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Infectivity Titration for Assessing Resistance to Leaf Scald Among Sugarcane Cultivars

June 2001 , Volume 85 , Number  6
Pages  592 - 596

S. A. Lopes , Unidade de Biotecnologia, Universidade de Ribeirão Preto, Ribeirão Preto SP 14096-380, Brasil ; K. E. Damann and J. W. Hoy , Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, Baton Rouge 70803 ; and M. P. Grisham , USDA-ARS, Sugarcane Research Unit, Houma, LA 70361

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Accepted for publication 2 January 2001.

Greenhouse experiments were conducted to determine potential of infectivity titration to evaluate resistance of sugarcane to leaf scald disease caused by Xanthomonas albilineans. In two experiments, single-bud cuttings were inoculated with suspensions containing 101, 105, or 108 CFU/ml of X. albilineans. The occurrence of symptoms was recorded every 15 days from 45 to 210 days after inoculation. At the final evaluation date, leaf vascular sap was plated onto selective medium to detect latent infections. ED50 (log10 of the bacterial concentration required to infect 50% of inoculated plants) was estimated for each cultivar based on probit analysis of cumulative infection frequency. Frequency of infected plants varied among inoculum doses and cultivars and resulted in ED50 values ranging from 3.0 to 12.3 and 3.1 to 9.8 in the first and second experiments, respectively. Good agreement between experiments was observed for ED50 values of individual cultivars. Differences in ED50 among cultivars agreed with field observations of natural disease incidence. Cultivar responses to leaf scald were compared based on the cumulative frequencies of death and recovery in symptomatic plants, and the frequencies of symptomatic plants observed at different evaluation dates for plants inoculated with 108 CFU/ml of X. albilineans. Good agreement between ED50 values and these responses was observed. Greenhouse inoculation tests using infectivity titration or just one inoculum concentration could provide an alternative to field tests for the assessment of sugarcane resistance to leaf scald.

Additional keyword: Saccharum

© 2001 The American Phytopathological Society