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The cultivated area devoted to rice crops (Oryza sativa) in Brazil has expanded in recent years, along with improvements in yield. This has prompted the continuous exchange of material from active germplasm banks between government breeding programs. When placed in a greenhouse for multiplication purposes, rice accessions resulting from exchanges between USDA-ARS (United States Department of Agriculture - Agricultural Research Service) showed little or no germination. The accessions were sent to the tissue culture laboratory of BAG-CNPAF (Embrapa National Rice and Bean Research Center) to recover embryos by aseptically removing the seed coat of 10 seeds from each accession. Bacterial colony growth concomitant to germination inhibition was observed in some accessions, from which four bacterial isolates were obtained. Made available in DSpace on 2017-12-26T23:23:54Z (GMT). No. of bitstreams: 1 CNPAF2018pdv102n1.pdf: 213919 bytes, checksum: c3d290b54a0663e654d67513d579c97c (MD5) Previous issue date: 2017-12-18 Disease notes.

Relative cross sections for the $4\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ ${\mathrm{H}}^{+}+{\mathrm{D}}_{2}$ $(^{1}\ensuremath{\Sigma}_{g}^{+})\ensuremath{\rightarrow}{\mathrm{H}}^{+}+{\mathrm{D}}_{2}^{+}(1s\ensuremath{\sigma})+{e}^{\ensuremath{-}}$ ionization process were measured as a function of the molecular alignment during the interaction. The angle between the molecular axis and the projectile was obtained by using a momentum imagining technique and isolating the events in which the ${\mathrm{D}}_{2}^{+}(1\mathrm{s}\ensuremath{\sigma})$ ions are excited to the vibrational continuum and subsequently dissociate. While anisotropic cross sections have been observed in the past for a number of collision processes involving both target electrons, the one electron process investigated here is isotropic within our experimental uncertainties.

The presence of geminiviruses has been recognised in Brazil since the 1950s. In the early 1990s, after the introduction of a new biotype of the whitefly vector, successive reports of geminivirus infection indicated the establishment of these pathogens in tomato crops. Initial reports suggested that new species were emerging in different parts of the country. Further studies indicated the presence of eight novel species. Similarities between tomato-and weed-infecting viruses suggested that indigenous viruses were being transferred to tomatoes by the insect vector. Sequence analysis indicated that recombination and pseudo-recombination were already taking place among these new viruses. Management of tomato geminiviruses has been a major challenge. Successful control depends on an integrated management approach. Although most growers rely solely on heavy pesticide application, cultural practices which help to reduce ‘viral load’ have displayed much better results. The main component of this approach is a tomato-free period of at least 30 days. In the areas where such measures were adopted, together with the use of virus-free transplants and rational chemical control of the vector, geminivirus incidence was greatly reduced. Meanwhile, novel approaches being developed include genetically-modified tomatoes using RNA silencing, either targeting the viral genome or host genes which are essential for viral replication.