Fungi associated with banana black leaf streak disease and phytochemical analysis of essential oil of bamboo (Bambusa vulgaris L.) for management in Nigeria

Abstract

Banana (Musa spp.) are important fruit crops that are widely cultivated worldwide for food and economic returns. However, they are constrained by black leaf streak disease (BLSD) which reduces its attainable yield. This study investigated fungi associated with BLSD and management using essential oil (EO) of bamboo (Bamboo vulgaris L.). Symptomatic banana leaves were collected for isolation of infecting fungi and pathogenicity was determined using detached leaf assay (DLA). Fungal isolates were identified using cultural and morphological characteristics. Bamboo EO was extracted using hydrodistillation and constituent compounds identified by gas chromatography-mass spectrometry (GC-MS). The EO efficacy was evaluated at five concentrations: 0.2, 0.4, 0.6, 0.8 and 1.0 mg/mL. Inhibitory effect of the EO on mycelial growth and conidia germination of the test fungi was evaluated using standard procedures. Six fungal species, Alternaria solani, Colletotrichum musae, Fusarium oxysporum, Lasiodiplodia theobromae, Aspergillus flavus and Pseudocercospora fijiensis were isolated from infected samples; while only P. fijiensis was pathogenic in the DLA experiment The GC-MS results identified 22 phytochemicals with sesquiterpenes and monoterpenes accounting for 63.6% of the EO composition. Antifungal activity of the EO differed significantly (p<0.05) at higher concentrations (>0.2 mg/mL) with 80.6-91.3% mycelial inhibition. Inhibitory effect on conidia germination varied between 81.81 and 92.46%. This study confirmed P. fijiensis as the causal organism of BLSD. GC-MS analysis revealed phytol, hexadecanoic acid, cedrol, citronell and farnasol as the major antifungal constituents of bamboo EO effective against BLSD. Based on the potential results obtained in this study, bamboo EO could be a candidate for further testing in the formulation and development as biofungicide in the integrated management of BLSD under field conditions.