Rice Breeding in Latin America - Plant Breeding Reviews - page 220

composition of the pathogen in commercial rice fields is important for

the rational deployment of resistance genes in breeding programs. Using
local differentials also allows the identi

cation of rare pathotypes that
pose a potential threat to the newly released cultivars (Barata da Silva
et al. 2011). Based on all studies at Embrapa, breeding for blast resistance
is now based on the diversi cation and incorporation of multiple host

resistance genes into their lines.
INTA in Argentina has for several years implemented a rice blast
resistance breeding program based on the characterization of the genetic
structure of the blast pathogen, identi

cation of races/pathotypes, iden-

ti cation of relevant resistance genes, and the use of marker-assisted

selection for the introgression of host resistance genes. Based on these
studies, improvement of blast resistance is based on the marker-assisted
introgression of the resistance genes Pi-1 , Pi-2 / Pi-9 , Pi-33 , and Pi-ta into a
single genotype (Colazo et al. 2011). Segregating populations are eval-
uated for different pathotypes, thus allowing the identi cation and

selection of resistance gene combinations.
In Venezuela, the rice genetic breeding program at Fundación Danac
has been focusing its resistance breeding efforts on rice blast, sheath
blight, and RHBV. Evaluation and selection of breeding lines are
conducted using field and greenhouse-screening methodologies devel-

oped at CIAT. Rice blast is evaluated under high disease pressure in the

field and breeding lines are exposed to individual races or isolates of
the pathogen in the greenhouse. Colonies of the insect vector of RHBV
are reared in the greenhouse and breeding lines are exposed to the
vector, evaluated, and selected for their resistance. The general health
status of the breeding lines is evaluated under

field conditions and
resistance to other secondary diseases is selected. The breeding pro-
gram has been successful in releasing several rice cultivars with resis-
tance to or tolerance of the main diseases (Arnao et al. 2008; Graterol
2012). Breeding for sheath blight resistance in Venezuela has been a
main responsibility of the Instituto Nacional de Investigaciones Agro-
pecuarias (INIA). Because of the complexity of selecting for resistance
to the pathogen, yield potential, and grain quality, recurrent selection
has been used as the breeding strategy. Parental rice materials are
evaluated and selected for high tolerance of the disease under

eld
conditions, while other materials are selected for their yield potential
and grain quality characteristics regardless of their susceptibility. The
breeding program has been successful in improving resistance to the
disease after several cycles of selection (Delgado and Rodriguez 2005).
Similarly, Argentina and Uruguay have breeding programs for rice
blast as well as diseases caused by Rhizoctonia , which are based on