Sunflower Rust Races in Manitoba Khalid Y. Rashid

Sunflower Rust Races in Manitoba
Khalid Y. Rashid
Agriculture and Agri-Food Canada, Morden Research Station, Morden, Manitoba
New races of rust virulent on sunflower hybrids create severe rust epidemics and
cause great losses in yield and quality in both oil and confection types
INTRODUCTION
Figure 3. Sunflower Rust Hot Spots 1990 & 2003
Rust caused by Puccinia helianthi Schwein. is a common disease affecting sunflower (Helianthus
annuus L) in North America and worldwide (Figure 1). This pathogen completes its life cycle on
sunflower with high frequency of sexual recombination and the formation of new races. Local
inoculum causes early infections and disease development provided the environmental conditions
are favorable for rust (Figure 2). The incidence and severity of rust vary between years and
regions of sunflower production (Figure 3). Rust epidemics occurred in 1999 and 2003 in the
North Central Plains where up to 25% reductions in yield were estimated in southern Manitoba.
The prevalence of new races and the lack of resistance to such races in most commercial
sunflower hybrids make the crop vulnerable to frequent epidemics and great losses in yield and
quality. The objective of this study was to determine the prevalent races in the sunflower rust
population in Manitoba.
Dauphin
Shoal Lake
Teulon
Minnedosa
Selkirk
Beausejour
Carberry
Virden
Figure 1. Sunflower Rust Severity
Mid-season
Late-season
Brandon
1990
>50% LAI
Winnipeg
Portage
la Prairie
2003
Boissevain
Steinbach
Morden
Pilot Mound
Vita
Table 1. Prevalence and Severity of Rust (LAI = Leaf Area Infected)
Figure 2. Early Symptoms on Seedlings
Year
Infested Fields
% of Total
Mean Disease
% LAI
Range
% LAI
Prevalent
Races
2005
27
8
T-30
326 & 336
2004
60
8
T-30
300 & 700
2003
65
25
T-80
300 & 400
2002
50
15
T-80
Na
2001
27
8
T-20
Na
2000
40
15
5-60
Na
1999
60
5
T-20
Na
Table 2. Rust Races and Prevalence (R = Resistant Reaction, S = Susceptible Reaction)
Rust Races, Prevalence and Virulence
MATERIALS AND METHODS
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Disease survey in the major sunflower growing areas in Manitoba.
Collect rust samples from all infected fields.
Increase each isolate on susceptible sunflower in isolation in greenhouse.
Test each isolate on a set of nine sunflower differential lines (Table 1).
Assess the reaction of each isolates/differential line.
Identify the races and the prevalence of each race.
Sunflower
Differential
Lines
326
(61%)
336
(18%)
337
(4%)
376
(4%)
726
(4%)
776
(4%)
777
(4%)
S-37-388
S
S
S
S
S
S
S
CM-90RR
S
S
S
S
S
S
S
MC-29-3
R
R
R
R
S
S
S
P-386
R
S
S
S
R
S
S
HA-R1
S
S
S
S
S
S
S
HA-R2
R
R
R
S
R
S
S
HA-R3
R
R
S
R
R
R
S
HA-R4
S
S
S
S
S
S
S
HA-R5
S
S
S
S
S
S
S
Assessment of Virulence Among Rust Isolates
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Visual assessment of the infection type reaction; 0 to 4.
Visual estimate of the percent Leaf Area Infected (LAI).
Identify resistance reactions: IT 0 to 2 with low LAI.
Identify susceptible reactions: IT 3 to 4 with high LAI.
RESULTS
Rust was present in 27% of the 67 fields surveyed in Manitoba in 2005 (Table 1). The severity of
infection ranged from traces to 10% LAI in most infected fields, and up to 30% LAI in a few
fields. The rust incidence and severity in 2005 were lower than in other years especially the year
2003 (Table 1). Out of the 23 rust collections from infected sunflower fields in 2005, 14
collections (61%) were identified as race 326, 4 collections (18%) as race 336, and one collection
each (4%) of the races 337, 376, 726, 776, and 777 (Table 2). Races 326, 336, 337, and 376 are
variations of race 300 (traditional race 3). Races 726, 776, and 777 are variations of race 700
(traditional race 4), and are very virulent races. Presently, these virulent races are at low frequency
in the rust population, but can potentially cause serious epidemics if they become prevalent in the
sunflower growing areas in North America.
CONCLUSIONS
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Identified changes in the virulence in sunflower rust population.
Rust race 326 was the most prevalent in 61% of sunflower fields.
Race 336 was also widespread.
New virulent races 776 and 777 were present at low frequency.
ACKNOWLEDGEMENT
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AAFC-MII, ARDI / MRAC
NSAC of Canada, NSA of the USA
Technical Assistance: Tricia Walske and Maurice Penner
Agriculture and Agri-Food Canada, Morden Research Station, Unit 100 - 101 Route 100, Morden, Manitoba, Canada, R6M 1Y5
email: [email protected]