In a mapping population derived from the Ethiopian barley line L94 x Vada, natural infection by barley yellow dwarf virus (BYDV) occurred. While line L94 hardly showed symptoms, Vada was severely affected. The 103 recombinant inbred lines segregated bimodally. The major gene responsible for this resistance mapped to chromosome 6H. We propose to name the locus Ryd3. A subset of recombinant inbred lines, L94, and Vada were planted in a subsequent field test which confirmed the previous field observations. Double antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISA) indicated that the epidemic was due to a combination of the serotypes BYDV-PAV and BYDV-MAV. In the accessions with the least BYDV symptoms no virus was detected, justifying the consideration of the gene as conferring true resistance rather than tolerance to these viruses. In a laboratory/gauze house trial a near-isogenic line carrying the Vada chromosome 6H fragment in an L94 background was affected as much as Vada. The effect of Ryd3 was quantified, and compared with that of the only other known major gene for resistance to BYDV, Ryd2, which is also of Ethiopian origin and is located on chromosome 3H. Both genes seemed to reduce the chance of the viral isolate used in this study to establish infection. In plants in which it became established, the virus concentration reached a similar level as in susceptible accessions, but with less dramatic symptom development. Inoculated plants in which the virus failed to multiply tended to show an increase in the number of ears per plant, resulting in higher grain yield per plant. Ryd3 co-segregates with several PCR-based molecular markers that may serve for marker assisted selection.
A study to investigate the association of phytoplasmas with papaya dieback and citrus decline syndromes in Ethiopia was carried out between July 2009 and February 2010, with sampling performed in major papaya-and citrus-growing areas of the Rift Valley. Samples of plants with symptoms were collected from papaya, citrus and suspected phytoplasma weed hosts and crops in and around the papaya and citrus fields studied. Nested polymerase chain reaction (nested-PCR) was used for initial characterization, using primers that amplify regions of the 16S rRNA and secA genes, and results were then confirmed with rapid real-time group-specific LAMP (loop-mediated isothermal amplification) assays. The results identified the occurrence of a phytoplasma belonging to the stolbur (16SrXII-A) group in papaya plants showing dieback symptoms, whilst no phytoplasmas were found associated with citrus decline. These results contradict previous reports that a 16SrII phytoplasma was associated with both papaya dieback and citrus decline in Ethiopia, but correspond with the association of a 16SrXII phytoplasmas with Nivum-Haamir-Dieback of papaya in Israel and papaya dieback in Australia. No 16SrXII phytoplasmas were found in any of the weeds and potential alternative hosts studied, although 16SrII phytoplasmas were consistently found in Parthenium hysterophorus weed plants. These results indicate that a 16SrXII phytoplasma is associated with papaya dieback in Ethiopia, whilst the causal agent of citrus decline is not a phytoplasma and remains unidentified.
The objectives of the present study were to evaluate genetic variability parameters, correlations that exist for grain Zn concentration and yield related traits and identification of SSR markers linked to these traits in rice. One hundred seventy six Recombinant Inbred Lines (RILs) of Azucena X Moromutant were grown at University of Agricultural Sciences, Bangalore in augmented experimental design during wet seasons of 2010 and 2011. The study revealed significant genetic variability for all the traits. Grain yield per plant and grain zinc concentration showed higher phenotypic and genotypic co-efficient of variation. Significant positive correlation was observed for grain yield per plant with number of productive tillers per plant (r = 0.5) and number of tillers per plant (r = 0.4). Grain zinc concentration showed negative correlation with grain yield per plant (r = - 0.27). The path-coefficient analysis indicated the positive direct effect of number of productive tillers per plant on grain yield per plant (0.514). Grain zinc concentration showed negative direct effect on grain yield per plant (-0.186). Single-marker analysis using 26 SSR markers on RILs mapping population showed that RM212, RM263, RM6832, RM152, RM21, RM234 and RM3331 had association with grain zinc concentration and other yield related traits. But validation of these markers on fifty two rice genotypes showed that only three markers RM263, RM152 and RM21 had association with grain zinc concentration. Therefore, the genetic information generated and molecular markers identified from this study could be used for zinc biofortification programmes in rice.
Etiological studies of a recently emerged bushy top disease of tobacco in Ethiopia indicated that a ~4.5-kb dsRNA from infected plants represents an umbravirus, whereas a smaller band (~0.5 kb) is that of a new satellite RNA. Potato leafroll virus was also consistently associated with the disease. The three agents, whose experimental host ranges are restricted to members of the family Solanaceae, always occurred together in field samples and are transmitted together by the aphid Myzus persicae nicotianae. The umbravirus, which represents a new species, is most closely related to groundnut rosette virus, and the name Ethiopian tobacco bushy top virus is proposed.
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