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Articles by D. Fargette
Total Records ( 4 ) for D. Fargette
  R.D.S. Longue , A. Galzi-Pinel , I. Zinga , S. Semballa , D. Fargette , N. Barro and O. Traore
  Background: Rice yellow mottle virus (RYMV) of the genus Sobemovirus is the most important viral disease of rice in Africa, mainly occurring in the lowland and irrigated ecologies. Materials and Methods: The coat protein gene of forty six isolates of RYMV collected between 2011 and 2014 in Central African Republic was amplified and sequenced. Results: Analysis of sequences revealed that the average nucleotide diversity among isolates was low, 2.0% in nucleotide and 0.9% in amino acid. The ratio of non-synonymous over synonymous nucleotide substitutions per site was 0.07, indicating a virus diversification under a high conservative selective pressure. All isolates shared the amino acids specific of the serotype Ser1, a Val115 involved in the response with monoclonal A and a Thr115 which accounts for the lack of reaction with monoclonal D. Phylogenetic analyses showed that isolates of the south of Central African Republic belong to two sister monophyletic groups related to the S1ca strain, a strain which gathers all isolates from the East of West Africa to the West of Central Africa. Molecular clock dating of the age of each of the two groups and of their common ancestor suggests that RYMV was introduced a few decades ago in Central African Republic from the West of Central Africa. Conclusion: RYMV remained at a low level and undetected in wild hosts and in traditional rice fields until recently. RYMV emergence occurred less than ten years ago, likely favored by the on-going rice intensification and resulted in the current epidemics. This is the first study of the molecular diversity of RYMV in Central African Republic. It indicates that the isolates of the South of the country belonged to the S1 strain.
  D. Fargette , A. Pinel , M. Rakotomalala , E. Sangu , O. Traore , D. Sereme , F. Sorho , S. Issaka , E. Hebrard , Y. Sere , Z. Kanyeka and G. Konate
  The rate of evolution of an RNA plant virus has never been estimated using temporally spaced sequence data, by contrast to the information available on an increasing range of animal viruses. Accordingly, the evolution rate of Rice yellow mottle virus (RYMV) was calculated from sequences of the coat protein gene of isolates collected from rice over a 40-year period in different parts of Africa. The evolution rate of RYMV was estimated by pairwise distance linear regression on five phylogeographically defined groups comprising a total of 135 isolates. It was further assessed from 253 isolates collected all over Africa by Bayesian coalescent methods under strict and relaxed molecular clock models and under constant size and skyline population genetic models. Consistent estimates of the evolution rate between 4 x 10–4 and 8 x 10–4 nucleotides (nt)/site/year were obtained whatever method and model were applied. The synonymous evolution rate was between 8 x10–4 and 11 x 10–4 nt/site/year. The overall and synonymous evolution rates of RYMV were within the range of the rates of 50 RNA animal viruses, below the average but above the distribution median. Experimentally, in host change studies, substitutions accumulated at an even higher rate. The results show that an RNA plant virus such as RYMV evolves as rapidly as most RNA animal viruses. Knowledge of the molecular clock of plant viruses provides methods for testing a wide range of biological hypotheses.
  M.D. Traore , V.S.E. Traore , A. Galzi-Pinel , D. Fargette , G. Konate , A.S. Traore and O. Traore
  The roles of guttation fluid, irrigation water, contact between plants and transplantation into contaminated soil in the transmission of Rice yellow mottle virus (RYMV) were assessed. RYMV presence and infectivity were tested by Enzyme-Linked Immunosorbent Assay (ELISA) and by inoculation to susceptible rice cultivar BG90-2. The virus was readily detected in guttation fluid collected from infected rice plants. Transmission tests from this fluid led to high disease incidence (86.6%). Irrigation water collected at the base of infected plants growing in pots was less infectious, as inoculations led to disease incidences below 40%. No virus was detected and could be transmitted from field-irrigation water. Up to 44% healthy rice plants whose leaves were in contact with those of infected plants became infected but, no transmission occurred through intertwined roots. Transplantation of rice seedling into virus-contaminated soil also led to plant infection. However, virus survival in the soil decrease rapidly and infectivity was completely lost 14 days after soil contamination. Altogether, these results indicated that high planting densities of rice are likely to favour secondary spread of rice yellow mottle disease. Transplantation of rice seedlings not earlier than 2 weeks after soil preparation should prevent soil transmission of the virus. Although guttation fluid is highly infectious its contribution to virus infectivity in irrigation water is negligible as field-irrigation water was not found to be an infectious source for RYMV.
  S. Issaka , A. Onasanya , A. Basso , F. Sorho , A. Haougui , A.Y. Sido , S. Ake , D. Fargette and Y. Sere
  This study has been conducted in screen house with an aim to asses the Rice yellow mottle virus pathogenic diversity and the level of resistance of released varieties in Niger republic. Sixty RYMV isolates from 23 Niger rice perimeters were inoculated mechanically to nine rice cultivars. The disease symptoms were scored at 42 days after inoculation. Analysis of Variance (ANOVA) and Additive Main effect and Multiplicative Interaction (AMMI) analysis were performed on the percentage of severity. The reaction of the rice cultivars to the virus isolates was significantly different. The interaction between isolates and rice cultivars was also significant. AMMI cluster analysis revealed the existence of four major pathotypes (Path 1 to 4) of Rice Yellow Mottle Virus (RYMV) in Niger republic. Path 4 pathotype included 12 resistance breaking isolates (20%). Path 3 and Path 2 pathotypes consist of 15 and 26 isolates respectively and were typical of wild type isolates with moderate level of pathogeny, including none aggressive (path 3 = MP) and aggressive isolates (Path 2 = MPA). The fourth pathotype Path 1 was made of 7 isolates and typical of particular isolates which have a moderate pathogenic level (FP). Resistance Breaking (RB) isolates occupied 30% of Niger rice ecologies in variable proportion. The rice varieties (Bassiroumo, IR15-29-690-3-1 and Kassoumo) released in Niger were highly susceptible to RYMV and therefore constituted a favorable condition for the rice yellow mottle disease propagation. This information is useful in rice breeding programs in the development and deployment of RYMV resistant cultivars to different rice perimeters in Niger Republic.
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