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Ecology and Epidemiology

Comparison of Aerial Concentration, Deposition, and Infectiousness of Conidia of Pyricularia grisea by Spore-Sampling Techniques. H. O. Pinnschmidt, Tropeninstitut, Justus Liebig-Universitaet, Bismarckstrasse 16, W-6300 Giessen, Germany, Present address: Division of Plant Pathology, International Rice Research Institute, P.O. Box 933, Manila, Philippines; H. W. Klein-Gebbinck(2), J. M. Bonman(3), and J. Kranz(4). (2)(3)Division of Plant Pathology, International Rice Research Institute, P.O. Box 933, Manila, Philippines; (3)Present address: Agricultural Products Department, E. I. Du Pont De Nemours & Co., Stine-Haskell Research Center. P.O. Box 30, Newark, DE 19714; (4)Tropeninstitut, Justus Liebig-Universitaet, Bismarckstrasse 16, W-6300 Giessen, Germany. Phytopathology 83:1182-1189. Accepted for publication 15 April 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1182.

In three field trials on the epidemiology of blast disease in upland rice, different methods of sampling spores of Pyricularia grisea were compared to study aerial concentration, deposition, survival, and infectiousness of conidia of the pathogen. The methods included a Burkard spore trap, glass slides and rods, several trap-plant treatments, and leaf prints from trap plants. The results were mostly highly intercorrelated and revealed a unimodal pattern of disease progression, with peaks before or at the middle of the cropping seasons. The number of conidia per square centimeter deposited on leaf surfaces as measured by leaf prints made up one-fourth of the number caught with glass slides. The amount of deposited and potentially infective spores on leaves of trap plants of upland rice cultivar C22 incubated in a dew chamber after exposure in the field was 0.050.11, 0.42, and 0.44 of the spore density as measured by glass slides, leaf prints, and trap plants of the highly susceptible upland rice cultivar Co 39, respectively. The number of actually infectious spores on trap plants incubated in the greenhouse after exposure was 0.310.39 of total lesions observed on dew chamber-incubated trap plants. Few spores were observed on glass rods, indicating that sedimentation rather than impaction was the major factor for spore deposition. Nonlinear regression analysis revealed that the spore-catch results of the Burkard spore trap, glass slides, and leaf prints explained 0.580.65, 0.720.77, and 0.66 of the variability of the number of lesions on trap plants incubated in dew chambers, respectively. Similarly, the spore-catch results of the Burkard spore trap and the total lesions on dew chamber-incubated trap plants explained 0.420.76 and 0.650.79 of the variability of susceptible-type lesions on trap plants incubated in greenhouse conditions, respectively. The number of potentially infective spores tended to increase toward an asymptote at high inoculum concentrations. Depending on the method, the spore-catch results were significantly affected by several weather variables. Estimation of deposited and infectious conidia and of inoculum potential by means of comparison of spore-sampling methods can be improved considerably by adjusting for the effects of these variables.

Additional keywords: rice blast, spore catch, weather effects.