Agriculture Reference
In-Depth Information
America leaves breeding programs with a positive balance for the work
done over the past two decades, but underscores the necessity of
staying abreast of cutting-edge technologies to support ongoing efforts
to develop disease-resistant germplasm and new selection techniques
for the future.
VI. BREEDING FOR ADAPTATION TO ABIOTIC STRESSES
A. Abiotic Stresses in Rice
1. Description and Impact.
Rice production in unfavorable conditions
is mostly constrained by abiotic stresses. Abiotic stresses arise from
climatic extremes such as drought, heat, and cold; from soil toxicities of
elements such as Al and Fe; and from soil de
ciencies of major elements
such as N and P. Abiotic stresses constitute, as elsewhere, a major
constraint to agricultural production in LAC. Drought, high tempera-
tures, iron toxicity, and low soil fertility are common problems in LAC,
whereas low temperature is con
ned to southern Brazil, Uruguay,
Argentina, and Chile. Several countries in LAC are dependent on rainfed
rice production, which is always at high risk for drought. Drought
represents the primary limitation to improved production of rice as
well as other food crops in LAC. More than 85% of national production
in Guatemala, Honduras, Bolivia, and Panama is derived from the
rainfed sector. In Costa Rica and Ecuador, rainfed rice represents nearly
two-thirds of national production, in Nicaragua and Brazil 50%, and in
Colombia
30% of the rice area is grown under upland conditions
(Pulver 2003). Approximately 15 million hectares in 24 rice-growing
countries are susceptible to crop damage due to cold (Lou et al. 2007).
In the Southern Cone of LAC, the rice area threatened by cold is nearly
1.4 million hectares (FLAR 2008).
Rice breeding in LAC for conferring tolerance of abiotic stresses has
received attention for several decades. At CIAT the breeding program for
abiotic stresses has a particular focus on drought tolerance for upland
rice and cold tolerance for temperate irrigated rice. Heat stress tolerance
is in the primary stage. The activities related to tolerances of low N and
Fe toxicity are in the initial stages of germplasm characterization,
searching for sources of tolerance to transfer these traits into elite lines.
At Embrapa (Goiânia, Brazil), the breeding program for abiotic stresses
focuses on drought, heat, and low P for upland rice and cold tolerance
and Fe toxicity for lowland rice. For lowland rice, Embrapa has devoted
special effort to improving rice cold tolerance by an intensive search for
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