Impact of eight isolates of Rice Yellow Mottle Virus (RYMV) from Gagnoa (Côte d’Ivoire) on rice (Oryza sp) cultivars production

Rice yellow mottle virus, of the genus Sobemovirus, causes a major disease in Africa especially in the lowland and irrigated rice ecologies. Yield losses due to the virus were estimated between 5-100% and depend on genotype. This study, conducted in a screen house, aimed at assessing the impact of eight RYMV isolates from a restrictive environment Gagnoa (Côte d’Ivoire) on 10 differential rice varieties. The plants were inoculated manually by rubbing the leaves from the leaf base to the tip with fingers moistened with inoculum. Virus content and percentage yield reduction of different rice cultivars have been assessed. Result showed that an important variability was observed in the reaction of different rice genotypes infected by different isolates of RYMV. In susceptible cultivars Bouaké 189, PNA647F4-56 and H232-44-1-1 virus content and yield reduction varied respectively from 0.08 to 0.264 and 20 to 95%. In resistant cultivars, Gigante, Lac 23, Morobérékan and Faro 11, virus content and yield reduction varied respectively from 0.03 to 0.188 and 5 to 17%. The lowest virus content and yield reduction was observed with the isolate 7 from upland rice. The significant difference in the interaction observed between the different genotypes of rice and isolates of RYMV suggested the existence of different strains of RYMV within a restrictive environment.© 2015 International Formulae Group. All rights reserved.Keywords: AfricaRice, Sobemovirus, aggressive, virus content, yield reduction, virulenc

Morphological diversity and genomic DNA fingerprinting of the African rice gall midge, Orseolia oryzivora (Diptera: Cecidomyiidae) and of two other species of African Orseolia

A morphological diversity study was conducted on African rice gall midge Orseolia oryzivora Harris & Gagné and two other African species, Orseolia bonzii Harris and Orseolia nwanzei Harris & Nwilene, sp. n. Morphological differences between adult and immature stages of the three species are slight and mainly evident in pupal characters. Due to limited differences in morphological characters, genomic DNA fingerprinting of these three insect species was carried out using random amplified polymorphic DNA (RAPD) and sequence-characterized amplified region (SCAR) methods. Out of 90 operon primers, 15 showed polymorphism among the three species tested, generating 86 bands, 60 (70%) of which were polymorphic. Primer OPV6 produced three RAPD markers that distinguished the three Orseolia species. These markers were cloned and sequenced. Their sequence was then used to design six SCAR primer pairs. Each SCAR primer pair amplified and distinguished the three Orseolia species at genomic DNA level. Both SCAR and RAPD genomic DNA fingerprinting revealed that O. oryzivora and O. bonzii are most closely related and O. nwanzei is distinct. Each of the six SCAR primer pairs produced a specific DNA fragment size specific for O. nwanzei, O. oryzivora and O. bonzii. The DNA fingerprints will be useful for entomological survey, identification of new species and differentiating aggressive from non-aggressive species, aimed at the effective development of rice cultivars with durable resistance to African rice gall midge

Identification and differentiation of Orseolia species in Nigeria as revealed by SCAR-PCR analysis

Identification and differentiation of Orseolia species in Nigeria was carried out using SCAR-PCR analysis. Twenty-three insects from 9 localities in Nigeria and three reference insects (Orseolia bonzii, Orseolia nwanzei and Orseolia oryzivora) were analyzed. Out of the 60 SCAR primers screened, only four produced clear amplified DNA fragments at annealing temperature of 55°C that differentiated all the 26 Orseolia species. Cluster analysis revealed two major insect genotypes (OSG-1 and OSG-2). The OSG-1 was further divided into two subgroups (OSG-1a and OSG-1b). Eleven insects were genotyped as OSG-1a, 14 as OSG-1b and one as OSG-2. Only NG1 and NG2 were identical among the insects of OSG-1a genotype. OSG-1b genotype produced two different groups of identical insects. While O. bonzii and O. oryzivora were genotyped as OSG-1b along with other twelve insects, only O. nwanzei was genotyped as OSG-2. OSG-1b genotype constitutes about 54% O. bonzii and O. oryzivora in Nigeria, OSG-2 genotype represents 4% of O. nwanzei in Nigeria while OSG-1a genotype covers 42% of yet unknown Orseolia species in Nigeria. This information would strongly assist breeding programmes aiming at effective development of cultivars with durable resistance to African rice gall midge (AfRGM) in Nigeria