Maize Genetics Cooperation Newsletter vol 84 2010
Please Note: Notes submitted to the Maize Genetics
Cooperation Newsletter may be cited only with consent of authors.
Ottawa, Ontario, Canada
Eastern Cereal and Oilseed Research Centre
Expression of different Ht
genes to Northern Corn Leaf Blight in Ottawa, Ontario
Zhu, X., L. M. Reid, T. Woldmariam, C.Voloaca, and J. Wu
Twenty-nine inbred lines with different Ht resistance genes for northern corn leaf
blight [ Exserohilum turcicum (Pass.)
K.J. Leonard & E.G. Suggs (teleomorph = Setosphaeria
turcica (Luttrell) K. J. Leonard & E.G. Suggs; syn. = Helminthosporium turcicum Pass.] and four susceptible
inbred lines (A619, Pa91, CO388, and CO442) were evaluated for the expression of
resistance in our leaf blight breeding nursery at Agriculture and Agri-Food Canada (AAFC), Eastern Cereal and Oilseed
Research Centre (ECORC), Ottawa, Ontario in 2006 and 2007. Each genotype was planted in a five-row
plot with single row plots of 15 plants. All plants were inoculated twice with 0.1 g of ground
diseased leaf powder collected from the previous field season. The powder was placed into the whorl of
each plant using a Bazooka (Sistrunk
Inoculators, Starkville, MS 39759, USA) at
6-8 leaf-stages and again at the 10-12 leaf–stages. If there was no rain after inoculation,
the plots were irrigated for 10-15 minutes every day to provide suitable
environment for disease to develop.
Specific resistance were observed and recorded
first at 15-20 days after the first inoculation (about 12 leaf stage). Five specific
resistances were observed, classified as: highly resistant (HR), resistant
lesion (R), moderately resistant lesion (MR), moderately susceptible lesion
(MS), and susceptible lesion (S). For
HR types, there were no typical lesions and the infection point changed color
from yellow to brown, sometimes to purple, and had only limited extension. The R types have stripes or narrow
elliptical greenish-yellow lesions. MR types have narrow, long, elliptical gray lesions with
greenish-yellow or purple margins. MS lesions are long, elliptical, and gray
lesion with greenish-yellow or purple margins. The S lesions are long,
elliptical, and gray or tan in color. HR, R, and MR plants were selected to
self for further resistance breeding to northern leaf blight.
At
the soft dough stage (about 3 weeks after silk emergence), plants were observed
the specific resistance second time, its classification as above, whereas general
resistance were recorded. Based on
disease severity, the disease rating scale for general
resistance ranges from 1 to 7 where: 1= no symptoms; 2= < 1% of the leaves
are symptomatic; 3= 1- 10% of the leaves are symptomatic; 4= 11- 25% of the
leaves are symptomatic; 5= > 50% of the lower leaves and < 25% of the mid and upper
leaves are symptomatic; 6= lower leaves are dead, > 50% of the mid leaves
and < 25% of the upper leaves
are symptomatic; 7= plant is dead.
The mid leaves refer to the four leaves near the primary ear. Hand-pollinated
plants with HR, R, or MR, and disease rating �5 were selected continued
breeding. Plants with MS or S lesions, or disease rating �6, were discarded.
The screening results of inbred lines in 2006
and 2007 were shown in Table 1. Based
on these results shown in the table, we made the following conclusions on the
expression of the Ht genes in Ottawa:
1.
Three of
the initial sources of blight resistant inbreds [A509N, A553N (orange), and
A553N (red)] did not have uniform (pure) resistance since HR or R and S lesions
were observed in the 2006 screening. However, self pollination of the HR plants
resulted in all HR plants when screened the following year.
2.
We
observed distinct differences in the expression of the Ht genes at early stages (about 12 leaf stage) of plant growth and
as expected, symptoms in susceptible genotypes increased as the plants matured.
Some specific observations were:
a.
Lesions on
Ht and Ht1 plants were very similar. All Ht and Ht1 inbreds were susceptible
in Ottawa, Ontario, and are thus not suitable sources of resistance for our
region.
b.
All Ht2 and Ht3 inbred lines had similar MR type resistance in 2006 and 2007. They
all had long lesions with yellow or purple margins. During the later stages of plant development, some of these
lesions became larger and developed a gray center thus becoming MS type lesions.
c.
All Htm1 and HtN inbred lines had HR or R type resistance. As the plant
developed these either did not change or became slightly larger in size.
Table 1. Northern corn leaf blight screening results of inbred lines with
different resistance in 2006 and 2007 in Ottawa, Ontario, Canada
|
|
|
|
2006 |
2007 |
||
|
Source� |
Name |
Ht gene � |
Specific
Resistance |
General Resistance |
Specific
Resistance |
General Resistance |
|
Ames23458 |
A619HT |
Ht1? |
S |
5 |
S |
7 |
|
Ames23468 |
A632HT |
Ht1? |
S |
5 |
S |
6 |
|
Ames27065 |
B73Htrhm |
Ht1? |
S |
5 |
S |
6 |
|
PI601079 |
LH123Ht |
Ht1? |
S |
5 |
S |
6 |
|
Ames27138 |
N28Ht |
Ht1? |
S |
5 |
S |
7 |
|
Ames25219 |
A619Ht1 |
Ht1 |
S |
5 |
MR |
6 |
|
Ames25372 |
Pa91Ht1 |
Ht1 |
S |
5 |
S |
6 |
|
Ames25220 |
A619Ht2 |
Ht2 |
MR |
4 |
MR |
6 |
|
Ames25221 |
A619Ht3 |
Ht2 |
MR |
4 |
MR |
5 |
|
Ames25373 |
Pa91Ht2 |
Ht2 |
MR |
4 |
MR |
5 |
|
Ames25374 |
Pa91Ht3 |
Ht3 |
MR |
4 |
MR |
5 |
|
Cornell University |
73353 |
Htm1 |
R |
3 |
R |
3 |
|
PI550496 |
H102 |
Htm1 |
HR/R |
2 |
HR/R |
3 |
|
PI406112 |
A214N |
HtN |
HR/R |
2 |
HR/R |
3 |
|
PI406118 � |
A509N |
HtN |
95.2HR/R:4.8S |
2 or 4 |
HR/R |
3 |
|
PI406119 � |
A553N (Orange) |
HtN |
79.7HR/R:20.3S |
2 or 4 |
HR/R |
3 |
|
PI406120 � |
A553N (Red) |
HtN |
83.3HR/R:16.7S |
2 0r 4 |
HR/R |
3 |
|
Ames23469 |
A632HtN |
HtN |
HR/R |
2 |
HR/R |
3 |
|
PI406126 |
A661N |
HtN |
HR/R |
2 |
HR/R |
3 |
|
PI587142 |
A679 |
? |
-- |
-- |
R |
5 |
|
PI584529 |
B100 |
? |
-- |
-- |
R |
3 |
|
PI594045 |
B102 |
? |
-- |
-- |
R |
3 |
|
PI608777 |
B85 |
? |
-- |
-- |
R |
3 |
|
PI539870 |
B92 |
? |
-- |
-- |
R |
3 |
|
PI539871 |
B93 |
? |
-- |
-- |
HR/R |
2 |
|
PI561565 |
B95 |
? |
-- |
-- |
MR |
6 |
|
AAFC |
CO428 |
? |
R/MR |
3 |
R/MR |
3 |
|
PI587129 |
H99 |
? |
-- |
-- |
R |
4 |
|
Ames27141 |
NC290A |
? |
-- |
-- |
R |
4 |
|
PI587139 |
A619 |
N/A |
S |
7 |
S |
7 |
|
PI587174 |
Pa91 |
N/A |
S |
7 |
S |
7 |
|
AAFC |
CO388 |
N/A |
S |
7 |
S |
7 |
|
AAFC |
CO442 |
N/A |
S |
7 |
S |
7 |
|
Total |
|
|
|
24 |
|
33 |
� Name of organization from which the
inbred was obtained or United States Department of Agriculture NC-7 code.
� Ht resistant gene according to inbred
description or pedigree
� Resistance of these inbred lines was not uniform
upon first screening in 2006. The numbers for specific resistance lesion types
refer to the percentage observed for each type.
Specific Resistance: HR = highly
resistant; R = resistant lesion(s); MR = moderately resistant lesions; MS =
moderately susceptible lesions; and S = susceptible lesions.
General Resistance: 1= no symptoms; 2= < 1%
of the leaves are symptomatic; 3= 1- 10% of the leaves are symptomatic; 4= 11-
25% of the leaves are symptomatic; 5= > 50% of the lower leaves and < 25% of the mid and upper leaves are symptomatic; 6= lower
leaves are dead, > 50% of the mid leaves and < 25% of the upper leaves
are symptomatic; 7= plant is dead.