Abstract
Colletotrichum spp. are causal agents of anthracnose in many plant species. Biological control of Colletotrichum spp. utilizing bacterial isolates and fungi has been reported. However, chitinolytic bacterial isolate utilization to control anthracnose of cocoa leaf has not seemingly been studied yet. In this study, we used chitinolytic bacterial isolates to reduce anthracnose severity and incidence caused by Colletotrichum gloeosporioides. Identification of the chitinolytic isolates was conducted for their morphological and biochemical traits, and the sequencing of 16S rRNA was to know their related species. Assay of antagonistic bacterial chitinolytic to C. gloeosporioides was conducted in minimum salt medium agar with 2% colloidal chitin as sole carbon source. To examine ability of the chitinolytic isolates in reducing anthracnose severity and incidence, cocoa leaves were treated with the isolates prior infestation of the conidia. Identification of 16S rRNA showed that KR05, LK08, BK13, BK15 and BK17 isolates were Enterobacter sp., Enterobacter cloacae, Bacillus sp., Enterobacter sp., and Bacillus sp., respectively. All chitinolytic isolates inhibited growth of C. gloeosporioides in vitro to some extent. Microscopic studies showed morphological abnormalities of C. gloeosporioides hyphae that is, broken, lytic, rolled, twisted, curled and abnormal branching of hyphae as a result of antagonistic mechanism caused by the chitinolytic isolates. All chitinolytic isolates were able to reduce anthracnose severity and incidence on cocoa leaves from 0.8 to 3.2% and 4 to 12%, respectively. Key words: Anthracnose, biological control, chitinolytic bacteria, C. gloeosporioides, cocoa.
Highlights
The genus Colletotrichum represents an economically important group of fungal plant pathogens and is recorded from approximately 2.200 plant host species (Farr and Rossman, 2009)
Identification of chitinolytic bacteria showed that KR05, LK08 and BK15 and except that of colony color BK13 and
Various microbial antagonists have been investigated as potential antifungal biocontrol agents of plant diseases
Summary
The genus Colletotrichum represents an economically important group of fungal plant pathogens and is recorded from approximately 2.200 plant host species (Farr and Rossman, 2009). Leaf spots in plantation plant such as cacao (Rojas et al., 2010; Yee and Sariah, 1993) and para rubber tree (Adekunle and Ogbebor, 2009), and attacks other economic plants/fruits such as yellow passion fruit (Anaruma et al, 2010), mango (Nelson, 2008), avocado, and almond (Freeman et al, 1996) Control of this disease has been largely dependent on chemical fungicides inhibiting vegetative pathogen growth. Biological control using antagonistic microorganisms has been successfully demonstrated in a number of plant species Antagonistic microorganisms, by their interactions with various plant pathogens, play a major role in microbial equilibrium and serve as powerful agents for the biological control of diseases (Ozbay and Newman, 2004; Alabouvette et al., 2006). The use of naturally occurring bacteria (Sangeetha et al, 2010; Akinbode and Ikotun, 2008; Mahadtanapuk et al, 2007) and antagonistic fungi (Adekunle and Ogbebor, 2009; Akinbode and Ikotun, 2008; Shovan et al, 2008) for biocontrol of Colletotrichum spp. has been proposed
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