Response of banana germplasms to banana bunchy top virus

Banana bunchy top virus (BBTV) is one of the important viruses causing disease in bananas and its infection has the potential to cause yield loss. This study was conducted to evaluate the response of several commercial cultivars (Cavendish, Bebek, Goroho, Tanduk, and Barangan Merah) and wild accessions (Klutuk NTT, Halabanensis, SPn 001, LNT 001, and Microcarpa) of banana to BBTV infection. Transmission of BBTV was carried out through banana aphid Pentalonia nigronervosa, using 20 adult aphids per plant with an acquisition feeding period of 24 hours on BBTV-infected plants and an inoculation feeding period on healthy test plants for 48 hours. Observation on plant growth and disease intensity was conducted for 8 weeks after inoculation. At the end of the observation period, only 5 cultivars, i.e. Cavendish, Bebek, Goroho, Barangan Merah, and Halabanensis showed typical symptoms of BBTV with disease incidence reached 80%, 60%, 20%, 20%, and 20% respectively. Significant inhibition of plant height and leaves width occurred in Cavendish, Bebek, and Goroho i.e. 44.60%, 36.31%; 12.62%, 41.08%; and 25%, 10.13%, respectively. This paper discusses the need for banana germplasm exploration to find sources of resistance to BBTV.

Study of Bunchy Top of Banana Virus (BBTV) and its Control by Integrated Disease Management (IDM)

India is the top country by Banana production in the world as of 2019, bananas production in India was 30.5 million tonnes that accounts for 26.02% of the world's bananas production. The top 5 countries (others are China, Indonesia, Brazil, and Ecuador) account for 53.94% of it. The world's total bananas production was estimated at 117 million tonnes in 2019.In India, states like Andhra Pradesh, Gujarat, Tamil Nadu, Maharashtra, Kerala, Uttar Pradesh, Bihar and Madhya Pradesh contribute more than 70 per cent of the country's banana production. Banana and plantain (Musa spp.), produced in 10.3 million ha in the tropics, are among the world's top 10 food crops. They are vegetative propagated using suckers or tissue culture plants and grown almost as perennial plantations. They are vulnerable to pests and pathogens, especially viruses which causes reduction in yield and are also hinders to the international exchange of germplasm. The most economically important viruses of banana and plantain are Banana bunchy top virus (BBTV), a complex of banana streak viruses (BSVs) and Banana bract mosaic virus (BBrMV). BBTV is known to cause the most serious economic losses contributing to yield reduction of up to 100% and responsible for a dramatic reduction in cropping area. The BSVs exist as episomal and endogenous forms are known to be worldwide in distribution. In India and the Philippines, BBrMV is known to be economically important.

First report of banana bunchy top virus in banana and plantain (Musa spp.) in Tanzania

Banana (including plantain; Musa spp.) is an important vegetatively propagated food staple grown as a semi-perennial crop in fields and backyard gardens in Tanzania. Banana bunchy top disease (BBTD), caused by the banana bunchy top virus (BBTV, genus Babuvirus), is the most economically important viral disease of banana, infection of which results in severe stunting and reduction in fruit production by 90-100% within two seasons. The virus is spread by the banana aphid, Pentalonia nigronervosa, and through vegetative propagation of infected sources. BBTV is an introduced virus first reported in sub-Saharan Africa (SSA) in the 1960s in the Democratic Republic of Congo. Since then, BBTV spread was confirmed in 15 countries in Central, Southern, and Western African regions but was not detected in any previous surveys in the East African sub-region. During banana pests and disease surveys conducted in December 2020 – January 2021 in Buhigwe District in the Kigoma Region of Tanzania revealed banana plants with typical BBTV symptoms (severe stunting, leaves with shortened petioles, chlorotic streaks, and yellow leaf margins) in several banana fields in Muhinda (lon. 29.78662, lat. -4.53672) and Mwayaya (lon. 29.8218, lat. -4.49203) villages. Most of the affected plantations were 5 to 15 years old. Leaf samples (N=21) from symptomatic (N=6) and asymptomatic (N=15) banana plants were collected and used for total DNA extraction and BBTV detection by polymerase chain reaction (PCR) using the primer pair BBTV-1 and BBTV-2 to amplify ~240 bp sequence of DNA-R encoding for core master replication initiator protein gene. All samples from symptomatic plants tested positive and asymptomatic plants were negative. To further confirm the virus identity, four samples, each from symptomatic (PCR positive) and asymptomatic (PCR negative) plants from Muhinda and Mwayaya villages, were tested by Triple Antibody Sandwich-Enzyme-linked Immunosorbent Assay (TAS-ELISA) using BBTV ELISA reagent set (Cat. # SRA24700-1000, Agdia, France) following the manufacturer's protocol. Samples from symptomatic plants reacted positively in TAS-ELISA, and asymptomatic plants were negative. The 240-bp PCR product of two isolates was purified, and both strands were sequenced. A BLAST search of the nucleotide sequences (NCBI GenBank Acc.# MW711671 and MW711672) revealed 99% identity with DNA-R sequences of several other BBTV isolates from Africa (Acc. No# JF755994). Further analysis of the 240-bp nucleotide sequences with Maximum-likelihood phylogenetic analysis using MEGA-X software has grouped the two BBTV sequence isolates with the SSA sub-clade of the South-Pacific group. To our knowledge, this is the first report of BBTV infecting bananas in Tanzania, and East Africa endowed with rich banana diversity and popular East African Highland banana clone. BBTV presents a new threat to banana production in this sub-region due to the high risk of further spread through vegetative propagation, traditional planting material exchange practices, and the ubiquitous banana aphid vector. This study warrants delimitation surveys to assess the extent of spread, with simultaneous efforts to raise awareness about BBTD recognition and control measures among banana growers, including eradicating infected mats and replanting with healthy planting material to recover banana production.

Effect of Banana Bunchy Top Virus on the Heat Shock Protein Genes of Pentalonia nigronervosa during Temperature Susceptibility and Its Effect on Virus Transmission

Acquisition of plant viruses is known to exert various effects on vectors’ developmental biology. Pentalonia nigronervosa is the only known vector of banana bunchy top virus (BBTV), which is an economically detrimental virus infecting banana cultivars all over the world. In the present study, the developmental biology of viruliferous (Vr) and non-viruliferous (NVr) aphids was compared, with a marked reduction noted in the lifespan of aphids upon acquisition of BBTV. Among all the environmental parameters temperature is an important determinant of an insect’s abundance and geographical distribution. Temperature susceptibility of P. nigronervosa was scrutinized by comparing the mortality percentage and differential expression pattern of three heat shock proteins (Hsps; Hsp40, Hsp70, and Hsp90) at the mRNA level between NVr and Vr aphids. After exposure to different temperature stress (5 °C, 15 °C, 38 °C and 25 °C as control) highest mortality of Vr aphids were recorded at 5 °C. Analysis of expression levels of Hsp genes using qPCR showed that both cold and heat shock treatment stimulated higher expression of the three Hsps at various rates in Vr than NVr aphids.. Finally, the effect of temperature stress on the BBTV titer level and their transmission by P.nigronervosa was determined by absolute quantification. The transmission efficiency along with the virus titer was found to be the lowest at 15 °C compared to 38 °C. Overall, our results provide a novel insight into the intricate interaction between aphid fitness and thermal stress concerning the acquisition and transmission of BBTV, which could be a roadmap for the future epidemiological control system.

Genetic Structure and Diversity of Banana Bunchy Top Virus (BBTV) in the Philippines

Banana bunchy top virus (BBTV) is an important disease of banana in the Philippines and in other banana-producing countries. This study was conducted to investigate the genetic structure and diversity of Philippine BBTV isolates which remain unexplored in the country. BBTV-infected plant tissues were sampled from banana-growing provinces (i.e., Cagayan, Isabela, Quirino, Batangas, Laguna, Rizal, Quezon, Palawan, Cebu, Leyte, and Davao del Sur) and the partial DNA-R gene of BBTV was sequenced. Analysis of all local BBTV isolates showed a nucleotide diversity (π) of 0.00721, average number of nucleotide differences (k) of 5.51984, and haplotype diversity (hd) of 0.971. Neutrality tests using Fu′s Fs and Tajima′s D showed significant and highly negative values which suggest an excess number of rare alleles due to recent population expansion or from genetic hitchhiking. Haplotype network and phylogenetic analyses revealed that the local BBTV isolates were closely related to Southeast Asian (SEA) group and exhibited a monophyletic clade with distinct haplotype grouping from other SEA sequences. However, some Indonesian and Indian reference sequences were also clustered within the Philippine BBTV group suggesting sequence homology. Results also showed that the local BBTV isolates may be categorized into three major haplotype groups (HA, HB, and HC) but only the HC group remained distinct upon comparison with other Philippine and SEA reference sequences. BBTV isolates from Quezon were the most diverse while isolates from Palawan displayed low genetic diversity indices and belonged only in the HC group. The assessment of the degree of variability among Philippine BBTV isolates will provide a reference towards the development of high-throughput BBTV detection systems as well as enable to devise plant breeding strategies to manage the current BBTV spread and variations.

First report of banana bunchy top virus in banana (Musa spp.) and its eradication in Togo

Banana (including plantain; Musa spp.) is a vegetatively propagated semi-perennial crop in fields and backyard gardens in Togo. Banana bunchy top disease (BBTD), caused by banana bunchy top virus (BBTV, genus Babuvirus) is the most economically important viral disease, infection of which causes severe stunting and production losses of 90-100% within two seasons. The virus is spread by banana aphid, Pentalonia nigronervosa, and through vegetative propagation from infected sources. BBTV occurrence was first reported in West Africa in 2011 with confirmation in Republic of Benin and in Nigeria in 2012 . A regional alliance (www.bbtvalliance.org) has been established for BBTV surveillance through frequent surveys in countries neighboring those affected, such as Togo. The surveys conducted in September 2018 in banana growing areas in Togo revealed plants with typical symptoms (severe stunting, bunchy growth with shortened petioles with chlorotic streaks and yellow leaf margins) in three banana fields. Locations were Tsévié, Préfecture de Zio, (6.44°N, 1.21028°E), Lilicope, Préfecture de Zio in Maritime region (6.56583°N, 1.18639°E), and Amoutchou, Préfecture de l’Ogou in Plateaux region (7.3775°N, 1.17472°E). Leaf samples were collected from symptomatic (N=8) and asymptomatic plants (N=30) and used for DNA extraction followed by a polymerase chain reaction (PCR) for BBTV detection to amplify ~240 bp sequence of DNA-R encoding for core replicase gene. All samples from symptomatic plants (N=8) tested positive and asymptomatic plants were negative. To ascertain virus identity the 240-bp PCR product was purified and sequenced in both directions. A BLAST search of the sequence (NCBI GenBank Acc.# MK073116) revealed 99% identity with DNA-R sequences of BBTV isolates from Africa (e.g., JQ437549-Benin, JN290301-Nigeria). Further analysis of the 240-bp nucleotide sequence with Maximum-likelihood phylogenetic analysis using MEGA-X software has grouped the BBTV isolate with sub-Saharan African sub-clade of the South Pacific group. To further confirm the virus identity, two samples from symptomatic (PCR positive) and asymptomatic (PCR negative) plants from Tsévié were tested by TAS-ELISA using BBTV ELISA reagent set (Cat. No. SRA24700-1000, Agdia, France) following the manufacturers’ protocol. Only samples from two symptomatic plants that were positive in PCR reacted positively in TAS-ELISA; asymptomatic plants were negative. BBTV was not observed in any of the 22 locations surveyed as a follow-up in banana producing areas. To our knowledge, this is the first report of BBTV infecting banana in Togo. The plants detected in the three sites were eradicated in the follow-up action implemented by the alliance team together with the Direction de la Protection des Végétaux of Togo. Follow-up surveys were conducted in the same regions in 2019 and 2020 to ensure disease-free status in these sites and other banana producing regions in Togo. Efforts have been made to raise awareness about BBTD recognition, diagnosis, and eradication. To the best of our knowledge this is the first case of rapid detection and eradication of BBTD in sub-Saharan Africa. This study illustrates the importance of regular surveillance for early detection of invasive virus threats and the value of rapid eradication to contain viruses before spread and establishment in a new territory.