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Stem Elongation (stem + elongation)

Distribution by Scientific Domains

Life Sciences	71%

Selected Abstracts

Development of an interactive decision-support system on a Web site for control of Mycosphaerella graminicola in winter wheat,

EPPO BULLETIN, Issue 1 2000
J.-M. Moreau
A decision-support system (DSS) has been developed in Belgium to help farmers and advisers to manage Mycosphaerella graminicola in winter wheat during stem elongation. The system calculates in real time the interactions between winter wheat and M. graminicola development to simulate disease progression in the canopy in order to guide field observations on the different leaf layers and determine the risks for the crop. It has been structured to run with individual field input and local hourly meteorological data. An interactive Internet version of the system has been developed to facilitate the delivery of information. It allows users to base their decisions on advice tailored to conditions in their own fields, as well as to recent and validated hourly local meteorological data that is regularly updated on the server computer. [source]

Effects of 15N Split-application on Soil and Fertiliser N Uptake of Barley, Oilseed Rape and Wheat in Different Cropping Systems

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2007
K. Sieling
Abstract In intensive farming systems, farmers split up and apply the N fertilization to winter cereals and oilseed rape (OSR) at several dates to meet the need of the crop more precisely. Our objective was to determine how prior fertilizer N application as slurry and/or mineral N affects contributions of fertilizer- and soil-derived N to N uptake of barley (1997), oilseed rape (OSR; 1998) and wheat (1999). In addition, residual fertilizer N effects were observed in the subsequent crop. Since autumn 1991, slurry (none, slurry in autumn, in spring, in autumn plus in spring) and mineral N fertilizer (0, 12 and 24 g N m,2) were applied annually. Each year, the treatments were located on the same plots. In 1997,1999, the splitting rates of the mineral N fertilization were labelled with 15N. Non-fertilizer N uptake was estimated from the total N uptake and the fertilizer 15N uptake. All three crops utilized the splitting rates differently depending on the time of application. Uptake of N derived from the first N rate applied at the beginning of spring growth was poorer than that from the second splitting rate applied at stem elongation (cereals) or third splitting rate applied at ear emergence or bud formation (all three crops). In contrast, N applied later in the growing season was taken up more quickly, resulting in higher fertilizer N-use efficiency. Mineral N fertilization of 24 g N m,2 increased significantly non-fertilizer N uptake of barley and OSR at most of the sampling dates during the growing season. In cereals, slurry changed the contribution of non-fertilizer N to the grain N content only if applied in spring, while OSR utilized more autumn slurry N. In OSR and wheat, only small residual effects occurred. The results indicate that 7 years of varying N fertilization did not change the contribution of soil N to crop N uptake. [source]

Effect of Timing and Nitrogen Fertilizer Application on Winter Oilseed Rape (Brassica napus L.). I. Growth Dynamics and Seed Yield

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 5 2004
P. Bar
Abstract The field experiments conducted on the grey-brown podzolic soil in the four growing seasons (1998,2001) at Krzeslice Farm, central-western Poland comprised seven fertilization variants: 80NF + 80CAN; 80CAN + 80CAN; 80AN + 80AN; 80NF + 50CAN + 30CN; 80CAN + 50CAN +30CN; 80AN + 50AN + 30CN (where NF , nitrofos NPK; CAN , calcium-ammonium nitrate; AN , ammonium nitrate; CN , calcium nitrate) and control (without N) applied in split rates at the beginning of spring regrowth (80 kg N ha,1), stem elongation (80 or 50) and flower buds visible stages (30). The yielding effect of tested fertilization variants was significant in comparison with the control (2.24 t ha,1). The highest mean seed yield (3.64 t ha,1) was collected from 80AN + 80AN and 80CAN + 80CAN variants. Mean values of 4 years indicate that the second N rate division (80 + 50 + 30) decreased yield, although not significantly in comparison with these two N treatments. Plants grown on these treatments have developed different patterns of growth to yield the seeds. These patterns were characterized by very high crop growth rate during flowering (above 21 g m,2 day,1) and negative at maturation (down to ,2.5 g m,2 day,1). Plants fertilized with ammonium nitrate (80AN + 80AN) reached maximum growth rate earlier (65 days), which lasted longer (20 days) than plants fertilized with calcium-ammonium nitrate (71 days lasting 17.5 days). Plants grown on the control treatment reached the highest crop growth rate within 79 days (14.8 g m,2 day,1), which lasted 15 days. [source]

Strategies to Improve the Use Efficiency of Mineral Fertilizer Nitrogen Applied to Winter Wheat

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 3 2002
K. Blankenau
Recovery of fertilizer nitrogen (N) applied to winter wheat crops at tillering in spring is lower than that of N applied at later growth stages because of higher losses and immobilization of N. Two strategies to reduce early N losses and N immobilization and to increase N availability for winter wheat, which should result in an improved N use efficiency (= higher N uptake and/or increased yield per unit fertilizer N), were evaluated. First, 16 winter wheat trials (eight sites in each of 1996 and 1997) were conducted to investigate the effects of reduced and increased N application rates at tillering and stem elongation, respectively, on yield and N uptake of grain. In treatment 90-70-60 (90 kg N ha,1 at tillering, 70 kg N ha,1 at stem elongation and 60 kg N ha,1 at ear emergence), the average values for grain yield and grain N removal were up to 3.1 and 5.0 % higher than in treatment 120-40-60, reflecting conventional fertilizer practice. Higher grain N removal for the treatment with reduced N rates at tillering, 90-70-60, was attributed to lower N immobilization (and N losses), which increased fertilizer N availability. Secondly, as microorganisms prefer NH4+ to NO3, for N immobilization, higher net N immobilization would be expected after application of the ammonium-N form. In a pot experiment, net N immobilization was higher and dry matter yields and crop N contents at harvest were lower with ammonium (ammonium sulphate + nitrification inhibitor Dicyandiamide) than with nitrate (calcium nitrate) nutrition. Five field trials were then conducted to compare calcium nitrate (CN) and calcium ammonium nitrate (CAN) nutrition at tillering, followed by two CAN applications for both treatments. At harvest, crop N and grain yield were higher in the CN than in the CAN treatment at each N supply level. In conclusion, fertilizer N use efficiency in winter wheat can be improved if N availability to the crops is increased as a result of reduced N immobilization (and N losses) early in the growth period. N application systems could be modified towards strategies with lower N applications at tillering compensated by higher N dressing applications later. An additional advantage is expected to result from use of nitrate-N fertilizers at tillering. Strategien zur Verbesserung der Effizienz von Düngerstickstoff in Winterweizen Aus früheren Versuchen mit Winterweizen ist bekannt, daß zur Ernte die Wiederfindung von im Frühjahr zur Bestokkung gedüngtem Stickstoff (N) geringer ist, als die von N aus Spätgaben. Die Ursachen liegen in einer höheren mikrobiell-bedingten Netto-N-Immobilisation, aber auch N-Verlusten zwischen Bestockung und Schoßbeginn im Vergleich zu späteren Wachstumstadien begründet. In den vorliegenden Versuchen wurden zwei Strategien getestet, um insbesondere die früh in der Vegetation auftretende Netto-N-Immobilisation zu vermindern. Die dadurch erwartete erhöhte N-Verfügbarkeit sollte zu einer erhöhten N-Effizienz (höherer N-Entzug/Ertrag bezogen auf die N-Düngung) führen. 1996 und 1997 wurden jeweils 8 Feldversuche mit Winterweizen durchgeführt, um den Einfluß einer reduzierten Andüngung bei gleichzeitig erhöhter Schossergabe im Vergleich zur konventionellen N-Düngung zu untersuchen. Tatsächlich wurden in dem Prüfglied 90-70-60 (N-Sollwertdüngung: 90 kg N ha,1, Schossergabe: 70 kg N ha,1, Ährengabe: 60 kg N ha,1) im Mittel bis zu 3.1 % höhere Erträge und 5.0 % höhere N-Abfuhren mit dem Korn im Vergleich zur konventionellen Variante 120-40-60 (N-Sollwertdüngung: 120 kg N ha,1, Schossergabe: 40 kg N ha,1 und Ährengabe: 60 kg N ha,1) erzielt. Die höhere N-Abfuhr kann auf eine erhöhte N-Verfügbarkeit infolge geringerer mikrobieller N-Festlegung zurückgeführt werden. Da die vornehmlich heterotrophen Bodenmikroorganismen bevorzugt NH4+ gegenüber NO3, immobilisieren, kann eine höhere N-Immobilisation bei Ammonium-Düngung erwartet werden. Tatsächlich wurden in einem Gefäßversuch nach Düngung von Ammoniumsulfat (+ Nitrifikationshemmer Dicyandiamid) geringere Trokkenmasseerträge und N-Aufnahmen von Weizenpflanzen erzielt als mit Calciumnitrat. Für die Ammoniumsulfatvariante ergab sich eine höhere Netto-N-Immobilisation. Danach wurde in fünf Feldversuchen mit Winterweizen der Einfluß einer Andüngung mit Nitrat (Calciumnitrat) im Vergleich zur Verwendung des ammoniumhaltigen Kalkammonsalpeters (KAS) auf die N-Aufnahme und den Kornertrag untersucht (beide Varianten erhielten KAS als Spätgaben). In der nitratangedüngten Variante wurden zum Teil signifikant höhere Ertäge und N-Aufnahmen in Korn und Stroh ermittelt. Aus den dargestellten Versuchen kann gefolgert werden, daß die Düngerstickstoff-Effizienz verbessert werden kann, wenn vor allem die N-Immobilisation (und eventuell auch N-Verluste) in frühen Wachstumsstadien zwischen Bestockung und Schoßbeginn verringert und so die N-Verfügbarkeit erhöht wird. Es kann empfohlen werden Winterweizenbestände mit geringeren N-Mengen , als nach N-Sollwert 120 kg N ha,1 vorgesehen , anzudüngen und die Schossergabe entsprechend zu erhöhen. Die Verwendung von nitrathaltigen Düngern bei der Andüngung ist von Vorteil. [source]

Effect of Different Crop Densities of Winter Wheat on Recovery of Nitrogen in Crop and Soil within the Growth Period

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 3 2001
K. Blankenau
Previous experiments have shown that, at harvest of winter wheat, recovery of fertilizer N applied in early spring [tillering, Zadok's growth stage (GS) 25] is lower than that of N applied later in the growth period. This can be explained by losses and immobilization of N, which might be higher between GS 25 and stem elongation (GS 31). It was hypothesized that a higher crop density (i.e. more plants per unit area) results in an increased uptake of fertilizer N applied at GS 25, so that less fertilizer N is subject to losses and immobilization. Different crop densities of winter wheat at GS 25 were established by sowing densities of 100 seeds m,2 (Slow), 375 seeds m,2 (Scfp= common farming practice) and 650 seeds m,2 (Shigh) in autumn. The effect of sowing density on crop N uptake and apparent fertilizer N recovery (aFNrec = N in fertilized treatments , N in unfertilized treatments) in crops and soil mineral N (Nmin), as well as on lost and immobilized N (i.e. non-recovered N = N rate , aFNrec), was investigated for two periods after N application at GS 25 [i.e. from GS 25 to 15 days later (GS 25 + 15d), and from GS 25 + 15d to GS 31] and in a third period between GS 31 and harvest (i.e. after second and third N applications). Fertilizer N rates varied at GS 25 (0, 43 and 103 kg N ha,1), GS 31 (0 and 30 kg N ha,1) and ear emergence (0, 30 and 60 kg ha,1). At GS 25 + 15d, non-recovered N was highest (up to 33 kg N ha,1 and up to 74 kg N ha,1 at N rates of 43 and 103 kg N ha,1, respectively) due to low crop N uptake after the first N dressing. Non-recovered N was not affected by sowing density. Re-mineralization during later growth stages indicated that non-recovered N had been immobilized. N uptake rates from the second and third N applications were lowest for Slow, so non-recovered N at harvest was highest for Slow. Although non-recovered N was similar for Scfp and Shigh, the highest grain yields were found at Scfp and N dressings of 43 + 30 + 60 kg N ha,1. This combination of sowing density and N rates was the closest to common farming practice. Grain yields were lower for Shigh than for Scfp, presumably due to high competition between plants for nutrients and water. In conclusion, reducing or increasing sowing density compared to Scfp did not reduce immobilization (and losses) of fertilizer N and did not result in increased fertilizer N use efficiency or grain yields. Einfluß unterschiedlicher pflanzendichten von Winterweizen auf die Wiederfindung von Stickstoff in Pflanze und Boden während der Vegetationsperiode Aus Wintergetreideversuchen ist bekannt, daß zur Ernte die Wiederfindung von Düngerstickstoff aus der Andüngung (Bestockung, [GS-Skala nach Zadok] GS 25) im Aufwuchs und in mineralischer Form im Boden (Nmin) niedriger ist als die von Düngerstickstoff der Schosser-und Ährengaben. Dies kann auf höhere Verluste bzw. eine höhere Immobilisation von Düngerstickstoff zwischen GS 25 und Schoßbeginn zurückgeführt werden, da hier die N-Aufnahme der Pflanzen im Vergleich zu späteren Wachstumsstadien gering ist. Daraus wurde abgeleitet, daß eine Erhöhung der Pflanzendichte zu einer erhöhten Aufnahme von früh gedüngtem N führen könnte, so daß weniger Dünger-N für Verlust- und Immobilisationsprozesse im Boden verbleibt. Unterschiedliche Pflanzendichten wurden durch unterschiedliche Aussaatstärken im Herbst erreicht (Slow= 100 Körner m,2, Scfp [herkömmliche Praxis]= 375 Körner m,2, Shigh= 650 Körner m,2). In der folgenden Vegetationsperiode wurde der Einfluß der verschiedenen Aussaatstärken auf die N-Aufnahme, die apparente Wiederfindung von Dünger-N (aFNrec = N in gedüngten , N in ungedüngten Prüfgliedern) in Pflanzen und Nmin, sowie auf potentielle Verluste und Immobilisation von Dünger-N (N-Defizit = N-Düngung , aFNrec) für zwei Phasen im Zeitraum zwischen der ersten N-Gabe (GS 25) und der Schossergabe zu GS 31 (d. h. zwischen GS 25 und 15 Tagen später [GS 25 + 15d] und von GS 25 + 15d bis GS 31), sowie zwischen GS 31 und der Ernte (d. h. nach der zweiten und dritten N-Gabe) untersucht. Die N-Düngung variierte zu den Terminen GS 25 (0, 43, 103 kg N ha,1), GS 31 (0, 30 kg N ha,1) und zum Ährenschieben (0, 30, 60 kg N ha,1). Unabhängig von der Aussaatstärke war das N-Defizit zum Termin GS 25 + 15d am höchsten (bis zu 33 kg N ha,1 und 74 kg N ha,1 bei einer N-Düngung von 43 bzw. 103 kg N ha,1), da die N-Aufnahme durch die Pflanzen während der Bestockungsphase am geringsten war. Das N-Defizit zeigt vornehmlich immobilisierten N an, da zu späteren Terminen eine Re-Mobilisation von N auftrat. Zwischen GS 31 und der Ernte wurden für die Aussaatstärke Slow die geringsten Aufnahmeraten von Düngerstickstoff aus der Schosser- und Ährengabe errechnet, so daß für Slow die höchsten N-Defizitmengen ermittelt wurden. Obwohl die N-Defizitmengen für Scfp und Shigh annähernd gleich waren, wurden bei N-Düngung von 43 + 30 + 60 kg N ha,1 für Scfp die höchsten Kornerträge erzielt. Diese Kombination von Aussaatstärke und N-Düngung kann als praxisüblich bezeichnet werden. Für Shigh wurden vermutlich niedrigere Kornerträge erzielt, weil die Konkurrenz um Nährstoffe und Wasser zwischen den Pflanzen aufgrund der hohen Pflanzendichte am intensivsten war. Die Ergebnisse lassen den Schluß zu, daß eine Verringerung oder Erhöhung der Pflanzendichte über entsprechende Aussaatstärken nicht zu einer Reduktion der Dünger-N-Immobilisation (oder von N-Verlusten) führt und demnach auch nicht die Dünger-N-Ausnutzung durch die Bestände erhöht wird. [source]

Plant response to solar ultraviolet-B radiation in a southern South American Sphagnum peatland

JOURNAL OF ECOLOGY, Issue 4 2002
Peter S. Searles
Summary 1Plant growth and pigmentation of the moss Sphagnum magellanicum and the vascular plants Empetrum rubrum, Nothofagus antarctica and Tetroncium magellanicum were measured under near-ambient (90% of ambient) and reduced (20%) ultraviolet-B (UV-B) radiation for three growing seasons in a Sphagnum peatland in Tierra del Fuego, Argentina (55° S). 2Reduction of solar UV-B increased height growth but decreased volumetric density in S. magellanicum so that biomass production was not influenced during the 3 years. The morphology of vascular plants tended not to respond to UV-B reduction. 3A 10,20% decrease in UV-B-absorbing compounds occurred in T. magellanicum under solar UV-B reduction. No effects were seen on chlorophyll or carotenoids in S. magellanicum, although, for UV-B-absorbing compounds, a significant interaction between UV-B and year suggests some response to solar UV-B reduction. 4The climate-related growth of the dwarf shrub E. rubrum was assessed retrospectively by correlating an 8-year record of annual stem elongation with macroclimatic factors including solar UV-B and visible radiation, precipitation and temperature. 5No significant negative correlations were found between annual E. rubrum stem elongation and ambient solar UV-B, the ratio of UV-B : visible radiation, or the 305-nm : 340-nm irradiance ratio for an 8-year record (1990,91 to 1997,98), nor was stem elongation affected by solar UV-B reduction in our experimental field plots after 3 years. 6The role of solar UV-B radiation on plant growth in Sphagnum peatlands in Tierra del Fuego, Argentina, is likely to depend on the severity of stratospheric ozone depletion over the next several decades. The increases in ambient solar UV-B associated with ozone depletion over the last 20 years are less than the difference between our radiation treatments. Therefore, providing that the ozone layer substantially recovers by the middle of this century, only modest effects of increased solar UV-B on plant growth may be expected. [source]

How do UV Photomorphogenic Responses Confer Water Stress Tolerance?,,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2003
Dennis C. Gitz
ABSTRACT Although ultraviolet-B (UV-B) radiation is potentially harmful, it is an important component of terrestrial radiation to which plants have been exposed since invading land. Since then, plants have evolved mechanisms to avoid and repair UV radiation damage; therefore, it is not surprising that photomorphogenic responses to UV-B are often assumed to be adaptations to harmful radiation. This presupposes that the function of the observed responses is to prevent UV damage. It has been hypothesized that, as with blue light, UV-B provides a signal important for normal plant development and might be perceived within developing plants through nondestructive processes, perhaps through UV-specific signal perception mechanisms. UV signal perception can lead to photomorphogenic responses that may confer adaptive advantages under conditions associated with high-light environments, such as water stress. Plant responses to UV radiation in this regard include changes in leaf area, leaf thickness, stomatal density, photosynthetic pigment production and altered stem elongation and branching patterns. Such responses may lead to altered transpiration rates and water-use efficiencies. For example, we found that the cumulative effect of ambient UV-B radiation upon stomatal density and conductance can lead to altered water-use efficiencies. In field settings, UV might more properly be viewed as a photomorphogenic signal than as a stressor. Hence, it might be insufficient to attempt to fully evaluate the adaptive roles of plant responses to UV-B cues upon stress tolerance by the simultaneous application of UV and drought stress during development. We propose that rather than examining a plant's response to combinations of stressors one might also examine how a plant's response to UV induces tolerance to subsequently applied stresses. [source]

Photomorphogenic regulation of increases in UV-absorbing pigments in cucumber (Cucumis sativus) and Arabidopsis thaliana seedlings induced by different UV-B and UV-C wavebands

PHYSIOLOGIA PLANTARUM, Issue 1 2010
James R. Shinkle
Brief (1,100 min) irradiations with three different ultraviolet-B (UV-B) and ultraviolet-C (UV-C) wave bands induced increases the UV-absorbing pigments extracted from cucumber (Cucumis sativus L.) and Arabidopsis. Spectra of methanol/1% HCl extracts from cucumber hypocotyl segments spanning 250,400 nm showed a single defined peak at 317 nm. When seedlings were irradiated with 5 kJ m,2 UV-B radiation containing proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm; full-spectrum UV-B, FS-UVB), tissue extracts taken 24 h after irradiation showed an overall increase in absorption (91% increase at 317 nm) with a second defined peak at 263 nm. Irradiation with 1.1 kJ m,2 UV-C (254 nm) caused similar changes. In contrast, seedlings irradiated with 5 kJ m,2 UV-B including only wavelengths longer than 290 nm (8% of UV-B between 290 and 300 nm; long-wavelength UV-B, LW-UVB) resulted only in a general increase in absorption (80% at 317 nm). The increases in absorption were detectable as early as 3 h after irradiation with FS-UVB and UV-C, while the response to LW-UVB was first detectable at 6 h after irradiation. In extracts from whole Arabidopsis seedlings, 5 kJ m,2 LW-UVB caused only a 20% increase in total absorption. Irradiation with 5 kJ m,2 FS-UVB caused the appearance of a new peak at 270 nm and a concomitant increase in absorption of 72%. The induction of this new peak was observed in seedlings carrying the fah1 mutation which disrupts the pathway for sinapate synthesis. The results are in agreement with previously published data on stem elongation indicating the existence of two response pathways within the UV-B, one operating at longer wavelengths (>300 nm) and another specifically activated by short wavelength UV-B (<300 nm and also by UV-C). [source]

Herbivory and Abiotic Factors Affect Population Dynamics of Arabidopsis thaliana in a Sand Dune Area

PLANT BIOLOGY, Issue 5 2005
A. Mosleh Arany
Abstract: Population dynamics of the annual plant Arabidopsis thaliana (L.) Heynh. were studied in a natural habitat of this species on the coastal dunes of the Netherlands. The main objective was to elucidate factors controlling population dynamics and the relative importance of factors affecting final population density. Permanent plots were established and plants were mapped to obtain data on survival and reproductive performance of each individual, with special attention to herbivore damage. In experimental plots we studied how watering, addition of nutrients, artificial disturbance, and natural herbivores affected survival and growth. Mortality was low during autumn and early winter and high at the time of stem elongation, between February and April. A key factor analysis showed a high correlation between mortality from February to April and total mortality. The specialist weevils Ceutorhyncus atomus and C. contractus (Curculionidae) were identified as the major insect herbivores on A. thaliana, reducing seed production by more than 40 %. These herbivores acted in a plant size-dependent manner, attacking a greater fraction of the fruits on large plants. While mortality rates were not affected by density, fecundity decreased with density, although the effect was small. Adding water reduced mortality in rosette and flowering plant stages. Soil disturbance did not increase seed germination, but did have a significant positive effect on survival of rosette and flowering plants. Seed production of A. thaliana populations varied greatly between years, leading to population fluctuations, with a small role for density-dependent fecundity and plant size-dependent herbivory. [source]

A semi-dominant mutation in the ribosomal protein L10 gene suppresses the dwarf phenotype of the acl5 mutant in Arabidopsis thaliana

THE PLANT JOURNAL, Issue 6 2008
Akihiro Imai
Summary Disruption of the Arabidopsis thaliana ACAULIS5 (ACL5) gene, which has recently been shown to encode thermospermine synthase, results in a severe dwarf phenotype. A previous study showed that sac51-d, a dominant suppressor mutant of acl5-1, has a premature termination codon in an upstream open reading frame (ORF) of SAC51, which encodes a putative transcription factor, and suggested the involvement of upstream ORF-mediated translational control in ACL5 -dependent stem elongation. Here we report the identification of a gene responsible for sac52-d, another semi-dominant suppressor mutant of acl5-1. SAC52 encodes ribosomal protein L10 (RPL10A), which is highly conserved among eukaryotes and implicated in translational regulation. Transformation of acl5-1 mutants with a genomic fragment containing the sac52-d allele rescued the dwarf phenotype of acl5-1. GUS reporter activity under the control of a SAC51 promoter with its upstream ORF was higher in acl5-1 sac52-d than in acl5-1, suggesting that suppression of the acl5-1 phenotype by sac52-d is attributable, in part, to enhanced translation of certain transcripts including SAC51. We also found that a T-DNA insertion allele of SAC52/RPL10A causes lethality in the female gametophyte. [source]

A role for ethylene in the phytochrome-mediated control of vegetative development

THE PLANT JOURNAL, Issue 6 2006
Eloise Foo
Summary Members of the phytochrome family of photoreceptors play key roles in vegetative plant development, including the regulation of stem elongation, leaf development and chlorophyll accumulation. Hormones have been implicated in the control of these processes in de-etiolating seedlings. However, the mechanisms by which the phytochromes regulate vegetative development in more mature plants are less well understood. Pea (Pisum sativum) mutant plants lacking phytochromes A and B, the two phytochromes present in this species, develop severe defects later in development, including short, thick, distorted internodes and reduced leaf expansion, chlorophyll content and CAB gene transcript level. Studies presented here indicate that many of these defects in phyA phyB mutant plants appear to be due to elevated ethylene production, and suggest that an important role of the phytochromes in pea is to restrict ethylene production to a level that does not inhibit vegetative growth. Mutant phyA phyB plants produce significantly more ethylene than WT plants, and application of an ethylene biosynthesis inhibitor rescued many aspects of the phyA phyB mutant phenotype. This deregulation of ethylene production in phy-deficient plants appears likely to be due, at least in part, to the elevated transcript levels of key ethylene-biosynthesis genes. The phytochrome A photoreceptor appears to play a prominent role in the regulation of ethylene production, as phyA, but not phyB, single-mutant plants also exhibit a phenotype consistent with elevated ethylene production. Potential interactions between ethylene and secondary plant hormones in the control of the phy-deficient mutant phenotype were explored, revealing that ethylene may inhibit stem elongation in part by reducing gibberellin levels. [source]

Defoliation of Brassica napus increases severity of blackleg caused by Leptosphaeria maculans: implications for dual-purpose cropping

ANNALS OF APPLIED BIOLOGY, Issue 1 2010
Susan J. Sprague
Canola (Brassica napus) crops for grazing and grain (dual-purpose) production provide an economic break-crop alternative for dual-purpose cereals in Australian mixed farming systems. Infection by Leptosphaeria maculans is the most prevalent disease in Australian canola crops with airborne inoculum released throughout the autumn and winter when crops are grazed. Glasshouse and field experiments were conducted to investigate the effect of mechanical defoliation (simulated grazing) on disease severity at plant maturity. In glasshouse experiments, stem canker severity increased from 4% to 24% in severely defoliated plants, but light defoliation had no effect compared with undefoliated control plants. Disease severity was increased with defoliation in all field experiments. Defoliation increased crown canker severity from 22.6% to 39.3% at Wagga Wagga and from 3.0% to 7.1% at Canberra and lodging from 9.6% to 11.9% at Naracoorte in the same set of cultivars assessed at each site. The increase in disease severity with defoliation was less in canola lines with moderate to high levels of stem canker resistance. Plants defoliated before stem elongation tended to develop less disease than those defoliated during the reproductive phase of plant growth. These findings suggest that the impact of grazing on L. maculans infection of canola crops can be minimised by sowing cultivars with a high level of stem canker resistance and grazing during the vegetative stage of plant growth prior to stem elongation. Further research is required to determine whether these management strategies are applicable in canola crops defoliated by grazing animals. [source]

Key phenological events in globe artichoke (Cynara cardunculus var.scolymus) development

ANNALS OF APPLIED BIOLOGY, Issue 3 2009
A. Virdis
Abstract A priority for the field vegetable grower is to be able to schedule a regular supply of product throughout the growing season. This requires a predictive framework, based on the identification of key developmental events of the crop, and an understanding of how genotypic and environmental factors interact to determine plant development. Four globe artichoke (Cynara cardunculus var. scolymus) cultivars, representing the existing phenological range, were grown in a field experiment, and a range of environmental conditions was imposed by varying both the timing of the first irrigation (which determines the initiation of regrowth) and by repeating the experiment across two locations and 2 years. The timing of the appearance of the main stem capitulum was sensitive to both the growing environment and the cultivar. These differences persisted till flowering and were correlated with final leaf number. As the plant developed, the phyllochron decreased, resulting in three values of phyllochron, each of which was responsive to genotype, and hardly to environment. The timing of the first change in phyllochron was associated with the final leaf number and the appearance of the capitulum. For all the cultivars, the rate of development fell and the final leaf number increased as the length of the photoperiod increased. The later flowering cultivars shared a similar vernalisation requirement, but ,Spinoso sardo' did not require a cold period to flower. Leaf length reached a peak before the beginning of stem elongation, and maximum leaf length was correlated with final leaf number. The sensitiveness of the phyllochron to the genotype, and of the number of leaves and the timing of the appearance of the capitulum to both genotype and environment makes them suitable as variables in developmental models. The importance of the final number of leaves is not only because of its phenological significance, but also because of its effect on the ability of the canopy to intercept radiation. [source]