ARS | Publication request: PATHOGENICITY AND METALAXYL SENSITIVITY OF PHYTOPHTHORA INFESTANS ISOLATES OBTAINED FROM GARDEN HUCKLEBERRY, POTATO AND TOMATO IN CAMEROON

Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 17, 2004
Publication Date: February 28, 2005
Citation: Fontem, D.A., Olanya, O.M., Tsopmbeng, G.R., Owona, M.P. 2005. Pathogenicity and metalaxyl sensitivity of phytophthora infestans isolates obtained from garden huckleberry, potato and tomato in cameroon. Crop Protection Journal. Volume 24; pages 449-456

Interpretive Summary: Potato late blight is a significant disease in tropical highlands and temperate regions of the world. Metalaxyl and other chemical compounds are often used for disease control. It is therefore important to know the pathogenicity and metalaxyl sensitivity of fungal isolates in order to determine the efficacy of control and reduce costs. Pathogenicity and metalaxyl sensitivity of P. infestans isolates from distinct host species and various geographical regions were tested in lab and greenhouse experiments. Isolates from huckleberry, potato and tomato infected each of the three host-species although disease levels varied. Metalaxyl resistant isolates were detected in an average of 45 to 50% of the tested isolates indicating that the use of metalaxyl has not been effective for late blight control. The ability of isolates from huckleberry, potato and tomato to infect each of the three hosts mentioned above suggest that similar management strategies are needed for the three crops. The use of other late blight control options or chemicals will be important for effective disease control.

Technical Abstract: Late blight is a significant disease of solanaceous crops worldwide. Knowledge of pathogenicity of isolates and metalaxyl sensitivity is important for effective management of late blight. Solanaceous crops were surveyed in the highlands of west and northwest provinces of Cameroon during 2001 and 2002. A total of 233 isolates of P. infestans were collected, of which 53 were from huckleberry,104 from potato, and 76 were from tomato. Pathogenicity of the isolates on detached leaves of huckleberry, potato and tomato, was determined while metalaxyl sensitivity was assayed on leaf disks at 18 C. The results of pathogenicity tests showed that the potato, tomato and huckleberry isolates infected their primary hosts of origin as well as the other two hosts. The isolates of P. infestans from huckleberry were more aggressive on potato and tomato than on huckleberry. The potato isolates were most pathogenic on potato and least pathogenic on huckleberry. The tomato isolates were equally aggressive on potato and tomato, and significantly less pathogenic on huckleberry. Sensitivity of P. infestans isolates to metalaxyl varied with the geographic location where the isolates were collected and source of isolation (primary hosts). Among the 233 isolates tested for metalaxyl sensitivity, 49 % were metalaxyl-resistant (MR) in 2001 and 51% in 2002. The lowest percentage of MR isolates (34 %) were obtained on huckleberry. The ability of cross-infectivity of the isolates, and their increased metalaxyl resistance, suggests that integrated management options are essential for effective disease control.