Cinnamyl alcohol dehydrogenase (CAD) is known to be involved in the defense related responses in many host-pathogen systems. Induction of CAD enzyme in bacterial spot disease resistance in tomato (Solanum lycopersicum Mill.) was investigated in the present studies. Twenty different tomato cultivars were screened for resistance against bacterial spot disease incited by Xanthomonas axonopodis pv.vesicatoria under field conditions. Field screening was performed by artificially inoculating X. axonopodis pv. vesicatoria suspension to four-week-old tomato seedlings and observed for the typical symptoms of bacterial spot disease. They were categorized into highly resistant, resistant, susceptible and highly susceptible cultivars on the basis of disease incidence under field conditions. Tomato cultivars were subjected for estimating CAD - a defense-related enzyme. Temporal pattern of the enzyme was estimated using four cultivars representing each category of tomato cultivars by inoculating with six isolates of X. a. vesicatoria. Native PAGE analysis of CAD was carried out for the time course of enzyme activity and also by selecting three different tomato cultivars, after infecting with the pathogen. Based on the inducible amounts of the enzyme upon pathogen infection, the tomato cultivars were correlated with that of disease incidence under field conditions. A significant (P≤0.05) correlation was observed between the degree of host resistance and the enzyme level. In highly resistant tomato cultivar the enzymatic level was increased in comparison with highly susceptible tomato cultivars. Isoform analysis of CAD enzyme indicated a clear difference between the number of isoforms and also the intensity of each isoform after pathogen infection with the resistant and susceptible tomato cultivars. A possible regulation of CAD in imparting host resistance is discussed here.
Key words: Tomato, Solanum lycopersicum, bacterial spot, Xanthomonas axonopodis pv. vesicatoria, cinnamyl alcohol dehydrogenase, resistance, susceptibility.
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