An update on current knowledge of the wheat blast pathogen Pyricularia graminis-tritici in Brazil

1. The
Recent
Emergence
of
Wheat
Blast
in
Brazil
Paulo
C.
Ceresini,
Vanina
L.
Castroagudín,
João
L.
N.
Maciel,
Bruce
A.
McDonald

2. Wheat
Blast
is
Caused
by
a
Pyricularia
Species
Closely
Related
to
the
Rice
Blast
Pathogen

3. The
Recent
Origin
and
Spread
of
Wheat
Blast
in
South
America

4. CollecJons
of
Pyricularia
From
Wheat
and
Other
Grasses
(N
=
553)
Sampling:
Eight
regional
populaJons
of
Pyricularia
from
Central-­‐Southern
Brazil.
Two
host-­‐disJnct
Pyricularia
populaJons
from
weedy
grass
species
invasive
to
wheat
areas
from
MS
and
PR.
Brachiaria
(Urochloa)
brizantha
Cenchrus
echinatus
Chloris
dis6chophylla
Cynodon
dactylon
Digitaria
horizontalis
Digitaria
insularis
Digitaria
sanguinalis
Echinochloa
crus-­‐galli
Eleusine
indica
Panicum
maximum
Panicum
repens
Rhynchelytrum
repens
Sorghum
sudanense
One
rice-­‐adapted
Pyricularia
populaJon

5. CharacterizaJon
of
Pyricularia
From
Wheat
and
Other
Grasses
Genotypes
11
SSRs
(microsatellites)
PCR
assays
AvrCO39
AvrPITA
MaJng
types
DNA
Sequences
10
housekeeping
genes
cytB
(mtDNA)
AvrCO39
Phenotypes
Virulence
on
leaves
(7
wheat
culJvars
+
barley
+
rice)
Virulence
on
ears
(7
wheat
culJvars
+
barley)
SensiJvity
to
QoI
(strobilurins)
fungicides

6. Comparisons
of
10
Genes
in
121
Pyricularia
Strains
Shows
Divergence
Between
Strains
InfecJng
Wheat
(97)
and
Rice
(24)
3340
bp
sequenced
172
parsimony
informaJve
sites
*AcJn
*Cadherin
*Beta
tubulin
*Calmodulin
ChiJn
synthase
TranscripJon
elongaJon
factor
MPG
hydrophobin
NUT
Zinc
finger
CH7BAC7
CH7BAC9
*%
divergence
human/chimp
=
1%
*%
divergence
wheat/rice
=
2%
Wheat
blast
isolates
don’t
infect
rice,
but
they
all
infect
barley

7. Major
InterpretaJon
1
The
wheat
blast
pathogen
and
the
rice
blast
pathogen
represent
disJnct
species
We
propose
that
the
wheat
blast
pathogen
should
be
named
Pyricularia
tri6ci
to
clearly
disJnguish
it
from
the
rice
blast
pathogen
Pyricularia
oryzae
(Klaubauf
et
al.
2014,
Studies
in
Mycology
79:85-­‐120)

8. Mato Grosso
do Sul
MS
Minas Gerais
MG
Goiás
GO
São Paulo
SP
Paraná
PR
Rio Grande
do Sul
RS
Distrito
Federal
DF
BRASIL
Pairwise population differentiation
N = 288 MLMS genotypes
Wheat - derived isolates from 2012 - 2013 Other Poaceae - derived
RST values
DF 0.03
GO 0.07 -0.03
MG 0.04 0.01 0.03
MS 0.13 0.15 0.16 0.04
PR 0.16 0.24 0.24 0.12 0.02
RS 0.13 0.13 0.13 0.04 0.03 0.10
SP 0.09 0.17 0.17 0.09 0.05 0.04 0.15
MS 0.08 0.06 0.10 0.06 0.08 0.08 0.05 0.08
PR 0.09 0.13 0.19 0.13 0.10 0.08 0.18 0.02 0.06
Rice 0.73 0.84 0.86 0.83 0.85 0.85 0.82 0.83 0.55 0.73
2005 DF GO MG MS PR RS SP MS PR
RST values
0
0.25
0.50
1.00
0.75
completly
differentiated
nondifferentiated
RST
values in bold colored had significant P values at = 0.001 (after Bonferroni correction for multiple comparisons)
PopulaJon
GeneJc
Structure
of
Pyricularia
tri6ci
(11
SSR
loci)
Signature
of
sex,
high
clonality
in
some
populaJons,
low
clonality
in
others
(288
MLHTs
out
of
553
isolates),
random
associaJons
among
loci
in
some
pops
but
not
others,
both
MAT
in
most
populaJons
but
skewed
towards
MAT1-­‐1.
Gene
flow
occurs
over
long
distances
(100s-­‐1000s
km).
Significant
gene
flow
among
wheat/grass
populaJons,
including
shared
genotypes
(MLHTs).
No
gene
flow
among
wheat/rice
populaJons
Maciel
et
al.
2014.
Phytopathology
104:95-­‐107

9. Major
InterpretaJon
2
Pyricularia
tri6ci
has
a
mixed
reproducJve
system
There
is
no
gene
flow
between
P.
tri6ci
and
P.
oryzae
There
is
high
gene
and
genotype
flow
among
P.
tri6ci
populaJons
on
both
wheat
and
weedy
grasses
(esp.
Urochloa,
pasture
grass
on
~160
million
ha)
Hypothesis
1:
The
wheat
blast
pathogen
is
both
seed-­‐
borne
(shared
genotypes)
and
dispersed
by
air-­‐borne
ascospores
Hypothesis
2:
There
is
on-­‐going
gene
flow
between
the
Pyricularia
tri6ci
populaJons
on
wheat
and
weedy
grasses

10. Comparisons
of
Pyricularia
tri6ci
on
Wheat
and
Urochloa
440
isolates
from
wheat
17
out
of
88
weedy
grass
isolates
were
from
Urochloa
(all
unique
SSR
MLHTs)
5
of
17
MLHTs
were
idenJcal
to
MLHTs
found
in
wheat
fields
(shared
clones)
The
2
isolates
from
Urochloa
sequenced
for
10
housekeeping
genes
clustered
within
the
clade
containing
Pyricularia
tri6ci
isolates
Two
idenJcal
AvrCo39
sequences
between
isolates
from
Urochloa
and
wheat
The
same
cytb
resistance
allele
was
found
in
both
Urochloa
and
wheat,
shared
resistance
to
strobilurins
Both
maJng
types
were
found
on
Urochloa,
but
MAT1-­‐1
dominates
on
wheat
Strains
sampled
from
Urochloa
cause
disease
on
wheat
and
have
the
same
virulence
profile
on
5
differenJals
as
strains
sampled
from
wheat

11. Major
InterpretaJon
3
The
Pyricularia
tri6ci
populaJon
on
Urochloa
appears
idenJcal
to
the
Pyricularia
tri6ci
populaJon
on
wheat
Hypothesis
1:
The
wheat
blast
fungus
emerged
through
a
host
ship/jump
from
a
pathogen
populaJon
infecJng
Urochloa
Hypothesis
2:
The
pathogen
populaJon
on
Urochloa
is
a
major
source
of
primary
inoculum
for
the
wheat
blast
disease
Hypothesis
3:
Pyricularia
tri6ci
is
using
Urochloa
as
the
primary
host
for
sexual
reproducJon
(both
maJng
types
present,
lower
clonality)
Hypothesis
4:
Given
that
Urochloa
was
introduced
into
Brazil
from
Africa,
either
P.
tri6ci
was
introduced
into
Brazil
from
Africa
on
Urochloa,
or
P.
tri6ci
jumped
onto
Urochloa
aper
it
was
introduced
into
Brazil

12. Rapid
Local
AdaptaJon
in
Pyricularia
tri6ci
PopulaJons:
They
Have
Become
Host
Specialized
in
~30
Years
Emergence
of
14
pathotypes
that
show
wheat
culJvar
specializaJon
and
host
Jssue
specializaJon
CrisJna
Boareso,
Anderson
Danelli,
João
L.
Nunes
Maciel
Maciel
et
al.
2014.
Phytopathology
104:95-­‐107

13. Rapid
Local
AdaptaJon
in
Pyricularia
tri6ci
PopulaJons:
They
Have
Become
Resistant
to
Fungicides
in
~20
Years
Castroaguden
et
al.
2015.
Phytopathology
105:284-­‐294
Haplotype
%
Isolates
Host
H1
(QoI-­‐R)
71%
wheat/weeds
H2-­‐H4
(QoI-­‐R)
2%
weeds
H5-­‐H8
(QoI-­‐R)
7%
weeds
H9
(QoI-­‐S)
20%
wheat/weeds

14. Major
InterpretaJon
4
Pyricularia
tri6ci
has
all
of
the
properJes
associated
with
a
high
evoluJonary
potenJal
and
appears
to
have
already
undergone
significant
local
adaptaJon,
including
to
the
cooler
climate
of
ArgenJna
(?),
and
may
now
be
spreading
onto
oats
(?)
Pyricularia
tri6ci
may
pose
a
risk
to
wheat
crops
grown
on
other
conJnents
QuaranJnes
should
be
strengthened
to
prevent
the
movement
of
this
pathogen
to
other
conJnents
where
wheat
is
grown
Pyricularia
perithecia
on
oat
straw

15. Summary
Pyricularia
tri6ci
is
a
new
wheat
pathogen
that
likely
emerged
de
novo
in
Brazil
~30
years
ago
Pyricularia
tri6ci
did
not
emerge
through
adapJve
evoluJon
from
the
rice
blast
pathogen
Pyricularia
tri6ci
may
have
emerged
through
a
host
jump
from
Urochloa
(out
of
Africa?)
Urochloa
may
be
the
preferred
host
of
Pyricularia
tri6ci,
a
place
for
sexual
recombinaJon
and
a
reservoir
of
sexual
and
asexual
inoculum
(new
focus
for
control
efforts?)
Pyricularia
tri6ci
appears
to
have
a
high
evoluJonary
potenJal
and
poses
a
risk
of
becoming
an
invasive
pathogen
on
wheat
crops
on
other
conJnents
QuaranJnes
should
be
used
to
limit
the
movement
of
this
new
pathogen

16. 16!
!
!
Funding institutions and collaborators!
!
CNPq - Brazilian National Research Council, grant Pq 307361/2012-8!
EMBRAPA - Monsanto Research Macroprogram!
FAPESP - Sao Paulo State Foundation for Research Advancement, grant 2013/10655-4!
!
Research team: !
!
Dr. João Maciel (PI/Embrapa Monsanto Research Macroprogram’s grant)!
Dr. Paulo Ceresini (PI/FAPESP’s grant) !
Dr. Ana Lídia Bonato (EMBRAPA Wheat)!
Post-Doc: Dr. Vanina Castroagudin (UNESP), CNPq/PDJ grant 150490/2013-5!
!
Students: Juliana Reges (PhD), Samanta de Oliveira (MSc), Adriano Dorigan
(undergrad)(UNESP), scholarships from CAPES, CNPq or FAPESP.!
!
Acknowledgements