Graduate Thesis Or Dissertation


Chloride fertilizer effects on stripe rust development in winter wheat Public Deposited

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  • 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.
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