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S02-16
Ecological aspects of understanding cassava witches’ broom
and its vector candidates in Southeast Asia.
Nami Minato1*, Chi Thi Tran2, Juan Manuel Pardo3, Ignazio Graziosi1, Vi Xuan Le2, Hoat
Xuan Trinh2, Quan Van Mai2, Dung Van Ha2, Phyllis G. Weintraub4, Elizabeth Alvarez3, Kris
A.G. Wyckhuys1
1) International Center for Tropical Agriculture (CIAT), HaNoi, Vietnam;
2) Plant Protection Research Institute (PPRI), HaNoi, Vietnam;
3) International Center for Tropical Agriculture (CIAT), Cali, Colombia;
4) Gilat Research Center, Agricultural Research Organization (ARO), Israel.
* [email protected], Registrant ID# 4507
In Southeast (SE) Asia, cassava (Manihot esculenta Crantz) is grown by millions of
smallholder farmers as a food, starch or bio-energy crop. Over the past decade, several nonnative pests and diseases have made their arrival in SE Asia, and are impacting cassava
productivity to substantial extent. Cassava witches broom (CWB) is a systemic plant disease,
thought to be caused by insect-borne bacteria, Candidatus Phytoplasma. The disease causes
dwarfism, leaf proliferation, shortened internodes and, at times, smaller roots, bringing
about yield losses of 32±22%. In a 5-country survey of cassava fields during the 2014 dry
season, CWB was reported from 64% of local cassava plots, at incidence levels of 32±26%.
We employed a step-wise approach to identify vector candidates for CWB. First, we
employed PCR-based approaches to detect phytoplasma from whole insect bodies. Next, we
allowed field-caught insects to feed on a buffer solution, thus assessing their phytoplasma
vectoring ability. Laboratory-based membrane-feeding assays showed that four cicadellid
species and two delphacids readily transmit phytoplasma to buffer solutions. Hence, three
species of Cicadellidae (Nephotettix virescens, Balclutha incisa, and Graminella sonora) and
two Delphacidae (Stenocranus pacificus and Nilaparvata lugens) do retain and transmit
phytoplasma. Two of the above species feed exclusively on Poaceae, while three others are
generalist herbivores. Third, we compared leaf- and planthopper species composition and
abundance in CWB-infected fields, versus asymptomatic fields. Important differences were
found in the abundance of various hopper species, and CWB-affected fields counted with
lower diversity of hoppers. In CWB-affected fields, abundance of G. sonora was significantly
higher than in asymptomatic plots. In conclusion, molecular trials and in-field population
abundance studies generate initial evidence of insect vector candidates of CWB
phytoplasma in SE Asian cassava fields.
Our work highlights the importance of CWB as a limiting plant health threat, provides
critical information on CWB ecology, and contributes substantially to the development of
effective management tactics for this disease in SE Asian cassava crops.