Influence of vesicular-arbuscular mycorrhizal infection and P addition on growth and P nutrition of Anthyllis cytisoides L. and Brachypodium retusum (Pers.) Beauv.

The effect of P applications and mycorrhizal inoculation on the growth and P nutrition of Anthyllis cytisoides L. (Fabaceae) and Brachypodium retusum (Pers.) Beauv. (Poaceae) was studied. Both plants are widely distributed and well adapted to semi-arid habitats in southern Spain. In all treatments, even with high P doses, mycorrhizal plants showed a higher concentration of phosphorus in their tissues than non-mycorrhizal plants. Mycorrhizal inoculation enhanced the growth of the plants when no P was applied. At high P addition, non-mycorrhizal plants showed higher growth than mycorrhizal plants. The response of each plant type to P application was somewhat different.     

Chromosome numbers in Brachypodium Beauv. (Gramineae)

A summary of previous chromosome counts of Brachypodium is given in addition to a large number of new reports. The present work does not support claims made for extensive infraspecific variation in certain species. The implication of cytological knowledge for a taxonomic and evolutionary understanding of the genus is discussed.     

Prolamin storage proteins and alloploidy in wild populations of the small grass Brachypodium distachyon (L.) P. Beauv.

This paper reports the glutenin diversity of a collection of 23 wild populations of the grass Brachypodium distachyon collected in the Mediterranean and southern areas of the Iberian Peninsula. The plant material studied included the three different cytotypes of this species: 2n?=?10, 2n?=?20 and 2n?=?30. A specific method of extraction was used to isolate the glutenin subunits from the caryopsis. Separation by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed them to correspond to wheat low-molecular-weight glutenin subunits (LMW-GS). Twenty-two LMW-GS?Clike were identified that showed great diversity within and between populations. All the populations investigated were polymorphic for the endosperm proteins studied. The 2n?=?30 forms had the largest number of subunits; these were also more diverse than those of the 2n?=?10 or 2n?=?20 forms. The 2n?=?10 forms, the most common in the higher, interior areas of the Iberian Peninsula, showed the smallest subunit variation. In fact, negative correlations were found between subunit diversity and altitude and longitude. In contrast, a positive correlation was detected with the annual average temperature and the indices of thermicity and Mediterraneity. The similarity between the populations was estimated using the Sorensen?CDice coefficient, calculated on the basis of the presence/absence of the 22 LMW-GS proteins. The similarity indices were used to produce a dendrogram using the unweighted pair-group method with arithmetic means (UPGMA). This method produced three main groups corresponding to the three cytotypes. An analysis was made of the possible correlation between eco-geographic and climatic factors and the gene diversity and polymorphism shown in the populations. The diversity correlated positively with the number of chromosomes (2n), annual mean temperature, index of thermicity and index of Mediterraneity. In contrast, diversity correlated negatively with altitude, longitude and index of precipitation during the summer. The number of chromosomes correlated negatively with altitude, longitude and precipitation during summer and positively with all the other climatic indices. These results are coherent with the fact that diploid forms were more common in areas of the interior and at higher altitude, where the climate is more extreme.     

Protoplast liberation and regeneration in the ascomycete Hypomyces ochraceus (Pers.) Tul

A rapid and convenient method for producing protoplasts from 3 d old mycelium of the ascomycete Hypomyces ochraceus is described. The procedure involves a Helix pomatia enzyme preparation and sucrose (20%) for stabilization. Pretreatment with disulfide bond reducing agents reduced the amount of viable protoplasts. Formation of protoplasts and different stages of regeneration were observed by phase contrast microscopy. There was only one type of true regeneration from protoplasts to hyphae in 15-30% gelatine medium by direct forming a germ tube from the original protoplast. Cytological events and physiological conditions are discussed.     

Evidence for multiple sources of invasion and intraspecific hybridization in Brachypodium sylvaticum (Hudson) Beauv. in North America

We compared the levels and distribution of genetic diversity in Eurasian and North American populations of Brachypodium sylvaticum (Huds.) Beauv. (false brome), a newly invasive perennial bunchgrass in western North America. Our goals were to identify source regions for invasive populations, determine the number of independent invasion events, and assess the possibility that postinvasion bottlenecks and hybridization have affected patterns of genetic diversity in the invaded range. We tested the hypothesis that this Eurasian grass was accidentally introduced into two areas in Oregon and one site in California by examining nuclear microsatellites and chloroplast haplotype variation in 23 introduced and 25 native populations. In the invaded range, there was significantly lower allelic richness (R(S)), observed heterozygosity (H(O)) and within-population gene diversity (H(S)), although a formal test failed to detect a significant genetic bottleneck. Most of the genetic variation existed among populations in the native range but within populations in the invaded range. All of the allelic variation in the invaded range could be explained based on alleles found in western European populations. The distribution of identified genetic clusters in the North American populations and the unique alleles associated with them is consistent with two historical introductions in Oregon and a separate introduction to California. Further analyses of population structure indicate that intraspecific hybridization among genotypes from geographically distinct regions of western Europe occurred following colonization in Oregon. The California populations, however, are more likely to be derived from one or perhaps several genetically similar regions in the native range. The emergence and spread of novel recombinant genotypes may be facilitating the rapid spread of this invasive species in Oregon.     

Stochastic modeling of the transmission of respiratory syncytial virus (RSV) in the region of Valencia,Spain

In this paper, we study the dynamics of the transmission of respiratory syncytial virus (RSV) in the population using stochastic models. The stochastic models are developed introducing stochastic perturbations on the demographic parameter as well as on the transmission rate of the RSV. Numerical simulations of the deterministic and stochastic models are performed in order to understand the effect of fluctuating birth rate and transmission rate of the RSV on the population dynamics. The numerical solutions of stochastic models are calculated using Euler-Maruyama and Milstein schemes, and confidence intervals for stochastic solutions are given using Monte-Carlo method. Analysis of the numerical results reveals that perturbations on the transmission rate are more decisive in the dynamics of RSV than perturbations on demographic parameters. In addition, the stochastic models show the advantage of reproducing more effectively the noisy RSV hospitalization data. It is concluded that these stochastic models are a viable option to provide a realistic modeling of the RSV dynamics on the population.     

Population dynamics and ecology of subdominant phytoplankton species in a shallow hypertrophic lake (Albufera of Valencia,Spain)

Long-term population dynamics and ecology of the abundant but non-dominant phytoplankton species of the shallow hypertrophic lake the Albufera of Valencia (Spain) are described for the period 1980–1988. The lake is used as a reservoir for the surrounding ricefield cultivation. It is continuously dominated by three filamentous blue-green algae, Planktothrix agardhii, Pseudanabaena galeata and Geitlerinema sp. Horizontal differences of the phytoplankton were less important than annual and seasonal variations. An annual increasing trend was observed for Planktolyngbya subtilis, Planktolyngbya contorta, Cylindrospermopsis raciborskii, Microcystis incerta, Nitzschia palea var. tenuirostris and Rhodomonas lacustris var. nannoplanctica, whereas Anabaenopsis elenkinii, Scenedesmus acuminatus, Scenedesmus quadricauda and Cyclotella meneghiniana showed an opposite trend. This pattern seems related to the increase of nitrogen and phosphorus loading in the lake and certain hydrological changes occurred in the latter years of the study. Seasonal pattern of the subdominant species showed the presence of Cyclotella meneghiniana, Scenedesmus species and Chlamydomonas spp. in spring, during moderate water renovation rates and phosphate availability. Periodicity shifted to blue-green algae and Nitzschia species in summer and early autumn, during reduced phosphate levels and initial low but later high water renewal. Autumn and winter species, such as Monoraphidium contortum, Nitzschia gracilis, Rhodomonas lacustris var. nannoplanctica and Cryptomonas erosa, were mainly related to light intensity and temperature. Although the lake has a typical hypertrophic phytoplankton assemblage, the general seasonal variation of the species is similar to that often described in temperate lakes. Diatom species composition differs to that cited in other shallow hypertrophic lakes of Europe.     

Isolation and characterization of nine microsatellite markers for Brachypodium sylvaticum (Huds.) Beauv., a recently invasive grass species in Oregon

The patterns of genetic diversity caused by rapid range expansions following recent colonizations are best observed using highly polymorphic genetic markers. We characterized nine microsatellite markers for Brachypodium sylvaticum, a bunchgrass invasive in the Northwestern United States and native to Eurasia. Loci exhibited from two to 10 alleles, and generally had high F(IS) values. These loci will help identify sources of new populations in the region, and they will be useful for studying patterns of genetic diversity during rapid range expansions.     

Initiation, Orientation and Early Development of Primary Rhizomes in Sorghum halepense (L.) Pers.

Axillary buds on the most basal portion of the seedling shootof Sorghum halepense differentiate directly into rhizome buds.The initial orientation of these buds is upwards, but this orientationstarts to be reversed almost immediately. The reversal is causedby the combined effect of differential radial expansion of thebasal internodes immediately above and below the bud, and differencesin the extent of mitotic activity on the abaxial and adaxialsides of the bud. Reorientation is a geotropic and is progressivelyless with acropetal nodal position of the bud. Further growthof the rhizomes proceeds in the same orientation as that ofthe bud from which they had developed, until they change theirorientation again by exhibiting diageotropic, or negativelygeotropic responses. The second reorientation coincides moreor less with the onset of flowering and it exhibits a positionalgradient, such that the change is more extensive the higherthe nodal position of the rhizome. Sorghum halepense, rhizome, geotropism, morphogenesis, perennial weeds     

Herbicide Tolerance and Polyploidy in Cynodon dactylon (L.) Pers. (Gramineae)

Responses to treatment with the herbicide dalapon have beendetermined and the karyotypes studied in four chromosome racesof Cynodon dactylon. No relationship was found between toleranceto dalapon and the level of ploidy. At the dalapon concentrationwhere differences in response were most apparent (2·5mM), the difference in mean value of the two diploid cloneswas greater than any other pair of values. No positive correlationwas found between tolerance and the morphology of the leaf surface.Karyotype studies have not resolved the conflicting evidencerelating to the origin and inter-relationships of the chromosomeraces of this species.     

Monitoring butocarboxim resistance of the woolly whitefly (Homoptera: Aleyrodidae) in citrus from Valencia, Spain.

Glass vials coated internally with an insecticide were used as a resistance monitoring technique for testing field populations of the woolly whitefly, Aleurothrixus floccosus (Maskell), collected from citrus. The distribution of resistance to the insecticide butocarboxim in citrus orchards from Valencia (Spain) during 1993 and 1994 was determined by means of this technique. Adults resting on citrus shoots were captured with a portable vacuum cleaner and introduced into the vials. The technique provides control mortality of <25% when assessed 7 h after the insects are captured. In 21 populations tested, LC50s ranged from 1.8 to 42.3 mg/ml. This represents resistance ratios >20-fold among populations. Lower slopes of the concentration-mortality line were found in whitefly populations that exhibited a low level of the LC50. Resistance was widespread in the Valencia areabut spatially irregular, with nearby orchards occasionally showing wide differences in resistance levels. The levels of resistance to butocarboxim obtained with this technique closely matched the field efficacy of the insecticide. This residue bioassay provides a convenient and rapid method to monitor insecticide resistance in A. floccosus populations.     

Regeneration from the Leaf of Atrichum undulatum (Hedw.) P. Beauv.

Abstract

Regeneration of new plants from the leaves of Atrichum undulatum will take place after 6 weeks if they are placed with the abaxial surface in contact with damp filter-paper in a saturated atmosphere.

The new plants arise from the surface cells of the midrib area of the leaf where there is a discontinuity of the photosynthetic filaments. This occurs mainly in the distal third of the leaf.

As the leaf ages it loses it capacity for regeneration. There are two regeneration processes, one which occurs when the leaf is separated from the stem and the only wound is at the point of attachment to the stem, and the second when other wounds are inflicted on the leaf. Regeneration due to wounding is greatest in the distal half of the leaf, mutilations near the base of the leaf having less effect on the percentage of regenerated plants.

There seems to be a potential for regeneration (both normal and as a result of wounding) which is greatest in the distal third of the leaf and decreases towards the base of the leaf of A. undulatum. This is compared with the leaf of Physcomitrium turbinatum, and the greater complexity of the process in the former is considered to be the result of greater differentiation of the leaf.     

Penicillium in pre-harvest corn in Valencia (Spain) II. Study of the enzymatic and toxigenic capacities of the species

This paper presents data on plate assays of enzymatic activity and antibacterial effects of species of Penicillium isolated in samples of pre-harvest corn.In general, the species tested present high levels of amylolytic and lipolytic properties, while the proteolytic, urease, DNAse and cellulolytic levels are lower.The presence of ochratoxin A in the raw extracts of P. variabile, rubratoxin B in those of P. purpurogenum, and citrinin in those of P. steckii was detected by thin layer chromatography techniques against standards. Toxicity tests against brine shrimp larvae and 12 microorganisms indicated great variability among the extracts.The possibility of using the production of enzymes and mycotoxins in the classification of some groups of Penicillium is studied.     

Long-term post-fire dynamics of co-occurring woody species in Pinus brutia forests: the role of regeneration mode

Regeneration mode is one of the key attributes determining population structure and dynamics of plant species. We investigated long-term patterns after fire in the cover of plant species in a 100-year chronosequence of burned Pinus brutia forests in a humid Mediterranean climate region in Turkey. Significant trends were present in the change of cover in major species through post-fire chronosequence, and species with similar trends were clustered in relation to their regeneration modes. Obligate resprouters increased their cover from the early post-fire years to the later stages, while cover of obligate seeders with a soil seed bank increased in the early years, but then decreased through time. Facultative resprouters were at an intermediate position, with an increase in cover until mid-successional stages and then a decrease through time. The cover of the only obligate seeder with a canopy seed bank (P. brutia) followed a linear increasing trend during the succession. When species with the same regeneration mode were grouped, the same trends were observed with more explained variances. A few life-history traits were enough to explain the observed trends. Our study shows that regeneration mode is an explanatory functional grouping system for describing long-term post-fire dynamics of Mediterranean Basin woody species. We suggest that regeneration mode must be a major component of any vegetation or forest stand dynamics model in the Mediterranean Basin. This result has important implications for the management of Mediterranean Basin ecosystems, and can potentially be extrapolated to other Mediterranean-type fire-prone ecosystems.     

Isolation and characterization of microsatellites in Echinochloa (L.) Beauv. spp.

Five primer pairs were developed that amplify microsatellite loci in three agronomically important Echinochloa (L.) Beauv. species: E. colona (L.) Link, E. crus‐galli (L.) Beauv. and E. crus‐pavonis (Kunth) Schultes. The microsatellites were tested on 24 individuals representing three species collected in rice fields from different geographical regions and revealed 3–7 alleles per microsatellite. Gene diversity [1 ? Σp_ij²] for four polymorphic loci within E. crus‐galli ranged from 0.12 to 0.61. Alleles at a fifth locus were useful in discriminating the species. The microsatellites should provide useful markers for intraspecific diversity studies and aid classification of species within this complex genus.     

Adventitious regeneration of Juglans nigra L. (eastern black walnut)

Somatic embryos and adventitious shoots were initiated from immature cotyledons 10–14 weeks after anthesis. Maximum embryogenesis occurred 12 weeks after anthesis and maximum shoot organogenesis occurred 14 weeks after anthesis. The best treatment for induction of somatic embryos and adventitious shoots from immature cotyledon explants was on agar-solidified WPM supplemented with 0.1 M 2,4-D and 5.0 M TDZ and incubated in light for the first four weeks. Rooting of adventitious shoots was best if they were quickdipped in 2.5 mM IBA and 1.25 mM NAA in 1% dimethyl formamide and 3.9% ethanol (120 Wood's Rooting Compound: water, by volume). Plantlets from rooted adventitious shoots were acclimatized to the greenhouse.Abbreviations BA Benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - DKW Driver and Kuniyuki (1984) walnut medium - IBA indolebutyric acid - LP Long and Preece medium described herein - NAA naphthaleneacetic acid - PPF photosynthetic photon flux - TDZ thidiazuron - WPM Woody Plant Medium of Lloyd and McCown (1980)     

Pollen development in a submerged plant,Ottelia alismoides (L.) Pers. (Hydrocharitaceae)

Exine structure and its developmental program in a submerged plant,Ottella alismoides (L.) Per. were investigated with scanning and transmission electron microscopies. Verrucate protrusions initiate on microspore plasma membrane at early tetrad stage. The verrucate protrusions develop into spines during free microspore stage. A foot layer is formed by accumulation of lamellated structure. The pollen grains ofOttelia alismoides are inaperturate, not omniaperturate, because of the well-developed foot layer. The inaperturate pollen grains ofOttelia are characterized by the spinous protrusions and the granular foot layer.