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KEY MESSAGE: PCD role in unisexual flowers. The developmental processes underlying the transition from hermaphroditism to unisexuality are key to understanding variation and evolution of floral structure and function. A detailed examination of the cytological and histological patterns involved in pollen and ovule development of staminate and pistillate flowers in the dioecious Opuntia robusta was undertaken, and the potential involvement of programmed cell death in the abortion of the sex whorls was explored. Flowers initiated development as hermaphrodites and became functionally unisexual by anthesis. Female individuals have pistillate flowers with a conspicuous stigma, functional ovary, collapsed stamens and no pollen grains. Male individuals have staminate flowers, with large yellow anthers, abundant pollen grains, underdeveloped stigma, style and an ovary that rarely produced ovules. In pistillate flowers, anther abortion resulted from the premature degradation of the tapetum by PCD, followed by irregular deposition of callose wall around the microsporocytes, and finally by microspore degradation. In staminate flowers, the stigma could support pollen germination; however, the ovaries were reduced, with evidence of placental arrest and ovule abortion through PCD, when ovules were present. We demonstrate that PCD is recruited in both pistillate and staminate flower development; however, it occurs at different times of floral development. This study contributes to the understanding of the nature of the O. robusta breeding system and identifies developmental landmarks that contribute to sexual determination in Cactaceae.

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BACKGROUND: Pollen development is an energy-consuming process that particularly occurs during meiosis. Low levels of adenosine triphosphate (ATP) may cause cell death, resulting in CMS (cytoplasmic male sterility). DNA sequence differences in ATP synthase genes have been revealed between the N- and S-cytoplasms in the cotton CMS system. However, very few data are available at the RNA level. In this study, we compared five ATP synthase genes in the H276A, H276B and fertile F1 (H276A/H268) lines using RNA editing, RNA blotting and quantitative real time-PCR (qRT-PCR) to explore their contribution to CMS. A molecular marker for identifying male sterile cytoplasm (MSC) was also developed. RESULTS: RNA blotting revealed the absence of any novel orf for the ATP synthase gene sequence in the three lines. Forty-one RNA editing sites were identified in the coding sequences. RNA editing showed that proteins had 32.43% higher hydrophobicity and that 39.02% of RNA editing sites had proline converted to leucine. Two new stop codons were detected in atp6 and atp9 by RNA editing. Real-time qRT-PCR data showed that the atp1, atp6, atp8, and atp9 genes had substantially lower expression levels in H276A compared with those in H276B. By contrast, the expression levels of all five genes were increased in F1 (H276A/H268). Moreover, a molecular marker based on a 6-bp deletion upstream of atp8 in H276A was developed to identify male sterile cytoplasm (MSC) in cotton. CONCLUSIONS: Our data substantially contributes to the understanding of the function of ATP synthase genes in cotton CMS. Therefore, we suggest that ATP synthase genes might be an indirect cause of cotton CMS. Further research is needed to investigate the relationship among ATP synthase genes in cotton CMS.

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BACKGROUND: Pollen development is an energy-consuming process that particularly occurs during meiosis. Low levels of adenosine triphosphate (ATP) may cause cell death, resulting in CMS (cytoplasmic male sterility). DNA sequence differences in ATP synthase genes have been revealed between the N- and S-cytoplasms in the cotton CMS system. However, very few data are available at the RNA level. In this study, we compared five ATP synthase genes in the H276A, H276B and fertile F1 (H276A/H268) lines using RNA editing, RNA blotting and quantitative real time-PCR (qRT-PCR) to explore their contribution to CMS. A molecular marker for identifying male sterile cytoplasm (MSC) was also developed. RESULTS: RNA blotting revealed the absence of any novel orf for the ATP synthase gene sequence in the three lines. Forty-one RNA editing sites were identified in the coding sequences. RNA editing showed that proteins had 32.43% higher hydrophobicity and that 39.02% of RNA editing sites had proline converted to leucine. Two new stop codons were detected in atp6 and atp9 by RNA editing. Real-time qRT-PCR data showed that the atp1, atp6, atp8, and atp9 genes had substantially lower expression levels in H276A compared with those in H276B. By contrast, the expression levels of all five genes were increased in F1 (H276A/H268). Moreover, a molecular marker based on a 6-bp deletion upstream of atp8 in H276A was developed to identify male sterile cytoplasm (MSC) in cotton. CONCLUSIONS: Our data substantially contributes to the understanding of the function of ATP synthase genes in cotton CMS. Therefore, we suggest that ATP synthase genes might be an indirect cause of cotton CMS. Further research is needed to investigate the relationship among ATP synthase genes in cotton CMS.

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Speciation can occur through the presence of reproductive isolation barriers that impede mating, restrict cross-fertilization, or render inviable/sterile hybrid progeny. The D. willistoni subgroup is ideally suited for studies of speciation, with examples of both allopatry and sympatry, a range of isolation barriers, and the availability of one species complete genome sequence to facilitate genetic studies of divergence. D. w. willistoni has the largest geographic distribution among members of the Drosophila willistoni subgroup, spanning from Argentina to the southern United States, including the Caribbean islands. A subspecies of D. w. willistoni, D. w. quechua, is geographically separated by the Andes mountain range and has evolved unidirectional sterility, in that only male offspring of D. w. quechua females × D. w. willistoni males are sterile. Whether D. w. willistoni flies residing east of the Andes belong to one or more D. willistoni subspecies remains unresolved. Here we perform fecundity assays and show that F1 hybrid males produced from crosses between different strains found in Central America, North America, and northern Caribbean islands are reproductively isolated from South American and southern Caribbean island strains as a result of unidirectional hybrid male sterility. Our results show the existence of a reproductive isolation barrier between the northern and southern strains and suggest a subdivision of the previously identified D. willistoni willistoni species into 2 new subspecies.

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Nectar is the most important floral reward offered by plants to insects. Minor components such as alkaloid compounds in nectar affect bee foraging, with great influence in seed production. CE is an advantageous tool for the analysis of unexplored samples such as onion nectar due to the limited amounts of samples. Considering the importance of these compounds, a simultaneous determination of nicotine, theophylline, theobromine, caffeine, harmaline, piperine in onion nectar by MEKC-UV is herein reported. The extraction of alkaloid compounds in nectar was performed by SPE using a homemade miniaturized column (C18 ). Effects of several important factors affecting extraction efficiency as well as electrophoretic performance were investigated to acquire optimum conditions. Under the proposed conditions, the analytes can be separated within 15 min in a 50 cm effective length capillary (75 µm id) at a separation voltage of 20 kV in 20 mmol/L sodium tretraborate, 100 mmol/L SDS. The amount of sample requirement was reduced up to 2000 times, when compared to traditional methods, reaching limits of detection as low as 0.0153 ng/L. For the first time, this study demonstrates that there are marked qualitative and quantitative differences in nectar alkaloids between open pollinated and male sterile lines (MSLs) and also within MSLs.

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BACKGROUND AND AIMS: Polyploidy has important effects on reproductive systems in plants and has been implicated in the evolution of dimorphic sexual systems. In particular, higher ploidy is associated with gender dimorphism across Lycium species (Solanaceae) and across populations within the species Lycium californicum. Previous research on the association of cytotype and sexual system within L. californicum sampled a limited portion of the species range, and did not investigate evolutionary transitions between sexual systems. Lycium californicum occurs in arid regions on offshore islands and mainland regions in the south-western United States and Mexico, motivating a more comprehensive analysis of intraspecific variation in sexual system and cytotype across the full range of this species. METHODS: Sexual system (dimorphic vs. cosexual) was determined for 34 populations across the geographical range of L. californicum using field observations of pollen production, and was confirmed using morphological measurements and among-plant correlations of primary sexual traits. Ploidy was inferred using flow cytometry in 28 populations. DNA sequence data from four plastid and two nuclear regions were used to reconstruct relationships among populations and to map transitions in sexual system and ploidy. KEY RESULTS: Lycium californicum is monophyletic, ancestrally diploid and cosexual, and the association of gender dimorphism and polyploidy appears to have two evolutionary origins in this species. Compared with cosexual populations, dimorphic populations had bimodal anther size distributions, negative correlations between male and female floral traits, and larger coefficients of variation for primary sexual traits. Flow cytometry confirmed tetraploidy in dimorphic populations, whereas cosexual populations were diploid. CONCLUSIONS: Tetraploidy and gender dimorphism are perfectly correlated in L. californicum, and the distribution of tetraploid-dimorphic populations is restricted to populations in Arizona and the Baja California peninsula. The analysis suggests that tetraploidy and dimorphism likely established in Baja California and may have evolved multiple times.

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UNLABELLED: • PREMISE OF THE STUDY: An association between polyploidy and gender dimorphism has been noted in several plant lineages. Whereas the majority of Lycium species are diploid and have hermaphroditic flowers in cosexual populations, gender dimorphism (gynodioecy, dioecy) has been shown to be uniformly associated with polyploidy in previous studies. Preliminary field observations suggested that some populations of Lycium carolinianum were dimorphic, providing a test of this association.• METHODS: We assessed sexual systems and cytotype variation (to infer ploidy) across 17 populations of L. carolinianum. Comparison of flowers in cosexual and dimorphic populations were used to infer changes in reproductive morphology associated with the evolution of gynodioecy.• KEY RESULTS: The majority of populations were cosexual in gender expression, but dimorphism was present in the Yucatán and in some populations in Hawaii. Populations varied in ploidy and were either diploid or tetraploid. Floral sexual dimorphism was present in all gynodioecious populations, though the magnitude differed and was cryptic in some cases. Our results are consistent with the hypothesis that following the evolution of gynodioecy, flowers on hermaphrodites increased in size.• CONCLUSIONS: Dimorphic sexual systems have likely evolved convergently in L. carolinianum. In contrast to previous studies, dimorphism is not perfectly associated with polyploidy. Although our sample from the Yucatán was both tetraploid and dimorphic, all populations in Hawaii were diploid regardless of sexual system. Ongoing phylogeographic and mating system studies will contribute to our understanding of reproductive evolution in this widespread, polymorphic species.

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The mature pollen grain displays a highly specialized function in angiosperms. Accordingly, the male gametophyte development involves many specific biological activities, making it a complex and unique process in plants. In order to accomplish this, during pollen development, a massive transcriptomic remodeling takes place, indicating the switch from a sporophytic to a gametophytic program and involving the expression of many pollen specific genes. Using microarray databases we selected genes showing pollen-specific accumulation of their mRNAs and confirmed this through RT-PCR. We selected five genes (POLLEN SPECIFIC GENE1-5) to investigate the pollen specificity of their expression. Transcriptional fusions between the putative promoters of these genes and the uidA reporter gene in Arabidopsis confirmed the pollen specific expression for at least two of these genes. The expression of the cytotoxin Barnase controlled by these promoters generated pollen specific ablation and male sterility. Through the selection of pollen specific genes from public datasets, we were able to identify promoter regions that confer pollen expression. The use of the cytotoxin Barnase allowed us to demonstrate its expression is exclusively limited to the pollen. These new promoters provide a powerful tool for the expression of genes exclusively in pollen.

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BACKGROUND AND AIMS: The sexual separation in dioecious species has interested biologists for decades; however, the cellular mechanism leading to unisexuality has been poorly understood. In this study, the cellular changes that lead to male sterility in the functionally dioecious cactus, Opuntia stenopetala, are described. METHODS: The spatial and temporal patterns of programmed cell death (PCD) were determined in the anthers of male and female flowers using scanning electron microscopy analysis and histological observations, focusing attention on the transition from bisexual to unisexual development. In addition, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling assays were used as an indicator of DNA fragmentation to corroborate PCD. KEY RESULTS: PCD was detected in anthers of both female and male flowers, but their patterns differed in time and space. Functionally male individuals developed viable pollen, and normal development involved PCD on each layer of the anther wall, which occurred progressively from the inner (tapetum) to the outer layer (epidermis). Conversely, functional female individuals aborted anthers by premature and displaced PCD. In anthers of female flowers, the first signs of PCD, such as a nucleus with irregular shape, fragmented and condensed chromatin, high vacuolization and condensed cytoplasm, occurred at the microspore mother cell stage. Later these features were observed simultaneously in all anther wall layers, connective tissue and filament. Neither pollen formation nor anther dehiscence was detected in female flowers of O. stenopetala due to total anther disruption. CONCLUSIONS: Temporal and spatial changes in the patterns of PCD are responsible for male sterility of female flowers in O. stenopetala. Male fertility requires the co-ordination of different events, which, when altered, can lead to male sterility and to functionally unisexual individuals. PCD could be a widespread mechanism in the determination of functionally dioecious species.

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Triticale (X Triticosecale Wittmack) is a good cereal for production of flour and feed. A segregating population of triticale was developed from a male-sterile (MS) plant. To determine whether this new source of male sterility in triticale is appropriate for use in breeding programs the expression of the male sterility phenotype was characterized through spike fertility, meiotic behavior, and pollen. Controlled crosses between male-sterile plants and control varieties male-fertile (MF) of triticale were also conducted, and cytological analyses were performed in the F2 and backcross plants. Plants with male-sterile phenotypes displayed reduced spike fertility when compared to plants with male-fertile phenotypes. Compared to male-fertile plants, male-sterile plants exhibited a lower percentage of normal meiotic cells, a reduced meiotic index and reduced pollen viability. The F2 plants had improved pollen fertility when compared to the male-sterile population; however there were no corresponding improvements in the percentage of normal meiotic cells or in the meiotic index. A single generation of backcrosses resulted in an improved meiotic index and increased pollen viability. However, no changes in the percentage of normal meiotic cells were observed. Meiotic instability, which was shown to be inheritable, was the likely cause of male sterility. Therefore, the use of this population in triticale breeding was considered to be inappropriate because it could promote or contribute to the maintenance of meiotic instability, which is commonly observed in this species.

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Triticale (X Triticosecale Wittmack) is a good cereal for production of flour and feed. A segregating population of triticale was developed from a male-sterile (MS) plant. To determine whether this new source of male sterility in triticale is appropriate for use in breeding programs the expression of the male sterility phenotype was characterized through spike fertility, meiotic behavior, and pollen. Controlled crosses between male-sterile plants and control varieties male-fertile (MF) of triticale were also conducted, and cytological analyses were performed in the F2 and backcross plants. Plants with male-sterile phenotypes displayed reduced spike fertility when compared to plants with male-fertile phenotypes. Compared to male-fertile plants, male-sterile plants exhibited a lower percentage of normal meiotic cells, a reduced meiotic index and reduced pollen viability. The F2 plants had improved pollen fertility when compared to the male-sterile population; however there were no corresponding improvements in the percentage of normal meiotic cells or in the meiotic index. A single generation of backcrosses resulted in an improved meiotic index and increased pollen viability. However, no changes in the percentage of normal meiotic cells were observed. Meiotic instability, which was shown to be inheritable, was the likely cause of male sterility. Therefore, the use of this population in triticale breeding was considered to be inappropriate because it could promote or contribute to the maintenance of meiotic instability, which is commonly observed in this species.

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Previous work on gene expression analysis based on RNA sequencing identified a variety of differentially expressed cDNA fragments in the genic male sterile-fertile line 114AB of Capsicum annuum L. In this work, we examined the accumulation of one of the transcript-derived fragments (TDFs), CaMF3 (male fertile 3), in the flower buds of a fertile line. The full genomic DNA sequence of CaMF3 was 1,951 bp long and contained 6 exons and 5 introns, with the complete sequence encoding a putative 25.89 kDa protein of 234 amino acids. The predicted protein of CaMF3 shared sequence similarity with members of the isoamyl acetate-hydrolyzing esterase (IAH1) protein family. CaMF3 expression was detected only in flower buds at stages 7 and 8 and in open flowers of a male fertile line; no expression was observed in any organs of a male sterile line. Fine expression analysis revealed that CaMF3 was expressed specifically in anthers of the fertile line. These results suggest that CaMF3 is an anther-specific gene that may be essential for anther or pollen development in C. annuum.

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La infertilidad masculina es considerada como uno de los factores que más contribuyen a la infertilidad de la pareja. En conjunción a los factores convencionales que la originan se ha identificado una causa de extraordinaria repercusión: el estrés oxidativo, el cual es el resultado del desequilibrio entre la generación de especies reactivas del oxígeno y los antioxidantes, que puede originar daños o deformidades a los espermatozoides y eventualmente infertilidad masculina. Las especies reactivas del oxígeno se producen por diversos mecanismos en el semen, por espermatozoides inmóviles o con problemas de movilidad, leucocitos y por espermatozoides normales morfológicamente pero funcionalmente anormales. Entre estos daños, se registran la peroxidación lipídica a la membrana espermática y la fragmentación del ADN tanto nuclear como mitocondrial. Los daños que causa el estrés oxidativo sobre el ADN pueden originar trastornos en la descendencia que incluyen cáncer y acondroplastia. La peroxidación lipídica, origina la alteración de la membrana que afecta su estructura y función. La membrana del espermatozoide humano contiene una elevada proporción de ácidos grasos poliinsaturados, por lo tanto su susceptibilidad a la peroxidación lipídica es muy elevada. Las especies reactivas del oxígeno tienen diversos efectos sobre las células espermáticas, constituyendo un tema muy controvertido, por lo que este artículo tuvo como propósito actualizar al lector sobre algunos de los aspectos bioquímicos relacionados con la producción de especies reactivas del oxígeno y los métodos de diagnóstico que se emplean para detectarlo en la infertilidad humana.

The male sterility is considered as one of the factors more contributing to couple sterility. Join to conventional factors originate it condition it was possible to identify a cause with a high level of repercussion: the oxidative stress, which is the result of the imbalance between generation of reactive oxygen species and the antioxidants that may to cause damages or deformities in the spermatozoa and eventually male sterility. The reactive oxygen species are produced due to different mechanisms present in semen, motionless spermatozoa or with motility disorders, leukocytes and morphologically normal spermatozoa but functionally abnormal. Among these damages it is present the lipid peroxidation to spermatic membrane and the nuclear and mitochondrial DNA fragmentation. The damages of oxidative stress on DNA may also to cause disorders in offspring including cancer and achondroplasia. Lipid peroxidation leads to an alteration in the membrane affecting its structure and function. The human spermatozoon membrane contains a high proportion of poly-non-saturated fatty acids therefore its oversensitivity to lipid peroxidation is very high. The reactive oxygen species have different effects on spermatic cells, being a very controversial topic. The aim of present paper was to update readers on some of the biochemical features related to the production of reactive oxygen species and the diagnostic methods used to detect the human sterility.

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This study was designed to control plant fertility by cell lethal gene Barnase expressing at specific developmental stage and in specific tissue of male organ under the control of Cre/loxP system, for heterosis breeding, producing hybrid seed of eggplant. The Barnase-coding region was flanked by loxP recognition sites for Cre-recombinase. The eggplant inbred/pure line ('E-38') was transformed with Cre gene and the inbred/pure line ('E-8') was transformed with the Barnase gene situated between loxp. The experiments were done separately, by means of Agrobacterium co-culture. Four T(0) -plants with the Barnase gene were obtained, all proved to be male-sterile and incapable of producing viable pollen. Flowers stamens were shorter, but the vegetative phenotype was similar to wild-type. Five T (0) -plants with the Cre gene developed well, blossomed out and set fruit normally. The crossing of male-sterile Barnase-plants with Cre expression transgenic eggplants resulted in site-specific excision with the male-sterile plants producing normal fruits. With the Barnase was excised, pollen fertility was fully restored in the hybrids. The phenotype of these restored plants was the same as that of the wild-type. Thus, the Barnase and Cre genes were capable of stable inheritance and expression in progenies of transgenic plants.

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This study was designed to control plant fertility by cell lethal gene Barnase expressing at specific developmental stage and in specific tissue of male organ under the control of Cre/loxP system, for heterosis breeding, producing hybrid seed of eggplant. The Barnase-coding region was flanked by loxP recognition sites for Cre-recombinase. The eggplant inbred/pure line ('E-38') was transformed with Cre gene and the inbred/pure line ('E-8') was transformed with the Barnase gene situated between loxp. The experiments were done separately, by means of Agrobacterium co-culture. Four T0-plants with the Barnase gene were obtained, all proved to be male-sterile and incapable of producing viable pollen. Flowers stamens were shorter, but the vegetative phenotype was similar to wild-type. Five T0-plants with the Cre gene developed well, blossomed out and set fruit normally. The crossing of male-sterile Barnase-plants with Cre expression transgenic eggplants resulted in site-specific excision with the male-sterile plants producing normal fruits. With the Barnase was excised, pollen fertility was fully restored in the hybrids. The phenotype of these restored plants was the same as that of the wild-type. Thus, the Barnase and Cre genes were capable of stable inheritance and expression in progenies of transgenic plants.

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Morphological changes have been investigated during plant programmed cell death (PCD) in the last few years due to the new interest in a possible apoptotic-like phenomenon existing in plants. Although PCD has been reported in several tissues and specialized cells in plants, there have been few reports of its occurrence during microsporogenesis. The present study reports a typical process of PCD during meiosis in an interspecific Brachiaria hybrid leading to male sterility. In this hybrid, some inflorescences initiated meiosis but it was arrested in zygotene/pachytene. From this stage, meiocytes underwent a severe alteration in shape showing substantial membrane blebbing; the cytoplasm became denser at the periphery; the cell nucleus entered a progressive stage of chromatin disintegration, and then the nucleolus disintegrated, and the cytoplasm condensed and shrunk. The oldest flowers of the raceme showed only the callose wall in the anthers showing obvious signs of complete sterility.

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The relationship between pre-flowering climatic conditions and sugary disease incidence was quantified in grain and forage sorghum genotypes at two sowing periods (mid November and mid December). The trials were carried out over the 2001/02 and 2002/03 growing seasons, in Lages, Santa Catarina State. Four commercial male-fertile sorghum hybrids (BR 600-forrage, BR 700-grain, BR 701-forage/silage and BR 800-forage) and one male-sterile inbred line (BR 001-A) were evaluated. When each genotype reached the flowering stage, 50 panicles were marked and sprayed with a suspension of Claviceps africana (1,000 spores mL-1). Air temperature, humidity and rainfall were recorded through out the growing cycle. Low temperatures three to four weeks prior to flowering, increased susceptibility. At both sowing periods, average night temperatures lower than 15°C during the critical period of pre-flowering turned the fertile hybrids as susceptible as the male-sterile inbred to ergot infection. The tested hybrids differed in their ability to tolerate pre-flowering cold stress. Seed set in uninoculated heads under pollination bags was also reduced, suggesting that increased susceptibility to sugary disease was the result of low temperature induced sterility.

A relação entre as condições climáticas no pré-florescimento e a incidência da doença açucarada em sorgo foi quantificada, em duas épocas de semeadura (metade de novembro e metade de dezembro) durante os anos agrícolas de 2001/02 e 2002/03. Experimentos foram conduzidos com quatro híbridos férteis (BR 600-forragem, BR 700-grão/silagem, BR 701-forragem/silagem and BR 800-corte/pastejo) e uma linhagem macho-estéril (BR 001-A) de sorgo granífero e forrageiro. Quando cada genótipo atingiu o florescimento, 50 panículas foram marcadas e aspergidas com uma suspensão de Claviceps africana (1.000 esporos mL-1). A temperatura e umidade relativa do ar e a precipitação foram registradas durante todo o ciclo da cultura. Baixas temperaturas noturnas entre três a quatro semanas que antecederam o florescimento, aumentaram a susceptibilidade à doença açucarada. Nas duas épocas de semeadura, temperaturas médias noturnas abaixo de 15°C durante o período crítico de pré-florescimento induziram os híbridos férteis a serem tão suscetíveis quanto o genótipo macho-estéril à doença açucarada. Os híbridos testados diferiram na tolerância ao estresse causado pelo frio na fase de pré-florescimento. A taxa de formação das sementes em panículas não inoculadas cobertas por saco polinizador também foi reduzida, sugerindo que o aumento da susceptibilidade à doença decorreu da influência da baixa temperatura, induzindo à esterilidade.

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The relationship between pre-flowering climatic conditions and sugary disease incidence was quantified in grain and forage sorghum genotypes at two sowing periods (mid November and mid December). The trials were carried out over the 2001/02 and 2002/03 growing seasons, in Lages, Santa Catarina State. Four commercial male-fertile sorghum hybrids (BR 600-forrage, BR 700-grain, BR 701-forage/silage and BR 800-forage) and one male-sterile inbred line (BR 001-A) were evaluated. When each genotype reached the flowering stage, 50 panicles were marked and sprayed with a suspension of Claviceps africana (1,000 spores mL-1). Air temperature, humidity and rainfall were recorded through out the growing cycle. Low temperatures three to four weeks prior to flowering, increased susceptibility. At both sowing periods, average night temperatures lower than 15°C during the critical period of pre-flowering turned the fertile hybrids as susceptible as the male-sterile inbred to ergot infection. The tested hybrids differed in their ability to tolerate pre-flowering cold stress. Seed set in uninoculated heads under pollination bags was also reduced, suggesting that increased susceptibility to sugary disease was the result of low temperature induced sterility.

A relação entre as condições climáticas no pré-florescimento e a incidência da doença açucarada em sorgo foi quantificada, em duas épocas de semeadura (metade de novembro e metade de dezembro) durante os anos agrícolas de 2001/02 e 2002/03. Experimentos foram conduzidos com quatro híbridos férteis (BR 600-forragem, BR 700-grão/silagem, BR 701-forragem/silagem and BR 800-corte/pastejo) e uma linhagem macho-estéril (BR 001-A) de sorgo granífero e forrageiro. Quando cada genótipo atingiu o florescimento, 50 panículas foram marcadas e aspergidas com uma suspensão de Claviceps africana (1.000 esporos mL-1). A temperatura e umidade relativa do ar e a precipitação foram registradas durante todo o ciclo da cultura. Baixas temperaturas noturnas entre três a quatro semanas que antecederam o florescimento, aumentaram a susceptibilidade à doença açucarada. Nas duas épocas de semeadura, temperaturas médias noturnas abaixo de 15°C durante o período crítico de pré-florescimento induziram os híbridos férteis a serem tão suscetíveis quanto o genótipo macho-estéril à doença açucarada. Os híbridos testados diferiram na tolerância ao estresse causado pelo frio na fase de pré-florescimento. A taxa de formação das sementes em panículas não inoculadas cobertas por saco polinizador também foi reduzida, sugerindo que o aumento da susceptibilidade à doença decorreu da influência da baixa temperatura, induzindo à esterilidade.

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In the Drosophila repleta group the establishment of subgroups and complexes made on the basis of morphological and cytological evidences is supported by tests of reproductive isolation. Among species in the repleta group, the buzzatii cluster, due to its polymorphism and polytipism, is an excellent material for ecological and speciation studies. Some interspecific crosses involving Drosophila seriema, Drosophila sp. B, D. koepferae and D. buzzatii strains were completely sterile while others involving strains from these species produced F1 hybrids that did not yield F2. In the present work, data on courtship duration and copula occurrence obtained in the analysis of flies from parental sterile crosses and on spermatozoon mobility observed in F1 hybrids that did not yield F2 are presented. Copula did not occur during one hour of observation and the spermatozoon also did not show mobility at any of the analyzed stages (3, 7, 9 and 10 days old). There was a high variation in courtship average duration and in the percentage of males that courted the females. The reproductive isolation mechanisms indicated by these observations were pre and post-zygotic, as supported by the absence of copula and male sterility. Data obtained also showed the occurrence of different degrees of reproductive compatibility among the strains classified as the same species but from distinct geographic localities.

No grupo repleta de Drosophila, o estabelecimento de subgrupos e complexos realizado com base em evidências citológicas e morfológicas é suportado por testes de isolamento reprodutivo. Entre as espécies do grupo repleta, o cluster buzzatii, devido a seu politipismo e polimorfismo, é um excelente material para estudos ecológicos e de especiação. Alguns cruzamentos interespecíficos envolvendo linhagens de Drosophila seriema, Drosophila sp. B, D. koepferae e D. buzzatii foram completamente estéreis, enquanto outros produziram híbridos F1 que não deixaram F2. No presente trabalho são apresentados dados sobre a duração da corte e ocorrência de cópula dos intercruzamentos estéreis e dados sobre a mobilidade dos espermatozóides dos híbridos F1 que não deixaram F2. Não houve ocorrência de cópula no período de 1 hora de observação e os espermatozóides dos híbridos analisados não foram móveis em qualquer das idades testadas (3, 7, 9 e 10 dias de idade). Houve alta variação na duração média da corte e na porcentagem dos machos que cortejaram as fêmeas. A ausência de cópula e esterilidade dos machos F1 indica mecanismos pré e pós-zigótico operando entre as espécies desse cluster. Os dados também mostram diferentes níveis de compatibilidade reprodutiva entre linhagens classificadas como da mesma espécie mas de diferentes localidades geográficas.

RESUMEN

In the Drosophila repleta group the establishment of subgroups and complexes made on the basis of morphological and cytological evidences is supported by tests of reproductive isolation. Among species in the repleta group, the buzzatii cluster, due to its polymorphism and polytipism, is an excellent material for ecological and speciation studies. Some interspecific crosses involving Drosophila seriema, Drosophila sp. B, D. koepferae and D. buzzatii strains were completely sterile while others involving strains from these species produced F1 hybrids that did not yield F2. In the present work, data on courtship duration and copula occurrence obtained in the analysis of flies from parental sterile crosses and on spermatozoon mobility observed in F1 hybrids that did not yield F2 are presented. Copula did not occur during one hour of observation and the spermatozoon also did not show mobility at any of the analyzed stages (3, 7, 9 and 10 days old). There was a high variation in courtship average duration and in the percentage of males that courted the females. The reproductive isolation mechanisms indicated by these observations were pre and post-zygotic, as supported by the absence of copula and male sterility. Data obtained also showed the occurrence of different degrees of reproductive compatibility among the strains classified as the same species but from distinct geographic localities.

No grupo repleta de Drosophila, o estabelecimento de subgrupos e complexos realizado com base em evidências citológicas e morfológicas é suportado por testes de isolamento reprodutivo. Entre as espécies do grupo repleta, o cluster buzzatii, devido a seu politipismo e polimorfismo, é um excelente material para estudos ecológicos e de especiação. Alguns cruzamentos interespecíficos envolvendo linhagens de Drosophila seriema, Drosophila sp. B, D. koepferae e D. buzzatii foram completamente estéreis, enquanto outros produziram híbridos F1 que não deixaram F2. No presente trabalho são apresentados dados sobre a duração da corte e ocorrência de cópula dos intercruzamentos estéreis e dados sobre a mobilidade dos espermatozóides dos híbridos F1 que não deixaram F2. Não houve ocorrência de cópula no período de 1 hora de observação e os espermatozóides dos híbridos analisados não foram móveis em qualquer das idades testadas (3, 7, 9 e 10 dias de idade). Houve alta variação na duração média da corte e na porcentagem dos machos que cortejaram as fêmeas. A ausência de cópula e esterilidade dos machos F1 indica mecanismos pré e pós-zigótico operando entre as espécies desse cluster. Os dados também mostram diferentes níveis de compatibilidade reprodutiva entre linhagens classificadas como da mesma espécie mas de diferentes localidades geográficas.