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Articles by Y. Sere
Total Records ( 21 ) for Y. Sere
  S.K. Akator , D.K. Adjata , S. Drissa , S. Awande , L. Zadji , G. Sangare , Y. Sere and Y.M.D. Gumedzoe
  Study for the genetic diversity of P. oryzae populations, under natural inoculation, trapping of virulence races present in ecosystems, was done during the period of 2008 to 2010 in two countries. One location/country was surveyed to highlight that resistance genes: Pi1; Pi11; Pi12; Pi19; Pib; Pi20; Pi5; Pi7; Pia; Pia+Pi19; Pia+Pish; Pif, Pii, Pik, Pik-p, Pish, Pit, Pit, Pita-2, Piz, Piz-t, Piks at M'be and and those at Ouedeme: Pi1, Pi12, Pi19, Pi1b, Pi3, Pi5, Pi7, Pia, Pii, Pik, Pi-p, Pit, Pita, Piks incidence. It was shown that they were overcome by a large proportion of the virulence gene of P. oryzae population. However, virulence genes that are capable of overcoming resistance genes: Pi33, Pi5 (t), Pi7, Pi9, Pikh+Pi-1+Pita+Pita, Pik-m ,Pish, Pitta-2, Piz-5, were absent or rare. These genes were effective against the pathogen population studied. This study also showed that Pi5 and Pi7, Pikh +Pi-1+Pita+Pita, genes association which were individually inefficient, has conferred a sustainable resistance to blast that was observed in Moroberekan and Tetep. This work will help rice breeders and plant pathologists to select rice varieties with durable resistance to blast disease.
  Y. Sere , A. Onasanya , V. Verdier , K. Akator , L.S. Ouedraogo , Z. Segda , M.M. Coulibaly , A.Y. Sido and A. Basso
  As little information is available in Africa on Xanthomonas oryzae pv. oryzae, a highly destructive pathogen of rice, and its relationship with released rice varieties, a disease survey and samplings were carried out in Niger, Burkina Faso and Mali which indicated a wide spread of Bacterial Leaf Blight (BLB) in farmers’ fields. Sixty pure BLB isolates cultures were obtained. Pathogenicity of 4 Malian isolates against four important rice varieties revealed differences in pathogenicity among isolates and in resistance of the varieties tested. The results obtained in these initial studies revealed the future research directions to increasing rice production in West Africa.
  M. Sie , Y. Sere , S. Sanyang , L.T. Narteh , S. Dogbe , M.M. Coulibaly , A. Sido , F. Cisse , E. Drammeh , S.A. Ogunbayo , L. Zadj , B. Ndri and B. Toulou
  The immense potential of the lowlands in West and Central Africa for durable intensification of rice cropping have not been realised due to biotic and abiotic constraints. There is a need to replace existing rice varieties with others that are better adapted to the lowland conditions. After the success of the upland interspecific varieties, Africa Rice Center (WARDA) and its partners developed NERICA varieties suitable for irrigated and rainfed lowlands. The stable varieties resulting from this work were evaluated under preliminary yield trials in eight countries at 19 sites. The entries included 61 interspecific (O. glaberrima x O. sativa indica) varieties and 9 intraspecific (O. sativa indica x O. sativa indica) varieties. The aim of the study is to introduce new lowland NERICAs through a participatory approach and to identify ideotypes that are adapted to lowland conditions. Variations did exist among the 73 rice varieties with respect to the five traits that were evaluated. Total number of tillers, panicle number and flowering dates were observed to greatly influence the yield among the 73 varieties that were evaluated. A principal components plot clustering analysis were used to group the accessions. The interspecific varieties formed the most interesting group and have a better capacity for adaptation to the diversity of lowlands. They have acceptable yields, sometimes higher than those of intraspecific varieties and checks. Thus, most lowland NERICAs varieties tested in three ecologies could produce more than 5 t ha-1. The results obtained were quite encouraging and showed that, the varieties possess good agronomic traits that are well adapted to intensified lowland rice farming. The recent naming of some of these interspecific varieties as NERICA-L (New Rice for Africa Lowland) by Africa Rice Center has confirmed that they compare well with the traditional varieties. Thus, from this study, we now have a new set of interspecific varieties that are adapted to lowland conditions and which the national research programs can use in various tests for satisfying farmers` needs.
  A. Onasanya , M.M. Ekperigin , Y. Sere , F.E. Nwilene , J.O. Ajele and G. Oboh
  Isozyme fingerprinting and differentiation of Xanthomonas oryzae pv. oryzae (Xoo) isolates, causing rice Bacterial Leaf Blight (BLB) disease in West Africa, was carried out. Of 13 enzyme systems screened, Glucose 6-phosphate dehydrogenase (G6PH) showed adequate resolution and enzyme activity. Thus total proteins from all the 30 isolates were then analyzed using G6PH. This enzyme system was potentially useful as they differentiate all the 30 Xoo isolates studied. The study revealed 40-96.7% polymorphism in G6PH loci within the Xoo enzyme profile. These polymorphic isozyme loci were used to construct phylogenetic relationship cluster dendrogram among the 30 Xoo isolates. All the 30 Xoo isolates were classified into two major genetic groups (Xoo-A and Xoo-B) with five subgroups. Xoo-A possibly covers 46% and Xoo-B 54% of BLB population across West Africa. This study suggests the emergence of subgroup genotypes possibly the result of mutations and interactions among isolates and strains that originally made up Xoo-A and Xoo-B genotypes. The isozyme fingerprint defined for each race of Xoo could be useful for epidemiological surveys, disease diagnoses and in the identification of new virulent strains, isolates and their origin. This information could be useful in rice breeding programs aiming at development of durable Xoo resistant rice cultivars to different rice ecologies and localities in West Africa.
  A. Onasanya , A. Basso , E. Somado , E.R. Gasore , F.E. Nwilene , I. Ingelbrecht , J. Lamo , K. Wydra , M.M. Ekperigin , M. Langa , O. Oyelakin , Y. Sere , S. Winter and R.O. Onasanya
 

Case No: 26082013

This article has been withdrawn due to technical issue.

  A. Onasanya , M.M. Ekperigin , Y. Sere and J.O. Ajele
  Genetic diversityof 30 Xanthomonas oryzae pv. oryzae (Xoo) isolates, causing rice bacterial leaf blight disease in West Africa, was carried out using isozyme PAGE analysis. Of 13 enzyme systems evaluated, SKDH, EST and G6PH showed adequate resolution, enzyme activity and polymorphism and were used to analyze the total proteins from all the 30 isolates. The study revealed 23 isozyme loci in which SKDH produced 33.3-93.3% polymorphism, EST and G6PH equally gave 40-96.7% polymorphism within the Xoo isolates enzyme profile. These 23 isozyme loci were used to construct phylogenetic relationship cluster among 30 Xoo isolates, of which the Xoo isolates were classified into two major genetic groups (Xoo-A and Xoo-B) with two subgroups each (Xoo-A1 and Xoo-A2) and (Xoo-B1 and Xoo-B2). The 23 isozyme markers obtained clustered into 3 major groups (Gp-1, Gp-2 and Gp-3). Genetic study revealed that Gp-1 is genetically linked to the identification of Xoo-A1 genotype, Gp-2 to Xoo-A2 and Gp-3 characterized Xoo-B1 and Xoo-B2 genotypes. The distinct pattern of each isolate obtained suggests high level of genetic variation and frequent occurrence of mutants in Xoo isolates in different host cells. This information could be useful in rice breeding programs aiming at development of durable Xoo resistant rice cultivars to different rice ecologies and localities in West Africa.
  A. Joseph , D.B. Olufolaji , F.E. Nwilene , A. Onasanya , M.M. Omole , R.O. Onasanya and Y. Sere
  Chlorophyll reduction in rice leaves is a prominent feature of rice yellow mottle virus-infected plants. This research work was carried out to investigate the effect of rice yellow mottle disease on the chlorophyll content of eight differential rice cultivars screened for resistance to rice yellow mottle virus (RYMV) with vector transmission technique. Border row rice seedlings mechanically inoculated with RYMV isolate at 21 days after sowing metamorphosed into infected rows, following which the rice cultivars were sown 15 days after. Two days after sowing the test cultivars, life adults of three vectors (Oxya hyla, Locris rubra and Chnootriba similis) of rice yellow mottle virus were released onto the infected rows inside separate insect-proof screen house to acquire and transmit the virus to the test cultivars. The chlorophyll contents of the leaves were then measured at 42, 56 and 70 days after sowing. The result of the genotype by environment interaction showed that environment exerted the most profound effect on chlorophyll reduction (36.26%) in the rice cultivars screened with O. hyla while the least effect (5.87%) was recorded when the screening was carried out with C. similis. Findings from this research work showed that chlorophyll reduction varied among the rice cultivars at different stages of rice plant. Though, the photosynthetic rate of the rice leaves were not investigated, it could be deduced that this physiological function would invariably reduce in the rice cultivars.
  Y. Sere , A. Onasanya , F.E. Nwilene , M.E. Abo and K. Akator
  The study aimed to investigate the potential of insect vector Rice yellow mottle virus (RYMV) cultivar screening method. Screening rice cultivars against RYMV under artificial conditions is usually carried out inside the screen house by mechanical inoculation of RYMV isolates. Such an approach may be highly criticized as not fully representative of how RYMV disease is spread or transmitted under field conditions. Consequently, the potential of three RYMV insect vectors, Oxya hyla, Locris rubra and Chnootriba similes, was evaluated in comparing the cultivar screening method with mechanical transmission using eight differential rice genotypes against a highly virulent RYMV Nigerian isolate. The study revealed that each of the three insect vector methods is different from the mechanical transmission method and all methods screened rice cultivars in the same way. This study revealed the potential of the insect vector screening method to provide a basis not only for the development of durable resistant cultivars to RYMV disease but also for further investigation on vectors, virus and rice plants interaction.
  J.T. Onwughalu , M.E. Abo , J.K. Okoro , A. Onasanya and Y. Sere
  The study on the resistance of Gigante, Moroberekan and Bouake 189 rice varieties was investigated against the Rice yellow mottle virus (RYMV) infection relative to time of infection under screenhouse controlled condition. Rice varieties, Moroberekan, Gigante and Bouake 189, were inoculated with RYMV isolate at seedling, tillering, booting and flowering growth stages. Gigante, Moroberekan and Bouake 189 gave mean yield losses of 12.68, 78.06 and 94.4%, respectively at booting and seedling infection stages. The No. of grains plant-1 is mostly affected at booting infection stage in Bouake 189 and at seedling infection stage in Moroberekan. No significant difference in No. of empty spikelets plant-1 due to infection at different growth stages among the three varieties. Plant height was significantly affected by virus infection at seedling stage of the three varieties and other growth stages of Bouake 189. The highest yield loss of 94.4% obtained in Bouake 189 at seedling and booting infection stages establishes the fact that yield losses to RYMV are strongly influenced by host cultivars as well as time of virus infection. The study revealed that the period from seedling and booting represents the most vulnerable phase to RYMV infection in rice growth stages. This information would strongly assist breeding programmes in the development of durable resistant rice cultivars to RYMV disease.
  Y. Sere , A. Onasanya , K. Akator , A. Afolabi and M.E. Abo
  Serological diversity of 178 RYMV isolates was determined by phylogenetic analysis of Serological Differentiation Indices (SDI) data generated from antigen coated-plate enzyme-linked immunosorbent assay (ACP-ELISA) using 26 RYMV Polyclonal antisera. These RYMV isolates were obtained from northern, southern, eastern and western Cote d`Ivoire. All the RYMV isolates was classified into three main serogroups (Sg1, Sg2 and Sg3) and six subgroups (Sg1a, Sg1b, Sg2a, Sg2b, Sg3a and Sg3a). This indicates the existence and levels of serodiversity among RYMV isolates in Cote d`Ivoire. These results provide evidence of a possible relationship between serological property, host plant and ecological origin of RYMV isolates. Phylogenetic classification of each RYMV isolate defined by SDI data in ACP-ELISA is potentially useful in epidemiological studies to assess isolate identity and interaction as well as to assist breeding programs aiming at the development of cultivars with durable resistant to RYMV in Cote d`Ivoire.
  F.E. Nwilene , A.K. Traore , A.N. Asidi , Y. Sere , A. Onasanya and M.E. Abo
  The study aimed to investigate the vectorial capacity of twelve insect species to transmit Rice Yellow Mottle Virus (RYMV) from diseased seedlings of a susceptible rice variety (Bouaké 189) and a perennial wild rice (Oryza longistaminata) to seven alternative host plants. Results indicated that Trichispa sericea, Chaetocnema pulla, Chnootriba similis, Conocephalus longipennis, Oxya hyla, Paratettix sp., Zonocerus variegatus, Euscyrtus sp., Cofana spectra, Cofana unimaculata, Locris rubra and Locris maculata were capable of transmitting RYMV from infected Bouaké 189 and Oryza longistaminata to alternative weed hosts Leersia hexandra, Imperata cylindrica, Digitaria horizontalis, Echinochloa colona, Echinocloa crus-pavonis, Eleusine indica and Brachiaria lata. Only Chaetocnema pulla, Trichispa sericea, Chnootriba similis, Oxya hyla, Zonocerus variegatus, Euscyrtus sp., Parattetix sp., Cofana spectra, Cofana unimaculata and Locris rubra played an important role in transmitting the disease from rice to O. longistaminata, Leersia hexandra and Imperata cylindrica. The present study confirmed the vectorial capacity of these vectors out of which eight were reported for the first time in West Africa.
  A. Koudamiloro , F.E. Nwilene , D. Silue , A. Togola , O. Oyetunji , Y. Sere and M. Akogbeto
  Insects represent a major group of vectors of Rice yellow mottle virus (RYMV). This study aimed at identifying the main entomofauna transmitting RYMV to rice crop in Benin. Therefore, the transmission ability of 13 insect species was tested during the rice vegetative stages. These species belong to the Orthoptera order (Oxya hyla, Conocephalus longipennis, Paracinema tricolor, Acrida bicolor and Stenohippus aequus), the Coleoptera order (Chnootriba similis, Aulacophora foveicollis and Xanthadalia effusa), the Homoptera order (Cofana spectra, Nephotettix modulatus, Cofana unimaculata and Poophilis costalis) and the Diptera order (Diopsis thoracica). Among them, four species including P. tricolor, S. aequus, N. modulatus and P. costalis were identified for the first time as RYMV vectors. The species belonging to the Homoptera order appeared to be the most virulent, with higher values of viral titer. Virus distribution in the vector body parts was specific to each order. Basically, virus was more important in the Orthopteran, Coleopteran and Homopteran insects head part. It was also evident in the abdomen part of the Homopteran and the Orthopteran especially for P. tricolor, C. spectra and P. costalis. Disease severity was only observed in C. similis after inoculation and persisted until rice maturity with a score of 5 compared to the control which was 1 from a 1 to 9 scale. This study allowed identifying the presence of RYMV insect vectors in Benin among which, four are reported for the first time in Africa.
  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.
  S.K. Nutsugah , J.K. Twumasi , J. Chipili , Y. Sere and S. Sreenivasaprasad
  The present study describes the outputs of a collaborative research programme funded by the UK`s Department for International Development-Crop Protection Program to investigate the genetic (lineages) and pathogenic (pathotypes) diversity of the blast fungus populations and characterize the key sites suitable for resistance screening. Seventy-one Magnaporthe grisae isolates were collected from seven regions where rice is grown, representing blast populations in Ghana. Following molecular characterization, these isolates were grouped into four distinct lineages designated as GH-1, GH-2, GH-3 and GH-4 and 25 pathotypes. GH-1 was the major lineage comprising 52% of all the isolates and was present across the country on up to 24 rice cultivars. GH-2 comprising of 30% of the isolates sampled was restricted in distribution mainly from Hohoe area on up to seven cultivars. GH-3 consisted of six isolates from Western, Eastern and Central Regions while GH-4 consisted of two isolates from Nyankpala in Northern Region. Occurrence of blast pathogen on wild rice and weed hosts has been observed and their potential impact needs to be considered in blast/weed management. Baseline data new to Ghana on the diversity and distribution pattern of the blast pathogen populations have been established and key sites identified. Adaptive research is continuing to develop technologies suitable for long-term pathogen monitoring, identify sources of resistance and develop appropriate blast management strategies.
  A. Onasanya , P. Kiepe , A. Basso , G. Nkima , F.E. Nwilene , I. Ingelbrecht , J. Lamo , M.M. Ekperigin , R.O. Onasanya , O. Oyelakin , S. Winter and Y. Sere
  Genomic DNA fingerprinting is a useful tool for effective and reliable identification and differentiation of Xanthomonas oryzae pv. oryzae (Xoo) pathogen from rice. The study aimed to conduct molecular characterization and DNA fingerprinting of 23 Xoo isolates from East Africa and two Xoo isolates from IRRI (Philippines) as control. PCR analysis was carryout on genomic DNA of 25 Xoo isolates using 6 Xoo specific primer pairs. Cluster analyses of genetic data obtained from 25 Xoo DNA fingerprints revealed two major genotypes (GrpA and GrpB) among the 25 Xoo isolates. GrpA has three subgroups (GrpA1; GrpA2; GrpA3) and GrpB (GrpB1; GrpB2; GrpB3). GrpA genotype consists of 20 Xoo isolates from Uganda, Rwanda and Philippines while GrpB genotype has 5 Xoo isolates from Rwanda. Some Xoo isolates were identical (PX-1, PX-2; UX621, RX2101; RX554, UX623, RX4113; UX211, UX213, UX214, RX4112, UX215). The emergence of subgroup genotypes could possibly be due to mutations and interactions among isolates and strains in host cells. Some Xoo isolates from Rwanda and Uganda were identical suggesting possible pathogen migration between these countries and long-term survival. Durable resistance rice cultivars would need to overcome both GrpA and GrpB Xoo genotypes in order to survive after their deployment into different rice ecologies in East Africa.
  J.T. Onwughalu , M.E. Abo , J.K. Okoro , A. Onasanya and Y. Sere
  The study on Rice yellow mottle virus (RYMV) infection and reproductive losses in rice was carried out under screenhouse condition in Nigeria. Thirty-five rice varieties were evaluated for RYMV resistance. Percent productive tillers, date to 50% flowering and percent spikelets fertility per plant were between 43.2-96.7%, 57.67-112 days and 0-71.8%, respectively. Number of panicles per plant, number of grains per panicle and 1000 grain weight per plant were between 8.33-45.67, 0-77 and 0-27.57 g, respectively. Yield losses of between 17-100% were obtained from all the rice varieties evaluated. Out of the 35 rice varieties studied, only Gigante (18%), Moroberekan (19%) and NERICA-L 42 (32%), have the least yield losses and RYMV resistance characteristics. The three varieties (Gigante, Moroberekan and NERICA-L 42) are known to possess stable resistance characteristic to RYMV disease and will comparatively be suitable for cultivation in areas where RYMV incidence is endemic and on a long term be used by rice breeders as sources for breeding for durable resistance to RYMV disease in Nigeria.
  A. Joseph , D.B. Olufolaji , F.E. Nwilene , A. Onasanya , M.M. Omole , R.O. Onasanya and Y. Sere
  The physiological age of rice plant plays a significant role in Rice Yellow Mottle Virus (RYMV) infection. Both flag and old leaves of rice plant differ in their susceptibility to RYMV infection. The present study was, therefore, carried out to examine the effect of leaf age on RYMV severity and chlorophyll content in Moroberekan cultivar with mechanical inoculation and vector transmission method. Border row rice seedlings mechanically inoculated with RYMV isolate at 21 days after sowing metamorphosed into infected rows, following which seeds of Moroberekan were sown 15 days after. Eighty adults each of Locris rubra and Oxya hyla were released onto the infected rows inside separate screenhouse to acquire and transmit the virus to the rice plant. In another trial, three-week old seedlings of Moroberekan were mechanically inoculated with the RYMV isolate. In both experiments, RYMV severity and chlorophyll content of flag and old leaves were assessed at 42, 56 and 70 days after sowing. The highest disease severity (61.65%) was observed in the old leaves of mechanically inoculated plants at 42 DAS while the least disease severity (22.97%) was recorded in the flag leaves of O. hyla inoculated plants at 70 DAS. The highest chlorophyll content (49.29%) was observed at 70 DAS while the least (12.71%) was recorded at 56 DAS. Findings of this study showed that flag leaves of Moroberekan rice cultivar are more susceptible to RYMV infection than older leaves.
  R.O. Onasanya , D.B. Olufolaji , A. Onasanya , Y. Sere , F.E. Nwilene , M. Wopereis and P. Kiepe
  Rice Yellow Mottle Virus (RYMV) genus Sobemovirus is a highly variable pathogen that is very infectious to rice plant. This variability hinders rice breeding for durable resistance to the virus and effective deployment of improved cultivars in Southwest Nigeria. Disease surveys in 5 Southwest states (Lagos, Oyo, Ogun, Ekiti and Ondo) revealed RYMV disease incidence of between 15-70% in farmers’ fields and serological indexing confirmed 92% of collected leaf samples positive to RYMV with 24% from rice and 76% from weeds. The weed with 76% RYMV positive suggests being the main reservoir of RYMV in Southwest Nigeria. Biological test on collected fields leaf samples identified 3 groups (GroupA, GroupD and GroupE) of Resistance Breaking (RB) RYMV isolates and 2 groups (GroupB and GroupC) of normal isolates. Pathotyping 20 RYMV isolates against 10 differential varieties identified 17 isolates as Highly Pathogenic Isolates (HPI) and 3 as Mildly Pathogenic Isolates (MPI) while 4 rice varieties were Highly Resistant (HR), 2 were Moderately Resistant (MR) and 4 were susceptible. HPI isolates present in five states and MPI isolates in two states. Serological study using the same 20 RYMV isolates revealed two major Nigeria serogroup (NSg1 and NSg2) and four subgroups (NSg1a, NSg1b, NSg2a and NSg2b). NSg1a and NSg1b comprised both normal and RB isolates while NSg2a and NSg2b were typical of RB isolates only. This information would assist rice breeding programs to develop durable resistant cultivars to RYMV disease in Southwest Nigeria.
  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.
  A. Onasanya , A. Joseph , D.B. Olufolaji , M.M. Ekperigin , Y. Sere , F.E. Nwilene , P. Kiepe and R.O. Onasanya
  RYMV transmission by insect vectors is considered to fully represent how RYMV disease is spread under natural field conditions. The present study aimed to use Oxya hyla, Locris rubra and Chnootriba similes vectors after acquisition of the virus to determine RYMV movement and distribution in insect body and transmission to rice cultivars. RYMV susceptible BG 90-2 was sown in 5 L plastic pots each at 0.5, 1 and 1.5 m distance from test entries and seedlings were mechanically inoculated with a highly virulent RYMV Nigerian isolate 14 days after sowing. Seven days after inoculation of BG 90-2, test entries were sown in 5-litre plastic pots and same day Oxya hyla, Locris rubra and Chnootriba similes vectors were introduced into the screen house to feed on RYMV infected BG 90-2. RYMV content in Oxya hyla, Locris rubra and Chnootriba similes whole body was 71.8, 44.1 and 50 and head part was 42, 44.6 and 10.1%. RYMV incidence at 0.5, 1.0 and 1.5 m vector migration distance was 14.6, 16.0 and 19.0% for Oxya hyla, 31.3, 35.2 and 39.6% for Locris rubra and 13.7, 16.2 and 19.9% for Chnootriba similes. Cluster dendrogram revealed three groups (GrpA, GrpB, GrpC) of RYMV cultivar screening methods. GrpA was typical of Locris rubra, GrpB has mechanical and Oxya hyla while Chnootriba similes formed GrpC. The information reported in this study would help to better understand RYMV disease epidemic in farmers’ fields and to develop durable resistant rice varieties against the disease.
  A. Banito , E.A. Kadai , A. Onasanya and Y. Sere
  The present study aimed at determining Xanthomonas oryzae pv. oryzae pathogenic diversity. Therefore, the disease survey was conducted in three ecozones of Togo-Forest savanna transition, Forest and dry savanna zones and the diseased samples were collected, the bacteria isolated and characterized by testing their virulence on 21 rice genotypes. The results revealed the occurrence of the bacterial leaf blight in the three ecozones. High bacterial leaf blight incidence of 50-65% was observed in Forest savanna transition and Forest zones, while it was up to 70% in the dry savanna zone. The highest incidence (70%) was recorded in dry savanna zone and the lowest (25%) was frequently observed in Forest zone. Pathotyping analysis of 13 bacterial isolates from samples collected from the infected fields against 21 rice genotypes to isolate and characterize bacteria virulence was carried out. Thus, AMMI cluster analysis revealed the existence of 3 Pathotypes (Pt) among these isolates: PtA highly virulent has 1 isolate, PtB virulent was made up of 3 isolates and PtC moderately virulent was made up of 9 isolates. At ecozone the analysis revealed the presence of PtB and PtC in the Forest savanna transition zone, PtA and PtC in Forest zone and PtB and PtC in the dry savanna zone. The present results provided knowledge on the bacteria virulence and its structure across ecozones of Togo and provided useful information for selection of genotypes for durable resistance to the disease.
 
 
 
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