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Rp resistance Rp1-D-virulent isolates fungicides. Effect of rust on sweet corn yield EAR WEIGHT. Rp-resistance. Bands of chlorotic flecks (no sporulation). In the 1990s, Rp resistance added at least $3 million* annually to the value of processing sweet corn in the Midwest - PowerPoint PPT Presentation
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• Rp resistance• Rp1-D-virulent isolates• fungicides
Effect of rust on sweet corn yieldEAR WEIGHT
Y = 99.4 - 0.58 Xr = 0.81 n = 232
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70
Rust severity (%) one week before harvest
Pe
rce
nt
ma
xim
um
yie
ld (
ea
r w
eig
ht)
Rp-resistance
Bands of chlorotic flecks (no sporulation)
In the 1990s, Rp resistanceadded at least $3 million*annually to the value ofprocessing sweet corn in the Midwest * based on four, relatively conservative assumptions
250,000 A processing sweet corn Midwest
1. x 1/2 exposed to common rust
125,000 A exposed to rust
2. x 6.2 tons per A
775,000 tons
3. x $50 per ton
$38,750,000
4. x 15% rust severity*
x 0.5 % loss per 1% severity
$2,906,250 loss
* an average of 15% rust severity or more for hybrids rated MR to S
Rust severity %and (estimated Reactions of sweet corn hybridsyield reductions)** R MR M MS S 0-10% (3%) 0.63 0.26 0.11 0.11 0.1110-20% (9%) 0.37 0.47 0.16 0.11 020-30% (15%) 0 0.26 0.63 0.26 0.1630-40% (21%) 0 0 0.11 0.32 0.2640-50% (27%) 0 0 0 0.21 0.32>50% (>30%) 0 0 0 0 0.16 * probability based on 19 trials in 18 years of evaluations in University of Illinois sweet corn hybrid disease nurseries - plants inoculated as seedlings
** yield loss estimated by multiplying rust severity by 0.6
Probability* of severe rust
Susceptible Rp-resistant
Rp1-D resistant hybrid
Rock Falls, IL September 1999
Rp1-D resistance Los Mochis, Mexico
March 2000
1. How will hybrids react to the Rp1-D-virulent race? - non-Rp hybrids - Rp hybrids
2. Does Rp1-D have any “residual” effect on the new race?
Questions about theRp1-D-virulent race
Reactions of non-Rp hybrids
r = 0.90* * for non-Rp hybrids
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70
Severity (%) of rust Rp1-D avirulent isolates
Sev
erit
y (
%)
of
rust
R
p1-
D v
iru
len
t is
ola
tes
Rp1-D hybrids
RpX hybrids
Reactions to Rp1-D-virulent and avirulent isolates
2001 UI hybrid disease nursery
0
10
20
30
40
50
60
70
0 10 20 30 40Severity of rust (%)
Rp1-D-avirulent isolates
Se
ve
rity
of
rus
t (%
)R
p1
-D-v
iru
len
t is
ola
tes
Rp inbreds
r = 0.76 among non-Rp inbreds
2001 UI inbred disease nursery
Reactions to Rp1-D-virulent and avirulent isolates
Hybrids that do not have theRp1-D gene have the samereaction to Rp1-D-virulentand Rp1-D-avirulent rust
Reactions of Rp hybrids
- inoculated with Rp1-D-virulent rust
Populations of Rp hybrids compared to non-Rp hybrids
0
10
20
30
40
50
60
0 1-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60
Severity of rust (%) - Rp1-D virulent isolates
Num
ber
of h
ybrid
s
Rp1-Dnon Rp1-D
n Mean S.D.137 32.8 8.4 176 33.8 10.7
Rp1-D-virulent isolates - 2001
2001 UI hybrid disease nursery
Pairs of Rp hybrids and
non-Rp hybrids
- inoculated with Rp1-D-virulent rust
Pairs of Rp and non-Rp hybrids
non-Rp hybrid Rp hybrid
Bodacious Bodacious RustDay Star Morning Star GG Code 8 GG Code 23Primetime Prime PlusSch 5005 ChieftainSS 8102 SS 8102 R
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Severity (%) - non-Rp hybrid or inbred
Seve
rity
(%
) -
Rp h
ybrid o
r in
bre
d
r = 0.96 n = 43
slope = 0.95
Reactions of Rp and non-Rp pairs to Rp1-D-virulent rust
2001 UI Rp hybrid trial
• no residual resistance from Rp1-D
• no linkage of general resistance near rp1 region
Rp hybrids and
non-Rp hybrids
- inoculated with a mixture of Rp1-D-virulent and avirulent rust
0
5
10
15
20
25
30
35
0 1-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60
Severity of rust (%) - mixture of isolates
Nu
mb
er o
f h
yb
rid
s
Rp1-D
non Rp1-D
n Mean S.D. 86 15.5 6.4 156 27.5 11.4
Mixture of virulent and avirulent isolates - 2000
2000 UI hybrid disease nursery
Pairs of Rp and non-Rp hybrids
Pair 2000 (mix) 2001 (vir)CnS 710 R 15% 34%CnS 710 36% 37% Incredible Rust 10% 29%Incredible 24% 30%
Morning Star 22% 34%Day Star 41% 35%
Prime Plus 16% 39%Primetime 32% 40%
If virulence is frequent
Hybrids with Rp1-D have similar reactions as non-Rp hybrids - population distributions alike - Rp and non-Rp versions alike
If virulence is infrequent
Hybrids with Rp1-D are infected less severely than non-Rp hybrids - additional research on simple ways to detect frequency of virulence and relate frequency to potential severity
If virulence is infrequent
Rp hybrid non-Rp hybrid
Paired hybrid monitor plotsnon-Rp hybrid Rp hybrid
similar number of pustules per leaf - virulence frequent
fewer pustules on leaves of Rp hybrid - infrequent
Conclusions for Rp1-D are applicable to otherRp genes when virulence against those Rp genes are prevalent
Rp-G, Rp1-E, Rp1-I, Rp1-K compound rust genes
Fungicides• EBDCs
• TILT
• strobilurins (QUADRIS, F-500)
Fungicides*• fungicides are preventative• fungicides ARE NOT curative
Rule of thumb: one or two early applications are superior to multiple late applications • juvenile tissue is more susceptible• infection occurs in the whorl • pustules on lower leaves = inocula for 2o infection (5,000 urediniospores per pustule)
* EBDCs, Tilt
Early applications of fungicides
~ 2% severity
* EBDCs, Tilt
Later applications of fungicides
> 5-10% severity
* EBDCs, Tilt
Strobilurins
may change use of fungicides on sweet corn
• more efficacious • may have different thresholds ?
Rust & NLB - 'Florida XP-7' Leaf area necrotic (%) Rick Raid - UF-Belle Glade Planted: 17 Feb 1997
0
10
20
30
40
50
60
70
Non-treated
Manzate Tilt Folicur Quadris Tilt +Manzate
Folicur +Manzate
Quadris+Manzate
Quaddris+ Tilt
Lea
f ar
ea n
ecro
tic
(%)
Common rust - 'Silver Queen' Leaf area infected (%)
Helene Dillard, NYAES- Geneva Planted: 21 June 2000
0
5
10
15
20
25
30
Non-treated Quadris 0.38 28 July 09 August
Quadris 0.77 28 July 09 August
Tilt 0.25 28 July 09 August
Quadris 0.38 09 August 21 August
Quadris 0.77 09 August 21 August
Tilt 0.25 09 August 21 August
Per
cen
t le
af a
rea
infe
cted
Thresholds
• can rust be controlled if strobilurins are first applied at higher thresholds?
OR
• can strobilurins be applied after we determined that virulent isolates are frequent enough to cause severe infection?
Location: Urbana, IL - May 29, 2001
Hybrids: Snow White, Sterling
Compounds: Tilt, BASF F-500, Quadris (low, high rate)
Application: July 5 (2 to 4-leaf) 5% July 11 (4 to 6-leaf) 15%
July 17 (6 to 8-leaf) 30% July 24 (row tassel) 40%
21 treatments
• 3 replicates, 4-row plots 27.5 ft length, ~ 40 plants/row • 2 inoculated “spreader” rows adjacent to each plot (constant source of urediniospores) • rated rust weekly (severity - %) • harvested 20 consecutive plants/row
Snow White - % yield Y = 99.1 - 0.57 X
r2 = 0.83
50
60
70
80
90
100
10 20 30 40 50 60 70Rust severity (%)
Yie
ld (
% m
ax
imu
m)
Rust fungicide trial - 2001
% yield
Sterling - % yield Y = 100.3 - 0.42 X
r2 = 0.71
50
60
70
80
90
100
10 20 30 40 50 60 70Rust severity (%)
Yie
ld (
% m
axim
um
)
Rust fungicide trial - 2001
% yield
Rust fungicide trial - 2001
Non-treated
Non-treated
strobilurin-treated
strobilurin-treated
Controls - Snow White
0
10
20
30
40
50
60
70
5 July 11 July 16 July 23 July 30 July 7 August
Rus
t sev
erity
(%
)
non-treated check
Tilt 4 oz. - July 5,11,17,24
Application at 5% severity - Snow White
0
10
20
30
40
50
60
70
5 July 11 July 16 July 23 July 30 July 7 August
Rus
t sev
erity
(%)
Non-treated
Tilt - 4 applications
Tilt 4 oz. July 5
Strobilurins July 5
Application at 15% severity - Snow White
0
10
20
30
40
50
60
70
5 July 11 July 16 July 23 July 30 July 7 August
Rus
t se
verit
y (%
)
Non-treated
Tilt - 4 applications
Tilt 4 oz. July 11
Strobilurins July 11
Application at 30% severity - Snow White
0
10
20
30
40
50
60
70
5 July 11 July 16 July 23 July 30 July 7 August
Rus
t sev
erity
(%
)
Non-treated
Tilt - 4 applications
Tilt 4 oz. July 17
Strobilurins July 17
Application at 40% severity - Snow White
0
10
20
30
40
50
60
70
5 July 11 July 16 July 23 July 30 July 7 August
Rus
t sev
erity
(%
)
Non-treated
Tilt - 4 applications
Tilt 4 oz. July 24
Strobilurins July 24
Controls - Sterling
0
10
20
30
40
50
60
70
5 July 11 July 16 July 23 July 30 July 7 August
Rus
t sev
erity
(%
)
non-treated checkTilt 4 oz. July 5,11,17,24
Application at 5% severity - Sterling
0
10
20
30
40
50
60
70
5 July 11 July 16 July 23 July 30 July 7 August
Rus
t sev
erity
(%
)
non-treated Tilt 4 oz. 4 applicationsTilt 4 oz. July 5Strobilurins July 5
Application at 15% severity - Sterling
0
10
20
30
40
50
60
70
5 July 11 July 16 July 23 July 30 July 7 August
Rus
t sev
erity
(%
)
non-treated Tilt 4 oz. 4 applicationsTilt 4 oz. July 11Strobilurins July 11
5.5
6
6.5
7
7.5
8
5% 15% 30% 40% Tilt weekly Check
Yie
ld (
ton
s/A
Tilt Strobilurin
Rust fungicide trial - 2001
Sterling
• yield was reduced about 4% to 6% for each 10% rust severity Snow White• one application of strobilurin at 5%, 15% or 30% gave about the same level of control as weekly applications of Tilt Sterling • applications at 15% and 30% did not control as well as applications at 5%, but yield did not differ between applications at 5% and 15%
• Application thresholds for strobilurins may be high enough to determine whether or not Rp1-D-virulent rust is frequent enough or cause damage. • Thresholds for strobilurins probably will be in the 5% to 15% range.
Tentative conclusions
general or partial resistance
susceptible
Common rustfield corn vs. sweet corn - 2000 Field corn• 1573 field corn lines x FR 1064 • 1 replicate • 1 to 9 scale (~sq. rt. of %) PI accessions - 2001• 2000 accessions (So. America)• 2 replicates • 1 to 9 scale (~sq. rt. of %)
n = 244 n = 1573mean = 24% mean = 4.97SD = 11.6% SD = 0.67 BLSD = 6.7%
0
0.1
0.2
0.3
0.4
0.5
1-2% 2-4% 4-6% 7-10%
11-15%
16-20%
21-25%
26-30%
31-35%
36-40%
41-50%
>50%
Fre
quen
cy
Sweet corn Field corn
Common rust - 2000
sweet corn vs. field corn
Severity (%) or 1 to 9 rating (squared)
Reactions of PI accessions - 2001
0
50
100
150
200
250
300
350
0 > 0 to < 0.5
0.5 to < 1
1 to < 2 2 to < 3 3 to < 4 4 to < 5 5 to < 6 > = 6
Rust rating
Nu
mb
er
of
ac
ce
ss
ion
s
Antioquia, Columbia Ancash, PeruBoyaca, Columbia Apurimac, PeruCauca, Columbia Cajamarca, Peru
Lima, PeruJunon, Peru
B93 (PI 539871) B108 (PI 597926) IA DS61* (NSL 75976) * source of resistance to P. polysora
Sources of accessions with partial rust resistance?
Early Cogent Hawaii #9 Silver SucroEsteem Lancelot Sugar 73GG Code 27 Miracle Sugar 74 btGG Code 61 PX 9314639 Tendertreat EHGG Code 74 Seneca Horizon
Partial rust resistance in active* sweet corn hybrids
Champ GG Code 6 SensorGH 2757 Merlin Tuxedo
AVX 2539 Sugar Time Sweetie 82Dinner Time Sun 2577 SS 8801GG Code 14 Sun 2642 Tastee TreatPrime Pak Sun 2733 WH 3125Sugar Loaf Sweetie 76 Wintergreen
Partial rust resistance in inactive* sweet corn hybrids
• Rp genes• fungicides• general resistance