Severity and changed symptoms of vascular streak dieback caused by Ceratobasidium theobromae in several cocoa (Theobroma cacao) clones in Sulawesi, Indonesia
Abstrak
Vascular streak dieback (VSD), caused by the basidiomycete Ceratobasidium theobromae (syn. Oncobasidium theobromae),
is a serious disease of cocoa in Southeast Asia and Melanesia. In the last decade, in many cocoa growing areas in Malaysia
and Indonesia, the impact of this disease has increased considerably. In the same period, symptoms of the disease have
become dominated by necrotic lesions on infected leaves, in contrast to chlorotic symptoms, characterised by yellowing of
the leaf with a typical pattern of remnant green islands, which were formerly ubiquitous. Amplification of basidiomycete ITS
and LSU sequences in DNA extracts of VSD-infected plant tissues collected from Sulawesi, Indonesia, and Kerala, India,
showing chlorotic symptoms matched previous GenBank accessions (99%). However, neither isolation of an axenic culture
nor direct PCR amplification from necrotic leaf tissues was successful. Nevertheless, basidiocarps collected from branches
with either necrotic or chlorotic VSD symptom in Sulawesi produced basidiospores and basidia with similar dimensions
to those previously documented for C. theobromae suggesting that the same pathogen is associated with both symptoms.
Incidence of necrotic symptoms was correlated with disease severity in branches. VSD monitored in a range of resistant and
susceptible cocoa clones showed rankings for disease incidence and severity that were consistent for three seasons, confirming
that disease resistance was maintained despite the prevalence of necrotic leaf symptoms. A lower proportion of symptomatic
leaves on branches 5 months after early symptoms were observed in the resistant Malaysian clone PBC123 (32.6%) compared
to the more susceptible M04 (46.9%). Clones common to trials in three different districts in Sulawesi showed a consistently
high level of resistance to VSD, including PBC123 and two local selections, M05 and GeniJ.
is a serious disease of cocoa in Southeast Asia and Melanesia. In the last decade, in many cocoa growing areas in Malaysia
and Indonesia, the impact of this disease has increased considerably. In the same period, symptoms of the disease have
become dominated by necrotic lesions on infected leaves, in contrast to chlorotic symptoms, characterised by yellowing of
the leaf with a typical pattern of remnant green islands, which were formerly ubiquitous. Amplification of basidiomycete ITS
and LSU sequences in DNA extracts of VSD-infected plant tissues collected from Sulawesi, Indonesia, and Kerala, India,
showing chlorotic symptoms matched previous GenBank accessions (99%). However, neither isolation of an axenic culture
nor direct PCR amplification from necrotic leaf tissues was successful. Nevertheless, basidiocarps collected from branches
with either necrotic or chlorotic VSD symptom in Sulawesi produced basidiospores and basidia with similar dimensions
to those previously documented for C. theobromae suggesting that the same pathogen is associated with both symptoms.
Incidence of necrotic symptoms was correlated with disease severity in branches. VSD monitored in a range of resistant and
susceptible cocoa clones showed rankings for disease incidence and severity that were consistent for three seasons, confirming
that disease resistance was maintained despite the prevalence of necrotic leaf symptoms. A lower proportion of symptomatic
leaves on branches 5 months after early symptoms were observed in the resistant Malaysian clone PBC123 (32.6%) compared
to the more susceptible M04 (46.9%). Clones common to trials in three different districts in Sulawesi showed a consistently
high level of resistance to VSD, including PBC123 and two local selections, M05 and GeniJ.
Kata Kunci
Theobroma cacao · Ceratobasidium theobromae · Disease severity · Local genotypes · Resistance · Symptoms
Dokumen
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