Rosette Stage Research Articles

The Effect of Targeted Grazing and Biological Control on Yellow Starthistle (Centaurea solstitialis) in Canyon Grasslands of Idaho

Yellow starthistle (Centaurea solstitialis L.) is an invasive weed of significant importance on rangelands in the western United States. Field experiments were conducted in 2003 and 2004 to determine the effect of targeted grazing on yellow starthistle growth and bud production, and on the efficacy of four established biological control seed-head–feeding insects, which included three species of weevils and one fly species. We tested sheep and cattle grazing at three yellow starthistle growth stages—rosette, bolting, and late bud—at a site where all four biocontrol agents were established. The timing of grazing had a greater impact on yellow starthistle growth and bud production than the type of grazing animal. In comparison to the control, grazing at the rosette and bolting stage resulted in shorter plants both years of the study, but increased the number of buds following grazing at the bolting stage and at the rosette stage in 2003. Negligible seed production across treatments, in 2003, precluded detection of treatment effects. However, in 2004, grazing at the rosette and bolting stages resulted in a greater number of seeds per plant compared to the control and the late bud stage, which were similar. Results indicated that the timing of grazing did not negatively impact biocontrol efficacy. Eustenopus villosus adult injury and total insect larval damage were similar to control plants following each grazing treatment both years, indicating potential compatibility between targeted grazing and biocontrol for integrated management of yellow starthistle.

Identification of SSR and RAPD markers associated with QTLs of winter survival and related traits in Brassica napus L.

Because of importance of winter survival in winter type of Brassica napus, this study was performed to identify the QTLs controlling winter survival and related traits using SSR and RAPD markers. For this, an F2:3 population of 200 families derived from crossing between cv. ‘SLMO46’ (winter type and cold resistant) and cv. ‘Quantum’ (spring type and susceptible to low temperature) were used. Winter survival (WS), leaves per plant in rosette stage (L/P), crown wet weight (CWW), crown dry weight (CDW) and crown water content (CWC) were measured in F3 families. 350 SSR primer pairs and 250 RAPD primers were used to assess the parental polymorphism. The 32 SSR primer pairs and 47 RAPD polymorphic markers between parental lines were used to screen F2 individuals. Linkage map was constructed using polymorphic markers. The markers were assigned into 14 linkage groups with total length of 1199.1 cM and an average distance of 17.13 cM between adjacent markers. The relationship between measured traits and genotypic data was analyzed using CIM method and totally 12 putative QTLs were detected for studied traits. The explained phenotypic variance by identified QTLs ranged between 0.5 and 11%. The identified QTLs had positive and negative additive effects and transferred from both parents to F2 plants and F3 families. Some of these QTLs located in the same genomic regions.

Seasonal Changes and Effect of Harvest on Glucosinolates in Isatis leaves

The seasonal fluctuation of glucosinolates in five defined Isatis tinctoria and one Isatis indigotica accessions (first year, rosette stage), grown on field plots under identical conditions, was investigated. Analysis of the intact glucosinolates was carried out with shock frozen, freeze dried leaf samples using a recently developed and validated PLE (pressurized liquid extraction) protocol and ion-pair HPLC coupled with ESI-MS in the negative mode. When comparing the two Isatis species, significant qualitative and quantitative differences in the glucosinolate patterns were observed. Differences among the various Isatis tinctoria accessions were much smaller. We studied the effects of repeated harvesting during the growth season on glucosinolate concentrations and found that repeated harvest did not have a major effect on glucosinolate concentrations of newly grown leaves. Glucosinolates could not be detected in woad leaves submitted to conventional drying.

Flowering as a Condition for Xylem Expansion in Arabidopsis Hypocotyl and Root

In dicotyledons, biomass predominantly represents cell-wall material of xylem, which is formed during the genetically poorly characterized secondary growth of the vasculature. In Arabidopsis hypocotyls, initially proportional secondary growth of all tissues is followed by a phase of xylem expansion and fiber differentiation. The factors that control this transition are unknown. We observed natural variation in Arabidopsis hypocotyl secondary growth and its coordination with root secondary growth. Quantitative trait loci (QTL) analyses of a recombinant inbred line (RIL) population demonstrated separate genetic control of developmentally synchronized secondary-growth parameters. However, major QTL for xylem expansion and fiber differentiation correlated tightly and coincided with major flowering time QTL. Correlation between xylem expansion and flowering was confirmed in another RIL population and also found across Arabidopsis accessions. Gene-expression analyses suggest that xylem expansion is initiated after flowering induction but before inflorescence emergence. Consistent with this idea, transient activation of an inducer of flowering at the rosette stage promoted xylem expansion. Although the shoot was needed to trigger xylem expansion and can control it in a graft-transmissible fashion, the inflorescence stem was not required to sustain it. Collectively, our results suggest that flowering induction is the condition for xylem expansion in hypocotyl and root secondary growth.

Hydraulic lift by canola plants aids P and K uptake from dry topsoil

The role of hydraulic lift in nutrient uptake from dry topsoil is unclear. Vertically-split root systems were used to measure hydraulic lift and phosphorus (P) and potassium (K) uptake at the rosette and flowering stages of two canola (Brassica napus L.) cultivars (Trigold and Boomer with small and large root systems, respectively) grown in soil low in P and K. Rubidium (Rb) was used as a tracer to examine K uptake from K fertiliser banded in dry topsoil. During vegetative growth, statistically significant hydraulic lift was measured, irrespective of cultivar root size or a specific nutrient (P or K) placed in the topsoil. The Rb tracer revealed significant amounts of K were absorbed from the dry soil, but at rates five-fold lower than from the moist soil. The water lifted could not prevent cessation of P uptake by Boomer and a reduction in P uptake by Trigold. During mid to late flowering, ion uptake from the dry topsoil was impeded despite the continuation of hydraulic lift up to 28 days after the topsoil was dried. Minimal fine root growth following topsoil drying (and reduction in fine root biomass in some treatments) appeared to be the primary cause of impeded nutrient uptake.

The effect of chlormequat chloride (CCC) application at the bolting stage on the flowering and seed production of lettuce plants previously treated with water or gibberellic acid (GA 3)

Lettuce plants were sprayed with gibberellin (GA 3) or water at the rosette (8-leaf) stage and subsequently with water or CCC (500 or 1500 ppm) at the onset of bolting. GA 3 induced rapid bolting and increased seed yield, but seed stalks were longer and thinner than those that had been sprayed with water at the same stage. Treatment with CCC (500 ppm) at bolting decreased the flower stalk height of plants that had been sprayed with water at the rosette stage, but not that of GA 3 treated plants. CCC (500 ppm) increased the number of inflorescence branches per plant as well as seed yield in the autumn sown crop, but had no effect on the winter sown crop. When a higher concentration of CCC (1500 ppm) was applied at bolting, flower stalk height decreased, irrespective of whether the plants had been previously treated with GA 3 or not, and seed stalk diameter increased. However, 1500 ppm CCC reduced the number of inflorescence branches per plant and mean seed yield. It is concluded therefore that although the application of 500 ppm CCC at the onset of bolting may increase seed yield in the autumn sown crop, this treatment does not improve the seed stalk strength (e.g. increasing diameter or reducing height) of GA 3 treated plants. On the other hand, whereas a higher concentration of CCC (1500 ppm) improves seed stalk characteristics, it reduces seed yield.

Reduced gibberellin response affects ethylene biosynthesis and responsiveness in the Arabidopsis gai eto2‐1 double mutant

Ethylene and gibberellins (GAs) control similar developmental processes in plants. The role of ethylene is at least in part to regulate the accumulation of DELLA proteins, key regulators of plant growth, which suppress the GA response. To expand our knowledge of ethylene-GA crosstalk and to reveal how the modulation of the ethylene and GA pathways affects global plant growth, the gibberellin-insensitive (gai), ethylene-overproducing 2-1 (eto2-1) double mutant, which has decreased GA signalling (resulting from gai) and increased ethylene biosynthesis (resulting from eto2-1), was characterized. Both single mutations resulted in reduced elongation growth. The double mutant showed synergistic responses in root and shoot growth, in induction of floral transition, and in inflorescence length, showing that crosstalk between the two pathways occurs in different plant organs throughout development. Furthermore, the altered ethylene-GA interactions affected root-shoot communication, as evidenced by an enhanced shoot:root ratio in the double mutant. When compared with both single mutants and the wild type, double mutants had enhanced content of active GA(4) at both the seedling and the rosette stages, and, unlike the gai mutant, they were sensitive to GA treatment. Finally, it was shown that synergistic responses in the double mutant were not caused by elevated ethylene biosynthesis but that, in the light, enhanced sensitivity to ethylene may, at least in part, be responsible for the observed phenotype.

Ragweed Parthenium (Parthenium hysterophorus) Control with Preemergence and Postemergence Herbicides

Field and greenhouse experiments were conducted during 2005 and 2006 at Stoneville, MS, to determine control of ragweed parthenium with several preemergence (PRE) and postemergence (POST) herbicides registered for use in corn, cotton, peanut, rice, and soybean. Norflurazon, pendimethalin, clomazone, diuron, fluometuron, pyrithiobac, dimethenamid, flumetsulam, imazaquin, s-metolachlor, metribuzin, chlorimuron, atrazine, simazine, flumioxazin, and quinclorac were applied PRE. Ragweed parthenium control was highest with norflurazon (100%) and clomazone (100%) followed by fluometuron (96%), metribuzin (90%), diuron (87%), flumioxazin (84%), chlorimuron (77%), and quinclorac (67%) at 6 wk after treatment (WAT) under greenhouse conditions. Control of ragweed parthenium was less than 58% with all other herbicides. Ragweed parthenium appears to be highly sensitive to pigment and photosynthetic inhibitors compared to herbicides with other modes of action. Glyphosate, glufosinate, paraquat, bentazon, acifluorfen, chlorimuron, halosulfuron, MSMA, bromoxynil, atrazine, 2,4-D, flumioxazin, trifloxysulfuron, and clomazone were applied POST to field-grown rosette and bolted plants. Glyphosate, glufosinate, chlorimuron, and trifloxysulfuron applied at rosette stage provided greater than 93% control of ragweed parthenium at 3 WAT. Halosulfuron, MSMA, bromoxynil, 2,4-D, and flumioxazin controlled 58 to 90% rosette ragweed parthenium at 3 WAT. Ragweed parthenium control with all other POST herbicides was less than 38%. At bolted stage, glyphosate, glufosinate, and trifloxysulfuron controlled 86 to 95% ragweed parthenium and control was 61 to 70% with chlorimuron, halosulfuron, and 2,4-D 3 WAT. Overall, efficacy of POST herbicides was better on rosette plants than on bolted plants. Amino acid synthesis and glutamine synthase inhibitors were more active than herbicides with other modes of action. These results indicate that norflurazon, clomazone, fluometuron, flumioxazin, halosulfuron, chlorimuron, and trifloxysulfuron could provide effective control of ragweed parthenium.

Isolation and directed differentiation of neural crest stem cells derived from human embryonic stem cells

Vertebrate neural crest development depends on pluripotent, migratory precursor cells. Although avian and murine neural crest stem (NCS) cells have been identified, the isolation of human NCS cells has remained elusive. Here we report the derivation of NCS cells from human embryonic stem cells at the neural rosette stage. We show that NCS cells plated at clonal density give rise to multiple neural crest lineages. The human NCS cells can be propagated in vitro and directed toward peripheral nervous system lineages (peripheral neurons, Schwann cells) and mesenchymal lineages (smooth muscle, adipogenic, osteogenic and chondrogenic cells). Transplantation of human NCS cells into the developing chick embryo and adult mouse hosts demonstrates survival, migration and differentiation compatible with neural crest identity. The availability of unlimited numbers of human NCS cells offers new opportunities for studies of neural crest development and for efforts to model and treat neural crest-related disorders.

HY5 and HYH are positive regulators of nitrate reductase in seedlings and rosette stage plants

HY5 and HYH are bZIP transcription factors well known to be involved in photomorphogenesis and light signalling. Loss-of-function mutants of HY5 and HYH revealed that these genes are essential for induction of a key enzyme in nitrogen assimilation, nitrate reductase (EC 1.7.1.1). In Arabidopsis thaliana seedlings nitrate reductase was expressed under low irradiance far-red or red light at the same level as under higher irradiance, photosynthetic active, white light. However, high NR expression at low light levels occurred only in the presence of sucrose in the growth medium. Sucrose did not promote expression in darkness. Whereas HY5 was necessary for high nitrate reductase expression in far-red light, HYH was important in red light. COP1 is known to promote degradation of HY5 and HYH, and in the cop1 mutant, nitrate reductase activity was relatively high also in darkness. PhyA and PhyB mutants were tested, and confirmed the phytochrome dependency for far-red and red light induction of nitrate reductase in seedlings. In rosette leaves of 3-week-old green plants the daily increase in nitrate reductase expression in response to light-on was abolished in the hyh and hy5 hyh double mutant. The hy5 hyh double mutant had lower nitrate reductase activity than any of the single mutants in photosynthetic active light in both seedlings and rosette leaves.

Restoring Species Richness and Diversity in a Russian Knapweed (Acroptilon repens)–infested Riparian Plant Community Using Herbicides

Species richness and diversity are important indicators of ecosystem function and may be related to plant community resistance to invasion by nonindigenous species. Our specific objective was to determine the influence of clopyralid plus 2,4-D, glyphosate, and fosamine, at different application rates and timings, on richness and diversity of total species, total native species, and total nonnative species within a Russian knapweed–infested plant community. Twenty-eight treatments (3 herbicides by 3 rates by 3 application timings, and an untreated control) were applied to two sites located along the Missouri River riparian corridor in Montana. Clopyralid plus 2,4-D, glyphosate, and fosamine were applied in June (spring rosette stage of Russian knapweed), July (bud to bloom stage of Russian knapweed), and August (flowering stage of Russian knapweed). Herbicide rates were clopyralid plus 2,4-D at 0.08 (clopyralid) + 0.42 (2,4-D), 0.13 + 0.67, and 0.18 + 0.92 kg ai ha−1; glyphosate at 0.6, 1.2, and 1.8 kg ai ha−1; fosamine at 3.6, 7.2, and 10.8 kg ai ha−1. Density of each species was recorded during June and August of 2001 and 2002. Species richness and Simpson's Reciprocal Index (1/D) were calculated. By August 2002, only the glyphosate treatment (4.6 species m−2) yielded greater total richness over that of the control (3.5 species m−2). At that time, diversity after applying clopyralid plus 2,4-D remained similar to that of the control (1.4), but glyphosate (2.3) and fosamine (2.0) increased total species diversity. Nonnative grasses and forbs accounted for the increases in richness and diversity. Glyphosate may be appropriate for enhancing ecosystem function and possibly niche occupation to preempt reinvasion by Russian knapweed, but restoring native species seems unlikely using any of these herbicides alone.

First Report of Leaf Spot Caused by Cladosporium herbarum on Centaurea solstitialis in Greece.

Centaurea solstitialis L. (yellow starthistle), family Asteraceae, an invasive weed in California and the western United States, is targeted for biological control. In the summer of 2003, an epidemic of unknown etiology on dying C. solstitialis plants was observed near Kozani, Greece (40°22'07″N, 21°52'35″E, elevation, 634 m). Plants had necrotic light brown leaf spots on the lower leaves and the decurrent leaf bases along the stems. Often, necrotic lesions extended along the stems to the capitula. Virtually all plants in a solid stand of C. solstitialis (approximately 0.5 ha) showed disease symptoms. Diseased plants were collected, air dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. On the basis of culture growth (45-cm diameter after 2 weeks at 25°C on malt extract agar), fungal morphology (1), and comparison with 21 internal transcribed spacer sequences in GenBank, the putative causal organism was identified as Cladosporium herbarum (Pers.:Fr.) Link. (teleomorph = Davidiella tassiana (De Not.) Crous & U. Braun). Sixteen C. solstitialis plants in the rosette stage and 16 plants in the bolted stage were inoculated with an aqueous suspension of spores (106 conidia ml-1) and placed in an environmentally controlled chamber at 25°C with 8 h of dew and 12 h of light daily. Plants in the rosette stage were resistant, but the fungus was very aggressive on bolted plants. Within 4 to 6 days of inoculation, necrosis developed on leaves and stems and then spread up the stems to the capitula, often resulting in plant death. The fungus also infected developing flowers. Cladosporium herbarum was reisolated from each of the 16 bolted C. solstitialis plants in two separate tests at the FDWSRU and from all bolted inoculated plants at the European Biological Control Laboratory (EBCL) in Greece. In the greenhouse at the EBCL, the pathogen readily spread to (and was isolated from) another 10 noninoculated C. solstitialis plants in close vicinity to the inoculated C. solstitialis plants. Results of host range tests will establish if this isolate of Cladosporium herbarum has the potential as a biological control agent of C. solstitialis in the United States and does not pose a threat to other Centaurea spp. used in horticulture. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 863446). Live cultures are being maintained at the FDWSRU and EBCL, Greece. To our knowledge, this is the first report of a disease caused by Cladosporium herbarum on C. solstitialis. Reference: (1) M. H. M. Ho et al. Mycotaxon 72:115, 1999.

First Report on the Presence of Phoma Blackleg Pathogenicity Group 1 (Leptosphaeria biglobosa) on Brassica napus (Canola/Rapeseed) in Iran.

Canola/rapeseed (Brassica napus L.) is a new crop in Iran, grown since 1996. In 2006, 180,000 ha were planted. During the same year, leaf and upper stem lesions (3) were observed on cv. Hyola 401 at rosette and flowering stages in the Gorgan Province in northern Iran. Field disease incidence ranged from 1 to 40%. Several isolates from stem lesions were sent to the Department of Plant Science, Blackleg Research Lab, University of Manitoba, Canada from the Agricultural and Natural Resources Research Center of Golestan Province of Iran for pathogenicity group identification. The blackleg pathogen is divided into several pathogenicity groups on the basis of phenotypic interaction (IP) of isolates on differential cvs. Westar, Glacier, and Quinta. Isolates PG2, PG3, PG4, and PGT are highly virulent, but PG1, which recently has been named Leptosphaeria biglobosa (2), is weakly virulent. Colonies of the blackleg pathogen were reisolated from their original medium, potato dextrose agar, and grown onV8 agar medium and incubated under light for 2 weeks. Pure cultures of the pathogen were then characterized by colony morphology, pycnidia, and measurement and microscopic observation of pycnidio-spores. Fungal colonies formed with concentric rings containing pycnidia with pink ooze on V8 agar. Pycnidia were globose and as much as 200 μ 200 μm. They had a prominent beak on the ascomata that was enlarged, cylindrical, central, terete, erect, and 150 to 200 × 100 μm. Pycnidiospores were cylindrical, straight, 4 to 5 × 2 μm, and hyaline (2). To identify the pathogenicity group of the Iranian isolates, pycnidiospores were harvested from single-spore cultures after 14 days of incubation under continuous cool-white fluorescent light (1). One-week-old cotyledons from the differential cvs. Westar, Glacier, and Quinta were inoculated with pycnidiospore suspension concentration of 2 × 107 spores per ml of the four Iranian isolates. Each cotyledon lobe was punctured with forceps and inoculated with a 10-μl droplet of spore suspension. Disease evaluations were made 10 to 14 days after inoculation using a 0 to 9 rating scale. Inoculations were repeated twice with identical results yielding only the PG1 type reaction. To our knowledge, this is the first report of the presence of L. biglobosa (PG1; B-type) on canola in Iran. Differential testing fulfilled Koch's postulates. L. biglobosa seems to be less damaging compared with L. maculans, but severe phoma stem lesion epidemics have been associated with the L. biglobosa in Poland (3). The importance of this weakly virulent pathogen, whenever the relative humidity increases, has been demonstrated in greenhouse conditions (A. El-Hadrami, W. G. D. Fernando, and F. Daayf, unpublished data). Since the relative humidity in northern Iran is high, an epidemic may occur if appropriate management practices are not utilized to minimize inoculum levels.

7: Cardiocrinum cordatum (Thunb.) Makino (Liliaceae)

AbstractThe life‐history characteristics of Cardiocrinum cordatum (Thunb.) Makino (Liliaceae) are described here. This is a unique monocarpic perennial herb of temperate broad‐leaved deciduous forests in the Japanese Islands and adjacent Far East regions. New aerial shoots appear above ground in mid April to early May. Cardiocrinum cordatum comprises distinct growth stages, single‐leaf and multiple‐leaved rosette stages, and then a flowering stage with a large multiflowered inflorescence at the top of the stem. The flowering plants attain 0.7–2.0 m in height and bear several large cordate cauline leaves, and 2–15 laterally blooming, greenish white flowers, 12–18 cm in size, are borne at the top of the straight inflorescence. Cardiocrinum cordatum depends on two reproductive modes, sexual reproduction via seeds and vegetative reproduction forming a few to several bulblets at the base of mother bulbs. The flowers are furnished with large nectar glands at the base of corolla, and the amount of nectar secreted is very high; thus, many bumblebee species are attracted to the flowers. Each flower has 600–670 ovules and produces 393–531 seeds (average 410). The average seed‐setting rate per flower is high at 65–79%. An exceedingly large number of seeds with 4–5 mm thin filmy wings are produced, attaining several thousand (800–6000) in number per plant. Individuals asexually formed have large one‐leaf or multiple‐leaves, and can bypass crucial small juvenile stages with high mortality. In addition, because mature plants die after sexually reproducing once, ramets asexually reproduced can use the large spaces that the mother plants occupied.

Nitrogen deficiency enhances expression of specific MYB and bHLH transcription factors and accumulation of end products in the flavonoid pathway

Expression of regulators of the flavonoid pathway was examined in Arabidopsis thaliana wild type and pap1D plants, the latter being a T-DNA activation-tagged line over-expressing the PAP1/MYB75 gene which is a positive regulator of the pathway. Anthocyanin accumulation was induced in plants grown in soil, on agar plates, and hydroponics by withdrawing nitrogen from the growth medium. The agar-grown seedlings and rosette stage plants in hydroponics were further explored, and showed that nitrogen deficiency resulted in the accumulation of not only anthocyanins, but also flavonols. The examination of transcript levels showed that the general flavonoid pathway regulators PAP1 and PAP2 were up-regulated in response to nitrogen deficiency in wild type as well as pap1D plants. Interestingly, PAP2 responded much stronger to nitrogen deficiency than PAP1, 200- and 6-fold increase in transcript levels, respectively, for wild-type seedlings. In rosette leaves the increase was 900-fold for PAP2 and 6-fold for PAP1. At least three different bHLH domain transcription factors promote anthocyanin synthesis, and transcripts for one of these, i.e. GL3 were found to be sixfold enhanced by nitrogen deficiency in rosette leaves. The MYB12 transcription factor, known to regulate flavonol synthesis, was slightly induced by nitrogen deficiency in seedlings. In conclusion, four out of eight regulators involved in the flavonoid pathway showed an enhanced expression from 2 to 1,000 times in response to nitrogen deficiency. Together with MYB factors, especially PAP2, GL3 appears to be the BHLH partner for anthocyanin accumulation in response to nitrogen deficiency.

Effect of rust-causing pathogen (Puccinia thlaspeos) on auxin-like and cytokinin-like activity in dyer's woad (Isatis tinctoria)

The rust pathogen,Puccinia thlaspeos, is used for biocontrol of dyer's woad. Rust infection results in chlorotic leaves and abnormal flower and seed production of this noxious weed during its second year of growth. Auxin-like and cytokinin-like activity of healthy and infected plants (roots, shoots, and leaves) were determined during different growth stages. These samples were analyzed by use of the mung-bean rooting bioassay (auxin-like activity) and the soybean-callus bioassay (cytokinin-like activity). Rooting activity in the mung-bean bioassay was significantly higher in the infected-root extracts from Harvest 1 (rosette stage) compared with the healthy-root extracts and significantly higher in the healthy-shoot extracts from Harvest 2 (bolting plants) compared with infected-shoot extracts. Infected plants collected during Harvest 1 had greatly reduced cytokinin-like activity in the roots, shoots, and leaves compared with the healthy plants. Cytokinin-like activity increased slightly in the infected plants collected in subsequent harvests, with the highest activity recorded in root extracts. The results suggest potential ways that the rust-causing fungal pathogen is able to influence some physiologic processes in dyer's woad and so affect its growth.

Compatibility of Two Herbicides withCyphocleonus achates(Coleoptera: Curculionidae) andAgapeta zoegana(Lepidoptera: Tortricidae), Two Root Insects Introduced for Biological Control of Spotted Knapweed

Field studies were conducted in 2001 through 2004 to assess the compatibility of two herbicides, 2,4-D (2,4-dichlorophenoxyacetic acid) and clopyralid (3,6-dichloropicolinic acid), with two root insects, Cyphocleonus achates (Fahraeus), and Agapeta zoegana L., introduced for biological control of spotted knapweed, Centaurea stoebe Lamarck subsp. micranthos (formerly C. maculosa) in Montana. Both herbicides were applied at the fall and spring rosette stage. In 2003, both herbicides reduced knapweed canopy cover by ≈98% compared with ≈85% in 2004. The number of live larvae of both insect species was significantly lower in treated plots than in controls in 2003. In 2004, the number of live C. achates larvae was significantly lower in treated plots than in controls at the fall application, but larval numbers were not different at the spring application. Larval numbers of C. achates were not different between application times in 2003 but were significantly lower in fall-treated plots than in spring-treated plots in 2004. Numbers of A. zoegana larvae were not different between treated plots and controls in 2004. Larval numbers of A. zoegana were significantly lower in fall-treated plots than in spring-treated plots in 2003, but there was no difference between application times in 2004. Larval numbers of each insect species were similar between herbicides in both years. We conclude that fall applications of both herbicides are not compatible with the two insects. Spring applications of the two herbicides may be compatible with both insect species if delayed until late spring.

Physiological and molecular insight on the mechanisms of resistance to glyphosate in Conyza canadensis (L.) Cronq. biotypes

The physiological and molecular basis of glyphosate resistance in susceptible (S) and resistant (R) horseweed ( Conyza canadensis (L.) Cronq.) populations collected from regions across the USA (Arkansas, Delaware, Ohio, Virginia, Washington) was investigated. At two-leaf stage approximately the same ED 50 values were observed for the S and R populations, while at the rosette stage the R biotypes were approximately three times more resistant than the S biotypes. After treatment with severe glyphosate doses (more than 1× the recommended field rate), different morphological responses in R and S biotypes were observed. In S biotypes, the first phytotoxic effects were found in the meristematic tissues, while in the R biotypes the first phytotoxic effects were observed in leaves. At 2 to 4 weeks after the treatment, R plants recovered by emitting new leaves and/or new branches from the center of the rosette. A significant increase of the mean number of branches per surviving R plants as a function of glyphosate-applied dose was observed. As regards the physiological mechanism of resistance, the main difference between R and S biotypes was the dissimilar mobility of glyphosate in the whole plant. In the R biotypes the herbicide was less translocated in the downward direction (from leaves to roots) and more translocated in the upward direction (from culm to leaves) with respect to the S biotypes. Finally, in R biotypes the relative level of EPSPS mRNA was from 1.8 to 3.1 times higher than that found in S biotypes. On the basis of obtained results three factors may concur to glyphosate resistance in the investigated R biotypes: impaired translocation of the herbicide, increase in EPSP synthase transcript levels, and enhanced ramification.

EFFECTS OF Pb POLLUTION ON PHOTOSYNTHETIC CHARACTERISTICS, QUALITY, AND YIELD OF TOBACCO LEAVES

In order to examine the effects of Pb pollution on photosynthesis, quality, and yield of tobacco cultivar, pot experiment was carried out at the Research Station of Henan Agricultural University during 2002-2004. Cultivar of `Yunyan 85' was treated with seven concentration levels of Pb 2+ (0, 150, 300, 450, 600, 750 and 1 000 mg·kg -1) applied with (CH_3COO)_2Pb after transplanting. Twenty leaves were saved after topping. The net photosynthetic rate (P_n), intercellular CO_2 concentration (C_i), and stomatal conductance (G_s) of three identical functional leaves from the same position were measured during rosette, budding, and harvest stages respectively using a Li_6400 Portable Photosynthesis System. Maximal fluorescence (F_m),fixed fluorescence (F_o), and steady fluorescence (F_s) were determined in the dark (for 30 min) and maximal fluorescence in the light (F_m′) with a Hansatech FMS2 photo_fluorometer. PSⅡ activity (F_v/F_o), PSⅡ maximum light energy transformation (F_v/F_m), chemical quenching coefficient (q_P), non_photochemical quenching coefficient (NPQ), apparent photosynthetic electron transport rate(ETR), and the ratio of photochemical quantum yield of PSII (Ф_ PSⅡ) were calculated.The reductive sugar, total N, nicotine, Kalium contents of tobacco leaves and yield per plant were investigated.The results showed that P_n, G_s, and C_i occurred at the Pb concentrations of 300 mg·kg -1 in budding stage and the Pb concentrations up to 150 mg·kg -1 in rosette and harvest stages. F_v/F_o, F_v/F_m, q_P, NPQ, ETR, and Ф_ PSⅡ decreased with increasing Pb concentrations, resulting in declining ability of photosynthetic pigments assimilating light, photosynthetic light use efficiency, and P_n of tobacco leaves. Higher Pb concentrations led to increases in the ratios of reductive sugar/nicotine (9.52-11.96) and total_N/nicotine (1.05-1.23), which are used as the quality indexes of tobacco leaves, above the standards (7 and 1) of high quality of tobacco leaves, and then deteriorated the fragrance of tobacco leaves.

Canola cultivars differ in nitrogen utilization efficiency at vegetative stage

Previous research indicated genotype-specific responses in nitrogen utilization efficiency (NUE) for oilseed rape ( Brassica napus L.), but mechanisms behind those differences are unknown. Our objective was to determine whether cultivar variations in NUE (dry matter production per unit of N absorbed) could be related to the differences in N and nitrate uptake and partitioning. Four Australian spring canola cultivars (Eyre, Charlton, Pinnacle and Rainbow) were grown in glasshouse under conditions of low- and high-N supply. All cultivars were at the same growth stage when harvested 60 days after sowing (rosette stage with five leaves at low-N supply and nine leaves at high-N supply). Cultivars significantly differed in total N uptake in roots and shoots, but not when the whole plants were considered. Although all cultivars had similar total N uptake per plant, significant differences in NUE existed because of differences in plant biomass. N-efficient cultivars Charlton and Rainbow produced larger plant biomass and had lower N concentration in various aboveground plant parts (including dead leaves) than N-inefficient cultivars Pinnacle and Eyre. Nitrogen concentration in roots did not differ significantly among cultivars. Regardless of N supply, N concentrations in various plant parts were in the order: young blades > old blades > roots > young petioles > stems > old petioles > dead leaves. No significant variation in nitrate-N concentration in roots or various aboveground plant parts was found among tested cultivars. The absence of cultivar × N treatment interaction for plant dry weight, N concentration, N uptake, and consequently NUE, clearly indicated that cultivars that performed best at high-N supply also showed similar responses under N-deficient conditions. Despite similar total N uptake per plant, significant differences in NUE existed because more N-efficient cultivars produced larger plant biomass and tended to have lower N concentrations in all plant parts (except roots) compared with less N-efficient cultivars.