Banana bunchy top disease (BBTD), is a viral disease of banana, rapidly spreading in Africa. It affects production and seed systems, threatening the genetic diversity of banana and plantain. Early symptomatic detection and roguing are an effective way of managing this disease. However seasonal and cultivar variation in disease expression has been observed. We therefore sought to assess the relationship between symptom expression and infectivity of diseased plants to support refining roguing protocols. Plantlets from four varieties (FHIA 25; Aloga; Ebenga and Sotoumon) were inoculated using infected aphids and monitored for nineteen weeks. The plants were also used as inoculum sources to infect clean banana aphids that were transferred to healthy plants of a single variety every two weeks. An appearance of symptom in these test plants was recorded and infection tested by PCR. The hybrid FHIA 25 showed typical BBTD symptoms three weeks after inoculation, while the plantains Aloga and Ebenga showed the morse code symptom, on the leaf lamina but not on the petiole, four weeks after inoculation. The banana local variety, Sotoumon, only showed the first symptoms fifteen weeks later, and entirely missed the earlier typical symptoms. For all varieties, BBTV was only detectable and aphid transferable from plants showing the first symptoms. Overall, FHIA 25 was the most sensitive while the local banana Sotoumon the least sensitive to BBTV inoculation. The expression and spread of BBTD could be tested in the field. We discuss the implication of these observations on seed systems production losses.
Banana bunchy top disease (BBTD) is an invasive viral disease spreading in Africa. It is transmitted by banana aphids and infected planting material, causing production losses. Clean seeds and timely eradication of diseased plants are effective tools in BBTD management. These depend on timely disease detection. We assessed the relationship between symptom expression and infectivity of the virus in four cultivars of banana. Plantlets from four cultivars, ‘FHIA 25’; ‘Aloga’; ‘Ebenga’ and ‘Sotoumon’, were exposed to viruliferous aphids and monitored for symptom expression. They were also tested as sources for virus transmission fortnightly by allowing non-viruliferous aphids acquisition access prior to transfer to healthy test plants. The time required to show symptoms and the symptom expression were compared, and infection tested by PCR. Disease expression varied from four weeks in ‘FHIA 25’ to fifteen in ‘Sotoumon’. Only the symptomatic leaves tested positive and could act as infection sources. Overall, ‘FHIA 25’ was the most susceptible cultivar, while ‘Sotoumon’ was the least susceptible and most rapidly expressive of BBTD, yet there was no difference in the leaf emergence rate between the cultivars. These results present important aspects of BBTD control and the safety of planting materials that should be tested in the field.
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