Full Length Research Paper

Detection of latent infection by Ralstonia solanacearum in potato (Solanum tuberosum) using stems instead of tubers

Mwangi, J. K.¹, Nyende, A. B.², Demo, P.³ and Matiru, V. N.¹

¹Jomo Kenyatta University of Agriculture and Technology Botany Department, P.O. Box 62000, Nairobi, Kenya.

²Jomo Kenyatta University of Agriculture and Technology Horticulture Department, P.O. Box 62000, Nairobi, Kenya.

³International Potato Center (CIP) P. O. Box 21571, Nairobi, Kenya.

*Corresponding author. E-mail: jkmwangi2005@yahoo.com. 

Accepted 7 April 2008

The potential of using stems for the detection of latent infection caused by Ralstonia solanacearum (Rs) was studied. Forty plants each were collected from four farms with bacterial wilt incidence below 4% in two growing seasons (season A and season B of 2005). The tubers of all the selected plants including 10 cm of the all lower stems were collected. Samples were taken to the laboratory for indexing against R. solanacearu (Rs) using ELISA techniques. The Rs status of each of the composite samples of all the tubers and of stems was determined and then correlation coefficients computed. There was a notable difference in the percentage number of samples per farm with particular categories of R. solanacearum status. When stems were compared to tubers for detection of Rs, an average r – value of 0.4 was obtained when r-values for the four different farms were averaged. The lowest r-value recorded was 0.2 while the highest was 0.5. When individual farms were considered it was only in one farm out of the four that r was not significant (p = 0.2). Overall the r-value was significant (p < 0.05). These results indicate that there is scope for adoption of stems as an alternative sample to tubers for indexing against R. solanacearum in potato tuber seed certification schemes more so in screening for presence of R. solanacearum in seed potato fields. However, although significant, the low r-value calls for more investigations to be done prior to final recommendation on use of stems from potato fields.

Key words: Solanum tuberosum, ELISA, Ralstonia solanacearum.