Full Length Research Paper
Witches’ broom disease (WBD), caused by the fungus Moniliophthora perniciosa, is one of the main diseases in cocoa (Theobroma cacao) and has caused severe economic losses. Integrated disease management has been the focus for its control and therefore, the identification of new inducers of plant resistance is desirable. Thus, the goal of this work was to evaluate two potential inducers of resistance against WBD. A phosphorylated mannan oligosaccharide-based product (PMO) and acibenzolar S-methyl (ASM) were tested on M. perniciosa inoculated seedlings and in field experiments and showed a reduction on the incidence of WBD. The expression of two defense-related expressed sequence tags (ESTs) in cocoa, coding for peroxidase (Pox) and chitinase (Chi), were accessed by qPCR. Both products induced the expression of the Pox defense-related EST. In general, ASM induced the expression of chitinase (Chi) and peroxidase (Pox) in earlier time-points than PMO. However, PMO provided long-lasting and higher levels of expression. Chi expression was triggered in the time-points succeeding the spraying but was very low. On the other hand, peaks of Pox transcripts were detected in later time-points for both inducers. ASM and PMO modes of action might be explained, at least partially, by the overexpression of defense-related ESTs.
Key words: Cocoa, witches’ broom disease, disease control, peroxidase, chitinase, induced resistance, elicitors, quantitative reverse transcriptase PCR (qRT-PCR).
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