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.

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.

Transgenic Expression of dsRNA Targeting the Pentalonia nigronervosa acetylcholinesterase Gene in Banana and Plantain Reduces Aphid Populations

The banana aphid, Pentalonia nigronervosa, is the sole insect vector of banana bunchy top virus (BBTV), the causal agent of banana bunchy top disease. The aphid acquires and transmits BBTV while feeding on infected banana plants. RNA interference (RNAi) enables the generation of pest and disease-resistant crops; however, its effectiveness relies on the identification of pivotal gene sequences to target and silence. Acetylcholinesterase (AChE) is an essential enzyme responsible for the hydrolytic metabolism of the neurotransmitter acetylcholine in animals. In this study, the AChE gene of the banana aphid was targeted for silencing by RNAi through transgenic expression of AChE dsRNA in banana and plantain plants. The efficacy of dsRNA was first assessed using an artificial feeding assay. In vitro aphid feeding on a diet containing 7.5% sucrose, and sulfate complexes of trace metals supported aphid growth and reproduction. When AChE dsRNA was included in the diet, a dose of 500 ng/μL was lethal to the aphids. Transgenic banana cv. Cavendish Williams and plantain cvs. Gonja Manjaya and Orishele expressing AChE dsRNA were regenerated and assessed for transgene integration and copy number. When aphids were maintained on elite transgenic events, there was a 67.8%, 46.7%, and 75.6% reduction in aphid populations growing on Cavendish Williams, Gonja Manjaya, and Orishele cultivars, respectively, compared to those raised on nontransgenic control plants. These results suggest that RNAi targeting an essential aphid gene could be a useful means of reducing both aphid infestation and potentially the spread of the disease they transmit.

Gender Roles in Sourcing and Sharing of Banana Planting Material in Communities with and without Banana Bunchy Top Disease in Nigeria

Banana bunchy top disease (BBTD) is the most devasting disease of banana and plantain (Musa spp.). The disease spreads through the use of infected vegetative propagules and the banana aphid (Pentalonia nigronervosa) is the virus vector. This study seeks to understand the gender dimensions and sociocultural aspects of banana seed (vegetative propagule) sourcing and sharing practices among men and women farmers, and its influence on BBTD spread and disease control efforts. Data were collected from 300 banana farmers (187 men and 113 women) in BBTD and non-BBTD areas in southwest Nigeria. The results revealed that seed sharing within the communities is a social responsibility with members expected to share banana seed with the needy mainly as gifts rather than sold for cash. Men farmers mostly sourced seed from old fields, while women sourced seed from relatives. Harvesting of banana seed was predominantly the responsibility of men with women as helpers. Both men and women farmers in the non-BBTD area cultivated larger farm sizes and harvested more banana planting material than farmers in the BBTD area. The existing seed sourcing practices among men and women farmers heighten the risk of BBTD spread. Awareness raising on disease spread through infected seeds should consider gender-differentiated roles and social practices to reduce its spread within communities.

Genome Sequence of the Banana Aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae) and Its Symbionts

The banana aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae), is a major pest of cultivated bananas (Musa spp., order Zingiberales), primarily due to its role as a vector of Banana bunchy top virus (BBTV), the most severe viral disease of banana worldwide. Here, we generated a highly complete genome assembly of P. nigronervosa using a single PCR-free Illumina sequencing library. Using the same sequence data, we also generated complete genome assemblies of the P. nigronervosa symbiotic bacteria Buchnera aphidicola and Wolbachia. To improve our initial assembly of P. nigronervosa we developed a k-mer based deduplication pipeline to remove genomic scaffolds derived from the assembly of haplotigs (allelic variants assembled as separate scaffolds). To demonstrate the usefulness of this pipeline, we applied it to the recently generated assembly of the aphid Myzus cerasi, reducing the duplication of conserved BUSCO genes by 25%. Phylogenomic analysis of P. nigronervosa, our improved M. cerasi assembly, and seven previously published aphid genomes, spanning three aphid tribes and two subfamilies, reveals that P. nigronervosa falls within the tribe Macrosiphini, but is an outgroup to other Macrosiphini sequenced so far. As such, the genomic resources reported here will be useful for understanding both the evolution of Macrosphini and for the study of P. nigronervosa. Furthermore, our approach using low cost, high-quality, Illumina short-reads to generate complete genome assemblies of understudied aphid species will help to fill in genomic black spots in the diverse aphid tree of life.

Prévalence du Banana Bunchy Top Disease (BBTD) dans la zone de Ntoum au Gabon

Le Banana Bunchy Top Disease (BBTD) est la maladie virale la plus dévastatrice du bananier impactant considérablement sa production. Le BBTD a été signalé au Gabon pour la première fois par la FAO avec une prévalence de plus de 90%. La présente étude vise à déterminer la prévalence du BBTD, la sévérité et l’importance du vecteur dans la zone de Ntoum. Après une enquête, 1800 pieds de bananiers dans 6 foyers d’infestation, ont été examinés de façon aléatoire avec un système de notation randomisé en transect croisé X. La méthode d’enquête par observation visuelle des symptômes du BBTD avec une échelle de notation de 1 à 5 a été utilisée. Les foyers d’infestation retenus présentent une sévérité de la maladie avancée avec le symptôme visuel de niveau 5 prépondérant et une prévalence moyenne de 21%. Le vecteur, Pentalonia nigronervosa est un insecte présent dans la zone mais à des niveaux d’importance variable. Il serait souhaitable d’évaluer la résistance variétale des Musa spp. et de montrer l’influence des facteurs biotiques et abiotiques sur la propagation de la maladie.Mots clés : Bananier, Pentalonia nigronervosa, foyers d’infestation, sévérité, importance du vecteur. English Title: Prevalence of Banana Bunchy Top Disease (BBTD) in the Ntoum area in Gabon Banana Bunchy Top Disease (BBTD) is the banana's most devastating viral disease, with a significant impact on its production. BBTD was first reported in Gabon by FAO with a prevalence of more than 90%. This study aims to determine the prevalence of BBTD, the severity and importance of the vector in the Ntoum area. After a survey, 1800 feet of banana trees in 6 outbreaks, were examined randomly with a randomized scoring system in transect crossed X. The method of visual observation of BBTD symptoms with a rating scale of 1 to 5 was used. The selected outbreaks have an advanced disease severity with the predominant level 5 visual symptom and an average prevalence of 21%. The vector, Pentalonia nigronervosa is an insect present in the area but at varying levels. It would be desirable to assess the varietal resistance of Musa spp. and to show the influence of biotic and abiotic factors on the spread of the disease.Keywords: Banana, Pentalonia nigronervosa, source of infestation, severity, importance of vector.

Genome sequence of the banana aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae) and its symbionts

The banana aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae), is a major pest of cultivated bananas (Musa spp., order Zingiberales), primarily due to its role as a vector of Banana bunchy top virus (BBTV), the most severe viral disease of banana worldwide. Here, we generated a highly complete genome assembly of P. nigronervosa using a single PCR-free Illumina sequencing library. Using the same sequence data, we also generated complete genome assemblies of the P. nigronervosa symbiotic bacteria Buchnera aphidicola and Wolbachia. To improve our initial assembly of P. nigronervos a we developed a k-mer based deduplication pipeline to remove genomic scaffolds derived from the assembly of haplotigs (allelic variants assembled as separate scaffolds). To demonstrate the usefulness of this pipeline, we applied it to the recently generated assembly of the aphid Myzus cerasi, reducing the duplication of conserved BUSCO genes by 25%. Phylogenomic analysis of P. nigronervos a, our improved M. cerasi assembly, and seven previously published aphid genomes, spanning three aphid tribes and two subfamilies, reveals that P. nigronervos a falls within the tribe Macrosiphini, but is an outgroup to other Macrosiphini sequenced so far. As such, the genomic resources reported here will be useful for understanding both the evolution of Macrosphini and for the study of P. nigronervosa. Furthermore, our approach using low cost, high-quality, Illumina short-reads to generate complete genome assemblies of understudied aphid species will help to fill in genomic black spots in the diverse aphid tree of life.