This study on the epidemiology of banana bunchy top disease (BBTD) was carried out in the context of small-scale farms in Burundi for an integrated management approach. Banana trials were established in farmers' fields comparing different plot locations, while spatial and seasonal occurrence of aphid vectors was evaluated at three different altitudes. In addition, serological tests were performed on banana leaf samples to confirm the presence and titre of the virus. The results showed that BBTD incidence varied among banana cultivars and locations. Nine months after plot establishment, BBTD incidence ranged from 21AE8% to 56AE4% in plots within affected fields, while a range of 0-12AE3% was reported in plots located between 5 and 30 m away from affected banana fields. Aphid numbers were highest in the dry season. These aphids were able to acquire and transmit the virus irrespective of altitude. A mean incubation period of 21 and 84 days was observed at low (780 m a.s.l.) and high (2090 m a.s.l.) altitude, respectively. Thus, a holistic approach, taking into account banana cultivar, plot location, disease-free planting material and regular field sanitation, should be promoted for long-term BBTD management.

The removal of infected individuals is a common practice in the management of plant disease outbreaks. It minimizes the contact between healthy individuals and inoculum sources by reducing the infectious window of contaminated individuals. This requires early detection and consistent removal at landscape scale. Roguing of mats with symptoms of banana bunchy top disease (BBTD) in Cavendish banana production systems has been tested in Australia, using trained personnel, but has never been tested in smallholder systems. We studied the effectiveness of long‐term consistent roguing in prolonging the productivity of banana orchards under smallholder farming systems in highland banana and plantain dominated production systems in Africa. We assessed the possibility of low‐risk seed sourcing from the managed plots. Roguing reduced BBTD incidence to 2% in managed farmer fields and to 10% in experimental field plots, while a nonmanaged field eventually collapsed in the same period. With roguing, new infections decreased monthly compared to an exponential increase in a nonmanaged field. The emergence of new infections in both managed and nonmanaged farms followed a seasonal cycle. BBTD managed plots were a source of low‐risk seed for replacing the rogued mats in the same fields, but perhaps not safe for use in nonendemic areas. We conclude that it is possible for smallholder farmers to recover and maintain banana productivity with rigorous roguing, which would entail early identification of symptoms and early removal of diseased mats. Studies are needed on the intensity of roguing under different disease and production conditions.

Disease-driven selection favours evasive, tolerant, and resistant cultivars, changing cultivar diversity significantly. Since its outbreak in Burundi in the late 1980s, Banana Bunchy Top Disease (BBTD) has now spread to 5 out of 18 provinces across the country, principally through informal seed exchanges. Control approaches have focused on using tissue culture clean planting material and eradicating infected mats. This study investigated the impact of BBTD and its control measures on seed selection practices and banana cultivars diversity in Burundi, by comparing two BBTD endemic sites and one where the disease wasn’t reported. Results have shown that in addition to agronomic traits used in all sites, some BBTD-typical symptoms were used in seed selection in the endemic areas. Own seed provisioning and formal seed sources networks were more likely to be observed in BBTD-endemic areas, compared with the non-endemic area. Disease control using certified tissue culture planting materials reduced the varietal diversity of local cultivars but enabled the introduction of new cultivars. A general reduction in the diversity of local cultivars grown by farmers in the BBTD endemic zones was observed, with about half of the diversity per farmer compared to the non-endemic zone. Farmer demand for varieties (local and improved) was not different between the two areas. Sustainable conservation of crop genetic diversity in the presence of disease invasions remains a problem to be addressed. Thus, implementing seed system-linked intervention with an explicit and monitored diversity conservation objective would increase the sustainability of agricultural production in such situations.

Seed system network analysis can reveal exchange connections between stakeholders and test scenarios such as those of seed systems shocks. We investigated the seed exchange network structure, disease surveillance risk, and gender contribution in Burundi, under two banana disease risk scenarios. Two sites where banana bunchy top disease (BBTD) is endemic in Cibitoke Province were compared with a site free of the disease in Gitega Province. All sites had formal seed interventions using community nurseries. A quantitative survey on seed sharing was done followed by a qualitative evaluation through focus group discussions. Banana seed sourcing options were fewer in the disease-free site, which also had higher cultivar diversity. Most farmers sourced seed informally within a three-kilometer radius. Seed sharing within and between villages was based on social and family linkages, especially for women. The interaction between the formal system and informal seed exchange was more active where new cultivars, or better seed quality was expected. The BBTD endemic region had lower seed quality assessment stringency. Farmers used both direct mother plant assessment and seed source reputation in seed evaluation. The formal banana seed systems are sources of new varieties, and trusted for clean seed but the informal system was still used as a main source of seed, especially local cultivars. Assessing disease surveillance scenarios shows women in a weaker position for healthy seed acquisition. Identifying the roles of individuals in seed systems can support decision processes for seed interventions in vegetatively propagated crops.