Evidence of the viral etiology of sugarcane yellow leaf disease (SCYLD), occurring in southeast Brazil, was obtained by light and electron microscopy combined with serology. Light microscopy using epifluorescence illumination showed an abnormal yellow-green fluorescing material in the phloem of SCYLD-affected plants that was rarely observed in control plants. Immunolocalization in tissue-printed (or -blotted) nitrocellulose membranes, using barley yellow dwarf virus (BYDV) serotype PAV antiserum, showed a weak but clearly positive reaction in the phloem. Isometric viruslike particles of 24 to 26 nm in diameter were found by electron microscopy both in situ and in partially purified preparations. Examination of thin sections showed that phloem companion cells contained viruslike particles and presented cytological changes apparently related to the development of virus infection. Partially purified preparations produced UV absorption spectra typical of a nucleoprotein, with high absorbance at 260 nm, as expected for isometric virus particles. Virus particles were observed in extracts and partially purified preparations using immunosorbent electron microscopy with BYDV-PAV antiserum. Plate-trapped antigen enzyme-linked immunosorbent assays with the same antiserum indicate a weak serological relationship between BYDV-PAV and SCYLD-associated virus.

A previously uncharacterized luteovirus was associated with one form of yellow leaf syndrome (YLS), a widespread disease of sugarcane (Saccharum sp.). The virus was named Sugarcane yellow leaf luteovirus (ScYLV), and was identified in major sugarcane-producing areas of the world. Typical disease symptoms were reproduced when ScYLV was transmitted by Melanaphis sacchari or Rhopalosiphum maidis from infected to healthy sugarcane, suggesting that this virus may be the causal agent of one form of YLS. The only known hosts of ScYLV are Saccharum and Erianthus spp. Virions of ScYLV were 24 to 29 nm in diameter in sodium phosphotungstate at pH 5.0, had a buoyant density of 1.30 g/cm(3) in Cs(2)SO(4), and contained a 5.8-kb genomic ssRNA. The capsid protein had an estimated relative molecular mass of 27 kDa and was not glycosylated. A polyclonal rabbit antiserum raised against ScYLV did not detect any of eight other luteoviruses by enzyme-linked immunosorbent assay or immunosorbent electron microscopy, but in immunoblot assays, antibodies to ScYLV detected the RPV serotype of Barley yellow dwarf luteovirus. It is concluded that ScYLV is a previously undescribed luteovirus that is biologically and serologically distinct from other members of the group and may be the causal agent of one form of YLS of sugarcane.

Wheat is one of the main sources of calories and protein of the world's population and therefore the pathogens that cause rust diseases of the crop are a real threat to food security. Besides the continuous evolution of rust pathogens which repeatedly results in overcoming the resistance of commercial varieties throughout the world, plant breeders are also now challenged by the impacts of global climatic changes. Agricultural practices will need to keep pace with the intensification of sustainable food production in order to face the challenge of feeding a world population estimated to reach about nine billion by 2050. Contemporary wheat breeding has increasingly focused on the future, culminating in the emergence of a global partnership for breeding new wheat varieties with resistance to rust pathogens. Plant breeding now employs a wide range of both long-established and frontier technologies aimed at achieving the United Nations Millennium Development Goals of ending hunger and extreme poverty (MDG1), while concurrently promoting environmental sustainability (MDG7) through global partnerships for development (MDG8).

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RESUMONeste trabalho,objetivou-se analisar a viabilidade de grãos de pólen de 52 genótipos de triticale, oriundos do bloco de cruzamentos do programa de melhoramento genético da Embrapa Trigo do ano de 2005. A coleta das espigas foi realizada quando as plantas se encontravam na fase anterior à antese. As análises citológicas foram realizadas fixando as anteras de uma mesma espiga em fixador Carnoy. Para a análise polínica, as lâminas foram confeccionadas usando-se três anteras da mesma flor, oriundas das regiões basal, mediana e apical de uma espiga, totalizando nove lâminas por genótipo. Para cada lâmina, foram contados cerca de 200 grãos de pólen, classificando-os em duas categorias: 1) normais ou viáveis e 2) anormais. Os dados foram analisados e as médias comparadas pelo teste de Duncan 5%. A análise de variância demonstrou haver diferenças significativas em relação à viabilidade polínica entre os 52 genótipos observados. A grande maioria dos genótipos apresentou viabilidade polínica superior a 90 %. A seleção assistida, via análise citológica de grãos de pólens, é potencialmente útil para um programa de melhoramento genético vegetal, uma vez que cruzamentos feitos entre plantas portadoras de pólens inviáveis resultarão em plantas estéreis e numa menor produção de grãos. Termos para indexação:Triticosecale Wittmack, citogenética, grãos de pólen. ABSTRACTThe objective of this study was to analyze the pollen grain viability of 52 triticale genotypes from the 2005 crossing block of the Embrapa Wheat breeding program. The spikes were collected prior to anthesis and cytological analyses were performed upon fixing the anthers from the basal, medium, and apical regions of the spike and replicated three times for each sample. For each slide, about 200 pollen grains were analyzed and they were classified into two different groups: 1) normal or viable and 2) non-viable or abnormal. The obtained data were analyzed and the means were compared by the Duncan test at 5% propability. The results of analysis of variance demonstrated that the differences among the genotypes were highly significant. However, most of the genotypes studied showed a high percentage of normal pollens. Cytological analysis of the pollen grain is potentially useful as assisted selection in a breeding program, especially to decrease the possibility of obtaining sterile plants or plants with less grain production. O triticale é primário, quando provém diretamente do cruzamento entre espécies ancestrais (trigo e centeio) e secundário, quando resulta do cruzamento entre primários ou destes com outros secundários (Baier & Nedel, 1985). São denominados completos ou triticales hexaplóides, os que contêm todos os sete pares de cromossomos dos genomas "A" e "B", do trigo, e "R", de centeio. São denominados substituídos, os triticales hexaplóides em que um ou mais cromossomos de centeio foram substituídos por cromossomos de trigo (Baier et al., 1996).