Evaluation of suppressive potential of selected plant species against Phytophthora infestans in vitro

Globally, Phytophthora infestans causes annual potato losses estimated at over $6 billion with fungicides alone accounting for over $1 billion. In Kenya, potato yield loss estimates reach 119,500 tons annually. Several fungicides recommended for late blight have raised health concerns and have led to emergence of more aggressive strains of the pathogen. These concerns have led to the need for safer alternative which can best be offered by bio-pesticides. Bio-pesticides are classified into biochemical, microbial and plant derivatives derived from natural living organisms. The aim of this study was to source, identify and screen for the bioactive potential of selected plant species against Phytophthora infestans in vitro. Phytophthora infestans was isolated from infected potato leaves and bioactive plants were sourced from the Kenyatta University surroundings, identified and phytochemical compounds extracted through maceration. Bioassays involved food poisoning technique using the aqueous plant extracts. Data were subjected to analysis of variance using SAS software version 9.1. Tukey’s Studentized Range (HSD) at P<0.05 was used for mean separations where treatment effects were significant. All the plant extracts showed significant effect (P<0.05) on reducing mycelial growth of P. infestans. Azadirachta indica showed the highest overall percentage mycelia growth suppression with a mean of 54.3% at (P d” 0.05) at ten days after inoculation (DAI) which significantly differed from Callistermon citrinus which had the least overall suppressive effect with a mean of 26.75% at (P< 0.05). These findings show that potential for managing late blight exist in local plants.