Determinants of thermal balance in the Hawaiian giant rosette plant,Argyroxiphium sandwicense

The effects of leaf pubescence and rosette geometry on thermal balance were studied in a subspecies of a Hawaiian giant rosette plant, Argyroxiphium sandwicense. This species, a member of the silversword alliance, grows above 2000 m elevation in the alpine zone of two Hawaiian volcanoes. Its highly pubescent leaves are very reflective (absorptance in the 400–700 nm waveband=0.44). Temperature of the expanded leaves was very similar to, or even lower than, air temperature during clear days, which was somewhat surprising given that solar radiation at the high elevation sites where this species grows can exceed 1100 W m^–2. However, the temperature of the apical bud, which is located in the center of the parabolic rosette, was usually 25°C higher than air temperature at midday. Experimental manipulations in the field indicated that incoming solar radiation being focussed towards the center of the rosette resulted in higher temperatures of the apical bud. Attenuation of wind speed inside the rosette, which increased the thickness of the boundary layer surrounding the apical bud, also contributed to higher temperatures. The heating effect on the apical bud of the large parabolic rosette, which apparently enhances the rates of physiological processes in the developing leaves, may exclude the species from lower elevations by producing lethal tissue temperatures. Model simulations of apical bud temperatures at different elevations and laboratory estimates of the temperature threshold for permanent heat injury predicted that the lower altitude limit should be approximately 1900 m, which is reasonably close to the lower limit of distribution of A. sandwicense on Haleakala volcano.     

Leaf surface traits: overlooked determinants of birch resistance to herbivores and foliar micro-fungi?

Previous studies on the mechanisms of birch resistance to herbivores and foliar micro-fungi (both pathogenic and endophytic) have focused mainly on the role of internal leaf chemistry. In the present study, we examined genetic correlations between leaf surface traits (glandular trichome density and total concentrations of surface flavonoid aglycones) and occurrence of three species of foliar micro-fungi, one pathogenic rust (Melampsoridium betulinum) and two endophytic fungi (Fusicladium sp. and Melanconium sp.), and performance of autumnal moth larvae (Epirrita autumnata) in two birch species, Betula pubescens ssp. czerepanovii and B. pendula. The performance of autumnal moth larvae on B. pubescens ssp. czerepanovii was negatively correlated with density of glandular trichomes (RGR: r=–0.855; pupal mass: r=–0.709). In addition, rust infection was negatively correlated with trichome density in B. pendula (r=–0.675) and with epicuticular flavonoid aglycones in B. pubescens ssp. czerepanovii (r=–0.855). The frequency of the endophytic fungus Fusicladium sp., was related to epicuticular flavonoid aglycones (r=–0.782), while another endophytic fungus, Melanconium sp., showed no associations with any of the studied variables in B. pubescens ssp. czerepanovii. Our results indicate that leaf surface traits may be at least as important determinants of herbivore performance and micro-fungi abundance in birch as leaf internal chemistry.     

Effect of auxin physiological analogues on rapeseed (Brassica napus) cold hardening, seed yield and quality

The effect of the auxin physiological analogues analogues 1-[2-chloroethoxycarbonylmethyl]-4-naphthalenesulfonic acid calcium salt (TA-12) and 1-[2-dimethylaminoethoxicarbonylmethyl]naphthalene chlormethylate (TA-14) TA-14 on different winter rapeseed cultivars were studied with regard to their autumnal growth, cold hardening, accumulation of the stress-protective metabolites proline and saccharide in plant organs: apical bud and root collum, winter survival and productivity formation. The test cultivars were the very early ‘Libea’ medium-resistant to wintering, the medium-early ‘Sunday’ resistant to wintering, the medium–early ‘Valesca’ less than medium resistant to wintering, and the early ‘Hornet’ (hybrid) tolerant to stress growth conditions. During the period of cold hardening in natural field conditions, the test compounds TA-12 (2 mM) and TA-14 (4 mM), applied to different winter rapeseed cultivars at the 4th–5th leaf stage, stimulate accumulation proline and saccharides (sucrose and glucose) in the root collum and apical bud tissues, influence plants acclimation to cold, overwintering and productivity formation. Compounds TA-12 and especially TA-14 produced a stable effect on seed and crude fat yield in cvs. ‘Hornet’, ‘Sunday’ and ‘Libea’. The genotypic peculiarities of a cultivar and the meteorological conditions of the plant vegetation period were the factors that mostly determined fatty acid content in seed oil.     

The high‐quality genome of Brassica napus cultivar ‘ZS11’ reveals the introgression history in semi‐winter morphotype

Allotetraploid oilseed rape (Brassica napus L.) is an agriculturally important crop. Cultivation and breeding of B. napus by humans has resulted in numerous genetically diverse morphotypes with optimized agronomic traits and ecophysiological adaptation. To further understand the genetic basis of diversification and adaptation, we report a draft genome of an Asian semi‐winter oilseed rape cultivar ‘ZS11’ and its comprehensive genomic comparison with the genomes of the winter‐type cultivar ‘Darmor‐bzh’ as well as two progenitors. The integrated BAC‐to‐BAC and whole‐genome shotgun sequencing strategies were effective in the assembly of repetitive regions (especially young long terminal repeats) and resulted in a high‐quality genome assembly of B. napus ‘ZS11’. Within a short evolutionary period (~6700 years ago), semi‐winter‐type ‘ZS11’ and the winter‐type ‘Darmor‐bzh’ maintained highly genomic collinearity. Even so, certain genetic differences were also detected in two morphotypes. Relative to ‘Darmor‐bzh’, both two subgenomes of ‘ZS11’ are closely related to its progenitors, and the ‘ZS11’ genome harbored several specific segmental homoeologous exchanges (HEs). Furthermore, the semi‐winter‐type ‘ZS11’ underwent potential genomic introgressions with B. rapa (A_r). Some of these genetic differences were associated with key agronomic traits. A key gene of A03.FLC3 regulating vernalization‐responsive flowering time in ‘ZS11’ was first experienced HE, and then underwent genomic introgression event with A_r, which potentially has led to genetic differences in controlling vernalization in the semi‐winter types. Our observations improved our understanding of the genetic diversity of different B. napus morphotypes and the cultivation history of semi‐winter oilseed rape in Asia.     

The roles of ascospores and conidia of Pyrenopeziza brassicae in light leaf spot epidemics on winter oilseed rape (Brassica napus) in the UK

Ascospores of Pyrenopeziza brassicae were produced in apothecia (cup‐shaped ascomata) on oilseed rape debris. The conidia, which were morphologically identical to the ascospores, were produced in acervular conidiomata was greater than for lesions caused by ascospores. In June 2000, on the ground under a crop with light on the surface of living oilseed rape tissues. Ascospores were more infective than conidia on oilseed rape leaves. The proportion of lesions caused by conidia located on leaf veins leaf spot, numbers of petioles with apothecia decreased with increasing distance into the crop from the edge of pathways. Air‐borne ascospores of P. brassicae were first collected above debris of oilseed rape affected with light leaf spot on 5 October 1998 and 18 September 1999,12 or 23 days, respectively, after the debris had been exposed outdoors. P. brassicae conidia were first observed on leaves of winter oilseed rape on 6 January 1999 and 15 February 2000, respectively, after plots had been inoculated with debris in November 1998 and October 1999. In 1991/92, numbers of ascospores above a naturally infected crop were small from January to April and increased in June and July. P. brassicae conidia were first observed in February and the percentage plants with leaves, stems or pods with light leaf spot increased greatly in May and June. In 1992/93, in a crop inoculated with debris, numbers of airborne ascospores were small from October to January and increased from April to June. P. brassicae conidia were first observed on leaves in late November and light leaf spot was seen on stems and pods in March and June 1993, respectively.     

Improving of oilseed rape lateral root formation by physiological analogues of auxin

The aim of the present work was to study the effect of auxin physiological analogue TA-12 [1-(2-chloroethoksicarbonylmethyl)-4-naphthalenesulfonic acid calcium salt] on the formation of oilseed rape lateral root and on the mitotic activity of apical meristem cells. Spring oilseed rape (Brassica napus L. ssp. oleifera annua Metzg.) cultivar ‘Mascot’ was chosen as a test object. Anatomical, cytological and histological studies on root development suggest that compound TA-12 induces the activity of parent root pericycle cells, stimulates the formation of lateral roots and enhances the division of apical meristem cells. The auxin transport inhibitor 2,3,5-triiodobenzoic acid suppresses the division of apical meristem cells, while this process is restored by the auxin physiological analogue TA-12 and naphthaleneacetic acid. The compound TA-12, by stimulating primary root growth and lateral root induction, optimised the formation of the oilseed rape root system.     

Influence of growth conditions on production of capsular and extracellular polysaccharides byRhizobium leguminosarum

The influence of growth rate and medium composition on exopolymer production byRhizobium leguminosarum was studied. When grown in medium containing 10g/l mannitol and 1g/l glutamic acid,Rhizobium leguminosarum biovartrifolii TA-1 synthesized up to 2.0g/l of extracellular polysaccharide (EPS), and up to 1.6g/l of capsular polysaccharide (CPS). Under non-growing cell conditions in medium without glutamic acid, CPS synthesis by strain TA-1 could proceed to 2.1g/l, while EPS-production remained relatively low (0.8g/l). Maximal CPS-yield was 2.9g CPS/l medium in a medium containing 20g/l mannitol and 2g/l glutamic acid. TheEPS-deficient strain R. leguminosarum RBL5515,exo4::Tn5 was able to produce CPS to similar levels as strain TA-1, but CPS-recovery was easier because of the low viscosity of the medium and growth of the cells in pellets. With strain TA-1 in nitrogen-limited continuous cultures with a constant biomass of 500mg cell protein/l, EPS was the most abundant polysaccharide present at every dilution rate D (between 0.12 and 0.02 h^–1). The production rates were 50–100mg/g protein/h for EPS and 15–20mg/g protein/h for CPS. Only low amounts of cyclic -(1,2)-glucans were excreted (10–30 mg/l) over the entire range of growth rates.Abbreviations bv biovar - CPS capsular polysaccharide - EPS extracellular polysaccharide - HM_r high molecular mass - LM_r low molecular mass - YEMCR Yeast Extract-Mannitol-Congo Red agar     

Analogues of auxin modifying growth and development of some monocot and dicot plants

The dependence of morphogenetic processes in the formation of vegetative and generative organs in spring oilseed rape and barley on exogenously applied physiological analogues of auxin: 2,4-D (2,4-dichlorphenoxyacetic acid), NAA (naphthalene-1-acetic acid), TA-12 (1-[2-chloroethoxycarbonyl-methyl]-4-naphthalenesulfonic acid calcium salt) and TA-14 (1-[2-dimethylaminoethoxicarbonylmethyl]naphtalene chlormethylate) were investigated. The experiments were performed with hypocotyl tissue cultures of oilseed rape and barley microspores in vitro. The auxin analogues applied revealed differences of morphogenetic competence in dedifferentiation-redifferentiation processes that occurred in oilseed rape cultures. TA-12 and TA-14 applied together with NAA and BA (6-benzylaminopurine) caused more intensive callus growth in comparison with 2,4-D. Rhizogenesis was induced when 2,4-D was substituted by TA-12. Compound TA-14, unlike TA-12, facilitated the appearance and development of cotyledons in callus tissues. Hower the compounds TA-12 and TA-14 have no positive effect in monocot plant — barly anther culture for callogenesis and regeneration in comparison to indole-3-acetic acid (IAA). TA-14 and TA-12 showed similar but not identical auxin properties and demonstrated high efficiency as modifiers of rape-dicot plant growth and morphogenesis.     

Immobilization and mobilization of labelled sulphur in relation to soil arylsulphatase activity in rhizosphere soil of field-grown rape,barley and fallow

During plant growth, rhizosphere soils from fallow, barley (Hordeum vulgare L. cv Esterel) and rape (Brassica napus L. cv Capitole) grown in a calcareous soil were sampled 5 times (every fortnight) from May to July 2001 at plant maturity. In order to estimate the impact of C derived from photosynthesis, the aerial parts of rape and barley in an area of 1 m² were cut off about 2 cm from the soil surface, and left a fortnight before each sampling. Both soil arylsulphatase activity and a 1-week immobilization of S fertilizer in the sampled soils were then measured. The immobilization of S fertilizer was higher in fallow, followed by barley and rape rhizosphere soil. A strong positive linear correlation (r ²=0.71, P<0.001) was found between soil arylsulphatase activity and S fertilizer immobilized. Conversely, the mobilization of endogenous organic ³⁵S (obtained after leaching free and adsorbed SO₄ ^2–-³⁵S by 0.009 M Ca(H₂PO₄)₂) in the rhizosphere soil of each plant cover pooled at the end of the 5 samplings and materialized by ryegrass (Lolium perenne L. cv Massa) ³⁵S uptake, was about 3 and 2 times higher, respectively, in rape and barley than in fallow rhizosphere soil. Accordingly, strong inverse polynomial relationships were observed between soil arylsulphatase activity and ³⁵S uptake by the whole plant (r ²=0.904, P<0.02) and roots (r ²=0.970, P<0.01) of ryegrass. Plant cuttings affected both the immobilization and mobilization of S. It is concluded that the turnover of S freshly immobilized in rape rhizosphere soil was relatively high. Therefore, rape as a preceding crop in the rotations may have a beneficial effect by increasing S availability on the succeeding crop.     

Biology of afroalpineDendrosenecio (Asteraceae)

The genusDendrosenecio (giant groundsels), encompassing three species and 12 subspecies, is endemic to the high mountains of East and Central Africa where it constitutes the most conspicuous components of the afroalpine vegetation. Two lifeforms, the arborescent and the prostrate rhizomatous, are regarded as the results of evolution from forest-living woody or herbaceous ancestors. Due to the uninterrupted growth period in the tropics, there are no anatomical or morphological features which allow conventional age determination. However, stem elongation rates have been determined (3–5.5 cm per year) and indicate an age of about 250 years for the tallest arborescent Dendrosenecios which may reach a height of 10 m. 30 to 120 large leaves are clustered in an enormous terminal rosette, justifying the term giant rosette plants. A leaf bud, consisting of about as many developing leaves as the rosette contains, is found in the center. During the nocturnal frost period the adult rosette leaves form a so-called night-bud by nyctinastic upwards bending and thus protect the leaf bud from freezing by insulation. The stem is surrounded by a mantle of persistent dead leaves; this ameliorates the microclimate of the pith-cells which greatly contribute to water transport into the leaves. Below the leaf rosette a zone of putrefaction is found, from where the decay of the dead leaves apparently provides nutrients directly to the growing stem. The population dynamics of the arborescentD. keniodendron is characterized by a simultaneous inflorescence development at irregular intervals of up to more than twenty years. Due to sporadic flowering and a seedling survival rate of less than 1%, oscillations of the population size are to be expected.     

Patterns of molecular variation in a species-wide germplasm set of <Emphasis Type="Italic">Brassica napus</Emphasis>

Rapeseed (Brassica napus L.) is the leading European oilseed crop serving as source for edible oil and renewable energy. The objectives of our study were to (i) examine the population structure of a large and diverse set of B. napus inbred lines, (ii) investigate patterns of genetic diversity within and among different germplasm types, (iii) compare the two genomes of B. napus with regard to genetic diversity, and (iv) assess the extent of linkage disequilibrium (LD) between simple sequence repeat (SSR) markers. Our study was based on 509 B. napus inbred lines genotyped with 89 genome-specific SSR primer combinations. Both a principal coordinate analysis and software STRUCTURE revealed that winter types, spring types, and swedes were assigned to three major clusters. The genetic diversity of winter oilseed rape was lower than the diversity found in other germplasm types. Within winter oilseed rape types, a decay of genetic diversity with more recent release dates and reduced levels of erucic acid and glucosinolates was observed. The percentage of linked SSR loci pairs in significant (r ² > Q _{95 unlinked loci pairs}) LD was 6.29% for the entire germplasm set. Furthermore, LD decayed rapidly with distance, which will allow a relatively high mapping resolution in genome-wide association studies using our germplasm set, but, on the other hand, will require a high number of markers.     

Responses of generalist invertebrate predators to pupal densities of autumnal and winter moths under field conditions

• 1 Generalist natural enemies are usually not considered as being capable of causing population cycles in forest insects, but they may influence the population dynamics of their prey in the low density cycle phase when specialist enemies are largely absent.
• 2 In the present field study, the total response of the generalist invertebrate predator community to experimentally established pupal densities of the closely related autumnal (Epirrita autumnata) and winter moths (Operophtera brumata) was analysed.
• 3 Due to the high amount of variation in the dataset, the exact shape of the response curve could not be convincingly estimated. Nevertheless, two important conclusions can be drawn from the analyses.
• 4 Firstly, the natural invertebrate predator community seems to become saturated at rather low densities of both autumnal and winter moth pupae. Secondly, the predator community seems to become saturated at much lower densities of autumnal than of winter moth pupae.
• 5 Furthermore, pupal mass was significantly negatively correlated with invertebrate predation probability in autumnal moth pupae.
• 6 These results indicate that differences in the predator assemblage being able to consume pupae of the two moth species, as well as different handling times, could be responsible for the substantially higher predation rates in winter than in autumnal moth pupae.
• 7 As a consequence, the population dynamics of autumnal moths might be less affected by generalist invertebrate predators than those of winter moths, as autumnal moths seem able to escape from the regulating influence of generalist predators at much lower population densities than winter moths.

     

Corn (Zea mays L.) growth, leaf pigment concentration, photosynthesis and leaf hyperspectral reflectance properties as affected by nitrogen supply

Plant nitrogen (N)deficiency often limits crop productivity. Early detection of plant N deficiency is important for improving fertilizer N-use efficiency and crop yield. An experiment was conducted in sunlit, controlled environment chambers in the 2001 growing season to determine responses of corn (Zea mays L. cv. 33A14) growth and leaf hyperspectral reflectance properties to varying N supply. Four N treatments were: (1) half-strength Hoagland's nutrient solution applied throughout the experiment (control); (2) 20% of control N starting 15 days after emergence (DAE); (3) 0% N starting 15 DAE; and (4) 0% N starting 23 DAE (0% NL). Plant height, the number of leaves, and leaf lengths were examined for nine plants per treatment every 3–4 days. Leaf hyperspectral reflectance, concentrations of chlorophyll a, chlorophyll b,and carotenoids, leaf and canopy photosynthesis, leaf area, and leaf N concentration were also determined during the experiment. The various N treatments led to a wide range of N concentrations (11 – 48 g kg^–1 DW) in uppermost fully expanded leaves. Nitrogen deficiency suppressed plant growth rate and leaf photosynthesis. At final harvest (42 DAE), plant height, leaf area and shoot biomass were 64–66% of control values for the 20% N treatment, and 46-56% of control values for the 0% N treatment. Nitrogen deficit treatments of 20% N and 0% N (Treatment 3) could be distinguished by changes in leaf spectral reflectance in wavelengths of 552 and 710 nm 7 days after treatment. Leaf reflectance at these two wavebands was negatively correlated with either leaf N (r = –0.72 and –0.75^**) or chlorophyll (r = –0.60 and –0.72^**) concentrations. In addition, higher correlations were found between leaf N concentration and reflectance ratios. The identified N-specific spectral algorithms may be used for image interpretation and diagnosis of corn N status for site-specific N management.     

Field observations on nitrogen catch crops. III. Transfer of nitrogen to the succeeding main crop

In temperate climates with a precipitation surplus during autumn and winter, nitrogen (N) catch crops can help to reduce nitrogen losses from cropping systems by absorbing nitrogen from the soil and transfer it to a following main crop. In two field experiments the catch crop species winter rye (Secale cereale) and forage rape (Brassica napus ssp. oleifera (Metzg.) Sinsk) or oil radish (Raphanus sativus spp. oleiferus (DC.) Metzg.) were planted end of August and 3 weeks later with a non-limiting supply of N and zero-N controls. In the next spring catch crops were incorporated into the soil. In Expt 1, N transfer was measured as (i) the N uptake of a potato test crop, grown with zero and 12.5 g m^–2 N applied, and (ii) the increase in soil mineral N (0–30 cm) in uncropped soil covered with polythene film. In Expt 2, N transfer was measured as the increase in soil mineral N in covered cylinders placed in uncropped soil (in situ incubation). Subsidiary laboratory incubations were performed in Expt 2. In Expt 1, the apparent recovery in potato of fertilizer N (R _f) was 0.56. The recovery in potato of N mineralized from 'native' N pools other than catch crop material (R _n) ranged from 0.43 to 0.51, depending on the value assumed for the depth of N extraction by potato roots. The average recovery in potato of incorporated catch crop N (R _c) was 0.34. Expressed as `fertilizer N replacement factor' (F _r) the latter was 0.61 (i.e. 1 kg of N in catch crop material counts for 0.61 kg fertilizer N). Under the film in Expt 1 the fraction net mineralization of incorporated catch crop N (M _n) was 0.36 on August 11 and 0.43 on October 18. In Expt 2, the average value of M _n was 0.31, which was lower than in Expt 1 and probably associated with the drier soil in Expt 2. In the laboratory incubations (20°C) M _n showed values up to 0.54 after 84 days with the largest rates of change in mineralization occuring early after the start of the incubation. In conjunction with literature data it is concluded that cultivation of nitrogen catch crops shows promise as a means to reduce N input and N losses in temperate climates with wet winters.     

Occurrence of Diaphanosoma excisum (Sars) on a sandy beach at Balramgari (Orissa), India

The occurrence of Diaphanosoma excisum (Sars), a freshwater cladoceran, in benthic samples of an intertidal sandy beach is reported. Population density was seasonal. A relatively high density was recorded from June to September (south-west monsoon season) with a maximum (46 ind 10 cm^–2) in September at a depth of 10–15 cm of sediment. A sudden decline occurred during north-east monsoon (October to January), and in the fair season (February to May), the cladocerans disappeared. Mean density varied (P<0.001) with sediment depth and season and showed a contagious dispersion. Abundance was negatively correlated with salinity (r = –0.76) but positively with POC (r =0.79) and mean grain size of the sediment (r = 0.93). The density of D. excisum was highest in fine sand.     

Seasonal differences in green leaf breakdown and nutrient content of deciduous and evergreen tree species and grass in a granitic headwater stream

Litter processing was examined in autumn–winter and spring–summer in a second order stream in Galicia (NW Spain). We compared decay rate and nutrient dynamics of green leaves of several deciduous (riparian: Alnus glutinosa, Betula alba and Populus×canadensis; terrestrial: Castanea sativa, Quercus robur), and evergreen tree species (terrestrial: Pinus radiata and Eucalyptus nitens), in addition to ray-grass (Lolium perenne). In the autumn–winter period, the decay rates (–k) ranged between 0.0086 degree-days^–1 for poplar, and 0.0019 degree-days^–1 for birch leaves. Alder showed the most rapid breakdown in spring–summer (0.0124 degree-days^–1), and pine the slowest (0.0016 degree-days^–1). Deciduous species exhibited general higher processing rates than evergreen species and ray-grass. The initial nitrogen and phosphorus contents were higher in riparian species leaves and ray-grass, being higher in spring (2.28±0.14% and 0.24±0.04% of nitrogen and phosphorus, respectively) than in autumn (1.88±0.36% of nitrogen and 0.18±0.03% of phosphorus). A significant correlation coefficient was found only between mean nitrogen leaf packs contents during incubation and decay rates (r=0.61; p=0.012).In deciduous species, processing was faster during the spring–summer than in the autumn–winter period, which may be attributed to the greater nutritional value and less consistency of the leaves during this season. Within evergreen species, pine had a significantly faster processing rate in autumn, attributed in this study to greater physical fragmentation of the needles. Ray-grass and eucalyptus did not exhibit any seasonal differences in processing rate.During the spring–summer period, litterfall inputs are quantitatively less important than during the autumn–winter, but due to high retention and fast breakdown during the spring–summer, green inputs should contribute substantially to nutrient incorporation and cycling in benthic communities.     

Antagonistic activity of bacteria isolated from crops cultivated in a rotation system and a monoculture against <Emphasis Type="Italic">Pythium debaryanum</Emphasis> and <Emphasis Type="Italic">Fusarium oxysporum</Emphasis>

The effect of crop rotation and monocropping on the occurrence of bacteria with antagonistic activity toward Pythium debaryanum and Fusarium oxysporum was shown. Arthrobacter spp., fluorescent Pseudomonas spp. and actinomycetes were isolated from winter rape, sugar beet and winter barley rhizosphere and bulk soil from the plots of a long-term crop rotation experiment (18 years). The occurrence of mycoantagonistic isolates and their antibiosis level exhibited specificity for the site, crop and crop rotation. Mycoantagonistic activity was common among actinomycetes and fluorescent Pseudomonas spp. and less frequent among Arthrobacter spp. Antibiosis of fluorescent Pseudomonas spp. and Arthrobacter spp. was in general stronger against P. debaryanum than F. oxysporum. The highest percentage of antagonistic Pseudomonas spp. against P. debaryanum was in the plots of barley crop, while plots of winter rape showed higher frequency of antagonists against F. oxysporum. The highest antibiosis activity of Arthrobacter spp. against both pathogens occurred in isolates from barley and winter rape monoculture, and there were no F. oxysporum antagonists among these bacteria in sugar beet monoculture. Most of actinomycete isolates strongly inhibited growth of P. debaryanum and F. oxysporum. The percentage of mycoantagonistic actinomycetes and their antibiosis level were the highest in the 6-year crop rotation system.     

Development of shoot inHydrangea macrophylla I. Terminal and axillary buds

The structure of shoots, in particular of winter buds, ofHydrangea macrophylla was examined. The non-flower-bearing shoot is usually composed of a lower and an upper part, between which a boundary is discernible by means of a distinctly short internode. This internode is the lowermost of the upper part, and it is usually shorter than the internodes immediately above and below, although the internodes tend to shorten successively from the proximal to the distal part of the shoot. Variations exist in the following characters among the terminal bud, the axillary bud on the lower part of the shoot and the axillary bud on the upper part: (1) length of bud; (2) character of the outermost pair of leaf primordia; (3) degree of development of secondary buds in the winter bud; and (4) the number of leaf primordia. Usually, the terminal bud contains several pairs of foliage leaf primordia with a primordial inflorescence at the terminal of the bud, but the axiallary bud contains only the primordia of foliage leaves in addition to a pair of bud scales.     

Winter growth phenology and leaf orientation in Pachypodium namaquanum (Apocynaceae) in the succulent karoo of the Richtersveld,South Africa

Pachypodium namaquanum (Nyley ex Harb.) Welw., an unusual arborescent stem succulent from the succulent karoo of the arid Richtersveld in north-western South Africa and adjacent Namibia, is characterized by a striking curvature of the terminal 20–60 cm of the trunk toward the north. This orientation displays the single terminal whorl of drought-deciduous leaves with their flat surface angled at a mean inclination of 55° from horizontal. Inclination of 50–60° was found in 65% of individuals sampled, and 85% were inclined between 45 and 65°. Northward azimuth was also quite regular, but varied slightly between populations. The fixed leaf orientation in P. namaquanum maximizes radiation absorption during the winter months when leaves are present. Leaves normally form in early fall (April) and abscise early in spring (October). Growing season conditions in the Richtersveld are relatively mild, with mean maximum temperature dropping only to 21.6°C in July, the coldest month of the year. Frosts are rare. By the fixed orientation of its leaf whorl, P. namaquanum is able to maintain nearly twice the midwinter radiation absorptance that it would have with horizontal orientation. Over an annual cycle the angled leaves receive more radiation than would horizontal leaves for each of the 6 months in which they are present on the plant. This increased winter irradiance is hypothesized to singificantly increase net primary production by concentrating growth activities in winter months and allowing the species to remain dormant during the hyperarid conditions of the hot summer months. Midwinter flowering from apical buds in P. namaquanum may also be aided by its stem orientation. The evolution of this characteristic pattern of winter growth phenology and nodding stem orientation may have come about because of low but relatively regular autumn precipitation and moderate winter temperatures. Slow and regular growth of P. namaquanum leads to long lifespans which may reach 300 years or more.     

Root growth,macro-nutrient uptake dynamics and soil fertility requirements of a high-yielding winter oilseed rape crop

Shoot growth, root growth and macro-nutrient uptake by a high-yielding (5t/ha grain) winter oilseed rape crop have been measured. Maximum rooting density in the top 20cm of soil was 9.4 cm cm⁻³ and roots reached a depth of at least 1.8 m. Maximum nutrient uptakes were 364 kg ha⁻¹ for N, 43 kg ha⁻¹ for P, 308 kg ha⁻¹ for K, 287 kg ha⁻¹ for Ca and 16 kg ha⁻¹ for Mg. A 30-day drought coincided with the flowering period and root and shoot growth, as well as nutrient uptake rates, were reduced. Nutrient concentrations in the soil solution necessary to sustain the nutrient fluxes into the root system by diffusive supply have been calculated. Peak values were in the range 10 μM for P to 87 μM for N, lower than the observed concentrations, and it was concluded that nutrient transport to roots was not a limitation to uptake by this rape crop.