Resistant varieties come as a solution after rice blast outbreaks
160%, that is to say, an average of 1.6 ap-
plications take place per hectare a season.
In the 2015/16 growing season, in some
instances up to six applications were nec-
essary. The picture improved a little in the
2016/17 season because of the increasing
use of resistant varieties.
In a survey by the Federation of Agri-
culture in Rio Grande do Sul (Farsul), the
percentage of the share of fungicides in
the production cost of rice from 2012/13 to
2015/16 went up by over 300%. “The im-
pact might seem little representative, soar-
ing 1.5 to 2 percentage points over the to-
tal. However, in a sector where profits are
low, the margins are tight and a portion
of the rice farmers sell their crop at prices
below average, and this is significant”, ex-
plains Antonio da Luz, economist at Farsul.
Cláudio Ogoshi, researcher with the Rio
Grande do Sul Rive Institute (Irga), main-
tains that in the current decade, up to the
2015/16 growing season, more than 70% of
the cultivars were susceptible to rice blast.
There was a 52-percent predominance of
varieties fromArgentina. Kernel quality, pro-
ductivity and tolerance to herbicides en-
couraged the use of these varieties. Howev-
er, the lack of immunity to the fungus paved
theway for the disease to spread.
Part of the problem is being kept under
control with the introduction of the Irga
424 cultivars and their variable of the new
Clearfield generation, Irga 424 RI, both re-
sistant to the fungus, seeded in 49% of the
fields in Rio Grande do Sul in the 2016/17
growing season. Should this resistance be
broken? It is quite logical that this resis-
tance will be broken in the future, as it al-
ways happens, but at the moment it is
the variety immune to rice leaf blast and
rice collar blast”, says Rodrigo Schoenfeld,
manager at Irga’s ResearchDepartment. “It
is not possible to anticipate when new ge-
neticmaterials, withagronomic and senso-
rial qualities, resistant to all major diseas-
es, especially rice blast, will be generated,
but we our engaged in coming up with
themas soon as possible”, he adds.
According to Schoenfeld, the vast ex-
tension of the area cultivated with genet-
ic varieties that resist to the fungus (up-
wards of 500 thousand hectares in Rio
Grande do Sul alone, besides areas in San-
ta Catarina, Argentina, Paraguay and Uru-
guay in this growing season), a fact that
broadens the risk of resistance breaking.
“The bigger the seeded area, the bigger
the risk for fungi strains to go through nat-
ural selection or mutation and attack the
plants. This tends to reduce the response
time of research to the demands of the
supply chain”, he acknowledges.
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