CHARACTERIZATION OF PESTALOTIOPSIS MICROSPORA, CAUSAL AGENT OF LEAF BLIGHT ON RUBBER (HEVEA BRASILIENSIS) IN CAMEROON

Aurelie IC Nyaka Ngobisa, PA Owona Ndongo, Oumar Doungous, Godswill Ntsomboh-Ntsefong, SW Njonje, EE Ehabe

Abstract

Rubber tree (Hevea brasiliensis) is the only commercial source of natural rubber in Cameroon. Its cultivation can be severely limited by diseases A leaf blight disease was observed on rubber trees affecting 80% of plants in smallholder's fields in South West Cameroon. Symptomatic leaf samples were collected from infected plants and pathogens isolated from them on agar media. Single spore isolates from resulting colonies were identified as Pestalotiopsis microspora based on cultural and morphological characterisation. Culture media, incubation temperature and pH affected mycelial growth of P. microspora. Its inoculation on detached leaflets also revealed the pathogenic capacity of this fungus; re-isolation based on its symptoms confirmed Koch’s postulates. Morphological identification was confirmed by molecular sequence analysis of the Internal Transcribed Spacer (ITS) region 1 and 2 including 5.8S rDNA (ITS-5.8S-ITS2).  The effects of some fungicides were tested in vitro on P. microspora mycelial growth. Banko plus fungicide (Chlorothalonil 550g/l + Carbendazim 100g/l), Penncoz (Mancozeb 800g/kg) and Metalm 72 WP (Cuprous oxide 600g/kg + Metalaxyl 120g/kg) tested at different concentrations (100%, 75%, 50% and 25%) revealed inhibitory activity against P. microspora in vitro. Among these fungicides, a marked efficiency of chlorothalonil 550g/l was observed, though the inhibition of mycelial growth was more effective with Cuprous oxide 600g/kg + Metalaxyl 120g/kg at rates: 100%, 75% and 50% only. This study revealed that P. microspora  is the causative agent of new leaf blight on rubber in the South West Region of Cameroon. This is the first report of leaf blight caused by P. microspora on rubber in Cameroon.

Keywords: Pestalotiopsis microspora, Internal transcribed spacer, pathogenicity, rubber, leaf  blight.

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