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Articles by J.K. Okoro
Total Records ( 3 ) for J.K. Okoro
  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.
  J.T. Onwughalu , M.E. Abo , A.O. Nwankiti , J.K. Okoro and D. Silue
  The study was carried out to investigate pathotypes relationship of six Rice Yellow Mottle Virus (RYMV) isolates from North Central Zone of Nigeria in 2016 using some released Oryza species and Near Isogenic Lines (NILs). The experiment was laid out in a split-split plot design in the screen house at Badeggi, Niger State, Nigeria. Yield and agronomic data were subjected to statistical analysis using CropStat Version 7.2. The result showed a non-significant interaction effect of rice genotypes, disease isolates and inoculation regimes on spikelets sterility (%) and a highly significant effect (p = 0.01) on yield per plant (g) at harvest. The impact of the virus on the number of panicles per plant at maturity was significantly higher on test plants inoculated at active tillering stages which consistently produced lower mean panicle numbers across the levels of virus isolates. The result also showed that NIL 54 produced high resistance to the virus which is not due to immunity as the leaf extract from inoculated plant was infectious on susceptible FKR 28 during back inoculation test. NIL 54 did not also record significant reduction on the average leaf length (cm) per plant at maturity with the virus isolates; neither did it express the characteristic symptoms of the virus with the six isolates. Obubu-Ofu and Makurdi isolates circumvented the resistance in Gigante and showed obvious yellow mottle symptoms. The serological analysis and RYMV isolates characterization indicated that the six virus isolates belonged to sero groups 1 and 2 (S1 and S2). NIL 54 is recommended for further pathogenicity investigation with more isolates of RYMV in Nigeria or elsewhere, since, no obvious symptom of the virus was observed on the plant when challenged with S2 and S1 isolates in the present study.
  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.
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