This document summarizes the challenges of controlling wheat leaf rust in South America's Southern Cone region. Leaf rust remains the most widespread and economically important wheat disease in the region. Fungicides are widely used to control leaf rust and maintain yields of susceptible cultivars. However, the pathogen population is highly dynamic, limiting the duration of resistance in new cultivars. Breeding programs aim to develop cultivars with durable adult plant resistance, but introducing such genes into high-yielding backgrounds remains a challenge.

1. Challenges in controlling
leaf rust in the Southern Cone
region of South America
2011 BGRI Technical Workshop
St. Paul, Minnesota, USA
June 13-16, 2011
Silvia Germán, INIA La Estanzuela, Uruguay
Pablo Campos, INTA Bordenave, Argentina
Marcia Chaves, EMBRAPA-CNPT, Brazil
Ricardo Madariaga, INIA Quilamapu, Chile
- Uruguay Mohan Kohli, CAPECO, Paraguay

2. Updated information
of the wheat leaf rust
(Puccinia triticina)
situation
Genes present in
germplasm
Breeding for resistance
Challenges to control
the disease

3. Wheat leaf rust in the Southern Cone of S.A.
• Continues to be the most widespread and
important foliar disease of wheat
• In susceptible varieties losses can be higher
than 50% if fungicides are not used
• Favorable weather conditions for disease
development
• Local over-summering of the pathogen

4. High % of S cultivars used in all countries
Percentage of 2010 Uruguayan wheat area with cultivars
with different leaf rust field reaction
50
Information of
40 91% of total área
% of wheat area
30
20
46
10
15 10 9 11
0
R MR MRMS MS S
Field leaf rust characterization

5. The pathogen can over-summer in large areas
Early onset of severe epidemics
Uruguay
Uruguay
Early sowing date (April),
Late sowing date (August)
2006
2001

6. Highly variable Puccinia triticina population
Frequency of some P. triticina races. Uruguay. 1991-2009.
60
50 MBD-10,20
MCR-10 MCR-10 MCD-10,20
E.Federal Cardenal INIA Mirlo
E.Pelón 90 MDR-10,20
40 I Torcaza
Frecuencia
I Churrinche
30 MFP-20
I Tero
MC(H)P-10
20 K.Don
MCR-10
MFR E.Federal Enrique
10 I.Caburé
0
89
91
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
19
19
19
19
19
19
19
19
19
19
20
20
20
20
20
20
20
20
20
20
Años

7. Frequency of prevalent P. triticina races in Argentina,
Brazil and Uruguay. 2008-2010.
Brazilian Argentina Brazil Uruguay
Race code Detected 2008 2009 Detected 2008 2009 2010* Detected 2008 2009 2010*
MCP-10 2000 5.9 12.3 2000 1.2
MFT-20 B51 2002 3.4 15.4 2008 1.6
MDT 2008 2.4 0.9 2010 7.5
MDP 2005 25.9 28.3 2002 7.3 13.6 10.4
MFP 2005 5.4 9.9 2001 4.0 21.0 30.6
MDP-10,20 B58 2005 2.4 6.1 2007 2.5 2004 11.3 3.7 5.2
MFP-10,20 2005 1.0 4.2 2004 16.9 18.5 6.7
MDP-20 2004 6.8 2.4 2004 2.4 3.7 6.7
MFP-20 B56 2005 2.9 6.1 2006 0.7 2.5 2005 12.9 13.6 1.5
MDT-10,20 B55 2007 30.2 15.6 2005 10.7 7.4 2.2 2007 17.7 8.6 2.2
MFT-10,20 B55 2007 4.9 7.1 2005 64.4 51.9 71.7 2007 11.3 6.2 0.7
TDT-10,20 B57 2005 1.3 1.2 2.2 2010 14.9
TFT-10,20 B57 2005 10.7 8.6 23.2 2010 11.9
* Partial results

8. Cultivars affected by changes in the pathogen during 2008-2010
Paraguay, 2009: IAN 10, ITAPUA 55, ITAPUA 65
Argentina, 2010: BIOINTA 3004, Don Mario Themix, Don Mario Atlax
Uruguay, 2010: Atlax (TDT-10,20), INIA Carpintero
PARAGUAY
BRAZIL
CHILE
URUGUAY
ARGENTINA
Puccinia triticina population:
Extremely dynamic, determines
short duration of resistance of new cultivars

9. Chemical control
• Farmers continue to grow high yielding leaf rust
susceptible cultivars using fungicides
• Fungicides are widely used to control the disease
complex present in the region, leaf rust is the main target
Wheat Average % area of Highest Nª
area (Mill, % area with Nª of reference for applications
Country ha) fungicides applications av. Nº Appl. on S Cvs.
Argentina 4.0 25-40 1.2 40 in 2010 2
Chile 0.4 100 >1 100
Brazil 2.3 100 >1 100 4
Paraguay 0.5 100 >1 100 3
Uruguay 0.5 > 90 1.0-1.5 100 3
Brazil and Paraguay: mixtures of strobilurins + triazols
Argentina, Chile and Uruguay: triazols, and mixtures

10. Genetic basis of leaf rust resistance
Lr3, 3ka, 9, 10, 16, 24, 26, 34, 37, 39, 47 present in
popular Argentinean cultivars
Lr16, 24, 34, 37, 39 present in some Uruguayan cultivars
Limited information of Uruguayan cultivars
No information of cultivars from Brazil, Chile and Paraguay
Few major R genes appear to be present in the regional
germplasm (Germán et al. 2007, 2009)
Resistance appears to depend on different combinations
of seedling R genes or their combination with APR genes
Recently released cultivars have only APR likely of the slow
rusting type: Klein Capricornio (Argentina),
Canindé 12 and C. 13 (Paraguay

11. Breeding for resistance to leaf rust
Important breeding objective for most programs
Has become less important in some programs due to
efficient control of the disease through use of fungicides
Some programs have released high yielding S lines
Main target: introduce APR of the slow rusting type
(conferred by minor genes with additive effects) into
adapted germplasm.
Some programs also use major R genes,
although do not know which ones
Markers for Lr19, Lr47 and Lr34 are used in Argentina

12. Phenotypic selection
possible every year in
most of the Southern
Cone region of S. A.
Lalbahadur Lalbahadur
Lr46
Leaf rust nursery,
LE, Uruguay, 2010

13. Challenges to control leaf rust
in the Southern Cone region of S.A.
Reduce damage by increasing release and
adoption of resistant cultivars
Incorporate resistance into
high yielding backgrounds with
quality standards required by the market
adequate levels of R to other prevalent
diseases

14. Grain yield Industrial quality
Fusarium Stripe rust Stem rust
Head
blight
Tan spot
AND
Other diseases
Brusone (Pyricularia
LEAF RUST
Maturity, Lodging grisea) in Brazil, RESISTANCE
Sprouting Bolivia, Paraguay

15. Grain yield with and without fungicides, yield reduction and diseases
Capitán Miranda, Paraguay, average 2008-2009.
Yield (kg/ha) Fusarium
With Without % yield Leaf head Tan Head
Cultivars
fung. fung. reduction rust blight spot blast
Old
CD 104 4672 3505 25.0 S S MS S
Itapúa 40 4628 4307 6.9 MS MS MS MS
New
Canindé 1 4415 4228 4.2 R S MR R
Itapúa 70 4964 4986 -0.4 MR MS MS MS
Source: Wheat Program, CRIA, Cap. Miranda

16. Grain yield with and without fungicides, yield reduction and diseases
Balcarce, Argentina, 2010
Yield (kg/ha) % yield Leaf
Cultivars With fung. Without fung. reduction rust
French
Baguette 19 6580 5723 13.0 90S
Baguette 30 6257 5393 13.8 90S Source:
RET Trigo
Local
2010
ACA 303 5307 5350 0.0 5MS Subregión
Klein Capricornio 5233 4878 6.7 5MS IV INASE
BIOINTA 2004 4773 4960 -3.9 0 MAGPyA
La Estanzuela, Uruguay
Yield (kg/ha) % yield Leaf Foliar
Cultivars With fung. Without fung. reduction rust spots
French
NT 805 8358 a 6745 a 19 ** 99S
Local
I. DON ALBERTO 8170 a 7367 a 10 NS 2MRR 40
GENESIS 2354 8131 ab 7101 a 13 NS 3MR 3
LE 2369 7592 b 7194 a 5 NS 5RMR 25
Source: modified from Castro et al., 2011

17. Yield and leaf rust infection of INIA breeding lines.
La Estanzuela, Uruguay, 2010
Line Cross Yield (kg/ha) Leaf rust
LE2358 PI/FUNO*2/5/VLD/4/CO723595/3/TAM200*2//TAM107/TA2460/6/LE2220 6862 a 0
LE2346 PEETHREE NR2/2*OS//NWT/3/OS.VONA PYN COMP/4/ PIOPIO/5/LE2221 6766 a 0
F5 09-13158 I.TORCAZA*2//CEP8749/EMBRAPA27 6657 ab 0
F6 09-696 ITIJ/4/TRAP1/YACO/3/KAUZ*2/TRAP//KAUZ 6487 abc 15MSS
LE2359 ITIJ/LE2266 6459 abc 0
F6 09-10081 IGAR/LE2321 6096 abcd 10MS
F5 09-13139 I.TORCAZA*2//CEP8749/EMBRAPA27 6007 abcd 0
F6 09-599 IGAV/5/CEP85155/3/CEP7780*2//H499.71A/4*JUP/4/BR23 5999 abcd 15MSS
F5 09-13049 I.TIJERETA*2/SUZ6/OPATA 5986 abcd 0
F6 09-10027 IGAR/ALSEN 5935 abcd 0
F5 09-13177 I.GORRION*2/CHAPIO 5895 abcd 30MSS
I.GARZA ICAB/ITIJ 5856 abcd 10MS
BAGUETTE 19 5530 bcd 70S
BIOINTA 3000 5467 cd 50S
I.TIJERETA LE2132/ECAL 5196 de 15MSS
BIOINTA 3004 4122 e 70S
Source: M. Quincke, INIA wheat breeding program

18. BC1F5 lines from INIA-Uruguay combining APR
to leaf rust and resistance to other prevalent diseases
Fusarium Septoria Stem
head Tan leaf rust
Line Cross blight spot blotch Kenya
R09-19126 I.TIJERETA*2/TOROPI MR
R09-19008 PARULA/ORL 99192*2 MR MRMS
R09-19228 LE 2304*2/PARULA MRMS R
R08-10690 LE2252*2//GENARO*3/PARULA MR R
R09-19200 I.GORRION*2/CHAPIO MRMS
R09-19229 LE 2304*2/TOROPI R R
R09-19173 I.TORCAZA*2//CEP8749/EMBRAPA27 MR R
R08-4898 I.TIJERETA*2/AMADINA MR

19. Increase duration of resistance
by pyramiding resistance genes
One strategy: use of major genes
Introduce effective major R genes not present
in the regional germplasm in combinations
increase diversity within and among programs
reduce the risk of widespread epidemics
monitoring the pathogen
The other strategy: use APR genes (slow rusting)
Introduce several APR of the slow rusting type
Lr34, Lr46, Lr67, LrP and others
BUT…

20. Many resistant advanced lines of the regional breeding
programs have effective seedling resistance
It is more difficult to introduce APR in R backgrounds
Seedling IT of Uruguayan lines to 17 P. triticina races
MMD-10,20
MCD-10,20
MDR-10,20
MDP-10,20
KDG-10,20
MDT-10,20
MFR-10,20
MFP-10,20
MFT-10,20
TDD-10,20
MCR-10
MCT-10
MFP-20
SPG-10
MDP
MFP
CHT
Line
Facultative
LE 2359 0 0 0 0; 0 0 0 0 0 0; 0 0 0 0; 2 0 0
LE 2366 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
LE 2377 0 0; 0; 0;1= 0; 0; 0; 0 0; 0; 1-; 0 0 0 0; 0 0;
LE 2379 0 ;1= 1; 2-; ;1= 1-; 2 ;1= 12- 0; ;1- 0; ;1= 2=; ; 0 1;
Spring
LE 2354 0; 0; ;1= ;1= ;1= ;1= ;1= 0 0 ;1- 0; ; ;1- ; 0; 0; ;1=
LE 2382 0 0; 0; 0; 0; 0; 2-; ,1= 2=; 0; 0 0; 0; 2=; 2=; 0; ;1=
LE 2388 0 0; ,1= 12- 2=; 1-; 1-; ;1= 0; ;1= 0; ;1- ;1= ;1= ; 0 ;1=
LE 2390 0 0; 0 0; 0; 2=; 2 0; 2=; 0; ;1= 0; 0; 2-; 0; 0; 0;

21. Both strategies require:
Characterization of the type of resistance present
germplasm used in breeding
sources of resistance
Know genes present and genes to be introduced
More efficient use of available resources
Increase use of molecular markers will help
identification of some R genes present
facilitate identification of possible new R genes
genetic progress in breeding for leaf rust R

22. Generally adequate:
Resources Trained personnel
Greenhouses
Argentina
Laboratory
Brazil
Equipment
Uruguay
Funding for current projects
Chile: progressive reduction in human resources
Paraguay: serious deficiencies in resources
Better integration between disciplines related to breeding
would be beneficial
In general breeders require more training in methodology
to identify and select for APR
Communication among researchers in the region should
Improve. Workshops should be organized regularly

23. Research to identify mainly new APR genes
probably present in Southern Cone germplasm
QTL analysis of durable R (B.Mant, Sinvalocho, Toropi)
Projects using association mapping have
been approved recently in Argentina, Brazil
and Uruguay
Collaborative research with other programs
contributing with phenotyping of mapping pops.

24. Acknowledgements
Wheat Regional Project funded by INIA-España, CIMMYT,
PROCISUR, INIA-Uruguay
Brazilian Institutions funding research projects on
resistance to wheat rusts
Conselho Nacional de Desenvolvimento Científico e Tecnológico
Ministerio da Agricultura Pescuária e Abastecimento
Empresa Brasileira de Pesquisa Agropecuária
Fundação de Amparo à Pesquisa do Rio Grande do Sul
Technician and students

25. Pablo José A. Marcia Lidia Quintana
Campos, Martinelli, Chaves, de Viedma
Argentina Brazil Brazil Paraguay
Francisco
Sacco,
Julio Argentina Ricardo
Huerta- Madariaga,
Espino, Chile
México
Silvia
Germán
Uruguay
Mohan Kohli
Paraguay Thank you