Agriculture Reference
In-Depth Information
environmental variations. AN Cambará was the last highly dominant
variety in Brazil. Currently, several Embrapa cultivars are increasing in
terms of planted area, including BRS Sertaneja, BRS Monarca, and the
latest release, BRS Esmeralda.
3. Methodological Improvements.
The application of recurrent selec-
tion principles is a distinctive characteristic of the upland rice breeding
program led by Embrapa. Whereas most rice breeding programs apply
the pedigree method, crossing inbred lines, and focusing on plant-to-
progeny selection, the Brazilian program incorporates yield evaluation
of segregating families and recombination of plants before the advanced
inbreeding stage.
A 4-year recurrent selection cycle includes the following steps: F
1
plants are grown with irrigation in off-season nurseries and are har-
vested in bulk; single-plant selection is made on F
2
plots with
1000
plants, based on plant architecture, grain shape, and disease resistance
(year 1); F
3
nurseries are conducted without replication under favor-
able conditions for the expression of yield potential (year 2), where
the best families are harvested in bulk; F
2:4
seeds are used for prepara-
tion of Family Yield Trials (FYT), conducted under different environ-
mental conditions (year 3); and joint statistical analysis of those trials
results in the selection of families to be recombined in the next round
of crosses (year 4).
There are two types of upland rice populations under recurrent
selection: base populations, which encompass a broad genetic diversity
and are submitted to mild selection pressure, and elite populations,
which are constrained to a more speci
∼
c ideotype and are submitted to
high selection pressure. Currently, the main upland rice base popula-
tions are CG136
—
the result of merging the early-
owering populations
CG 1, CG 3, and CNA 6
and CG 2710, the result of merging the
intermediate cycle populations CG 2, CNA 7, and CNA 10. Those popu-
lations have been synthesized from many divergent parents, including
Brazilian landraces, improved cultivars, and exotic materials (Morais
et al. 1997).
The elite population includes the most productive germplasm availa-
ble, under strict standards of grain quality and plant architecture,
building upon 35 years of continuous breeding and the incorporation
of high-value exotic materials. The elite population comprises four
subpopulations, which rotate synchronously in a 4-year recurrent selec-
tion cycle. In order to avoid isolation and consequent differentiation
between those subpopulations, due to selection or genetic drift, some
plants from the previous years are used in the recombination step.
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