- Field and growth chamber experiments were conducted to
determine chloride effects on the progress of stripe rust disease
caused by Puccinia striiformis West., and to investigate turgor
potential as the mechanism of the chloride effect.
Seven winter wheat (Triticum aestivum) cultivars were
grown in the field in 1982 and 1983 on a Woodburn soil (Aquultic
Argixeroll) at pH 5.5. Spring topdressed mixtures of
(NH₄)₂SO₄ and NH₄C1 provided four chloride rates (0 kg/ha,
72 kg/ha, 152 kg/ha, and 304 kg/ha). Nitrogen rate was 120 kg/ha
for all treatments in each experiment.
Plants were inoculated as seedlings using a composite
collection of Puccinia striiformis spores from races prevalent
on wheat in the Willamette Valley. Infection type, growth stage, and foliar percent attack by stripe rust were recorded at 12 to 16
locations within each plot at weekly intervals for 5-10 weeks.
Disease progress curves were plotted to compare the effect of
different chloride rates on disease severity over time. A logit
transformation was used to convert percent attack data from sigmoid
curves into a line for each chloride treatment within cultivars.
Linear regression was conducted for each cultivar with composite
logit values within treatments as the dependent variable and day
after inoculation as the independent variable. The slope of the
logit line corresponds to the apparent infection rate of the
disease. Latent period is found by solving the regression equation
of the line at a given percent foliar attack (1%).
Chloride rates of 72 and 152 kg C1/ha reduced apparent
infection rates in 1983 for cultivars 'Rew' (12.4%), 'Yamhill'
(7.7%) and 'Purplestraw' (10.5%). Latent period was generally
lengthened by 0.5 to 2 days with added chloride. In most cases
there was no significant difference in disease development among
the three highest chloride rates.
Interaction of cultivar and chloride treatment at chloride
rates of 72 kg/ha or higher increased the percent chloride content
of leaf tissue for all cultivars. The magnitude of the increase
varied by cultivar. Yamhill showed the largest increase (.27 to
.73%), together with Rew (.23 to .68%), followed by OR 67-237 (.17
to .47%), Hill 81 (.20 to .50%), and Stephens (.13 to .42%) in
1982. The increases in chloride content was largest in 1983 for
Purplestraw (.30 to .99%) followed by Yamhill (.26 to .86%), Rew
(.28 to .82%), Hyslop (.28 to .80%), and Stephens (.18 to .49%). Leaf water potential components were affected by cultivar
rather than chloride treatment in 1982 and 1983, with a cultivar by
chloride treatment interaction increasing turgor potential on May
19, May 26 and June 23 in 1982.
Chloride rates of 72 kg Cl/ha increased test weight of all
cultivars in 1982 (0.64%) and 1983 (1.2%), kernel weight of all
cultivars in 1982 (1.3%) and 1983 (4.3%), and grain yield of all
cultivars in 1982 (6.5%) and 1983 (16.4%).
Laboratory experiments using nutrient solutions to supply
chloride (3.6 meq/1) or sulfate (4.4 meq/1) treatments with equal
nitrogen levels showed that chloride decreased disease incidence by
12% on 'Nugaines' in 1983 and 'Yamhill' in 1984. Added chloride
decreased foliar percent attack during the primary infection cycle
on all cultivars. Approximately 28 days after inoculation in 1983,
foliar percent attack for the chloride-treated plants surpassed
that of the sulfate-treated plants for 'Nugaines' second leaves and
for 'Purplestraw' flag and second leaves. Apparent infection rate
was increased for Purplestraw flag leaves and decreased for Yamhill
second leaves with added chloride. A significant increase in leaf
turgor potentials accompanied the increase in percent chloride in
leaf tissue at the 3.6 meq/1 chloride rate. Increased chloride
supply slightly increased the leaf area and the apoplastic water
content of cells in the leaves.
In field experiments, chloride rates of 72 and 152 kg Cl/ha
(as NH₄C1) slowed the development of Puccinia striiformis by
decreasing the apparent infection rate and limiting foliar percent attack during the reproductive growth stages of winter wheat.
Chloride treatment effects on leaf chloride content corresponded to
changes in disease progress only at the 72 kg/ha chloride rate.
Chloride effects on disease progress were not reflected in changes
in grain yield. Chloride effect on test weight, kernel weight, and
grain yield in the absence of visible stripe rust symptoms may
reflect: a) the impact of stripe rust infection on root growth and
carbohydrate translocation of wheat plants, and b) control of
take-all root rot disease of wheat. Grain yield in 1983 was 50
percent lower than in 1982 probably because of insufficient
nitrogen fertilization in 1983 since oats rather than fallow
preceded the wheat crop. Other possible explanations are
differences in location of experimental plots in the field,
different weather throughout the crop season, and possible
differences in level of take-all root rot disease.
In field experiments, there were no consistent effects of
added chloride on water potential components that would support
growth chamber observations and confirm changes in turgor potential
as a mechanism of chloride influence on stripe rust development.