Contrôle des germes endogènes par usage d’agents antimicrobiens et réponse de différents explants durant la phase d’initiation in vitro de l'ananas (Ananas comosus (L.) Mill var. comosus)

Objectif : La culture in vitro est aujourd’hui utilisée dans la production massive de rejets d’ananas. Mais, la réussite de sa  première phase (initiation) nécessite l’élimination des infections et un bon choix d’explant. Dans la présente étude, l’effet de deux agents antimicrobiens et du type d’explant sur la reprise in vitro de l’ananas a été évalué.Méthodologie et Résultats : Les bourgeons axillaires médians de  couronne d’ananas des cultivars Cayenne lisse (Hilo et Saint Michael) et Pain de sucre ont été ensemencés sur le milieu de Murashige et Skoog additionné de 5 mg/l de Benzylaminopurine : MC. L’hypochlorite de sodium (0,1 ; 0,2 ; 0,3 et 0,4%) et le Chlorothalonil (0,075 ; 0,15 ; 0,225 et 0,3%) ont été incorporés au milieu. Ensuite, des bourgeons axillaires médians de 8 à 10 semaines après floraison et ceux des parties supérieure, médiane et basale de 10 semaines ont été ensemencés sur le milieu MC additionné de 0,3% d’hypochlorite de sodium. La présence d’agent antimicrobien a réduit les infections mais avec une influence négative sur la reprise. L’hypochlorite de sodium à 0,3% a permis une meilleure élimination des infections (17,78%) sans significativement affecter la reprise (78,89%). Les contaminations sont plus prononcées chez Pain de sucre (37,40%) que chez Saint Michael (19,26%) et Hilo (9,63%). Les jeunes bourgeons médians des couronnes de 8 semaines et supérieurs de 10 semaines ont présenté une meilleure aptitude au débourrement avec respectivement des taux de 92,22% et 86,67%.Conclusion et applications : La désinfection de surface généralement effectuée à l’initiation ne permet pas d’éliminer efficacement les  infections chez l’ananas. L’introduction d’agent antimicrobien dans le milieu de culture a réduit les infections mais a eu un effet négatif sur le débourrement aux doses croissantes. L’utilisation des bourgeons axillaires supérieurs et médians de couronne de 8 semaines après floraison est souhaitée pour optimiser la reprise in vitro de l’ananas.Mots clés : Ananas, hypochlorite de sodium, chlorothalonil, position de l’explant, âge de l’explant, désinfection, débourrement

Contrôle des germes endogènes par usage d’agents antimicrobiens et réponse de différents explants durant la phase d’initiation in vitro de l'ananas (Ananas comosus (L.) Mill var. comosus)

Objectif : La culture in vitro est aujourd’hui utilisée dans la production massive de rejets d’ananas. Mais, la réussite de sa  première phase (initiation) nécessite l’élimination des infections et un bon choix d’explant. Dans la présente étude, l’effet de deux agents antimicrobiens et du type d’explant sur la reprise in vitro de l’ananas a été évalué.Méthodologie et Résultats : Les bourgeons axillaires médians de  couronne d’ananas des cultivars Cayenne lisse (Hilo et Saint Michael) et Pain de sucre ont été ensemencés sur le milieu de Murashige et Skoog additionné de 5 mg/l de Benzylaminopurine : MC. L’hypochlorite de sodium (0,1 ; 0,2 ; 0,3 et 0,4%) et le Chlorothalonil (0,075 ; 0,15 ; 0,225 et 0,3%) ont été incorporés au milieu. Ensuite, des bourgeons axillaires médians de 8 à 10 semaines après floraison et ceux des parties supérieure, médiane et basale de 10 semaines ont été ensemencés sur le milieu MC additionné de 0,3% d’hypochlorite de sodium. La présence d’agent antimicrobien a réduit les infections mais avec une influence négative sur la reprise. L’hypochlorite de sodium à 0,3% a permis une meilleure élimination des infections (17,78%) sans significativement affecter la reprise (78,89%). Les contaminations sont plus prononcées chez Pain de sucre (37,40%) que chez Saint Michael (19,26%) et Hilo (9,63%). Les jeunes bourgeons médians des couronnes de 8 semaines et supérieurs de 10 semaines ont présenté une meilleure aptitude au débourrement avec respectivement des taux de 92,22% et 86,67%.Conclusion et applications : La désinfection de surface généralement effectuée à l’initiation ne permet pas d’éliminer efficacement les  infections chez l’ananas. L’introduction d’agent antimicrobien dans le milieu de culture a réduit les infections mais a eu un effet négatif sur le débourrement aux doses croissantes. L’utilisation des bourgeons axillaires supérieurs et médians de couronne de 8 semaines après floraison est souhaitée pour optimiser la reprise in vitro de l’ananas.Mots clés : Ananas, hypochlorite de sodium, chlorothalonil, position de l’explant, âge de l’explant, désinfection, débourrement

Differential Roles of AC2 and AC4 of Cassava Geminiviruses in Mediating Synergism and Suppression of Posttranscriptional Gene Silencing

Posttranscriptional gene silencing (PTGS) in plants is a natural defense mechanism against virus infection. In mixed infections, virus synergism is proposed to result from suppression of the host defense mechanism by the viruses. Synergistic severe mosaic disease caused by simultaneous infection with isolates of the Cameroon strain of African cassava mosaic virus (ACMV-[CM]) and East African cassava mosaic Cameroon virus (EACMCV) in cassava and tobacco is characterized by a dramatic increase in symptom severity and a severalfold increase in viral-DNA accumulation by both viruses compared to that in singly infected plants. Here, we report that synergism between ACMV-[CM] and EACMCV is a two-way process, as the presence of the DNA-A component of ACMV-[CM] or EACMCV in trans enhanced the accumulation of viral DNA of EACMCV and ACMV-[CM], respectively, in tobacco BY-2 protoplasts. Furthermore, transient expression of ACMV-[CM] AC4 driven by the Cauliflower mosaic virus 35S promoter (p35S-AC4) enhanced EACMCV DNA accumulation by ∼8-fold in protoplasts, while p35S-AC2 of EACMCV enhanced ACMV-[CM] DNA accumulation, also by ∼8-fold. An Agrobacterium-based leaf infiltration assay determined that ACMV-[CM] AC4 and EACMCV AC2, the putative synergistic genes, were able to suppress PTGS induced by green fluorescent protein (GFP) and eliminated the short interfering RNAs associated with PTGS, with a correlated increase in GFP mRNA accumulation. In addition, we have identified AC4 of Sri Lankan cassava mosaic virus and AC2 of Indian cassava mosaic virus as suppressors of PTGS, indicating that geminiviruses evolved differently in regard to interaction with the host. The specific and different roles played by these AC2 and AC4 proteins of cassava geminiviruses in regulating anti-PTGS activity and their relation to synergism are discussed

Environment Determines Fidelity for an RNA Virus Replicase▿

The rate of insertion and deletion mutations of the replicase of Cucumber mosaic virus (CMV) was determined in planta by using a parasitic satellite RNA (satRNA) as a reporter. We found that the CMV replicase had different fidelity in different environments, with important implications in viral disease evolution. Insertions were very rare events, irrespective of the region of the satRNA genome assayed and independent of the hosts tested. On the other hand, deletion events were more frequent but were restricted to a highly structured region of the reporter. Deletion mutation rates were different for the two hosts tested, although the mutation distribution was not influenced by the hosts. Moreover, hot spots with high mutation rates were identified on the satRNA genome

Survey of farmers’ knowledge of cassava mosaic disease and their preferences for cassava cultivars in three agro-ecological zones in Benin

Abstract Background Cassava is an important crop in Africa that is widely cultivated for its starchy tuberous root, which constitutes a major source of dietary carbohydrates. Cassava mosaic disease (CMD) is the most devastating disease affecting cassava in Africa and causes enormous losses in yield. In Benin, specifically, cultivars resistant to CMD are not commonly planted, and even when CMD is observed in fields, farmers do not implement control measures, presumably because they lack proper knowledge and training. Our study aimed to evaluate farmers’ knowledge of CMD to determine whether there is consistency between farmers’ criteria for selecting cassava cultivars and the currently CMD-recommended cassava varieties. Methods We conducted structured interviews with 369 farmers in 20% of townships in each of three agro-ecological zones in Benin between November 2015 and February 2016. Farmers were selected randomly in each household, and their fields were assessed for CMD incidence and severity. Results All farmers surveyed, representing a broad demographic pool with regard to education level, age group, and years of experience in cassava production, successfully recognized CMD symptoms in photos, but most (98.60%) said they did not know the causes and vectors of the disease. Most farmers (93.51%) reported that they obtain planting material from neighboring fields or their own fields. In total, 52 unique cultivars were identified, of which 3 (5.76%) were preferred based on their yield and precocity and 3 (5.76%) were preferred based on taste or ability for transformation. The assessment of disease incidence and severity showed that the areas most affected by CMD were Comè Township (37.77% of fields affected) and agro-ecological zone VIII (26.33%). Conclusion Farmers already know how to recognize the symptoms of CMD and could implement control measures against it if they are trained by researchers. Across all surveyed areas, we identified six preferred cultivars based on the four most commonly stated preference criteria (precocity, yield, gari, and taste. Our results suggest that farmers will be more likely to use CMD-resistant cultivars and clean plant material if the plants meet their existing preference criteria. We suggest that CMD-resistant cultivars will be embraced only if the recommended cultivars are strategically aligned with the characteristics desirable to the cassava farmers in each region

Response of cassava cultivars to African cassava mosaic virus infection across a range of inoculum doses and plant ages.

Cassava production in Africa is constrained by cassava mosaic disease (CMD) that is caused by the Cassava mosaic virus (CMV). The aim of this study was to evaluate the responses of a range of commonly cultivated West African cassava cultivars to varying inoculum doses of African cassava mosaic virus (ACMV). We grafted 10 cultivars of cassava plants with different inoculum doses of CMV (namely two, four, or six CMD-infected buds) when the experimental plants were 8, 10, or 12 weeks old, using non-inoculated plants as controls. Three cultivars showed disease symptoms when grafted with two buds, and four cultivars showed disease symptoms when grafted with four or six buds. Most cultivars became symptomatic six weeks after inoculation, but one ('TMS92/0326') was symptomatic two weeks after inoculation, and two ('Ntollo' and 'Excel') were symptomatic after four weeks. Root weight tended to be lower in the six-bud than in the two-bud dose, and disease severity varied with plant age at inoculation. These results indicate that the level of CMD resistance in cassava cultivars varies with inoculum dose and timing of infection. This will allow appropriate cultivars to be deployed in each production zone of Africa in accordance with the prevalence of CMD