Localisation and movement of Plum pox virus in apricot stem tissues

Localisation and movement of Plum pox virus (PPV), sharka disease, in stem tissues of susceptible and resistant apricot (Prunus armeniaca L.) cultivars was studied. Two different assays were performed. In the first assay, apricot cultivars were grafted on to a non‐inoculated GF305 peach rootstock and, after two months, the sprouted apricot was inoculated by chip‐grafting. In the second assay, apricot cultivars were grafted on to a previously chip‐inoculated GF305 showing strong PPV symptoms. Localisation of virus was studied in apricot stem by immuno‐tissue printing and sharka symptoms in GF305 and apricot leaves were also observed. Virus was mainly localised in the xylem, and sometimes in the cortex and pith. Results revealed that, while all the cultivars allowed limited virus movement from the inoculation point, only the susceptible cultivars (Screara, Bebeco and Colomer) allowed long distance movement and even showed symptoms in leaves.     

Influence of the gene brevistylis on development of the flower in Oenothera

The mutant brevistylis of Oenothera (Onagraceae) is characterized mainly by malformations of the style and by female sterility. Morphological features of the style and stigmas, such as the length of the style and the number, size, and shape of the stigmatic lobes is very variable. The abscission layer between ovary and style is missing and the placenta with ovules is protruded into the style. An interpretation of the disturbances in development observed in the br/br homozygotes is presented. The primary influence of br on development is proposed to be a general delay in meristematic growth, followed by irregularities in the timing of morphogenetic events which in turn lead to the anomalies in morphology of style and stigmas.     

Behaviour of Apricot Cultivars Against Hop Stunt Viroid

The apricot species is susceptible to infection by different viruses and viroids including the Hop stunt viroid (HSVd), widely distributed around the world and described as the causal agent associated with fruit degeneration disease in apricot. However, to date, there are no ‘ad hoc’ studies about the resistance or susceptibility of apricot cultivars to this viroid. In this study, we tested the resistance/susceptibility to HSVd of 26 Mediterranean and North American apricot cultivars in controlled greenhouse conditions. All apricot cultivars assayed were infected by HSVd, showing a different range of susceptibility. As no sources of resistance among the apricot cultivars evaluated have been detected yet, it is necessary to continue the search for such sources to be included in apricot breeding programmes. In addition, the high level of susceptibility found highlights the importance of identifying this viroid in routine tests performed by nurseries and plant protection services.     

Stigmatic and stylar incompatibility in Prunus avium L.: Morphological and ultrastructural aspects

Abstract

Stigmatic and stylar structures of-sweet cherry (Prunus avium L.) «Malizia» were examined with light and electron microscopes (S.E.M. and T.E.M.).

It was demonstrated that the transmitting tissue, situated in the central portion of the style, extends below the stigmatic papillae and secretes an electrondense material accumulating in the intercellular spaces. Pollen tubes which germinated on the stigma, reached the ovules passing through this substance which facilitates their passage while trophic relations are established.

Some ultrastructural aspects of the pollen tubes observed inside the style were examined and discussed in relation to the phenomenon of self-incompatibility.     

Taxonomic and functional implications of stigma morphology in species ofCassia,Chamaecrista, andSenna (Leguminosae:Caesalpinioideae)

Two stigma forms occur inChamaecrista andSenna, but only one inCassia. In the common chambered form, a stigma pore is positioned on the reflexed style tip and is the entrance to a tapering chamber. The pore rim is fringed by hairs which vary in number, size, distribution and shape. In the alternative form the stigma is situated at the apex of the curved style and is crateriform. The crater rim is fringed by hairs of variable number and shape. The stigmatic hairs are predominantly unicellular and cutinized. Stigma and hair differences aid in the taxonomy of the genera. Their functions in pollination biology are discussed.     

Antioxidant enzymes as biochemical markers for sharka resistance in apricot

The activity of antioxidant enzymes in different apricot (Prunus armeniaca L.) cultivars, resistant or susceptible to Plum pox virus (PPV), was analyzed during the years 2002 and 2003. Resistant cultivars showed higher activities of catalase (CAT), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) than susceptible cultivars. Only CuZn-SOD isozymes were detected in the apricot cultivars. However, no correlation was observed between this isozyme pattern and the resistance to PPV. On the other hand, PPV-resistant apricot cultivars could have a greater capability for elimination of H₂O₂ and recycling of ascorbate-glutathione cycle, and they have at least two of these enzymatic activities (CAT, APX and DHAR) over the average. In contrast, this response was not observed in the susceptible cultivars. All these data suggest that the activities of CAT, APX and DHAR could be used as biochemical markers of sharka resistance in apricot.     

The stigmatic orifice in Cassia,Senna, and Chamaecrista (Caesalpiniaceae): morphological variation,function during pollination,and possible adaptive significance

In species of Cassia, Senna, and Chamaecrista an orifice leading into a stigmatic cavity is present at the tip of the style. The size of the orifice, the occurrence and morphology of surrounding trichomes or papillae, and the occurrence of a drop of secretion at its outlet were recorded in 17 species belonging to the three genera of the subtribe Cassiinae. Much of the observed variation in these characters apparently reflects different modes of pollen capturing and varying degrees of secretion exposure. In some of the species studied no secretion was noticeable at the entrance to the stigmatic cavity. The unusual type of stigma in the Cassiinae does not fit into any of the recognized main groups of angiosperm stigmas. It is conjectured that in the buzz-pollinated Cassiinae species with small stigmatic orifices, the secretory material is retained within the stigmatic cavity, to be extruded by vibratory movements of the style induced by a buzzing bee. It is also hypothesized that in the wet tropics, concealment of secretory materials within a cavity prevents their washing away or dilution by rain. Furthermore, in the Cassiinae, the considerable variation in features of the style and of the stigma may function as mechanisms isolating between sympatric, visitor-sharing, concurrently blooming species.     

Introduction and establishment of apricot in vitro through regeneration of shoots from meristem tips

Summary In this study different aspects of the in vitro introduction and establishment of apricot cultivars were investigated through meristem tip culture. The best time to introduce the meristems of ‘Canino’ was when buds were starting to swell. Various plant growth regulators were used at different concentrations on four distinct apricot cultivars to promote the development of the meristems to shoots which could then be micropropagated. Very diverse results were obtained depending on the genotype. In general, meristems did not survive without N⁶-benzyladenine. Concentrations of gibberellic acid from 2 to 4 mg 1⁻¹ (5.8–11.4 μM) promoted explant elongation. This step was critically important to obtain apricot shoots large enough to be transferred to proliferation medium.     

La componente lipidica dell'essudato stigmatico di Citrus limon (L.) Burm

Abstract

The lipidic component of Citrus limon (L.) Burm. stigmatic exudate. Chromatographic methods (Gas Chromatography and Thin Layer Chromatography) were used to investigate the lipids present in the stigmatic secretion of Citrus limon.

12 fatty acids, ranging from C 12 to C 24, were identified; they form 7 classes of different lipids, 3 of them having unsaturated components.     

Systemic infection of black currant flowers by Botrytis cinerea and its possible involvement in premature abscission of fruits

Emasculated flowers of several black currant cultivars were pollinated and then inoculated with dry conidia of Botrytis cinerea in the field and glasshouse. The infection of pistils was examined by U.V. fluorescence microscopy and the incidence of premature flower abscission recorded. Conidia germinated in the stigmatic fluid in all cultivars and hyphae spread symptomlessly throughout the style to infect the pericarp and ovules. Of six cultivars inoculated in the field, cv. Ojebyn was the most, and cv. Ben More the least resistant to flower shedding. Natural infection of stigmas by B. cinerea was common in the field and a high proportion of apparently healthy non-inoculated flowers which abscissed were found to contain infected ovules. Fewer flowers abscissed if inoculations were made 6 days after pollination. Symptomless or latent infection of black currant flowers by B. cinerea may be a contributory cause of premature abscission of developing fruits, or ‘running-off’, recorded in these experiments.     

THE FLORAL BIOLOGY OF CASSIA DIDYMOBOTRYA AND C. AURICULATA (CAESALPINIACEAE)

The flowers of Cassia didymobotrya and C. auriculata have three types of fertile anthers that differ in orientation, size, shape, and pollen production. Flowers with right-handed or left-handed style deflections, i.e., enantiostylous flowers, occur in the same raceme. In Israel, both species are pollinated by pollen collecting buzzing females of Xylocopa pubescens. Vibrations of the carpenter bee are necessary for release of pollen from poricidal anthers and, in C. didymobotrya, also for absorption of pollen through the stigmatic opening into a cavity of the style tip. The largest anthers supply pollen for pollination. Pollen for consumption by the bee, on the other hand, appears to be supplied by all fertile anthers. This is in contrast to the accepted view of a complete separation of functions in the heteromorphic anthers in Cassia. The pollen/ovule ratio in C. didymobotrya was 55,200, and that in C. auriculata 32,000. Only 0.01% of the pollen produced by a flower was found in the stigmatic pollen load, and this fraction allows for high seed sets. From a comparison of the pollen production and utilization in the Cassia species and in certain distylous plants, it is concluded that heteranthery in Cassia does not confer an advantage in pollen economy. The high pollen/ovule ratios are explained by lack of nectar as well as by the large area on which pollen is deposited on the bee's body relative to the small size of the stigma. Enantiostyly in Cassia is considered as part of a pollination syndrome whose characteristics are outlined. The function of enantiostyly as an outbreeding strategy is discussed. In the two Cassia species, opportunities for self- and geitonogamous pollinations and self-compatibility minimize an effect of enantiostyly in promotion of outcrossing. Instead, it is proposed that style deflections may clear access of the pollinator to the anthers and protect female parts from injury by a vibrating heavy-bodied visitor.     

Impact of Mapped SSR Markers on the Genetic Diversity of Apricot (<Emphasis Type="Italic">Prunus armeniaca</Emphasis> L.) in Tunisia

The impact of mapped microsatellites on the study of genetic diversity of Tunisian apricot accessions was assessed. The genetic variability of 47 traditional apricot cultivars originating from several areas in Tunisia was investigated with 32 polymorphic microsatellite loci selected for their location throughout the eight linkage groups of Prunus genome. The higher polymorphism and greater transportability of these markers among Prunus species were proved by the expected heterozygosity (He = 0.56) and Shannon’s index of diversity (I = 1.05), indicating that Tunisian apricot germplasm maintained a substantial level of genetic diversity. According to their geographical origin, the genetic differentiation among groups (north, center, and south; Fst = 0.04) was lower, while the gene flow among groups was consequent (Nm = 4.79), attesting a narrow genetic background of apricot in the country. Both unweighted pair-group method with arithmetic mean dendrogram, based on Nei’s genetic distances and factorial correspondence analysis, separated northern cultivars from central and southern cultivars, revealing the same molecular basis of apricot material in the Center and the South of Tunisia. These results revealed the efficiency of mapped markers for genetic variability measurements compared to randomly ones, however, no advantage was observed considering the genetic relationships among studied accessions.     

New set of microsatellite loci isolated in apricot

We report 99 simple sequence repeats (SSRs) newly isolated from an apricot (Prunus armeniaca L.) genomic library enriched for AG/CT repeats. Twenty SSRs were screened for their polymorphism in 16 apricot cultivars. The number of alleles ranged from two to nine, whereas the expected heterozygosity (H_E) ranged from 0.26 to 0.82. The same SSRs showed also an appreciable transportability across different Prunus species, such as peach, nectarine, almond, European plum, Japanese plum, sweet cherry and sour cherry, with 20% of primers giving successful amplifications in all Prunus species assayed. None gave amplification in apple.     

Floral micromorphology and its systematic implications in the genus Sinosenecio (Senecioneae-Asteraceae)

Several floral microcharacters (configuration of stigmatic areas on the inner surface of the style branch, shape of the anther apical appendage, anther size, and configuration of the endothecial thickenings and of the filament collar) in 63 populations representing 35 species and one variety of Sinosenecio (Senecioneae-Asteraceae) were investigated. The floral micromorphological data obtained are highly consistent with evidence from molecular systematics and cytology, strongly suggesting a polyphyletic nature of the currently circumscribed Sinosenecio and the necessity of a taxonomic change at generic level.     

Pollen walls of Araceae,with special reference to their fossilization potential

The pollen grains, the pistil, growth of the pollen tube and its pathway are described in Borago officinalis and Heliotropium europaeum. The exine is thick in both taxa but it is covered with dense gemmae in Borago. The intine seems to be thicker and contains more proteins in Borago than in Heliotropium. Starch is very abundant in the latter while it is lacking in the former. The style is hollow in Borago with a stylar canal running from the stigma to the ovary, while in Heliotropium it is broadly cone‐shaped with papillae located at the base of the cone (the “stigmatic ring") and not at the top of the style as usual. In Borago stigmatic papillae are unicellular, skittle‐shaped and have a thick pectocellulosic wall and an equally thick cuticular layer, while in Heliotropium the stigmatic papillae are unicellular, elongated cone‐shaped with a thin pecto‐cellulosic wall and have an apparently reduced cuticular layer. The stigmatic exudate is very abundant on the stigmas of Heliotropium even before anthesis while it is absent on those of Borago except when allo‐pollination occurs. Pollen tube growth has been followed from stigma to ovules in both taxa.     

Size,shape and sex differences in three subspecies of Black-tailed Godwits Limosa limosa

ABSTRACT

Capsule: Black-tailed Godwits Limosa limosa show sexual size dimorphism and size differences between the subspecies. The shape varies slightly between the subspecies, but not between the sexes.

Aims: To investigate whether and how the three subspecies of Black-tailed Godwits, and the sexes of these subspecies, differ in size and shape.

Methods: We collected body dimensions (lengths of the bill, total head, tarsus, tarsus-toe and wing) of adult Black-tailed Godwits from three locations (Iceland, the Netherlands and northwest Australia) corresponding to the breeding or wintering grounds of three known subspecies (islandica, limosa and melanuroides, respectively). Determining sex by molecular assays, we computed degrees of sexual size dimorphism. Using principal component analysis (PCA), we compared differences in size and shape among the different subspecies.

Results: The limosa subspecies was the largest and also showed the most significant sexual size dimorphism. Sexual size dimorphism was smallest for wing length and largest for bill length. The first two axes of the PCA that included all subspecies of both sexes explained 94% of the total variation. Most body dimensions were highly correlated with each other, but wing length varied independently of the other dimensions. Males and females differed only in size (the first axis). However, one of the two small subspecies, islandica, also differed in shape (the second axis) from limosa and melanuroides.

Conclusions: In all three subspecies of Black-tailed Godwits, females are larger than males. The fact that subspecies differed in the degree of size dimorphism and slightly in shape hints at sex-related differences in the ecological selection pressures between the different flyways.     

ParSOC1, a MADS-box gene closely related to Arabidopsis AGL20/SOC1, is expressed in apricot leaves in a diurnal manner and is linked with chilling requirements for dormancy break

Dormancy break is a physiological phenomenon associated with the ability of plants to cope with changing environmental conditions and adjust their growth habits accordingly. In order to understand the potential role of genes in the control of dormancy break ParSOC1, a distinct apricot MADS-box gene which is most closely related to the AGL20/SOC1 MADS-box family was studied in several apricot cultivars that differ in their chilling requirements. The ParSOC1 gene is expressed in a diurnal manner and is highly polymorphic among apricot cultivars in the transcribed region upstream to the putative ATG translation initiation site. Genotyping of 48 different apricot cultivars revealed 13 different ParSOC1 alleles. By associating the chilling requirements of the apricot cultivars with their ParSOC1 genotype, it was possible to demonstrate a significant correlation between the presence of specific ParSOC1 alleles and chilling requirements. The data provided suggest that ParSOC1 or a gene in its close proximity could be involved in the regulation of dormancy break of vegetative shoots in apricot.     

La composizione chimica dell'essudato stigmatico di Citrus limon (L.) Burm

Abstract

The composition of the stigmatic exudate of Citrus limon (L.) Burm. - Biochemical analyses of the stigmatic exudate of Citrus limon (L.) Burm. have revealed the presence of lipids, polysaccharides, proteins, phenols, free aminoacids and alkaloids. The role of stigma secretion is discussed in relation to pollen activation and recognition and the pollen tube growth.     

Variation in stigma morphology – How does it contribute¶to pollination adaptation in Pedicularis (Orobanchaceae)?

 Stigma morphology in Pedicularis and its role in pollination have not been evaluated. This paper reports for the first time the relationship between stigma morphology and other aspects of floral design. 17 species of Pedicularis representing all the different types of corolla structure in the genus were studied in the field and in the laboratory. Results indicate that the stigmatic surface morphology of Pedicularis species is related to the type of corolla structure occurring in the species. Pollination studies in eight Pedicularis species demonstrated adaptation between stigmatic surface morphology and other aspects of floral biology. Species with larger, more corrugated stigmatic surfaces always possess a subsidiary construction (“tooth” or “beak”) on the galea. In addition, they have relatively longer flower tubes, higher stigmatic pollen loads, bigger pollen size and a shorter blooming period for individual flowers. Finally, the authors discuss the evolutionary significance of floral design in genus Pedicularis. Received April 8, 2002; accepted June 11, 2002 Published online: December 11, 2002     

Reproductive significance of indirect pollen-tube growth in Dalechampia (Euphorbiaceae)

Most species of Dalechampia have expanded stigmatic surfaces that extend from the stylar tip part way down the sides of the elongated styles. Pollen grains landing at the stylar tip grow tubes directly down the style to the ovary. Pollen grains landing on the lateral stigmatic surfaces, however, exhibit indirect pollen-tube growth: the tubes grow first to the stylar tip, bend 180°, and then grow to the ovary. Indirect pollen-tube growth appears to be reproductively important: more than half the arriving pollen lands on the lateral stigmatic surfaces, and virtually all of these grains produce tubes that grow indirectly to the ovary; pollen on the lateral surface fertilizes seeds about as effectively as pollen at the tip (with direct tube growth). Indirect pollen-tube growth may be the result of a correlated response to selection for expanded stigmatic surfaces in Dalechampia, or it may be an adaptation to increase the intensity of pollen competition.