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1.
A study was undertaken from 2004 to 2007 to investigate factors associated with decreased efficacy of metalaxyl to manage damping-off of cucumber in Oman. A survey over six growing seasons showed that growers lost up to 14.6% of seedlings following application of metalaxyl. No resistance to metalaxyl was found among Pythium isolates. Damping-off disease in the surveyed greenhouses followed two patterns. In most (69%) greenhouses, seedling mortality was found to occur shortly after transplanting and decrease thereafter (Phase-I). However, a second phase of seedling mortality (Phase-II) appeared 9–14 d after transplanting in about 31% of the surveyed greenhouses. Analysis of the rate of biodegradation of metalaxyl in six greenhouses indicated a significant increase in the rate of metalaxyl biodegradation in greenhouses, which encountered Phase-II damping-off. The half-life of metalaxyl dropped from 93 d in soil, which received no previous metalaxyl treatment to 14 d in soil, which received metalaxyl for eight consecutive seasons, indicating an enhanced rate of metalaxyl biodegradation after repeated use. Multiple applications of metalaxyl helped reduce the appearance of Phase-II damping-off. This appears to be the first report of rapid biodegradation of metalaxyl in greenhouse soils and the first report of its association with appearance of a second phase of mortality in cucumber seedlings.  相似文献   

2.
Disease development was monitored weekly in field plots inoculated withPhytophthora infestans and treated with metalaxyl, mancozeb or metalaxyl/ mancozeb combinations. Late blight pressure was moderate to severe in 1981 and 1983 and was slight to moderate in 1982 and 1984. In 1982–84 all treated plots had significantly less foliar damage and late blight tuber rot than untreated plots. Use of metalaxyl alone resulted in the greatest increase in disease (up to 80% defoliation) in the latter part of the growing season. Under slight to moderate disease pressure, metalaxyl/mancozeb and mancozeb treatments provided significantly better disease control than metalaxyl. Under moderate to severe disease pressure, high levels of disease (65% defoliation) occurred by the end of the season with mancozeb and metalzxyl/mancozeb on 7- and 14-day spray schedules, respectively. However, significantly better control (about 20% defoliation) was obtained during early season, rapidly developing epidemic conditions when only three applications of metalaxyl/mancozeb were included in a 7-day mancozeb spray program.  相似文献   

3.
Seed coating with molybdenum compounds improves seedling establishment for rice, wheat, barley, and soybean when such seeds were sown under flooded conditions. Tungsten belongs to the same chemical group as molybdenum in the periodic table, and similar to molybdenum, inhibits the generation of sulfide ions. Here, the effects of tungsten and molybdenum containing seed coatings on seedling establishment under flooded conditions were compared using rice, wheat, barley, and soybean. In rice, the effects of tungsten compounds on seedling establishment varied. Tungsten trioxide had little effect but tungstic acid and ammonium phosphotungstate significantly improved seedling establishment when the amounts were at least .1–.2 mol W kg?1. Although the effect of tungsten coating varied depending on the compound used, ammonium phosphotungstate, along with other tungsten compounds, improved seedling establishment in a manner comparable with that of molybdenum compounds. For wheat and barley, ammonium phosphotungstate treatment resulted in a significant increase in establishment that was only slightly less than the results observed using molybdenum compounds. Tungstic acid and ammonium phosphotungstate treatments improved soybean establishment in a significant manner that was comparable with those of molybdenum compounds. Collectively, these results suggest that tungsten compounds, as well as molybdenum compounds, improve seedling establishment under flooded conditions.  相似文献   

4.
Damping-off and vine decline diseases affect most greenhouse cucumber crops in Oman, with losses frequently exceeding 25% of seedlings and adult plants. As a consequence of some recent reports that disease control using metalaxyl fungicides were ineffective, seven local and introduced rootstocks were assessed for their response to Pythium aphanidermatum. The rootstocks were also tested for grafting compatibility and production potential under greenhouse conditions. During artificial inoculation trials, no damping-off symptoms were observed in the Hercules and Titan varieties, ridge gourd or sponge gourd. In three separate greenhouse trials, Titan, Hercules and squash var. Magda showed no damping-off or vine decline symptoms up to 45 days after transplanting. When cucumber was grafted onto the seven rootstocks, no symptoms were observed in the cucumber plants grafted onto Titan and Hercules rootstocks, whereas the cucumber grafted onto the other rootstocks showed varying levels of damping-off and vine decline diseases (10–40%). The Titan and Hercules rootstocks significantly increased the vegetative growth and the fruit number, weight and length compared to the self-grafted cucumbers, non-grafted cucumbers and cucumbers that were grafted onto the other rootstocks (P < 0.05). To the best of our knowledge, this study is the first to examine the influence of grafting on the resistance to Pythium and on the vegetative growth and yield of greenhouse cucumbers.  相似文献   

5.
Wheat and barley are often cultivated also in paddy fields in winter in Japan. The drainage of paddy fields is often poor. The seedling establishment of wheat and barley is more prone to become poor if it rains heavily after sowing. The flooding damage on seedling establishment is thought to be caused by many factors. The generation of sulfide ions in flooded and reduced soil is thought to be one factor of the flooding damage. In this study, the effect of seed coating with molybdenum compounds, which suppress the generation of sulfide ions, on the flooding damage of wheat and barley seedling establishment. Two poorly soluble molybdenum compounds were coated on wheat or barley seeds at different amounts. Coated seeds were sown in soil and soon flooded for 2 d at 20 °C. When seeds were not coated with molybdenum compounds, rates of seedling establishment were no more than 32%. However, when any molybdenum compounds of .05–.5 mol-Mo kg?1 were coated, seedling establishment was significantly improved and rates of seedling establishment were no less than 54%. However, when sown seed were not flooded, the establishment rates of the seeds, which were coated with a molybdenum compound of no less than .1 or .2 mol-Mo kg-1, were significantly decreased. Accordingly, coating of molybdenum compounds could improve the seedling establishment of coated seeds under flooded condition, but might impair the seedling establishment of coated seeds under unflooded condition.  相似文献   

6.
Summary Volatiles from the headspace of Russet Burbank potato tubers, non-wounded non-inoculated (N-control), wounded-inoculated-with sterile water (W-control), wounded-inoculated withPhytophthora infestans, Pythium ultimum orBotrytis cinerea, respectively, were sampled at 3 and 6 days after inoculation (dai), using gas chromatography/mass spectrometry (GC/MS).Botrytis inoculated tubers produced two specific volatiles: 2-2-propenyl-l,3-dioxolane and 3, 5-heptadiyn-2-one, while thePythium inoculated tubers produced three: 2-methyl-l-butanol, 2-butanone and 2-methyl-2-butanamine. Similarly, ethoxy-ethene was specific forPhytophthora inoculated tubers. 5-l-methylethylidene-l,3-cyclopentadiene was specific to W-control tubers. Discriminant analysis models based on metabolic fingerprints of metabolites or of mass ions correctly classified 80 to 100% of the observations into respective inoculations/diseases. However, a test-validation correctly classified only 44, 50, 44, 50 and 44% of the fingerprints based on consistent metabolites and 44, 63, 38, 75 and 31% of fingerprints based on mass ions, intoBotrytis, N-control,Phytophthora, Pythium and W-control, respectively. The disease discriminatory metabolite markers and the discriminant models developed here can be used to differentiate the three diseases of Russet Burbank potato tubers, after further validation under commercial conditions.  相似文献   

7.
本文研究了利用药剂拌种方法,对大麻病虫害进行综合防治。首先通过药剂筛选试验,选出对大麻出苗率、保苗率、收获株数提高和原茎、纤维增产及防病虫效果优异的药剂组合两个;然后再进行比较试验,对这两个药剂组合防治大麻病虫害效果进行研究。研究结果表明：每公顷用10%甲霜灵（0.75kg）＋48%代森锰锌（0.9kg）＋75%克百威（1.0kg）拌种,对大麻虫害跳甲、螟虫和病害茎腐病、灰霉病的防治效果分别达71.4%、80%和75.0%、58.3%;每公顷用15%多菌灵（1.0kg）＋75%克百威（1.0kg）＋10%福美双（1.2kg）,对大麻虫害跳甲、螟虫和病害茎腐病、灰霉病的防治效果分别达57.1%、60.0%和100%、75.0%。  相似文献   

8.
《Plant Production Science》2013,16(4):294-300
Abstract

Soybean (Glycine max (L.) Merr.) is considered to be susceptible to flooding, a major agronomic problem in the world, and nitrogenase activity rapidly declines due to oxygen deficiency in root nodules. We investigated nodule acclimation to flooding at the morphological level using a soybean cultivar possessing the ability to form secondary aerenchyma. After 1 week of treatment, lenticels were formed on the surface of the root nodules, and secondary aerenchyma were observed through the lenticels under both irrigated and flooded conditions. As the plant grew, the nodule epidermis came off, and well-developed secondary aerenchyma covered the nodule surface. The secondary aerenchyma originated from the secondary meristem (phellogen) girdling the sclerenchyma, and the degree of development was greater in flooded nodules than in irrigated ones. Although root nodulation and total nitrogenase activity (TNA) decreased under flooded conditions, there were no differences in shoot N concentration, specific nitrogenase activity (SNA) and relative ureide-N in the xylem bleeding sap between plants in the irrigated and flooded conditions. Under flooded conditions, however, when the entry of oxygen into the secondary aerenchyma formed in the hypocotyl was inhibited by vaseline treatment (pasting on the surface of the hypocotyl), the shoot N concentration, TNA, SNA, the ureide-N concentration and the relative ureide-N in the sap declined remarkably. These results suggested that secondary aerenchyma formation in soybean plants is a morphological acclimation response to flooding stress, and that one of the functions is to supply atmospheric oxygen to root nodules, which consequently enables nodule activity to be maintained.  相似文献   

9.
Experiments were conducted to evaluate the effects of light, seed burial depth, and flooding on germination, emergence and growth of Ludwigia hyssopifolia. Germination was strongly stimulated by light, suggesting that seeds of this species are positively photoblastic. Seeds sown on the soil surface gave the greatest percentage of seedling emergence in plastic trays, and no seedlings emerged from seeds buried in soil at depths of ≥1 cm. Intermittent or shallow flooding suppressed emergence and growth of L. hyssopifolia. Flooding to a depth of 2 cm for 4 days out of 7 days reduced seedling emergence by more than 71% and seedling dry matter by 97% compared to where the soil had not been flooded. Flooding up to a depth of 10 cm however, when delayed to 21 days after sowing, did not significantly suppress growth of this species. This study illustrates the role of seed burial by tillage and flooding as two important tools for the management of L. hyssopifolia.  相似文献   

10.
《Plant Production Science》2013,16(3):276-279
Abstract

Direct-seeding has been proposed as a water- and labor-saving method to grow irrigated rice. Our objective was to compare the effects of flooded and aerobic conditions on the yield stability of direct-seeded rice. We set up four trials in the field: aerobic, near-saturated and flooded soils with direct seeding, and flooded soil with transplanting. Grain yield of direct-seeded rice was comparable to that of transplanted under flooded conditions. However, the yield of direct-seeded rice under aerobic conditions was up to 21% lower than that under flooded conditions. This poor performance was associated with reduced leaf growth during the vegetative stage. Our results indicate that the yield stability of direct-seeded rice could be lowered by the water-saving irrigation, compared with the conventional flooded culture. In order to save irrigation water, physiological research on direct-seeded rice should target the vulnerability of rice to aerobic soils or to soil moisture fluctuations.  相似文献   

11.
Summary TwoPythium spp. were isolated from diseased tubers exhibiting rots at harvest, in summer stores and also in refrigerated storage. Symptoms shared features described for both pink rot caused byPhytophthora erythroseptica and leak caused byPythium spp. The causal agents were identified asPythium aphanidermatum andP. ultimum by morphological and physiological observations and by fingerprinting using oomycete specific primers to amplify the internal transcribed spacer (ITS1) within ribosomal DNAs. The optimum temperatures for infection were 30°C forP. aphanidermatum and 25°C forP. ultimum, corresponding to the optimum temperatures for growth in vitro. The optimum concentration for infection of tubers inoculated by dipping in a suspension of oospores or hyphal swellings after wounding was found to be 103 reproductive organs/ml, whereas the infection threshold was 10 reproductive organs/ml.  相似文献   

12.
《Plant Production Science》2013,16(4):395-400
Abstract

We evaluated the varietal difference in the flood tolerance of germinated seed in 17 Japanese varieties of common buckwheat (Fagopyrum esculentum Moench), including both local varieties and bred varieties or lines of different agroecotypes. Germinated seeds were flooded for 1 day in a growth chamber in June, July and August. The mean rate of seedling emergence from the seeds sown on different dates varied with the variety ranging from 20.4 to 57.4%. The mean emergence rate of summer agroecotypes (29.9%) was significantly lower than that of intermediate and late-summer agroecotypes (42.8 and 40.1%, respectively), and that of local varieties (44.2%) was significantly higher than that of bred varieties or lines (31.2%). These results suggest that inherent variation in flood tolerance was decreased by breeding as a result of a bottleneck effect. The local variety ‘Kitou zairai’, which exhibited a high and stable seedling emergence rate, may be a suitable choice in breeding for flood tolerance during germination. We also attempted to select for flood tolerance under mild selection pressure. Mass selection after four generations increased seedling emergence rate in five of six selected lines (with the exception of ‘Kitawasesoba’) compared with those of unselected populations, although the results varied with the line. These results indicate the possibility of breeding for flood tolerance during the germination period.  相似文献   

13.
Abstract

Sulfide ion generation in strictly reduced soil might be a factor impairing rice seedling establishment. The molybdate ion is known to suppress the microbial transformation of sulfide ions from sulfate ions. I investigated the effect of molybdate on rice establishment in sulfate-applied submerged soil. The establishment of rice seeds sown in sulfate-applied submerged soil was markedly improved by application of potassium molybdate at a rate of 1.5?15 mmol kg-1 dried soil. The application of potassium molybdate delayed the decline of the sulfur concentration in the soil solution near the seeds and the appearance of circular black stains, or insoluble iron sulfide indicating the generation of sulfide ion, around seeds in the soil. Irrespective of the application of molybdate, the redox potential near the seeds was low enough to allow generation of sulfide ions, implying that molybdate suppresses the generation of sulfide ions with no effect on redox potential. These results suggest that the application of molybdate could improve rice seedling establishment in sulfur-rich submerged soil by suppressing the generation of sulfide ions, that is a possible factor suppressing the establishment of rice seeds sown in sulfur-rich submerged soil.  相似文献   

14.
The chemical properties of soil samples collected in August and November from an abandoned terraced paddy field dominated by reeds were examined by in vitro incubation under normal moisture and flooded conditions. Soil pH extracted with water [pH(H2O)] was higher in soil samples collected from a depth of 0–10 cm in November than in samples collected in August; a high pH(H2O) was maintained even during nitrification under normal moisture conditions. When soil samples collected in August from a depth of 0–10 cm were incubated under flooded conditions, a significant decrease in reduction potentials (Eh) and an increase in total Fe2+ concentrations were observed. Reductive conditions during sampling were strong in soil samples collected in August from a depth of 40–50 cm. Moreover, under normal moisture conditions, soil samples collected in August showed significant decreases in pH(H2O) and significant production of water-soluble SO4 2? than those collected in November. Glucose addition to soil samples collected from a depth of 0–10 cm caused nitrogen immobilization under normal moisture conditions, increases in exchangeable Fe2+ and Mn2+, and decreases in exchangeable bases (Ca2+, Mg2+, K+, and Na+) under flooded conditions. Seasonal changes in soil properties were probably due to microbial activity and vegetation phenology; thus, the timing of soil sampling influenced incubation experiment results. When abandoned terraced paddy fields are created as biotopes, seasonal changes in reductive soil conditions and slope position must be considered to prevent soil acidification and base cation elution.  相似文献   

15.
《Plant Production Science》2013,16(3):280-284
Abstract

A fiber reinforced plastic (FRP) pot, equipped with a slanted pipe through which water is supplied, has been used for assessment of rice herbicides. This pot may also be useful for controlling water table in upland conditions. In this experiment, early growths of soybean and morning glory grown under waterlogging and excess soil water conditions were evaluated. The waterlogging condition was attained by adjusting the top of the slanted pipe to soil surface level, and excess soil water condition (0.2 m3 m?3) by adjusting to 15 cm below the soil surface. The water content of the soil did not fluctuate during the treatment. Shoot growths of soybean and morning glory were poorer under waterlogging than excess soil water condition. The present experimental procedures using a FRP pot could be available for evaluation of wet damage of field crops grown under ill-drained field.  相似文献   

16.
Echinochloa crus-galli, a C4 grass, is one of the world’s most serious weeds. Weed management decisions for this species can be derived from knowledge of its seed biology. Studies were conducted to determine the effects of light on germination; seed burial depth and rice residue on emergence and growth; and flooding time and depth on emergence, survival and growth of this species. Light stimulated seed germination but it was not an absolute requirement for germination. The proportion of seeds germinating was greatest for seeds placed on the soil surface (92%), and emergence declined with increasing burial depth in soil; no seedlings emerged from the depth of 8 cm. A burial depth of only 0.4 cm reduced seedling emergence by 50%. Seedling emergence and seedling biomass were reduced by the addition of high level (6 ton ha−1) of rice residue to the soil surface. Early and deep flooding significantly suppressed growth of E. crus-galli seedlings. In flooded conditions, with increased water depth the weed allocated more biomass to shoots at the expense of roots. The information gained from this study could contribute to improve weed control approaches. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence, use of crop residue as mulch and early flooding of the crop could serve as important tools for managing E. crus-galli and other weed species with similar germination requirements. These management options, however, would need to be compatible with other crop management requirements.  相似文献   

17.
The mode of action of the systemic fungicide metalaxyl and possible changes in Phytophthora spp. leading to resistance to metalaxyl were investigated. Uptake of labelled uridine and thymidine into RNA and DNA were reduced by sub-lethal amounts of metalaxyl. There was no evidence that metalaxyl caused a build-up of nucleotides or blocked the DNA template. Metalaxyl metabolites were absent from the fungus and the medium; the unchanged fungicide is probably the primary toxic agent. Washing metalaxyl-treated mycelium with water removed about 80% of the fungicide but the rest was firmly bound. Metalaxyl-resistant and sensitive strains of Phytophthora had similar growth rates in vitro, took up similar amounts of fungicide and incorporated uridine into RNA at similar rates. The mechanism of resistance remains obscure: subtle alterations to nucleic acid synthesis may be involved but other possibilities remain.  相似文献   

18.
《Plant Production Science》2013,16(4):468-472
Abstract

Improvement of early seedling growth, such as seedling emergence and vigor is one of the most important agronomic traits in direct seeding rice cultivation. The effects of two plant growth regulators (PGRs), gibberellic acid (GA3) and ethephon (ET), on seedling growth under flooded soil conditions at different temperatures and water depths were investigated. The PGRs were applied during the seed soaking process. A single treatment with GA3 or ET increased seedling growth. However, combined application of GA3 and ET was more effective than that of GA3 or ET alone in many cases at both growing temperatures (15 and 20ºC). The growth of different organs in the rice seedlings, such as the coleoptiles, first leaves, and second leaves was also increased by PGR treatment. The nitrogen concentration of the shoot and the ratio of shoot dry weight to shoot length did not differ significantly among the treatments. The results of our study show that rice seedling growth in direct seeding cultivation may be improved by treatment with GA3 and ET in combination.  相似文献   

19.
《Plant Production Science》2013,16(4):460-467
Abstract

Delayed stem senescence (DSS) after pod maturation in soybean (Glycine max) lowers the quality of products in the mechanized harvest. The effects of drought and excess wet soil conditions on the occurrence of DSS were studied with special reference to remobilization of vegetative nitrogen and supply of cytokinin via xylem. Excess wet soil treatment was applied throughout the reproductive period to field-grown soybean in 2003 (Exp.1) and short-term drought stress treatment was applied during the reproductive period to pot-grown soybean plants in 2004 (Exp.2). The degree of DSS at pod maturing was evaluated by the DSS score from “1” for severe DSS to “5” for completely synchronous senescence of pods and vegetative parts. The DSS score in Exp.1 varied from 2.2 to 2.5 and that in Exp.2 from 2.8 to 3.7. Excess wet soil treatment in Exp.1 promoted the occurrence of DSS, while drought stress treatments during the periods of flowering to pod elongation, later seed-filling and seed maturing decreased it. The soybean plants that showed distinct DSS had lower ratios of seed number to vegetative dry weight at seed maturity and a lower rate of nitrogen remobilization from vegetative organs to seeds during the latter half of the reproductive period. The trans-zeatin riboside (t-ZR) level in xylem exudate tended to be higher in soybeans with severer DSS than in those normally matured in both experiments showing increased t-ZR concentration and/or higher exudation rate. These results suggest that DSS can be caused by a wet soil water condition, which lowers pod/seed number and increases vegetative organs mediated by the increased supply of cytokinin through xylem during seed-filling.  相似文献   

20.
The persistence of fungicides on two commercial cultivars of potato was determined under field conditions at Punjab Agricultural University, Ludhiana, Punjab. Initial deposits of mancozeb on potato leaves were found to be 26.9 and 38.7 mg kg(-1), following application of ready mixture of fungicide metalaxyl 8% + mancozeb 64% (Ridomil MZ) at the rate of 1260 and 2520 g a.i. ha(-1), whereas metalaxyl residues were found to be 35.1 and 49.5 mg kg(-1), respectively. The residue level of mancozeb in potato leaves 15 days after application at single and double doze were 19.0 and 27.0 mg kg(-1) showing a loss of 29.6 and 30.3%, whereas the values for metalaxyl at single and double doze were 0.40 and 0.80 mg kg(-1) showing a loss of 98.9 and 98.4%, respectively. Residues of mancozeb and metalaxyl were not detected at 0.04 and 0.02 mg kg(-1) level in potato tubers at harvest (PHI = 53 days) at both the dosages, respectively. The persistence and dissipation of mancozeb with the application of Ridomil MZ followed similar trend as in Indofil M-45. The rate of fungicide dissipation increased with time after application in both the potato cultivars 'Kufri Chandramukhi' and 'Chipsona'. No significant difference was observed on initial deposit, persistence and dissipation of the two molecules between the two potato cultivars.  相似文献   

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