The effect of root-absorbed PSII inhibitors on Kautsky curve parameters in sugar beet

The effects of the photosystem II inhibitors metamitron and terbuthylazine on the shape of the Kautsky (chlorophyll fluorescence induction) curve were investigated in sugar beet grown in hydroponic culture. The objective of the study was to trace recovery processes following herbicide injury using Kautsky curve parameters. Metamitron is used for selective weed control in sugar beet because it is metabolized in this crop. In contrast, terbuthylazine is toxic to sugar beet. Two hours after treatment, various fluorescence induction curve parameters, such as maximum quantum efficiency (F_V/F_m), the relative changes at the J step (F_vj) and area (the area between the Kautsky curve and maximum fluorescence, F_m), were affected by metamitron at concentration ranges of 70–280 mg active ingredient (a.i.) L^?1 in plants treated at the four‐true‐leaf stage. Shortly after herbicide application, F_v/F_m was more affected by the hydrophilic metamitron [log(K_ow) = 0.83] than by the lipophilic terbuthylazine [log(K_ow) = 3.21], but these differences between compounds were alleviated as metamitron was metabolized and terbuthylazine was not. Terbuthylazine at 1 mg a.i. L^?1 affected sugar beet at the four‐ and six‐true‐leaf stages to the same extent, whereas metamitron at a dose of 140 mg a.i. L^?1 affected much more at four‐ than at the six‐true‐leaf stage. Sugar beet recovered from metamitron injury even at high doses (140 and 280 mg a.i. L^?1). Fluorescence induction curve parameters were similarly affected by terbuthylazine and, although sugar beet recovered from terbuthylazine injury at low doses (<0.2 mg a.i. L^?1), the Kautsky curve was irreversibly affected at higher doses (1–10 mg a.i. L^?1), leading finally to plant death. Older plants were affected later, and recovered sooner, from both herbicides.     

Metamitron activity in tolerant and susceptible plants

The herbicidal activity of metamitron, its inhibition of photosynthesis and its metabolism were studied in a number of plant species. An enzymic, light-independent deamination produces an inactive metabolite. Metabolism is rapid in plants tolerant to metamitron, e.g. Mercurialis annua and particularly sugar beet (Beta vulgaris L.), but slower in susceptible plants, e.g. Amaranthus retroflexus.     

Inhibition of photosynthesis in intact plants of biotypes resistant or susceptible to atrazine and cross-resistance to other herbicides

A concentration of atrazine of 0?1 mm 1^?1 in the nutrient solution resulted in complete inhibition of photosynthesis in intact leaves of susceptible biotypes of Amaranthus retroflexus L., Polygonum lapathifolium L., Chenopodium album L., Solanum nigrum L., Poa annua L. and Stellaria media (L.) Vill. within a few hours of treatment, whereas the inhibition of the resistant biotypes by the same concentration varied from small to moderate. In contrast, diuron (10 or 20 μm 1^?1) produced only minor differences between resistant and susceptible biotypes. The influence of some other herbicides on photosynthesis of these resistant biotypes was also smaller than that on the susceptible biotypes. This cross-resistance was evaluated with the resistance factor for intact leaves of Brassica napus L., A. retroflexus, and S. nigrum. This factor is equal to the ratio of the herbicide concentration in leaves of the resistant biotype to that in leaves of the susceptible biotype with inhibition to half-maximum rate of photosynthesis. This concentration in the leaves was calculated from the concentration in the nutrient solution, and the total transpiration divided by leaf area from the beginning of the herbicide treatment until the moment of half-maximum of photosynthesis. The resistance factors for intact leaves of A. retroflexus, S. nigrum and B. napus were 26–30 for atraton, 3–7 for metamitron, 2–9 for bromacil, 3–5 for monolinuron, 1 for diuron and < 1 for bentazone. For isolated chloroplasts much higher values have been reported. The reason for this discrepancy is not clear. A somewhat higher resistance factor (around 50–60) was derived after infiltration of detached leaves of these species with atraton solutions.     

Differential effect of diclofop-methyl on fatty acid biosynthesis in leaves of sensitive and tolerant plant species

The herbicide diclofop-methyl caused an early and pronounced inhibition of the incorporation of [¹⁴C]acetate into leaf lipids of the sensitive plant species maize (Zea may L.), wild oat (Avena fatua L.), and barnyardgrass (Echinochloa crus-galli L.). With an EC₅₀ value of approximately 10^?7M inhibition was already apparent 0.5–4 hr after herbicide application. The fatty acid biosynthesis of tolerant bean (Phaseolus vulgaris L.), sugar beet (Beta vulgaris L.), and soybean (Glycine max L.) was not affected, with one exception [wheat (Triticum aestivum L.) belongs to the more tolerant species]; the inhibition of fatty acid biosynthesis, however, was in the same order of magnitude as in sensitive plants. More detailed studies showed that in wheat a recovery from inhibition of fatty acid biosynthesis occurred. Four days after herbicide application (0.18 kg diclofop-methyl/ha) in wheat normal fatty acid biosynthesis was restored, whereas in sensitive maize a 60% inhibition was maintained over the whole experimental period (8 days). The results support the view that tolerance of wheat to diclofop-methyl is based on its inactivation in leaves, whereas the tolerance of dicotyledonous species may probably lie at the level of the site of action of diclofop-methyl. In experiments with intact leaves, the inhibition of fatty acid biosynthesis resulted in an enhanced flow of [¹⁴C]acetate into organic acids and amino acids. This effect, however, was not always reproducible in experiments with leaf pieces or isolated root tips.     

Absorption, translocation and metabolism of metamitron in Chenopodium album

BACKGROUND: In recent years, common lambsquarters (Chenopodium album L.) populations from sugar beet fields in different European countries have responded as resistant to the as‐triazinone metamitron. The populations have been found to have the same D1 point mutation as known for atrazine‐resistant biotypes (Ser₂₆₄ to Gly). However, pot experiments revealed that metamitron resistance is not as clear‐cut as observed with triazine resistance in the past. The objectives of this study were to clarify the absorption, translocation and metabolic fate of metamitron in C. album. RESULTS: Root absorption and foliar absorption experiments showed minor differences in absorption, translocation and metabolism of metamitron between the susceptible and resistant C. album populations. A rapid metabolism in the C. album populations was observed when metamitron was absorbed by the roots. The primary products of metamitron metabolism were identified as deamino‐metamitron and metamitron‐N‐glucoside. PABA, known to inhibit the deamination of metribuzin, did not alter the metabolism of metamitron, and nor did the cytochrome P450 inhibitor PBO. However, inhibition of metamitron metabolism in the presence of the cytochrome P450 inhibitor ABT was demonstrated. CONCLUSION: Metamitron metabolism in C. album may act as a basic tolerance mechanism, which can be important in circumstances favouring this degradation pathway. Copyright © 2011 Society of Chemical Industry     

A rapid bioassay for the detection of photosynthesis inhibitors in water

A modified leaf disc buoyancy procedure for the detection of photosynthesis-inhibiting residues in water is described. The modifications proposed, mainly the presence of sodium hydrogen carbonate in the infiltration solution, increased the sensitivity of the method and reduced the time required. The substituted urea and 1,3,5-triazine herbicides diuron, linuron, monuron, atrazine, ametryn and atraton were detected below 0.7 mg litre^?1 using cucumber (Cucumis sativus L., cv. ‘Dalia’) leaf discs. A concentration as low as 0.09 mg diuron litre^?1 could be detected. Although bean (Phaseolus vulgaris L., cv. ‘Bulgarian’) leaf tissue was less sensitive in this bioassay than cucumber, 0.3 mg diuron litre^?1 could still be detected. The test, being very rapid (less than 30 min per determination) and relatively sensitive, could be used for the detection of photosynthesis inhibitors in recycled water used for irrigation.     

First report of little leaf disease associated with phytoplasma on sugar beet (Betavulgaris L. subsp. vulgaris var. altissima Doll) in India

Sugar beet (Beta vulgaris L. subsp. vulgaris var. altissima) is a biennial, sugar-producing tuber crop grown in different parts of the world. Diseased sugar beets with symptoms of little leaf were observed during 2008 in Tamil Nadu, India. Phytoplasmas were detected in symptomatic leaves of three separate plants using PCR with primer pair fU5/rU3, which amplify an 880-bp fragment of the 16S rRNA region of phytoplasmas. The nucleotide sequence analysis of a 766-bp fragment had 100% identity among the sequence from the three plants (GQ184437) and 96% nucleotide sequence identity with 16S ribosomal RNA gene sequences of eggplant phyllody phytoplasma.     

Differential sensitivity of Atriplex patula and Chenopodium album to sugar beet herbicides: a possible cause for the upsurge of A. patula in sugar beet fields

In the last decade, the prevalence of Atriplex patula as a weed in the Belgian sugar beet area has increased. Possible reasons for its expansion in sugar beet fields, besides a poor implementation of the low‐dose phenmedipham/activator/soil‐acting herbicide (FAR) system, might be low sensitivity or evolved resistance to one or more herbicides used in sugar beet. Dose – response pot bioassays were conducted in the glasshouse to evaluate the effectiveness of five foliar‐applied sugar beet herbicides (metamitron, phenmedipham, desmedipham, ethofumesate and triallate) and three pre‐plant‐incorporated herbicides (metamitron, lenacil, dimethenamid‐P) for controlling five Belgian A. patula populations. Local metamitron‐susceptible and metamitron‐resistant populations of Chenopodium album were used as reference populations. Effective dosages and resistance indices were calculated. DNA sequence analysis of the photosystem II psbA gene was performed on putative resistant A. patula populations. Overall, A. patula exhibited large intraspecific variation in herbicide sensitivity. In general, A. patula populations were less susceptible to phenmedipham, desmedipham, ethofumesate and triallate relative to C. album populations. Two A. patula populations bear the leucine‐218 to valine mutation on the chloroplast psbA gene conferring low level to high level cross‐resistance to the photosystem II inhibitors phenmedipham, desmedipham, metamitron and lenacil. In order to avoid insufficient A. patula control and further spread, seedlings should preferentially be treated with FAR mixtures containing higher‐than‐standard doses of metamitron and phenmedipham/desmedipham and no later than the cotyledon stage.     

Photosynthetic inhibition in Phaseolus vulgaris

Similar injuries to the leaves of bean plants (Phaseolus vulgaris L. cv. Berna) were produced by exposure to CO₂-free air in the light and by ireatnient with simeton. The rate of production of leaf injuries and the degree of photosynthetic inhibition induced in plants exposed to CO₂-free air increased with exposure time and with light intensity. Exposure to CO₂-free nitrogen delayed the onset of the inhibition and the development of the injuries. These results showed some analogies with the action of herbicides which affect photosynthesis.     

A Greenhouse Test for Screening Sugar Beet (Beta Vulgaris) for Resistance to Rhizoctonia Solani

Rhizoctonia solani Kühn is a serious plant pathogenic fungus, causing various types of damage to sugar beet (Beta vulgaris L.). In Europe, the disease is spreading and becoming a threat for the growing of this crop. Plant resistance seems to be the most practical and economical way to control the disease. Experiments were carried out to optimise a greenhouse procedure to screen plants of sugar beet for resistance to R. solani. In the first experiment, two susceptible accessions were evaluated for root and leaf symptoms, after being grown in seven different soil mixtures and inoculated with R. solani. The fungus infected all plants. It was concluded that leaf symptoms were not reliable for the rating of disease severity. Statistically significant differences between the soil mixtures were observed, and there were no significant differences between the two accessions. The two soil mixtures, showing the most severe disease symptoms, were selected for a second experiment, including both resistant and susceptible accessions. As in the first experiment, root symptoms were recorded using a 1–7 scale, and a significant expression of resistance was observed. The average severity of the disease in the greenhouse experiment generally was comparable with the infection in field experiments, and the ranking of the accessions was the same in the two types of experiments. It was concluded that evaluation procedures in the greenhouse could be used as a rapid assay to screen sugar beet plants for resistance to R. solani.     

Uptake and translocation of [14C]asulam and [14C]bromacil by roots of maize and bean plants

The uptake and translocation of ¹⁴C-ring-labeled asulam (methylsulfanilcarbamate) and bromacil (5-bromo-3-sec-butyl-6-methyluracil), were compared after root application to maize (Zea mays L.) and bean (Phaseolus vulgaris L.). Autoradiographs showed the distribution of bromacil throughout these and other plant species, and the retention of asulam in the roots. The recovery of both compounds in quantitative radioassays was between 90 and 100%. The absorption of bromacil and asulam was rather similar. Absorption of bromacil increased up to 20% of the applied dose in bean plants after 2 days of exposure, and up to 11% in maize plants after 4 days. Absorption of asulam in bean plants was 22% of the applied dose after 2 days, and 8% in maize plants after 4 days. The pattern of distribution of bromacil and asulam was completely different. After 4 h of exposure of the roots about half of the absorbed bromacil had accumulated in the shoots, while two-thirds or more was translocated to the shoots after exposure periods of 1 to 4 days. Not more than one-eighth of the absorbed asulam was found in the shoots. In consequence, the bromacil content in the transpiration stream relative to that in the ambient solution was much higher than that of asulam. The leakage of asulam from bean and maize roots into herbicide-free nutrient solution was lower than that of bromacil. The reasons for these differences are not yet clear. There was only some metabolism of asulam in maize, but not in bean plants. No metabolites of bromacil were detected in the two plant species.     

Effect of Pythium spp. and glyphosate on phytoalexin production and exudation by bean (Phaseolus vulgaris L.) roots grown in different media

Kievitone, phaseollinisoflavan and phaseollin were detected in roots of bean seedlings (Phaseolus vulgaris L.) grown in natural soil. Comparison of phytoalexin production by roots grown in different media indicated that these phytoalexins were probably induced by microorganisms in soil. The influence of common root rot pathogens of bean, Pythium spp., on phytoalexin production was determined. Pythium ultimum elicited kievitone, phaseollinisoflavan and phaseollin in roots grown in sterilized silica sand. P. sylvaticum induced only kievitone and phaseollin in the same growth medium. Glyphosate did not significantly affect the accumulation of phytoalexins within 3 days. However, by day 5, significantly more phaseollin was detected in the roots of Pythium inoculated plants treated with glyphosate than in Pythium inoculated plants not treated with glyphosate. In a hydroponic system, both Pythium spp. elicited accumulation of kievitone and phaseollin in root tissue, and both phytoalexins were exuded into the bathing solution. Glyphosate application did not significantly affect accumulation or exudation of phytoalexins by bean roots in the hydroponic system. The results from this study illustrate the nature and extent of phytoalexin production by bean roots in the absence and presence of microbes.     

Prediction of the competitive effects of weeds on crop yields based on the relative leaf area of weeds

For implementation of simple yield loss models into threshold-based weed management systems, a thorough validation is needed over a great diversity of sites. Yield losses by competition wsth Sinapis alba L. (white mustard) as a model weed, were studied in 12 experiments in sugar beet (Beta vulgaris L.) and in 11 experiments in spring wheat (Triticum aestivum L.). Most data sets were heller described by a model based on the relative leaf area of the weed than by a hyperbolic model based on weed density. This leaf area model accounted for (part of) the effect of different emerging times of the S. alba whereas the density model did not. A parameter that allows the maximum yield loss to be smaller than 100% was mostly not needed to describe the effects of weed competition. The parameter that denotes the competitiveness of the weed species with respect to the crop decreased the later the relative leaf area of the mustard was determined. This decrease could be estimated from the differences in relative growth rate of the leaf area of crop and S. alba. However, the accuracy of this estimation was poor. The parameter value of the leaf area model varied considerably between sites and years. The results strongly suggest that the predictive ability of the leaf area model needs to be improved before it can be applied in weed management systems. Such improvement would require additional information about effects of abiotic factors on plant development and morphology and the definition of a time window for predictions with an acceptable level of error.     

The fate of [3-14C]metamitron in sugar beets after preemergence application in a lysimeter study

In a lysimeter experiment, [3-¹⁴C]metamitron was sprayed in a preemergence treatment of sugar beets, corresponding to approx 4.9 kg metamitron (7 kg Goltix)/ha. After 6 months, the beets contained metamitron equivalents amounting to 0.1 mg/kg fresh wt, calculated on the basis of the specific radioactivity of the [3-¹⁴C]metamitron employed. Radioactivity was also detected in the pure sugar isolates. The ¹⁴C activity represented approx 0.2 mg metamitron equivalent/kg pure sugar. Since the specific radioactivities of the sugar fractions were too low to employ physicochemical methods, a microbial degradation was used to investigate whether the radiocarbon was incorporated in the sucrose molecule. Microorganisms (Proteus vulgaris) degraded [U-¹⁴C] sucrose and the sugar isolates at the same ¹⁴CO₂ release rates under strictly controlled experimental conditions. This result indicates that about one fourth of the carbon from the C-3 position of the triazine ring of the metamitron, found in the sugar beets at harvest time, is partly being used as a substrate in the production of sucrose possibly via assimilation of mineralized ¹⁴CO₂.     

Genetic variability among isolates of Fusarium oxysporum from sugar beet

Fusarium yellows, caused by the soil‐borne fungus Fusarium oxysporum f. sp. betae (Fob), can lead to significant yield losses in sugar beet. This fungus is variable in pathogenicity, morphology, host range and symptom production, and is not a well characterized pathogen on sugar beet. From 1998 to 2003, 86 isolates of F. oxysporum and 20 other Fusarium species from sugar beet, along with four F. oxysporum isolates from dry bean and five from spinach, were obtained from diseased plants and characterized for pathogenicity to sugar beet. A group of sugar beet Fusarium isolates from different geographic areas (including nonpathogenic and pathogenic F. oxysporum, F. solani, F. proliferatum and F. avenaceum), F. oxysporum from dry bean and spinach, and Fusarium DNA from Europe were chosen for phylogenetic analysis. Sequence data from β‐ tubulin, EF1α and ITS DNA were used to examine whether Fusarium diversity is related to geographic origin and pathogenicity. Parsimony and Bayesian MCMC analyses of individual and combined datasets revealed no clades based on geographic origin and a single clade consisting exclusively of pathogens. The presence of FOB and nonpathogenic isolates in clades predominately made up of Fusarium species from sugar beet and other hosts indicates that F. oxysporum f. sp. betae is not monophyletic.     

Genetic diversity and pathogenicity of Pseudomonas syringae pv. aptata isolated from sugar beet

Pseudomonas syringae pv. aptata is the causal agent of bacterial leaf spot disease of sugar beet (Beta vulgaris). During 2013, 250 samples were collected from leaf lesions with typical symptoms of bacterial leaf spot in commercial fields of sugar beet in Serbia, and 104 isolates of P. syringae pv. aptata were obtained. Identification and characterization was performed using biochemical, molecular and pathogenicity tests. Identification included LOPAT tests and positive reactions using primers Papt2F and Papt1R specific for P. syringae pv. aptata. Repetitive (rep) sequence‐based PCR typing with ERIC, REP and BOX primers revealed high genetic variability among isolates and distinguished 25 groups of different fingerprinting profiles. Pulse‐field gel electrophoresis (PFGE) and multilocus sequence analysis (MLSA) of representative isolates showed higher genetic variability than in rep‐PCR analysis and distinguished three and four major genetic clusters, respectively. A pathogenicity test performed with 25 representative isolates on four cultivars of sugar beet confirmed the occurrence of leaf spot disease and showed correlation between the most aggressive isolates and the genetic clusters obtained in MLSA. All these findings point to the existence of several lines of P. syringae pv. aptata infection in Serbia that are genetically and pathologically different.     

Life tables of Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) (Lepidoptera: Noctuidae) on different cultivated plants

Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) is a cosmopolitan species that feeds on numerous cultivated plants and herbaceaus plants. Agrotis ipsilon causes significant economic losses in various agricultural products, especially in indisturial plants and vegetables in Turkey and worldwide. In this study, the effects on the biology and reproductive potential of lettuce (Lactuca sativa L., Asteraceae), maize (Zea mays L., Poaceae), sugarbeet (Beta vulgaris var. saccharifera Alef.,Amaranthaceae) and potato (Solanum tuberosum L., Solanaceae) which are essential host plants of A. ipsilon were investigated under climatized conditions of 28?±?1 °C, 60%?±?10 r.h., and 16 h daily artificial light. The data obtained were analyzed by using an age-stage two-sex life table. Agrotis ipsilon had five larval stages fed on lettuce, whereas seven larval stages were fed on other host plants. Agrotis ipsilon showed the best development and reproduction on lettuce, followed by sugar beet. When A. ipsilon is reared on lettuce the intrinsic rate of increase (r?=?0.1237 d^?1), finite rate of increase (λ?=?1.1317 d^?1) and net reproductive rate (R₀?=?403.06 offspring/individual) were found higher and the mean generation times (T?=?48.51 d) is shorter than those in other host plants. According to these results, A. ipsilon can cause the most damage to lettuce among studied plants.

     

Monitoring of proteobacteria and phytoplasma in sugar beets naturally or experimentally affected by the disease syndrome ‘Basses richesses’

The disease syndrome ‘Basses richesses’ (SBR) affects sugar beet (Beta vulgaris) crops and causes important economic damage in eastern France. Up to now two phloem-restricted prokaryotes which cannot be cultivated, a stolbur phytoplasma and a γ-3 proteobacterium (called SBR proteobacterium), have been associated with the disease. The SBR proteobacterium is closely related to endosymbionts of Hemiptera in the genus Arsenophonus. Both the phytoplasma and the proteobacterium are transmitted by the insect vector Pentastiridius sp. (Hemiptera: Cixiidae). In the present work, we developed sensitive PCR tools for routine detection of SBR proteobacteria in sugar beets. The monitoring with PCR since 1997, of both SBR pathogen agents, showed the predominant aetiological role of SBR proteobacteria in SBR disease. Detection of SBR proteobacteria in sugar beet was correlated with development of SBR symptoms and reduction of sugar content in the taproot. Severity of symptoms and sugar content in experimentally inoculated sugar beet plants were a function of the number of Pentastiridius sp. used for transmission or the length of inoculation access period (IAP), suggesting a direct relationship between importance or precocity of populations of inoculative insects in fields and low sugar yield of crops.     

Weeds in the traditional slash/mulch practice of frijol tapado: indigenous characterization and ecological implications

Weeds in the secondary vegetation of the fallow in slash/mulch or shifting cultivation systems have been identified as important components of the system. Weeds found in the traditional slash/mulch or frijol tapado bean (Phaseolus vulgaris L.) production system in southern Costa Rica were identified and given preliminary rankings based on fanner surveys. The variance of these rankings was used as a measure of farmer uncertainty. Weed rankings were further characterized by key informant interviews. This study also investigated the ecological implications of the vegetative dynamics in the system. Biomass estimates of individual weed species, nutrient dynamics and crop yield response are considered in conjunction with the farmers' rankings of weeds. A negative correlation was found between weed rankings and bean yield, and between weed rankings and C:N ratios.     

Foliar spray of a cell wall protein fraction from the biocontrol agent <Emphasis Type="Italic">Pythium oligandrum</Emphasis> induces defence-related genes and increases resistance against Cercospora leaf spot in sugar beet

After a cell wall protein fraction (CWP) of Pythium oligandrum was sprayed on sugar beet leaves, we screened leaves for induced expression of defence-related genes and for resistance against Cercospora leaf spot. In a western blot analysis, the CWP was primarily retained on the surface of leaves without degradation for at least 48 h after spraying. In northern blot analyses, four defence-related genes (β-1, 3-glucanase, acidic class III chitinase, 5-enol-pyruvylshikimate-phosphate synthase and oxalate oxidase-like germin) were expressed more rapidly in CWP-treated leaves compared to control leaves treated with distilled water (DW). When CWP was applied to a suspension of cultured cells of sugar beet, an oxidative burst was observed that did not occur after the DW treatment. In growth chamber trials after inoculation with Cercospora beticola, the severity of Cercospora leaf spot was significantly reduced in CWP-treated plants compared to the DW-treated controls. In a field experiment, CWP treatment was also effective against the disease. CWP did not reduce growth rate of the pathogen in plate tests. The results together suggest that the CWP from P. oligandrum can be retained on the leaf surface and induce expression of disease resistance genes, thereby reducing Cercospora leaf spot on sugar beet.