Understanding the role of latency in banana bunchy top virus symptom expression (BA19002)
What’s it all about?
Beginning in early 2020, this investment is helping the Australian banana industry better understand how banana bunchy top virus spreads and reoccurs. Previous levy-funded work through the project Banana bunchy top virus control data (BA17001) revealed that any relaxation of current bunchy top control procedures is likely to result in a significant increase in the disease, and highlighted the importance of confining the disease to its current distribution. This earlier work also identified gaps in the knowledge of how bunchy top spreads and infects banana plantations, which this subsequent project is addressing in order to improve the Australian banana industry’s banana bunchy top control program.
Key activities for this investment include:
- Investigating possible latency (long delays in the expression of symptoms), which could explain recurrent infection on farms after long intervals
- Assessing and improving the efficacy of current eradication practices through a better understanding of the timing of disease spread from infected plants
- Investigating a possible role of alternative hosts of banana bunchy top virus.
Filling these knowledge gaps will assist industry in maximising the effectiveness and cost-efficiency of the bunchy top control program, which is implemented through inspection staff for the benefit of banana growers and biosecurity agencies. Learn more about the current levy-funded control program Banana bunchy top virus project, phase 4 – national surveillance and education (BA18000).
The winter experiment which investigated the effects of herbicide (glyphosate) and aphicide (imidacloprid) on BBTV-infected plants was completed. Results indicated that the plants injected with herbicide and aphicide take longer to die in winter compared with summer and greater chemical dose or uptake could be linked with a lack of transmissions.
Two field experiments in autumn investigating the timing of infectivity and symptom development were completed. BBTV was transmitted with similar efficiency from both symptomatic and presymptomatic leaves, with 16 of 24 transmissions successful for symptomatic leaves and 20 of 35 transmissions successful for presymptomatic leaves.
The team report that late summer and autumn were busy with seasonally-dependent experimental work.
It was confirmed that the current banana aphid (Pentalonia nigronervosa) colony was more efficient at transmitting BBTV between banana plants than the previous colony.
To investigate the mechanism behind instances of extended latency, 85 eyes (axillary meristems) on banana planting material bits were inoculated using virus-carrying banana aphids. The inoculated bits were potted up and are being observed for symptom development as they grow.
Some infected, originally asymptomatic leaves developed typical bunchy top symptoms over several weeks, while other leaves remained symptomless but with high virus levels. A total of 95 healthy banana plantlets were inoculated using banana aphids fed on pre-symptomatic leaves (and appropriate controls). These plants are being monitored for symptom development.
Additionally, a fenced field trial site with 24 healthy banana plants was established at the Pinjarra Hills Campus of The University of Queensland. Controlled field inoculations will be conducted in June 2021, and the plants closely monitored for virus level and symptom development.
In preparation for alternative host experiments, plants of six banana-related species have been established in the insecticide-free shadehouse at the Ecosciences Precinct. Establishment of cardamom aphid (P. caladii) colonies is anticipated in June 2021, with inoculation experiments planned for spring 2021.
After experiencing disruption in beginning this project due to COVID-19 restrictions, the project team began work in September 2020 and have reported progress in the following areas:
- A biosecurity plan has been developed, detailing how risks associated with project activities will be minimised, and the team are consulting with relevant authorities for plan approval.
- The team have identified a suitable fenced field trial site at the Pinjarra Hills Campus of the University of Queensland, with the necessary agreements being organised.
- An experiment to assess the efficiency of transmission of the current banana aphid colony has commenced, to understand how long BBTV-infected plants remain sources of inoculum following injection of treatment aphicide and herbicide.
This project is a strategic levy investment in the Hort Innovation Banana Fund