Les virus du bananier et plantain (Musa spp.) en République démocratique du Congo : occurrence, identification de nouveaux virus et diversité génétique

Viruses are considered as major constraints to the exchange of germplasm, genetic improvement and breeding of banana and plantain (Musa spp) through the world. To date, six viruses are recognized to affect Musa spp: Banana bunchy top virus (BBTV), Banana streak viruses (BSV), Cucumber mosaic virus (CMV), Banana bract mosaic virus (BBrMV), Banana mild mosaic virus (BanMMV), Banana virus x (BVX). BBTV, the most devastating virus of banana, is currently spread in 14 countries of Africa including the Democratic Republic of Congo (DRC), where the virus was observed for the first time in 1950 in Yangambi, Kisangani region. The situation of others banana viruses remains unknown however, some of these viruses were observed in DRC bordering countries. The main aim of this work was to elucidate the epidemiological situation, the genetic variability and the origin of banana viruses in Democratic Republic of Congo. Epidemiological surveys were conducted in southwestern part of DRC, with a special emphasis on Bas Congo province, in order to search major banana viruses. Up to 666 samples were collected from at least 122 locations and analysed using PCR based method. BBTV is a multi component virus, which possesses six DNA components named DNA-R, M, N, C, U3, S. To understand the BBTV epidemiology, 52 complete sequences of DNA-R and 30 full sequences of DNA-R, U3, M, N, C, S were study. Phylogenetic analysis was carried out by isolates nucleotides sequences comparison, for all viruses detected (BBTV, BSV, CMV). Result show that BBTV is the most widespread banana virus in DRC. The main factor contributed to the spread of this threat is the human exchange of infected planting material. Data reveals a low genetic variability of BBTV isolates, which are grouped in South Pacific group. Theses BBTV isolates are close between them and with those of other sub-Saharian Africa countries. The earliest report of BBTV in Africa relates to an isolate described in Egypt in 1901. Since the earliest BBTV report in sub-Saharian Africa was in Democratic Republic of Congo in 1950, it is likely that Banana bunchy top virus spread from DRC to other SSA countries rather than from Egypt and that at least two Banana bunchy top virus introductions occurred in Africa from Java and Taiwan respectively. However, at a global scale, molecular analyses support infrequent Banana bunchy top virus dispersal events among continents. Democratic Republic of Congo seems to be the primary center of Banana bunchy top virus spread in Africa. Haplotypes analysis based on the coding region m-Rep protein showed 39 haplotypes (H1 to H39) (haplotype diversity value of 0.944±0.013). The most frequent haplotypes were H17, H9, H7 and H24 representing 31.6, 21.1, 21.1 and 27% of the BBTV isolates, respectively. Symptoms of banana streak disease including yellow streak, splitting of pseudo-stem, death of cigar leaf, were associated to the presence of Banana streak virus species (frequency = 20 %). The most widespread was Banana streak GF virus (BSGFV) (frequency = 68%) and Banana streak OL virus (BSOLV)(frequency = 25.5%). Musa acuminata cultivars are infected although no banana streak disease epidemic was reported any more, since the study revealed the transmission of BSV species from plantain (B genome) to banana (A genome). The frequency of mealybugs was about 9.3%, suggesting transmission of the disease. The sequenced isolate of BSGFV and BSOLV gather in the clade I, recognized to gathering the BSV species with endogenous counterpart. Cucumber mosaic virus was detected (frequency = 9.3%) mainly on asymptomatic samples collected. Genetic diversity analysis reveals the high similarity between Congolese CMV isolates and with South African isolates. These results suggest the hypothesis of the existence of the Cucumber mosaic virus single strain that dispersed througthout the study area. Banana bract mosaic virus was not detected in the collected samples despite the targeted sampling approach developed. The result suggests that the virus still absent in Bas Congo, Democratic Republic of Congo.Les virus constituent une contrainte majeure à l’amélioration et aux échanges de germplasm du bananier et plantain (Musa spp) dans le monde. Les études récentes rapportent que six virus affectent le bananier et plantain (Musa spp) dont le Banana bunchy top virus (BBTV), le Banana streak virus (BSV), Cucumber mosaic virus (CMV), Banana bract mosaic virus (BBrMV), Banana mild mosaic virus (BanMMV), le Banana virus x (BVX). Le BBTV est considéré comme le virus le plus dévastateur présent dans au moins 14 pays africains y compris la République démocratique du Congo (RDC) où il a été détecté pour la première fois, en 1950, à Yangambi dans la région de Kisangani. La situation des autres virus du bananier demeure inconnue malgré que certains d’entre eux aient été détectés dans les pays limitrophes de la RDC. Le principal objectif de cette thèse a été d’élucider la présence des virus impactant la culture du bananier (Musa spp.) en RDC, leurs origines et leurs diversités génétiques. Les enquêtes épidémiologiques ont été menées en vue de rechercher les principaux virus du bananier. Un accent particulier a été mis sur les zones moins investiguées en RDC, particulièrement la province du Bas Congo, à cause de sa position géographique, pour la recherche des nouveaux virus. Plus de 666 échantillons de feuilles de bananier ont été collectés dans 122 sites et analysés en utilisant la PCR comme base technique. Le BBTV est un virus à génome multipartite composé d’au moins six ADN nommés ADN-R, M, N, C, U3, S. Au total 52 séquences complètes d'ADN-R et 30 séquences complètes de M, N, C, U3, S ont été étudiées en vue de comprendre son épidémiologie. Les analyses phylogénétiques et la comparaison des séquences nucléotidiques ont été réalisées pour tous les virus détectés (BBTV, BSV, CMV). Les résultats indiquent que le BBTV est le virus du bananier le plus répandu en RDC. Le facteur humain constitue le principal moteur de dispersion de ce virus, particulièrement à travers l’échange de matériel de plantation infecté. Les données indiquent une faible variabilité génétique des isolats BBTV et leur regroupement dans le sous-groupe Sud Pacifique. Les isolats congolais de BBTV sont proches entre eux et aussi proches de ceux des autres pays d’Afrique sub-Saharienne (SSA). Les résultats confirment aussi que l’Afrique aurait subi une double introduction du BBTV venant respectivement de Java et de Taiwan. La première introduction du BBTV fut en Egypte en 1901 et la seconde en RDC en 1950. Au niveau moléculaire, les données supportent une distribution sur le continent africain - la RDC semble être un foyer primaire de dispersion en Afrique. L’analyse des haplotypes basée sur la région codante de la protéine m-Rep montre la présence de 39 haplotypes (H1 à H39) avec des valeurs de diversité de 0,944±0,013 dont les plus répandus sont H17, H9, H7 et H24, représentant respectivement 31,6 ; 21,1 ; 21,1 et 27,0 % des isolats BBTV. Les symptômes de banana streak disease incluant les stries jaunes, l’éclatement du pseudo-tronc, le dépérissement de la feuille cigare ont été associés à la présence des espèces Banana streak virus (fréquence de 20 %). Les espèces BSV les plus répandues sont Banana streak GF virus (BSGFV) (fréquence = 68 %) et Banana streak OL virus (BSOLV) (fréquence = 25,5 %). Les bananiers à génome Musa acuminata sont les plus infectés par le BSV, ce qui suggère le développement d’une épidémie BSV suite à la transmission du virus des hybrides interspécifiques (génome B) vers le bananier dessert (génome A). La fréquence de la cochenille a été évaluée à 9,3 %, ce qui renforce l’hypothèse d’une transmission de Banana streak virus. Les isolats de BSGFV et ceux de BSOLV séquencés, se groupent dans le clade I reconnu comme un clade ressemblant les espèces BSV ayant une contrepartie endogène. Cucumber mosaic virus a été détecté (fréquence = 9,3%) principalement sur les échantillons asymptomatiques. L’analyse de la diversité génétique révèle une similarité élevée entre les isolats de la RDC. Ce qui appuie l’hypothèse de l’existence d’une unique souche de CMV qui se disperse à travers le pays. Malgré l’approche de collecte d’échantillons utilisée, Banana bract mosaic virus n’a pas été détecté dans les échantillons collectés. Ces résultats suggèrent que Banana bract mosaic virus demeure absent du Bas Congo, RDC.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201

Occurrence and Distribution of Banana bunchy top virus Related Agro-Ecosystem in South Western, Democratic Republic of Congo

Banana bunchy top virus (BBTV) is one of the most severe and widespread virus limiting produc- tion and distribution of planting material of banana (Musa spp.) crops in the world. In Democratic Republic of Congo (DRC), these crops play a major role in daily life of almost 70% of citizen. Many factors influence banana production negatively such as Banana bunchy top disease. Epidemiol- ogical survey was conducted in experimental stations and farmers’ fields for two consecutive sea- sons covering 72 sites in five provinces of south western of RDC. The objective of this study was to evaluate the presence and distribution of the Banana bunchy top virus in five provinces of South Western of DRC, with emphasis on the agro-ecological factors. A total of 174 Musa spp. leaves samples were collected and analyzed by PCR. The results revealed the presence of BBTV in all provinces investigated. The frequency of BBTV was 6.3% in Bandundu, 12.1% in Kasaï Oriental, 17.8% Bas Congo, 1.1% in Katanga and 7.5% Kinshasa Urban and Peri-urban. Results also re- vealed that BBTV occurred in experimental station and farmers’ fields, both having all cooking and dessert bananas. The high prevalence of BBTV seemed to be linked to multiple introductions of planting materials in the Bas Congo province during 1990 and 2002. However, the province of Katanga had not experienced the introduction of planting material. This factor would explain the lowest prevalence of Banana bunchy top virus in this province. The results indicated that there was a real need to facilitate access to genetically improved and healthy certified planting material in these provinces

Development and integration of entomopathogenic fungi for crops protection in Democratic Republic of Congo

The Democratic Republic of the Congo (DR Congo) has enormous agricultural potentialities likely to contribute to its economic development. However, the sector is characterized by significant yield losses due notably to the pressure of pests. In response to this situation, most farmers use synthetic chemical pesticides, despite the problems of residues on harvested materials and their widely documented side effects on biodiversity. Up to now, efforts are made to promote healthy farming in the long term, taking into account both economic and environmental aspects. According to this principals, pest management is now achieved through the combination of agronomic, biological and physical means, chemical control being the last resort if necessary. Considering the context of DR Congo, biological control remains by far the least developed of all means in pest management. This is due to the lack of technical equipment. Nevertheless, compared to entomophagous macroorganisms, microorganisms offer the advantage of not requiring substantial resources for their integration into agriculture. This is notably the case for entomopathogenic fungi (EF): in addition to the fact that they may be multiplied on readily available substrates, their abundance in nature makes it possible to isolate new, more efficient strains with more or less marked selectivity. However, very little research on EF is carried out in this country. The present study aims to integrate these biological control agents into the pest management strategy in DR Congo. This research project will focus on two approaches: (1) evaluation of the genetic diversity of EF strains in DR Congo, which will lead to the establishment of a reference collection; and (2) screening of potential candidates for biopesticide development. Researches will be carried out on the southwestern part of the country, focusing on insect cadavers and soil samples from cultivated areas. Pure strains will be isolated on synthetic culture media then identified according to their morphological, physiological and molecular traits. Biological tests including virulence and effectiveness under various environmental conditions in laboratory will be carried out against the most important agricultural pests to be determined following a field monitoring. Finally, culture trials of EF with locally available resources at low cost will be conducted to encourage the adoption of the technology

Molecular characterization of Banana bunchy top virus reveals widespread low genetic variation among isolates in Democratic Republic of Congo

Banana bunchy top virus (BBTV), is the most devastating and widespread banana virus. Banana and plantain (Musa spp.) are major crops in terms of household income and food security in Democratic republic of Congo (DRC) (1). Despite the large territory under banana and plantain cultivation in the country, the genetic characterization of BBTV isolates has been undertaken for two provinces. The main objectives of this work were to understand the genetic variability of DRC BBTV isolates and to determine their origin

Current status of occurrence, genetic diversity and epidemiology of Banana (Musa spp.) viruses in Democratic Republic of Congo

Viruses are major constraints to the production and exchange of banana and plantain (Musa spp.) germplasm in the world. Several viruses are recognized to affect Musa spp: Banana bunchy top virus (BBTV), Banana streak GF virus (BSGFV), Banana streak OL virus (BSOLV), Banana streak IM virus (BSIMV), Banana streak MY virus (BSMYV), Cucumber mosaic virus (CMV), Banana bract mosaic virus, (BBrMV). To date, in Democratic Republic of Congo (DRC), except BBTV, others banana viruses are not yet reported. The main aim of this work was to elucidate the epidemiological situation, genetic variability and origin of Musa spp. viruses in DRC

Low genetic diversity of Banana bunchy top virus, with a subregional pattern of variation, in Democratic Republic of Congo

Banana bunchy top virus (BBTV), belonging to the genus Babuvirus, is the most devastating and widespread banana virus. Banana and plantain are major crops in terms of household income and food security in Democratic Republic of Congo (DRC). Despite the large area under banana and plantain cultivation in the country, before this study, the genetic characterization of BBTV isolates had only been undertaken for two provinces. In the study presented here, genetic variation in BBTV was assessed from 52 BBTV isolates collected in five out of 11 provinces in DRC (Bandundu, Bas-Congo, Katanga, Kinshasa and Kasaï Oriental) and in two provinces using sequences previously described in databases. Full genome sequencing of DNA-R components was performed, revealing low genetic variation (98–100 % nucleotide identity) among the BBTV isolates detected. The phylogenetic analyses showed that all the DRC isolates were clustered in the South Pacific clade of BBTV. Based on the coding region for the replication initiator protein, haplotype diversity was estimated to be 0.944 ± 0.013, with 30 haplotypes from 68 isolates in DRC. Such diversity shows a haplotype distribution mainly at the sub-regional level in DRC. In addition, the sequence determination from the whole genome of selected isolates confirmed low genetic variation among isolates from seven DRC provinces (97–100 % nucleotide identity). This study strengthened the hypothesis of a single BBTV introduction some time ago, followed by the spread of the virus in the country