EPIDEMIOLOGY AND MULTISPECTRAL SENSING OF LEAF RUST OF WHEAT
Abstract
Leaf rust of wheat (caused by Puccinia recondita Rob. ex Desm.) is a destructive, widely distributed disease of wheat. When the flag leaf or the leaf immediately below it become infected with P. recondita before or during flowering, severe losses in grain quality and quantity can occur. Early detection of rust infections could give advance warning when and where an epidemic will likely occur, so that decisions about control measures can be made. Multispectral sensing is a possible method to obtain information on early detection of the disease. The reflectance of light from the adaxial side of flag leaves of wheat cultivars with different levels of resistance to P. recondita was measured. Infected leaves of three cultivars had significantly higher reflectance at 0.75 (mu)m and 1.45 (mu)m wavelengths, prior to visible symptoms of the disease, than uninfected leaves. The differences in reflectance were probably too small to be detected in wheat under field conditions. The increase in reflectance was accompanied by a decrease in either transmittance or absorptance of light. Leaf rust was detected best under field conditions in the visible (0.5 to 0.7 (mu)m) and miccle infrared wavelengths (1.3 to 2.3 (mu)m) wavelengths. Reflectance of light at 0.65 (mu)m and 2.00 (mu)m was positively correlated with the logit (ln Y/(1-Y) rust severity. The temporal and spatial progress of leaf rust could be determined by changes in reflectance of infected wheat over time and space. Spectroradiometric measurements of reflectance were more sensitive than photography to low leaf rust severities. Infection by P. recondita caused significant losses in the bio-mass and grain yield of selected wheat cultivars. In general, those cultivars that could produce the most dry matter, had the greatest losses from severe rust infection. The results indicated that multispectral sensing can be used by plant pathologists for early detection and monitoring of leaf rust of wheat. Previsual infections by P. recondita can be detected in the laboratory, but not in the field. Leaf rust significantly reduces biological and economic yield of wheat. High yielding cultivars must be protected against P. recondita infections because these cultivars are more prone to heavier losses caused by leaf rust than are low yielding cultivars.
Degree
Ph.D.
Subject Area
Plant pathology
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