IncreasedresistanceofAsianrustfungal
strainsjeopardizeexistingtechnologies
andrequirestrictmanagementpractices
A
s soon as the fallow period
came to an end for the soybean
crop in the Brazilian Center-
West, planters broke the silence
in the cerrado region for seed-
ing the crops for the 2017/18 growing sea-
son. Besides ensuring the chance to seed
the second crop, the farmers were in a hur-
ry because they wanted to escape from the
Asian rust, as the first seeded areas are nor-
mally less affected by the fungus Phakopso-
ra pachyrhizi, responsible for the disease.
The fact is, if the fungal disease has al-
ready been a concern in the past, it has
now become even more damaging. Some
fungal strains have shown resistance to
the active ingredient of the latest and
most efficient pesticides for their control:
the so-called carboxamides, Cláudia Vie-
ira Godoy, Embrapa Soy researcher and
coordinator of the Anti-Rust Consortium,
which comprises several companies and
research institutions, reveals that chemical
rupture efficiency by these resistant fungal
strains hit mainly South Brazil in only two
seasons. This speed came as a surprise to
the researchers. Longer durability of the
technology had been expected.
On 8th March 2017, the Fungicide Resis-
tanceActionCommittee (Frac) reportedpub-
licly having found resistant fungi by muta-
tion. Cláudia, with a PhD in Phytopathology
from the University of São Paulo (USP), ex-
plains that it is a natural selection process,
which, sooner or later, will happen. There-
fore, when a fungicide is launched, scientists
are equally concerned with the longevity of
itssurveillancemechanisms,thatistosay,for
how long it will be efficient in the elimination
of thepathogenandplant protection.
Site-specific fungicides for the control of
Asianrustactinthreeways:tryasolsaredes-
Rust corrodes the
profit
Sector is not likely to have anewcontrol tool in themediumrun
methylation inhibitors (IDM); estrobilurines,
inhibitors of external quinone (Iqe); and car-
boxamides, inhibitors of succinic dehydro-
genase (ISDH). “The loss of sensitivity by the
fungus to IDM and IQe products has come
a long way”, the scientist acknowledges. In
some regions, chemical controls by some
products achieve only 20 percent of their ef-
ficiency, greatly increasing the costs of pes-
ticides and labor, whilst requiring the farm-
ers to come up with creative solutions. And
chances are for crop losses.
Researchers and farmers are greatly con-
cerned about the fast genetic variability of
the Phakopsora pachyrhizi strains and the
speedy propagation of the spores, a reality
thatislikelytojeopardizethecontroloverthe
pathogen in other regions, too. In the South,
resistance to the fungicide is now inferior to
50%.Asaresult,manyfarmersresorttostrat-
egies like the use of pesticide mixtures, rota-
tion of control mechanisms and different ac-
tion methods, with the target to delay the
selection of the resistant population in the
cultivated areas, whilst expanding the effi-
ciencyof the controlmeasures.
n
Inor Ag. Assmann
70
