recommended for
cultivation in southern Brazil, presents genetic tolerance of cold in the
reproductive phase. The Instituto de InvestigacionesAgropecuarias (INIA)
in Chile developed and improved synthetic populations for adaptation to
the temperate climate with particular selection pressure for tolerance of
low temperature at the seedling stage (Hernaiz-L et al. 2005). The CIAT
-
FLAR breeding program for cold tolerance embodies various steps con-
sisting of parental characterization, crossing (single or three-way crosses),
production of segregating populations, and their evaluation for cold
tolerance at different stages under controlled conditions. Tolerant geno-
types are transplanted in the
field and selected for other characteristics
such as low sterility, adequate growth cycle, absence of diseases, and
excellent grain quality. The nurseries (F
2
or F
3
families) are sent to FLAR
partners in the Southern Cone that are then responsible for continuing the
breeding process up to variety release.
For iron toxicity, Embrapa
'
s work focuses on searching for sources of
tolerance and transferring the trait to elite lines. Introgression of key
