Relationship Between the Hypersensitive Reaction and Field Resistance to Tomato Race 1 of Xanthomonas campestris pv. vesicatoria . G. Cameron Somodi, University of Florida, GCREC, 5007 60th Street East, Bradenton 34203. J. B. Jones, and J. W. Scott, University of Florida, GCREC, 5007 60th Street East, Bradenton 34203; and J. F. Wang and R. E. Stall, University of Florida, Plant Pathology Department, Gainesville 32611. Plant Dis. 80:1151-1154. Accepted for publication 1 July 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1151.

In this study the relationship between hypersensitivity lo tomato race 1 (TI) of Xanthomonas campestris pv. vesicatoria and field resistance in an F2 population derived from crosses made between Hawaii 7998 (H7998) (resistant to TI) and Walter (susceptible to TI) was determined. Two techniques were used for quantifying the hypersensitive reaction: (i) measurement of speed of confluent necrosis following infiltration of a high concentration of the bacterium and ii) measurement of internal populations of X. campestris pv. vesicatoria after infiltration of a low concentration of the bacterium into leaflets. Bacterial populations were assayed by an indirect enzyme-linked immunosorbent assay (ELISA) procedure termed lysozyme ELISA (L-ELISA), which when used in combination with an amplification system allowed the detection of populations as low as 104 CFU. When the cultigens H7998 and Waller were infiltrated with 105 CFU/ml and population levels were determined over lime by direct plating and amplified L-ELISA, relationships between the two parameters were significant (r2 = 0.86 and 0.78) in two experiments. Comparisons were made between field susceptibility and the speed of confluent necrosis and internal populations of X. campestris pv. vesicatoria as measured by amplified L-ELISA in an F2 population (a cross between Walter and H7998). There was a significant correlation (0.52) between the speed of confluent necrosis and populations as delected by amplified L-ELISA. When amplified L-ELISA and confluent necrosis were compared with field susceptibility, significant correlation coefficients were 0.26 and 0.20, respectively, for the first field rating; and 0.52 and 0.34, respectively, for the second field disease rating. In a second experiment in which confluent necrosis was compared with field susceptibility, the correlation was 0.31. Confluent necrosis appears to provide some information regarding resistant genotypes; however, much of the field reaction could not be explained by hypersensitive reaction.