Elecrophoretic variation in potato (Solanum tuberosum) clones susceptible and resistant to bacterial wilt (Pseudomonas solanacearum)
Okeyo, Philip Obara
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Electrophoretic technique was used to determine biochemical differences, between potato clones resistant and susceptible to bacterial wilt. This study was based on two isozyme systems – peroxidases and esterases. The relationship between peroxidase activity and resistance to P. solanacearum as well as the effect of inoculation on pattern and activity of peroxidases were also investigated. Four resistant and four susceptible potato clones to P. solanacearum to study the effect of inoculation on the isozyme patterns and peroxidase activity. The clones were inoculated with race 3 of the pathogen. According to the present study, there were differences in intensities and patterns of bands between resistant and susceptible potato clones. The intensities were higher in the resistant than susceptible cloens for all the stages studied. Where the difference was in band distribution, such bands stained mainly in resistant clones and were either missing in the susceptible clones or appeared only in a few such clones. These differences occurred only at some stages of development. Such stages were 4 days and 48 days old stages. These stages are therefore important for screening work. The peroxidase enzyme system can be used with a good level of accuracy for screening purposes. The cathodic band C3 at 4 days old and C2 at 48 days old can be used as ‘gerntic and biochemical markers’. Esterase isoxyme patterns and intensities gave no clear-cut difference between resistant and susceptible clones and can therefore not be used to screen for resistance. Comparisons between inoculated and non-inoculated resistant and susceptible plants indicated that infection induced changes in both amounts and kinds of peroxidases, but that these changes are more markedly so in susceptible than resistant clones and occurred even before the appearance of disease symptoms. This indicated that resistant and susceptible clones responded to infection in the same directions but with different magnifudes. Spectrophotometric assays of total peroxidase activities done alongside electrophoretic comparisions showed differences between resistant and susceptible clones. Healthy resistant clones had higher perosidase activities than healthy susceptible ones and there was direct proportionality between resistance and peroxidase activity. This indicates that total peroxidase activity can be used to screen for resistance. Infection led to increase in peroxidase activity in both resistant and susceptible clones. This increase was however, greater in susceptible clones than resistant clones, suggesting that changes in amounts and numbers of peroxidase isozymes induced by infection, led to increase in peroxidase activity. The electrophorectic technique and assay of peroxidase activity in this case as in other studies, can be used as an aid to the traditional screening techniques for resistance to bacterial wilt. This can be done quite an early stage of development.