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Occurrence of Powdery Mildew, Caused by Erysiphe cichoracearum, on Endive and Radicchio in California. S. T. Koike, University of California Cooperative Extension, Salinas 93901. G. S. Saenz, Department of Plant Biology, University of California, Berkeley 94720. Plant Dis. 80:1080. Accepted for publication 27 June 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1080C.

In January 1996, outbreaks of powdery mildew occurred on commercial plantings of endive (Cichorium endivia L.) and radicchio (Cichorium intybus L.) in coastal counties in California. On both hosts the white ec-tophytic mycelial and conidial growth was amphigenous on leaves, caused slight twisting of foliage, and resulted in quality loss of the harvested product. Mycelia ranged from effused and thin (endive) to moderately thick (radicchio) and grew in patches or covered the entire surface of the leaves. Morphological characters were similar for both endive and radicchio isolates. Appressoria were nipple-shaped and conidiophores were straight. Foot cells were cylindrical and straight, sometimes slightly attenuated at the basal septum, and sometimes had a curved basal part. Foot cells measured 9.0 to 11.5 x 48.0 to 67.0 µm, and were followed by one to three shorter cells. Conidia were produced in chains, cylindrical to slightly doliform in shape, and measured 11.5 to 16.0 x 28.0 to 39.0 µm. The conidial length-to-width ratio was 2.2. No fibrosin bodies were observed in the conidia, and conidia germinated at the ends. Cleistothecia were not present. The fungus was identified as Erysiphe cichoracearum DC. (1,2). Pathogenicity was demonstrated by collecting and suspending diseased leaves over test plants in an enclosed settling chamber for 24 h, incubating the plants in a moist chamber for 48 h, and then maintaining plants in a greenhouse. After 12 to 14 days, field isolates of E. cichoracearum from endive and radicchio colonized both endive (cvs. Ruffec and Tres Fine Maraicchere) and radicchio (cv. Rossana Rogers). Because of the extensive lettuce (Lactuca saliva L.) crop present in the coastal region, one radicchio isolate was inoculated onto lettuce plants (cvs. Red Eye Cos and Salinas), using the same inoculation method, to see if the isolate would be cross-infective. However, after four attempts, the radicchio isolate failed to infect lettuce. Although powdery mildew has been previously observed in California on endive and radicchio, this is the first report characterizing this pathogen on these crops in the state.

References: (1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980. (2) U. Braun Nova Hed-wigia89:I, 1987.