In vivo use of extracts from Ocimum gratissimum and Cymbopogon citratus against Phytophthora palmivora causing blackpod disease of cocoa

Abstract

Crude steam di!>tillate from Ocimum graflssimum sprayed onto infectum courts on detached cocoa pods moments after moculat1on with Phvtophthora palmu,ora completely mhibitcd the pathogen and blackpod lesion development on 75% of the infection courts. Disease suppression obt<uned w1th the extract was com­ parable to that obtained with a 2°.-f Kocide 101 suspen<.ion In the field. the 0. gratis.mnum extract also suppressed ksJOn development although to a sig­ nificantly lower (P = 0.05) extent m companson \\lth Kocide 101. Blackpod lesion expansion rates of 1.80. 3.56. 2 71 and 0.7X cm/dav. respectivcl. wen associated w1th pods treated 1n the field w1th C. cttratus extract, tap water. 0 gratissimum extract and 2% Kocide 101. The extract from Cymbopogon caratu.\ was also ineffective on detached pods. Sporangia of P. palmivora from sporu lating blackpod lesions on both detached and non-detached pods lost thetr infectivity within 1 h of treatment with the 0 gratissimum extract Th1s effect was superior to that obtained with Kocide 101. Fungitoxicity of the extract on pods, however, was lost withtn 1 h of application. Thus. desp1te its 111 l'LPO effectiveness as an eradicant. the 0. grati.mmum extract. in its present form. has limtted ut1lity as a protectant fung1c1de.