Molecular and socio-ecological characterization, and mapping of bunchy top disease of abaca (Musa textilis Nee) in Catanduanes, Philippines

Bunchy top is the most destructive virus disease affecting abaca production in Catanduanes [Philippines], the top abaca producer in the Philippines. This study aimed to identify the ABTD hot spot areas in the province and determine the factors associated with high disease incidence. Disease mapping showed high disease incidence (DI 50%) in the West District (Pandan, Caramoran, San Andres) with DI = 80-88%, and the East District (Baras, Viga) with DI= 76-96%, and thus considered as ABTD hot spots. Bato in the East District has a relatively low DI of 46%. Molecular characterization of the virus causing ABTD has detected the Banana bunchy top virus (BBTV) as the prevalent Babuvirus species in all the surveyed areas. Abaca bunchy top virus (ABTV) was detected in Caramoran and Pandan, and it occurred in mixed infection with BBTV in two of the 90 samples tested. Infected plants are symptomatic, showing bunchy top symptoms, while some are asymptomatic. BLASTn analysis revealed that Catanduanes BBTV isolates were highly homologous (96.59-99.47%) with Philippine BBTV isolates for DNA-R and Indonesian BBTV isolates (99.01-99.87%) for DNA- S. Phylogenetic analysis showed that Catanduanes BBTV isolates from Viga, Caramoran, and Bato grouped with BBTV Indian isolate of the South Pacific group for DNA-R, while Baras and Pandan clustered with Asian group, Philippine and Indonesian isolates, respectively, and San Andres isolate branched separately. On the other hand, Bato, Caramoran, Pandan, and Baras isolates were strongly related (86- 99%) and branched with BBTV Taiwan isolate of the Asian group for DNA-S. Catanduanes ABTV isolates for both DNA components have the closest sequence identity (98.53-99.11%) with Albay ABTV isolate Q1108 (Accession no EF546807) and are consistently grouped together in the phylogenetic tree. Socio-ecological characterization revealed that farmers' lack of training drives the Dl increase based on the principal component analysis, which is consistent with inadequate knowledge of the biology of the disease and cultural and disease management practices.