Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

Session 6C — D.E. Fraser, J.P. Murphy, and S. Leath
164
Greenhouse tests
Seeds of each genotype were
over-planted and thinned to two
plants per pot and allowed to grow
in alternating 12-hour light and
dark periods at 16 to 26 o C.
Experimental design was a
randomized complete block with
four replications in time.
At GS 10 the penultimate leaf of
one plant/pot was marked and a 2
ml droplet of a single isolate spore
suspension standardized to 1 x 10 6
spores ml -1 applied to the leaf.
Presence/absence of a lesion at 5
and 10 days was recorded.
Following the last rating on the
penultimate leaf of one plant, the
flag leaf of the other plant/pot was
marked. Spore suspensions of each
isolate treatment were applied to 50
genotypes per population using
hand atomizers until run-off
occurred. Glass slides placed in the
plant canopy during inoculation
indicated that 50-75 spores were
deposited per mm -2 . Incubation
period and % LAD on each plant
were recorded.
Growth chamber
Seeds of each genotype were
planted and grown for 21 days in
12 h light and darkness periods in
day/night temperatures of 22/
18 o C. At the 2-leaf stage, spore
suspensions of the same four
isolate treatments as described
previously were applied to 50
genotypes per population using
hand atomizers until run-off
occurred, with approximately 65
spores deposited per mm -2 of leaf
tissue. Incubation period and %
LAD on each plant were recorded.
Experimental design was a
randomized complete block with
four replications.
Detached leaf test–adult and
juvenile
Seeds of each genotype were
planted and grown in the
greenhouse for three weeks
(juvenile) and ten weeks (adult),
respectively. For the juvenile test,
fully expanded second leaves were
cut from each genotype in both
populations. For the adult test,
plants were grown to Feeke’s GS
10.1, and the flag leaf was excised
from each plant. Each single leaf
was cut into four equal sized pieces
and placed on 150 ppm
benzimidazole agar in a box
divided in 4-cm grid squares. Each
grid square represented each of the
isolate treatments on a single
genotype. A 2 ml droplet of a single
isolate spore suspension was
placed in the center of each leaf
piece. Incubation period, lesion
expansion rate, and final lesion size
was recorded. Both the adult and
juvenile tests were replicated four
times.
Results and Discussion
The level of resistance in the
breeding population was generally
higher than the biparental
population in all tests. The AUDPC
values indicated significant
differences among isolate
treatments in the field at Laurel
Springs in 1997 and at both
locations in 1998 (Table 1).
Genotype by environment
interaction was significant.
Isolate treatments in
greenhouse evaluations were
significantly different for most of
the components of resistance
measured (Tables 2 and 3). Results
of inoculations with the most and
least aggressive isolates in
combination (AD) were similar to
inoculations with the most
aggressive isolate alone and both of
these treatments resulted in higher
numbers of lesions, more rapid
rates of lesion expansion and
higher % LAD than inoculation the
least aggressive isolate. Shorter
incubation periods were not
consistently associated with the
most aggressive isolate or the most
and least aggressive isolate
together. Components of resistance
measured in controlled
environments were highly
correlated with each other (Table 4).
Few components of resistance
measured in controlled
environments correlated with field
measured disease severity. A
comparison of the controlled
environment studies with field data
from Kinston in 1998 indicated that
adult plant incubation period and
% LAD on the flag leaf for adult
plant spray inoculation were highly
correlated (P>0.01) with field
Table 1. Area under the disease progress curve values for disease severities measured on hill
plots inoculated with isolates of Stagonospora nodorum.
Laurel Springs 1997 Laurel Springs 1998 Kinston 1998
Isolate treatments Breeding Biparental Breeding Biparental Breeding
A (most) a 2724b 1669b 2196a 1678a 1587a
D (least) 2783a 1667b 1972c 1557c 1561c
AD (both) 2770a 1806a 1733d 1608b 1628a
NI (control) 2694c 1829a 2087b 1367d 1452d
a ‘Most’ and ‘least’ aggressive refer to isolate reaction measured in the isolate screening assay done on
seedlings in controlled conditions.