Characteristics of selected hybrids of abaca (Musa textilis Nee) with resistance to bunchy top

Two abaca hybrids namely, Hybrid 2 and Hybrid 7, which were delivered from a cross between the resistant wild banana (Musa balbisiana) var. Pacol and the susceptible abaca var. Abuab possessing the high fiber quality trait, have been previously selected with promising resistance to bunchy top disease. In this study, the responses of these hybrids to virus inoculation by the aphid (Pentalonianigronervosa) under screenhouse condition and to natural infection in the field were characterized. Under screenhouse condition, Hybrid 7 did not show the bunchy top disease symptoms of dark green streaks on veins and midribs, marginal leaf chlorosis, narrow and stiff leaves or upright and crowding of leaves at the apex of the plant, while Hybrid 2 expressed the disease in only 1 of 15 (7%) plants tested over the 6-mo observation period. The virus was not detectable by enzyme-linked immunosorbent assay (ELISA) using polyclonal antibody against Banana bunchy top virus (BBTV) in all asymptomatic Hybrid 2, Hybrid 7 and 'Pacol'. Plants were confirmed negative for BBTV when tested by polymerase chain reaction (PCR) using the primer pair BBT1 and BBT2 that Amplifies the 349-bp fragment of viral DNA-R component. The response was observed under condition of high disease pressure wherein the susceptible Inosa and 'Abuab' developed severe disease characterized by high disease incidence, high amount of disease (measured by the Area Under Disease Progress Curve), and severe symptoms. The results observed under screenhouse condition were consistent with the response to natural infection involving plants that had been grown for 5 yr (2012-2017) in the field located at the Caraga State University, Ampayon, Butuan City, Philippines. Disease index was 4% for Hybrid 2 and 0% for Hybrid 7, indicating a resistant response to bunchy top. Knowledge on the resistance characteristics would be useful information for proper filed development of these hybrids, and for breeding varieties with resistance to bunchy top.