Sporogenous Tissue Research Articles

How do fertile stamens and staminodes go differently in Kingdonia uniflora? Evidence from stamen numbers, ontogeny, and structure

Kingdonia uniflora is in Circaeasteraceae and has fertile stamens and staminodes which are both variable in number; however, the differentiating process of these two types of stamens and the nectariferous structure of staminodes are still unclear. Variation in number and ontogeny (including the degeneration stage of staminodes) of stamens in K. uniflora are investigated under SEM, TEM and LM. The results indicate that there are 63 floral formulas in 80 flowers counted, and the most frequent flower floral formula (4 flowers) is P5A°11A5G6. The correlation between the stamen number and the total floral organ number is high (0.61), while the highest correlation with the total number of floral organs is the number of carpels, and there is a weak correlation between the two types of stamens (-0.23). The stamen development period is divided into five stages, with differentiation of stamens occurring at stage 2. The anther wall formation of fertile stamens is of the basic type, and the simultaneous meiosis form tetrahedral tetrads, while mature pollens are 2-celled and tricolpate. Sporogenous tissue of staminodes fails to develop further at an earlier stage, without the formation of secondary sporogenous cells. The head of mature staminodes has nectary tissue consisting of the secretory epidermis (two types of secretory cells), nectary parenchyma (about 15 layers) and vascular tissue with vessel and sieve tube elements. There are well-developed microchannels in epidermal cell walls, and the cells related to secreting nectar are rich in mitochondria, endoplasmic reticula and small vesicles. In addition, microsporogenesis, male gametophyte development, the secretory function of staminodes, and other characteristics in K. uniflora are similar to those in Ranunculaceae. This study clarifies the differentiating stage of fertile stamens and staminodes and explores the new structure (nectary) that staminodes formed, and also, it enriched the secretion modes in Ranunculales.

Electron microscopy of the uredinial and telial stages of the rust fungus, Puccinia imperatae

The purpose of this work was to assess the morphology and ontogeny of Puccinia imperatae urediniospores and teliospores growing on its host, Imperata cylindrica, for the first time using scanning (SEM) and transmission (TEM) electron microscopy. The first evidence of uredinial development is the aggregation of hyphae in host intercellular spaces under the epidermis to form an uredinial initial. Uredinial primordia become evident as compact masses of fungal hyphae. The mycelia are dikaryotic and originated from dikaryotic urediniospores, which infect a new host. Dikaryotic sporogenous cells begin to form from dikaryotic mycelium as the uredinium develops further. The fundamental cell in the urediniospore and teliospore formation is the sporogenous cell. The teliospores with their persistent pedicels arise from dense dikaryotic sporogenous tissue, which later becomes highly vacuolated. The sporogenous cell forms a spore bud, which later divides into a pedicel and teliospore mother cell with two nuclei that produce the mature teliospore. SEM examination revealed that the urediniospores are echinulate bearing conical spines on their surfaces, sometimes curving near their tips, and the echinulate ornaments are distributed over the entire urediniospore surface. SEM examination also indicated that the teliospore surface shows rugose ornamentations. This investigation proved that the morphology of the uredinia of different Puccinia species is not related to the host species, but to the rust species. The possibility of using this fungus as a biological control agent for the noxious weed, Imperata cylindrica, was also discussed.

Особенности биологии развития Orthosiphon aristatus (Lamiaceae) в условиях интродукции на Южном берегу Крыма

The paper presents the results of the study of the biological features of Orthosiphon aristatus (Blume) Miq. (awned orthosiphon) in open ground conditions on the Southern Coast of the Crimea and in a greenhouse. Features of flowering, structure of male and female generative structures are revealed. It has been established that when grown in open ground against the background of regular artificial irrigation, active growth and development of Orthosiphon aristatus is observed at a minimum air temperature not lower than +15 °C and a soil surface temperature not lower than +10 °C. Mass flowering falls on the 2nd–3nd decade of August. At this time, the air temperature is +25 °C. On average, the duration of flowering of one plant is 25–40 days. In the structure of the flower of O. aristatus, the phenomenon of hercogamy is observed, which promotes cross-pollination. Sporogenic tissue in microsporangium is represented by one, very rarely two, rows of large cells with a clearly defined nucleus and nucleolus. Pollen grains are 3-celled, most of them are sterile. The ovule of O. aristatus is anatropic, unitegmal and media-nucellar, the vascular bundle reaches chalase and the integumental tapetum is clearly expressed. The maturation of male and female gametes does not coincide in time, protandry is observed. The end of flowering of O. aristatus falls at the end of September – the beginning of October. In September, in protected ground conditions, slight seed formation is possible.

The tapetal tissue is essential for the maintenance of redox homeostasis during microgametogenesis in tomato.

The tapetum is a specialized layer of cells within the anther, adjacent to the sporogenous tissue. During its short life, it provides nutrients, molecules and materials to the pollen mother cells and microsporocytes, being essential during callose degradation and pollen wall formation. The interaction between the tapetum and sporogenous cells in Solanum lycopersicum (tomato) plants, despite its importance for breeding purposes, is poorly understood. To investigate this process, gene editing was used to generate loss-of-function mutants that showed the complete and specific absence of tapetal cells. These plants were obtained targeting the previously uncharacterized Solyc03g097530 (SlTPD1) gene, essential for tapetum specification in tomato plants. In the absence of tapetum, sporogenous cells developed and callose deposition was observed. However, sporocytes failed to undergo the process of meiosis and finally degenerated, leading to male sterility. Transcriptomic analysis conducted in mutant anthers lacking tapetum revealed the downregulation of a set of genes related to redox homeostasis. Indeed, mutant anthers showed a reduction in the accumulation of reactive oxygen species (ROS) at early stages and altered activity of ROS-scavenging enzymes. The results obtained highlight the importance of the tapetal tissue in maintaining redox homeostasis during male gametogenesis in tomato plants.

Genesis of the generative structures <i>Platycodon grandiflorus </i>(family Сampanulaceae)

The article presents the research results of the genesis of the elements of the microsporangium wall, sporogenous tissue, microspores, megaspores, male and female gametophytes of the Platycodon grandiflorus . The types of formation of the structures mail generative sphere (dicotyledonous type of microsporangium wall formation, simultaneous type of the tetrad microspores development, 3-cells of the pollen grains with 6-th pores, Polygonum - type of the formation embryo sac) have been established. A high viability of pollen grains was established during pollination and possibility of obtaining complete seeds when growing this species in the conditions of the Southern Coast of the Crimea.

A new epiphyllous fly-speck fungus from the Early Cretaceous Potomac Group of Virginia (125–112 Ma): Protographum luttrellii, gen. et sp. nov.

ABSTRACT Fly-speck fungi reproduce via thyriothecia that consist of sporogenous tissue appressed to cuticle surfaces of plant leaves and covered by a shield-like scutellum. Thyriothecial scutella likely evolved repeatedly in Dothideomycetes (Ascomycota), and their morphology varies by lineage. Fly-speck fungi have an exceptionally good fossil record that begins in the Mesozoic. The interpretation of scutellum characters in fossils may provide insights into origins of Dothideomycetes and help calibrate the timing of ascomycete evolution. From sediments of the Lower Cretaceous (125–112 Ma) Potomac Group of Virginia, from Dutch Gap Canal, lower Zone 1, we found scutella similar to those of extant Aulographaceae (Dothideomycetes), attached to a single piece of dispersed coniferous cuticle. We analyze hyphae and scutellum development among four extant Aulographaceae species for comparison with the fossil. The excellent preservation of fungi on the leaf cuticle surface allows us to infer a developmental sequence for the fossil. Scutellum development begins with coordinated growth of multiple neighboring generator hyphae and continues with hyphae producing two-dimensional pseudomonopodial, dichotomous, radial growth. Asci and ascospores were not found. We coded states for seven morphological characters using direct observations of the fossil and eight extant taxa, and using the literature for 28 others. We inferred a phylogeny using nuclear 18S and 28S rDNA of 36 extant taxa, 34 Dothideomycetes and two Arthoniomycetes. The phylogeny includes newly determined sequences from five species, two from Aulographaceae. With a branch-and-bound search, we inferred the most parsimonious placements of the fossil given the molecular tree topology. The parsimony analysis constrained by the rDNA phylogeny places the fossil taxon among stem lineages near Aulographaceae or among the known living members of Aulographaceae. We describe the fossil morphotype as Protographum luttrellii, gen. et sp. nov. The fossil provides the oldest evidence of morphological characters restricted among extant fungi to Aulographaceae.

Evidence of accelerated and altered pollen development after Imazapyr treatment in resistant sunflower

ABSTRACT Imazapyr (IM) treatment applied at early reproductive developmental stages have been associated with induced male sterility in sunflower (Helianthus annuus L.). The aim of this work was to determine the effects induced by two different doses of IM-treatment (1X and 2X; 80 and 160 g a.i.·ha-1) on pollen grain yield, pollen viability and on the exine surface, in an intermediate resistant (I) and a completely resistant (R) genotype. An anatomical analysis of some stages during the microsporogenesis and microgametogenesis was also achieved by confocal microscopy. Plants of both genotypes survived the herbicide treatments and showed no external injury symptoms. Differential response to different doses of IM was obtained in R and I genotypes. The pollen grains per flower and the viability in seeds were significantly reduced in the I genotype by the 2X treatment; however, the pollen viability of the remaining grains was not altered, and the diameter of the pollen grains was increased by the herbicide treatment. Anatomical and cytological observations of the sporogenous tissue development were made via confocal microscopy. IM treatment induced alterations in sporogenous cells during the initial phases of microsporogenesis in both genotypes, and the 2X dose accelerated the microgametogenesis process, particularly in the I genotype. These findings improved the understanding of the mechanism underlying the gametocide effects of the imidazolinones in sunflower.

Morphological Studies of Insect-Induced Galls in Flower and Fruit of Alstonia scholaris (L.) R. Br

Morphological changes in insect-induced galls in flowers and fruits of Alstonia scholaris (L.) R. Br. (Apocynaceae) were recorded. The insect Pauropsylla tuberculata Crawford (Homoptera: Psyllidae) penetrates the thalamus of young flowers inducing hypertrophy and hyperplasia in the parenchymatous tissue resulting in the formations of green galls of various sizes and shapes. The reproductive organs, stamens, and pistil of galled flowers are sterile. Pollen sterility was associated with abnormal behaviour of endothecium and the tapetum. In young anthers of severely infested flowers, the sporogenous tissue and tapetum degenerate. In anthers of some infested flowers, the callose wall surrounding pollen mother cells was thick although tapetal cells showed normal signs of degeneration. In anthers of a few infested flowers, the microspores were formed but they degenerated along with tapetal cells. Anthers of some diseased flowers contained thick-walled vacuolated and sterile microspores surrounded by degenerated tapetum layer and radially elongated endothecial cells which lacked the usual fibrous thickenings. The size of gynoecium and the size and number of ovules were reduced in galled flowers. Ovules failed to differentiate and represented by a globular undifferentiated mass of cells. A large number of green, conical galls are formed on fruits by hypertrophy and hyperplasia in the parenchymatous pericarp. Size of severely infested fruits was reduced, and they became thick, circular and seedless. As a consequence, sexual reproduction of the host tree was completely inhibited.

Polysporangiate anthers in Microlicia D.Don (Melastomataceae Juss.)

Polysporangiate anthers are found in a small number of Microlicia species, a genus of Melastomataceae with a large number of endemic species in Brazil. This study describes for the first time the processes of formation and degeneration of the septa found in these particular anthers of Microlicia, providing relevant information about the structure and the functional role of septate anthers in the genus, which is an uncommon condition in angiosperms. The formation of septa begins when some initial cells enlarge and differentiate into sporogenous tissue, while other, more peripheral cells, are not affected by this increase and form the parenchymatous septum. The septa are present up until microgametogenesis, degenerating after the formation of the pollen grains. The mechanism of pollen release in stages, as suggested previously by some authors, could not be demonstrated for the studied species since the septa degenerated at flower anthesis. Thus, we propose that the transverse septa present during the formation of the sporogenous tissue and microspores are associated with providing better nutritional conditions for pollen development.

Partial Male Sterility in Imisun Sunflower: Imazapyr Treatment in Advanced Vegetative Stages Decreases Pollen Yield and Alters ahas Gene Expression

Imidazolinones are powerful herbicides that inhibit branched‐chain amino acid biosynthesis by targeting the catalytic subunit of acetohydroxyacid synthase (AHAS). Imidazolinone application in the advanced vegetative or early reproductive developmental stages is associated with male sterility in resistant sunflower (Helianthus annuus L.); however, the underlying mechanism of this sterility remains unknown. This study describes the morphological, cytoembryological, and molecular alterations induced by imazapyr (IM) treatment on reproductive tissues at different developmental stages in two sunflower genotypes, resistant and intermediate resistant, respectively. Pollen and seed physiological variables were compared between the treated and control plants. The number of pollen grains per flower and viable seeds were negatively affected by IM treatment in the intermediate‐resistant genotype, and the biometric traits of early developed disc flower were also significantly different in this genotype. Differential interference contrast microscopy revealed that IM treatment slightly accelerates megagamethophyte development. Anther observations at microsporogenesis using confocal microscopy show that the sporogenous tissue was damaged. Furthermore, the expression profiles of the sunflower AHAS paralogs (ahas1, ahas2, and ahas3) were measured by quantitative polymerase chain reaction in the anthers and pistils of two developmental stages in treated and control plants. Imazapyr treatment in early reproductive growth stages clearly induces divergent expression patterns in the ahas gene family. These findings provide new insight into a novel chemical method for inducing male sterility in sunflowers and enhance our understanding of the effects of AHAS‐inhibitor herbicides in reproductive tissues.

Autophagy is associated with male sterility in pistillate flowers of Maytenus obtusifolia (Celastraceae)

Programmed cell death (PCD) is defined as a sequence of genetically regulated events leading to controlled and organised cellular degradation. It plays a vital role in plant development; however, little is known about the role of PCD in reproductive development. Sterility in pistillate flowers of Maytenus obtusifolia Mart. has been shown to be related to cytoplasmic male sterility (CMS) based on reproductive biology and anatomical analysis. The recurrent PCD led us to investigate changes in the tapetum and sporogenic tissue during the establishment of male sterility using light and transmission electron microscopy combined with the use of TUNEL (terminal deoxynucleotidyl transferase mediated dUDP end-labelling) assay. The interruption of pollen development in pistillate flowers is a result of premature PCD in the tapetum and consequently in the sporogenic cells. Autophagy, via macroautophagy, occurs in the sporogenic cells and involves the formation of autophagosomes, through rough endoplasmic reticulum, and of complex macroautophagic structures. In the final stage of PCD, massive autophagy takes place. Male sterility in female individuals is thus reasonably interpreted as sporophytic CMS associated to autophagy.

Development of abnormal strobili inLycopodium annotinumas an example of the reversion phenomenon in lower vascular plants

The formation of strobili, which are groups of sporangia-bearing sporophylls on shoot apices, terminates the axis growth in the majority of lycopods. Here, we present an interesting developmental aberration in Lycopodium annotinum L. The structure of abnormal strobili was histologically analyzed using the anatomical sections. Additionally, the expression patterns of LAMB1 and LAMB2, which are known to be specific to L. annotinum sporogenous and vegetative tissues, respectively, were comparatively analyzed in normal and abnormal strobili. Histological analyses revealed that the morphological and anatomical changes in abnormal strobili were related to the resumption of the vegetative growth of the strobilus apex after the production of several sporophylls and sporangia. The identity of both distinct zones of abnormal strobili, i.e., the basal sporangial part and the apical proliferative part, was confirmed by expression patterns of LAMB1 and LAMB2, indicating that microphylls in the apical proliferative zone were of the vegetative type. The results strongly suggest a change of meristem fate and activity in the process of abnormal strobilus formation. The abnormal strobili in L. annotinum could be a specific example of reversion in lower vascular plants. This phenomenon in lycopods is discussed in a developmental context.

First Report of Asiatic Brown Rot (Monilinia polystroma) on Apple in Croatia

HomePlant DiseaseVol. 99, No. 8First Report of Asiatic Brown Rot (Monilinia polystroma) on Apple in Croatia PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Asiatic Brown Rot (Monilinia polystroma) on Apple in CroatiaA. Di Francesco, M. Fruk, C. Martini, T. Jemric, and M. MariA. Di FrancescoSearch for more papers by this author, M. FrukSearch for more papers by this author, C. MartiniSearch for more papers by this author, T. JemricSearch for more papers by this author, and M. MariSearch for more papers by this authorAffiliationsAuthors and Affiliations A. Di Francesco , Criof, DipSa, University of Bologna, Via Gandolfi, 19, 40057, Cadriano, Bologna, Italy M. Fruk , University of Zagreb Faculty of Agriculture, Department of Pomology, Svetosimunska 25, 10000, Zagreb, Croatia C. Martini , Criof, DipSa, University of Bologna, Via Gandolfi, 19, 40057, Cadriano, Bologna, Italy T. Jemric , University of Zagreb Faculty of Agriculture, Department of Pomology, Svetosimunska 25, 10000, Zagreb, Croatia M. Mari , Criof, DipSa, University of Bologna, Via Gandolfi, 19, 40057, Cadriano, Bologna, Italy. Published Online:23 Jun 2015https://doi.org/10.1094/PDIS-12-14-1290-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Brown rot caused by Monilinia spp. is one of the most important postharvest diseases causing economic losses in stone and pome fruit. In November 2014, during a survey for fungal disease on apple (Malus domestica Borkh.) in an orchard near Vratisinec (Croatia), circular and brown to black decay spots covered by a large number of yellowish or buff-colored stromata were observed on ‘Pink Lady’ apple, while decayed tissues remained firm, similar to the symptoms of M. polystroma. The pathogen was isolated by collection of infected tissues of the rot lesion of fruit from the boundary to the center with a sterile knife. A little piece of infected tissue was transferred directly on PDA after surface sterilization with incubation at 25°C in darkness. After 7 days of incubation, the colonies showed yellowish color and then irregular black stromatal crusts occurred on the edges of the colonies after additional 3 to 5 days at 25°C. Sporogenous tissue was present on the margin, slightly elevated above the colony surface with a buff to pale luteous color. The conidia were one-celled, ovoid or limoniform, smooth and hyaline, measuring 12.2 to 20.4 × 8.4 to 12.3 μm (Hilber-Bodmer et al. 2012). The identification of the isolates obtained using the universal primers designed by Petroczy and Polkovics that amplified an uncoding zone of Monilinia spp. (Petróczy et al. 2012) revealed the presence of M. polystroma. The pathogenicity was confirmed using twenty fruits of ‘Pink Lady’ apple wounded two times with a sterile needle, inoculated with 20 μl of pathogen conidial suspension (104 cell/ml) and incubated at 20°C in plastic containers with high humidity (>95%), while the control samples were inoculated with sterile water. The experiment was performed twice. After 7 days, the mean lesion diameters measured 47 mm and after 15 days all apples showed M. polystroma symptoms: yellowish, exogenous stromata. The fungus isolated from inoculated apples exhibited the same morphological features as the first isolate. Molecular analyses were conducted on 5 isolates using ITS1 and ITS4 primers that amplified the ribosomal ITS1-5.8S-ITS2 region and a BLAST search in GenBank confirmed the previous molecular results obtained with Petróczy et al. (2012) primers (GenBank Accession Nos. KJ814976.1). The presence of M. polystroma has been already documented in neighboring countries on apricots in Serbia (Vasić et al. 2013), apple in Hungary (Petrózy and Palkovics 2009), and peach in Italy (Martini et al. 2014); this is the first report of M. polystroma on Croatian apples. Knowledge about this new pathogen in Croatian orchards will facilitate the adoption of control strategies to prevent postharvest losses.

Chromatin dynamics in pollen mother cells underpin a common scenario at the somatic-to-reproductive fate transition of both the male and female lineages in Arabidopsis.

Unlike animals, where the germline is established early during embryogenesis, plants set aside their reproductive lineage late in development in dedicated floral organs. The specification of pollen mother cells (PMC) committed to meiosis takes place in the sporogenous tissue in anther locules and marks the somatic-to-reproductive cell fate transition toward the male reproductive lineage. Here we show that Arabidopsis PMC differentiation is accompanied by large-scale changes in chromatin organization. This is characterized by significant increase in nuclear volume, chromatin decondensation, reduction in heterochromatin, eviction of linker histones and the H2AZ histone variant. These structural alterations are accompanied by dramatic, quantitative changes in histone modifications levels compared to that of surrounding somatic cells that do not share a sporogenic fate. All these changes are highly reminiscent of those we have formerly described in female megaspore mother cells (MMC). This indicates that chromatin reprogramming is a common underlying scenario in the somatic-to-reproductive cell fate transition in both male and female lineages.

Microsporangium development in two species of Oxalis (Oxalidaceae) with different male fertility

Mid-styled (M, with stigma between two height-levels of stamens), short-styled (S, with stigma placing lower than the two height-levels of stamens) and semi-homostyled morph (SH, with stigma and low-height level stamens at the same position) of Oxalis corymbosa populations were previously found in Taiwan. Low pollen viability (0–4%) was found in flowers bearing the anthers of the S and M morph, while there was no pollen in those of the SH morph. In contrast, 50% pollen viability was found in O. corniculata, which is sympatric with O. corymbosa in Taiwan. We made histological sections and compared the process of microsporogenesis and pollen development of the two species, aiming to find out what possible defects are causing the low pollen viability in O. corymbosa. The process of microsporogenesis and pollen development in the two species of Oxalis was divided into six stages: sporogenous tissue, microspore mother cell, tetrad, free microspore, young and mature pollen grain stage. The results revealed that microsporangium abnormalities of O. corymbosa, including incomplete callose deposition or cytokinesis failure at tetrad stage (M and SH morphs) and persistent/highly vacuolated middle layer cells during free microspore stage (SH morph), might be associated with male-sterility of the species in Taiwan. Besides, more deviations during microsporogenesis and pollen development were observed in the SH morph than in M morphs, which might result in different male fertility within the two floral morphs of O. corymbosa.

New observations of the early land plant Eocooksonia Doweld from the Pridoli (Upper Silurian) of Xinjiang, China

As an early land plant previously reported from the Upper Silurian (Pridoli) of Xinjiang, Northwest China and Central Kazakhstan, the circumscription of Eocooksonia sphaerica (Senkevitsch) Doweld remains ill-defined because of the paucity of specimens and poor preservation in marine deposits. New specimens of this plant are described from the Pridoli-aged Wutubulake Formation of the Junggar Basin, Xinjiang. New observations and comparisons with the type material from Kazakhstan confirm the pseudomonopodial branching pattern, which forms an apparent main axis with lateral dichotomously branching systems. Our specimens demonstrate that the terminal sporangia of Eocooksonia Doweld consist of a central body and a border with four to eight elongate-triangular emergences, a character shown in the published illustrations of the type material but not mentioned in the original diagnosis. Eocooksonia may be close to Cooksonia Lang and Pertonella Fanning, Edwards et Richardson in affinities, particularly to the latter that has terminal discoidal sporangia with spiny emergences. It is deduced that the sporangial central body of Eocooksonia contains sporogenous tissues, which are covered by a distal surface wall with radiated emergences. One sporangium specimen of an unnamed plant is also described from the Wutubulake Formation of Xinjiang; it shows a central body with a wide border lacking emergences, and represents a taxon superficially similar to Eocooksonia.

First Report of Asiatic Brown Rot Caused by Monilinia polystroma on Peach in Italy.

Monilinia spp. are well-known pathogens causing brown rot of fruit trees in many fruit production areas worldwide. In Italy, three Monilinia species are particularly significant with regard to fruit trees, causing blossom and twig blight and brown rot in fruits: Monilinia laxa (Aderhold and Ruhland) Honey, M. fructicola (Winter) Honey, and M. fructigena (Aderhold and Ruhland). In 2009, a new species, M. polystroma, was distinguished from M. fructigena based on morphological and molecular characteristics in Europe (3). M. polystroma is not known to occur in Italy and to date has been reported from the Czech Republic (1), Hungary (3), Poland (4), Serbia (5), and Switzerland (2). In July 2013, during a survey for fungal postharvest pathogens, stored peaches (Prunus persica (L.) Batsch) belonging to different cultivars showing brown rot symptoms were observed in the Emilia Romagna and Sardinia regions of Italy. Typical decay spots were circular and brown, tending toward black, and 5% of peaches presented a large number of yellowish or buff-colored stromata and firm decayed tissues, the symptoms originated by M. polystroma. The pathogen was isolated on V8 agar (V8A) and culture plates were incubated at 25°C in darkness for 5 days. A conidial suspension was spread on malt extract agar (MEA) and single spores were selected. M. polystroma colonies grown on potato dexstrose agar (PDA) were yellowish in color. Irregular black stromatal crusts occurred on the edges of the colonies after 10 to 12 days of incubation and on the margin was present sporogenous tissue slightly elevated above the colony surface, color buff/pale luteous (1). The conidia were one-celled, ovoid or limoniform, smooth and hyaline, and 12 to 20 × 8 to 12 μm in distilled water when grown on V8A at 22°C. The ribosomal ITS1-5.8S-ITS2 region was PCR-amplified from genomic DNA obtained from mycelium using primers ITS1 and ITS4. A BLAST search in GenBank revealed the highest similarity (99%) to M. polystroma sequences (GenBank Accession No. GU067539). Pathogenicity was confirmed using surface-sterilized mature 'Red Heaven' peaches. The fruits were wounded (2 × 2 × 2 mm) twice with a sterile needle and inoculated with 2-mm plugs of 7-day-old mycelia from fungal colony margins. The sample unit was represented by 10 fruits. Control fruits were inoculated with PDA. After 7 days of incubation at 20°C in plastic containers with high humidity, typical symptoms of brown rot developed on both the wounds of all inoculated fruits, while control fruits remained symptomless. By the 14th day, all fruits had rotted and the yellowish exogenous stromata appeared on the surface of infected peaches. The fungus isolated from inoculated fruit exhibited the same morphological and molecular features of the original isolates; the molecular analysis performed using the primers by Petroczy (3) confirmed the result of the PCR with ITS1 and ITS4 primers. To our knowledge, this is the first report of M. polystroma on peach in Italy. This is relevant because the new pathogen could spread into other European countries that are main peach producers (such as Spain), causing economic losses. Bringing it to the attention of the scientific community allows the arrangement of research studies for assessing potential resistances with a significant impact on disease control management. Further studies are necessary to determine geographic distribution, prevalence, and economic importance of this organism in Italy.

Seasonal temperature variations influence tapetum mitosis patterns associated with reproductive fitness.

Environmental stress in plants impacts many biological processes, including male gametogenesis, and affects several cytological mechanisms that are strongly interrelated. To understand the likely impact of rising temperature on reproductive fitness in the climate change regime, a study of tapetal mitosis and its accompanying meiosis over seasons was made to elucidate the influence of temperature change on the cytological events occurring during microsporogenesis. For this we used two species of an environmentally sensitive plant system, i.e., genus Cymbopogon Sprengel (Poaceae), namely Cymbopogon nardus (L.) Rendle var. confertiflorus (Steud.) Bor (2n = 20) and Cymbopogon jwaruncusha (Jones) Schult. (2n = 20). Both species flower profusely during extreme summer (48 °C) and mild winter (15 °C) but support low and high seed fertility, respectively, in the two seasons. We have shown that tapetal mitotic patterns over seasons entail differential behavior for tapetal mitosis. During the process of tapetum development there are episodes of endomitosis that form either (i) an endopolyploid genomically imbalanced uninucleate and multinucleate tapetum, and (or) (ii) an acytokinetic multinucleate genomically balanced tapetum, with the progression of meiosis in the accompanying sporogenous tissue. The relative frequency of occurrence of the two types of tapetum mitosis patterns is significantly different in the two seasons, and it is found to be correlated with the temperature conditions. Whereas, the former (genomically imbalanced tapetum) are prevalent during the hot summer, the latter (genomically balanced tapetum) are frequent under optimal conditions. Such a differential behaviour in tapetal mitosis vis-à-vis temperature change is also correspondingly accompanied by substantial disturbances or regularity in meiotic anaphase disjunction. Both species show similar patterns. The study underpins that tapetal mitotic behaviour per se could be a reasonable indicator to elucidate the effect of climate change on reproductive fitness.

Structure and development of 'witches' broom' galls in reproductive organs of Byrsonima sericea (Malpighiaceae) and their effects on host plants.

Galls are anomalies in plant development of parasitic origin that affect the cellular differentiation or growth and represent a remarkable plant-parasite interaction. Byrsonima sericea DC. (Malpighiaceae) is a super host of several different types of gall in both vegetative and reproductive organs. The existence of galls in reproductive organs and their effects on the host plant are seldom described in the literature. In this paper, we present a novel study of galls in plants of the Neotropical region: the 'witches' broom' galls developed in floral structures of B.sericea. The unaffected inflorescences are characterised by a single indeterminate main axis with spirally arranged flower buds. The flower buds developed five unaffected brownish hairy sepals and five pairs of elliptical yellow elaiophores, five yellow fringed petals, 10 stamens and a pistil with superior tricarpellar and trilocular ovary. The affected inflorescences showed changes in architecture, with branches arising from the main axis and flower buds. The flower buds exhibited several morphological and anatomical changes. The sepals, petals and carpels converted into leaf-like structures after differentiation. Stamens exhibited degeneration of the sporogenous tissue and structures containing hyphae and spores. The gynoecium did not develop, forming a central meristematic region, from which emerges the new inflorescence. In this work, we discuss the several changes in development of reproductive structures caused by witches' broom galls and their effects on reproductive success of the host plants.

Graft-transmissible movement of inverted-repeat-induced siRNA signals into flowers.

In plants, small interfering RNAs (siRNA) and microRNAs move to distant tissues where they control numerous developmental and physiological processes such as morphogenesis and stress responses. Grafting techniques and transient expression systems have been employed to show that sequence-specific siRNAs with a size of 21-24 nucleotides traffic to distant organs. We used inverted-repeat constructs producing siRNA targeting the meiosis factor DISRUPTED MEIOTIC cDNA 1 (DMC1) and GFP to test whether silencing signals move into meiotically active tissues. In grafted Nicotiana tabacum, a transgenic DMC1 siRNA signal made in source tissues preferably entered the anthers formed in the first flowers. Here, the DMC1 siRNA interfered with meiotic progression and, consequently, the flowers were at least partially sterile. In agro-infiltrated N. benthamiana plants, a GFP siRNA signal produced in leaves was allocated and active in most flower tissues including anthers. In hypocotyl-grafted Arabidopsis thaliana plants, the DMC1 silencing signal consistently appeared in leaves, petioles, and stem, and only a small number of plants displayed DMC1 siRNA signals in flowers. In all three tested plant species the systemic silencing signal penetrated male sporogenic tissues suggesting that plants harbour an endogenous long-distance small RNA transport pathway facilitating siRNA signalling into meiotically active cells.