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1.
Experiments at Bharatpur, Pantnagar, Berhampur, Mohanpur, New Delhi, S.K. Nagar, Kangra and Sriganganagar, India were sown with oilseed Brassica cultivars Varuna and an important cultivar for the area on 10 dates at weekly intervals. Data of experiments conducted previously at Hisar and Ludhiana as available in reports were also used for the study. Mustard aphid (Lipaphis erysimi) appearance on inflorescences of the plants was positively correlated to a maximum temperature between 20–29 °C in the preceding week and also to a morning relative humidity (RH) >92% and daily mean RH of >75%. Long hours of leaf wetness and minimum temperature >5 °C also favoured aphid infestation. Regional and cultivar specific models were developed to predict the crop age at which the mustard aphid first appears on the crop, the peak number of aphids and the crop age at peak number at least 1 week ahead of first appearance of the pest on the crop. These will allow growers to apply insecticides in a more timely and effective manner. Here we report only the models that were found effective based on validation in the 2 years.  相似文献   

2.
The effect of inoculum concentrations, temperature, relative humidity (RH), incubation period and leaf age on sporulation of Pestalotiopsis disseminata and the development of grey blight disease on som (Persea bombycina Kost.) were studied in controlled environmental conditions. These factors had a significant role on spore germination and germ tube development of P. disseminata, the causal organism of the disease. The optimum inoculum concentration of the pathogen were found to be 1 × 107 spores ml−1 for maximum infection percentage. A nonlinear relationship was found between temperature and germination percentage of spores at a given relative humidity (RH). However, 25 °C (±2) temperature and 70% RH were the optimum parameters for better spore germination of the pathogen. Young leaves (leaf no. 1–4 from the top) were more susceptible for development of the diseases in a controlled environment than the older leaves. The germination of spores started at 8 h of incubation and gradually increased up to 20 h (maximum). The disease severity was favoured in the optimum range of temperature (25 ± 2 °C) and RH (70%) which had a combined effect. These epidemiological parameters could help in the management practices of the disease.  相似文献   

3.
Melon collapse caused by the heat-tolerant soil-borne fungus Monosporascus cannonballus is not controlled by current solarization technology applied to large soil volumes because the temperatures achieved are not high enough to kill the pathogen's ascospores. The efficacy of improved solarization achieved by mulching a shallow layer of growth medium in containers was studied in terms of disease control and yield increase over two growing seasons. Compared to solarization of a regular container, solarization of a shallow layer (5–6 cm) of growth medium resulted in a 3–5°C elevation in maximal temperature at a depth of 3 cm, and in a 7–10°C increases at the bottom of the shallow layer. This led to a higher disease reduction and higher yields in the 1996 experiment. In 1997, both methods of solarization were highly effective. Yield was highly correlated with disease reduction in both experiments. In the 1997 experiment, ascospore viability declined faster in the shallow container treatment than in the regular container. This study demonstrates the potential of an additional approach for improving solarization of containerized plant growth medium and improving its reliability, with the aim of controlling heat-tolerant pathogens.  相似文献   

4.
橡胶树炭疽菌生物学和侵染特征研究   总被引：8，自引：0，他引：8  
橡胶树炭疽病是危害我国橡胶树的一种重要叶部病害,致病菌为胶抱炭疽菌。对其生物学特性研究结果表明,在28 ℃下,有利于菌丝体生长、产孢和孢子萌发 。最适合菌丝体生长的pH值为6。黑暗下有利于孢子萌发和菌丝体生长,但产孢则不如在光照条件下。在100 %相对湿度下孢子萌发率最高。在葡萄糖、橡胶叶汁和琼脂胶等营养液中, 孢子萌发率高于清水对照。对其侵染特征研究结果表明,主要侵染源为受害嫩梢和半枯死枝条,寄主范围广泛。病菌可从伤口、气孔和表皮3种途径入侵,风雨是传播媒介。潜育期一般3~6d,条件最适宜时潜育期为1~ 2d。田间气温21~24℃、相对湿度大于95%时,病菌产孢多,侵人迅速,病斑扩展快  相似文献   

5.
The genus Lesquerella is a promising source of hydroxy fatty acids (HFA). Several species such as Lesquerella fendleri and Lesquerella mendocina are candidate crops for arid and semi-arid cropping systems. Several reports are available on the environmental effects on growth and yield in Lesquerella, but information on the effect of temperature on plant growth and development specifically during the reproductive period in Lesquerella is limited. The objective of this work was to determine the effect of two contrasting thermal regimes after flowering on time to maturity, plant growth and biomass allocation to the different organs in L. fendleri and L. mendocina. A greenhouse experiment was conducted with plants grown at a range of 11–23 °C during the vegetative phase. After this stage, 50% of the plants of each species remained under the same temperature regime until maturity, whereas the other 50% was transferred to another module subjected to a range of 17–31 °C until maturity. The duration of the reproductive phase was reduced by 23 days in plants of both species in the 17–31 °C treatment compared to those at 11–23 °C, although no differences were observed when the length of the reproductive phase was measured in thermal-time units. Total plant biomass for both species was 20% greater in the 11–23 °C treatment. In L. fendleri, this increment occurred due to more vegetative shoot biomass, whereas in L. mendocina it was associated with greater reproductive and root biomass. No changes in biomass allocation were produced by temperature in L. fendleri, while in L. mendocina the lower temperature regime increased allocation to the reproductive organs, at the expense of a lower allocation to vegetative shoot. These results could be used to predict the specific temperature effects after flowering on yield under field conditions, and suggest that L. mendocina might be a promising perennial alternative for cooler sites.  相似文献   

6.
Powders prepared from sweetflag Acorus calamus rhizomes collected at both high (1700 m) and low (900 m) altitude in Eastern Nepal were admixed with wheat at concentrations in the range 0.05–2% w/w and the wheat infested with Sitophilus oryzae or S. granarius adults. Following a 7 day incubation, the mortality of both species was significantly lower at 20 °C than at 30 °C, and the material collected from high altitude was slightly less toxic than that from low altitude. The moisture content of the wheat (14 or 17%) and the part of the rhizome used to prepare the powder (young or mature growth) had no apparent effect on the toxicity of the preparation. Sitophilus granarius (L.) adults were more tolerant of the material than S. oryzae (L.), while the converse was true for larvae developing in treated grain. An admixture rate of approximately 2% w/w admixed rhizome powder was required to give complete kill of adults of both species following 7 days exposure at 20 °C, while a concentration of 1% w/w either prevented the emergence of adults or killed them rapidly following emergence when wheat containing eggs of either species was incubated for 7–8 weeks at 30 °C.

The β-asarone content of the rhizome powders was determined by GC-MS as 6.4 and 4.7% w/w (mature section of rhizomes collected at high and low altitudes, respectively) and 3.6 and 4.0% w/w (young sections of rhizomes collected at high and low altitudes, respectively). It is anticipated that, under field conditions and in the temperature range 20–30 °C, the initial residue of approximately 1300 mg/kg β-asarone required to disinfest wheat containing these weevil species would decline rapidly due to evaporation.  相似文献   


7.
Avoidable losses and economic injury levels (EILs) were computed for the sorghum head bug, Calocoris angustatus Leth., on three cultivars during three rainy seasons (1985–1987) at ICRISAT. Grain yield in plots protected with 2–5 insecticide sprays (carbaryl at 500 g a.i./ha) between the half-anthesis and the dough stage was significantly higher than in untreated plots, with cost-benefit ratios > 1. Plots that were not protected at half-anthesis and/or complete-anthesis, and at milk and dough stages, suffered a significant loss in yield. Bug damage spoiled the grain quality in terms of germination, 1000-grain mass, grain hardness and percentage floaters. Three to four sprays between complete-anthesis and the dough stage prevented a significant reduction in grain quality. Head bug density at half-anthesis, complete-anthesis, milk and dough stages was significantly and negatively associated with grain yield. Bug density at different stages explained 43–94% of the variance in yield. Direct effects of bug numbers at the milk stage and the indirect effects of head bug density at other stages through the milk stage contributed towards maximum reduction in yield. Maximum avoidable losses were recorded in cultivar ICSV 1 (88·6%), followed by CSH 1 (69·9%), and CSH 5 (53·9% in 1986 and 55·0% in 1987). Loss in grain yield/ha due to one insect/panicle at half-anthesis and that based on natural increase, were 548 and 232 kg in CSH 5 during 1986 and 1987, respectively, 251 kg in ICSV 1, and 77 kg in CSH 1. EILs based on a cost-benefit ratio of 1:1 ranged from 1·3–1·4 insects/panicle for CSH 1, 0·4 for ICSV 1, and 0·4–0·6 and 0·2–0·4 for CSH 5 during 1986 and 1987, respectively. Simple cost estimates for insecticide sprays and the resultant saving in grain yield are a useful tool for decision-making in pest management.  相似文献   

8.
The importance of sowing dates to the development of sorghum ergot (Claviceps africana) was determined at Tlayca, Morelos, Mexico during the rainy seasons of 1998–2000. Annual variation in ergot incidence occurred, with the highest levels in the year 2000. Sowing dates between June 15 and July 14 had the lowest levels of ergot incidence and severity. Temperatures below 15°C 3 weeks before flowering increased ergot incidence. The optimal weather factors for ergot development were a mean day temperature of 25°C, a maximum relative humidity of 96%, a maximum temperature of 28°C, and nighttime relative humidity of 86%.  相似文献   

9.
Five bacterial isolates collected from dogwood leaves were evaluated for powdery mildew control in shadehouse and greenhouse environments by using foliar sprays and/or root drenching. Two isolates displayed superior bioactivity and suppressed powdery mildew similar to conventional fungicide thiophanate methyl (Cleary’s 3336F®). The two bacteria disrupted powdery mildew spore germination and ruptured spore membranes causing spore lyses. Bacterial filtrates without bacterial cells were also effective in suppressing powdery mildew and disrupting spore germination and suggested the involvement of secondary metabolites. The two biocontrol agents (BCAs) colonized roots endophytically and promoted plant growth.  相似文献   

10.
Chilling temperatures at flowering cause floral abortion in most chickpea cultivars. Recent evaluations of germplasm showed distinct genotypic differences in pod and seed set at low temperature but the morpho-physiological basis for such variation is unclear. Observations in the field during cold spells of December and January, and at 15/5°C and 15/0°C (day/night) regimes in growth rooms showed distinct genetic variation in flower morphology, gamete development (viability and size of pollen and ovules) and function (pollen germination and tube growth, ovule viability and fertilization, etc.). The greater pod-setting ability of tolerant lines (ICCVs 88502 and 88503) than the sensitive cultivars (Annigeri, Pant G 114, etc.) was associated with a higher pollen vigour (germination and tube growth) and ovule viability at low temperature in the former. The number of ovules was not affected by cold stress in all cultivars/lines but pollen size and viability were reduced in Annigeri. The reduced ovule fertilization, associated with decline in pollen tube growth and ovule viability, was the major cause for poor seed set at low temperatures. The magnitude of effects on gamete function varied with cultivar/line and severity of stress. Function of both pollen and ovules was adversely affected in Annigeri in 15/5° and 15/0°C regimes. In contrast, the reduction in pollen vigour was more than in ovule viability in ICCV 88510 and Pant G 114 at 15/5°C. At 15/0°C, however, both pollen vigour and ovule viability were reduced. A small increase in pod set of sensitive genotypes from manual pollinations with pollen from plants in the warm regime further suggested that pollen function was more adversely affected than pistil function at moderately low temperatures.  相似文献   

11.
A high percentage of rose flowers collected during winter from greenhouses around Israel developed grey mould disease when incubated in the laboratory in favourable conditions. Symptomless flowers of various cultivars were incubated in a humidity chamber after surface disinfection. More than 50% of the symptomless flowers yielded the pathogen Botrytis cinerea Pers., thus showing the presence of latent infection which probably occurred 3–8 days earlier in the commercial greenhouses. Initially, the symptoms which occurred on affected petals were mainly restricted lesions. However, when flowers were incubated under favourable conditions, necrosis developed and spread. Chemical control of grey mould was tested on cut rose flowers. Partial control of the disease was correlated with reduction in necrosis and a relative increase in restricted lesions (<2 mm in diameter). Of the 18 fungicides which were tested, the following were the most efficient during incubation at 20°C: metomeclan, dichlofluanid, myclozolin, N-phenylcarbamate plus carbendazim (NPC + MBC), polyoxin D, prochloraz and iprodione. When incubated at 10°C, the most effective fungicides against grey mould of rose flowers were NPC + MBC, polyoxin D, chlorothalonil, the detergent Tween 20, and the inhibitor of ethylene activity, silver thiosulphate (STS). Diphenylamine was more effective at 4°C than at 10° or 20°C. STS in combination with each of the fungicides chlorothalonil, polyoxin B, myclozolin or merpan was additively more effective than STS or each of the respective fungicides alone.  相似文献   

12.
On-farm seed priming of maize (i.e. soaking seed in water overnight, 17 h) in the semi-arid tropics has been shown to improve crop establishment and yield but the benefits can be variable. In previous work, this variation was thought to result from the interaction between primed seeds and conditions in the seedbed following sowing. To investigate this interaction, experiments were carried out under controlled temperature conditions that represented those of seedbeds in the semi-arid tropics. The conditions during seed priming and during subsequent germination and emergence were investigated as potential causes of variable seedling emergence relative to that of untreated seeds. Priming advanced emergence from moist sand cores at 30 °C/20 °C (day/night), reduced emergence at 35 °C/28 °C and delayed and reduced emergence at 40 °C/28 °C. In drier cores (drained 8 days) at 35 °C/28 °C, priming advanced germination time and did not decrease final percentage emergence. These results confirmed earlier field observations that the effect of priming in maize can vary and lead to positive, neutral or negative effects. Priming decreased the optimum and ceiling temperatures for germination, and unlike untreated seeds, the relationship between germination rate and sub-optimal temperature was not linear in all cases. Pre-humidifying seeds did not enhance the effect of priming, but aerating the soak water did. These results indicate that variable results from priming recorded in the field were not due to imbibitional damage, but may result from the negative effects of hypoxia during soaking exacerbated by moist conditions and high temperatures at sowing. These effects differed between seedlots of different cultivars, indicating the importance of selecting more tolerant maize hybrids to reduce variation in response to priming following sowing in the field. The implications of these findings for the use of primed seeds in the field are discussed.  相似文献   

13.
S. Yücel 《Crop Protection》1995,14(8):653-655
Field trials conducted in the pepper growing area ( çel/Turkey) showed that solarization alone and combined with a reduced dose of methyl bromide (40 g/m2), were effective in controlling crown blight disease caused by Phytophthora capsici. Solarization was achieved by covering plots with a clear polyethylene sheet, 0.03 mm thick for 8 weeks. The temperature reached 47 °C and 35 °C at 5 cm and 30 cm soil depth, respectively, an average of 3–8 °C higher than those at equivalent depths in the untreated plots. The average incidence of the disease in solarization plus a reduced dose of methyl bromide, the recommended dose of methyl bromide, solarized and untreated plots in 1991 and 1992 were 17.6 and 13.3%; 20.8 and 16.8%; 24.1 and 19.7%; 39.8 and 42.9%, respectively. All treatments significantly reduced disease incidence.  相似文献   

14.
Sulphur dioxide (SO2) concentrations required to kill the spores and mycelium of Botrytis cinerea and control post-harvest decay of fresh grapes were determined in chamber studies. Effective concentrations and exposure times were simulataneously expressed in a single dosage term, parts per million-hours (p.p.m.-h). This unit is the product of the concentration of SO2 in parts per million multiplied by the duration of the fumigation in hours. SO2 dosages that killed 99% of the spores (ED99) were 78.3 ± 22.3 p.p.m.-h at 0°C and 20.3± 2.0 p.p.m.-h at 20°C. These values were determined with continuous concentrations of 25, 50, 100 and 200 p.p.m. SO2 at high humidity. The mycelium on the surface of infected berries was injured by dosages of 10 p.p.m.-h and was no longer viable after fumigation with dosages of 50–100 p.p.m.-h at 0°C. Infection of inoculated berries at 0°C compared with the controls was 68, 47, 2 and 0% after dosages of 20, 50, 100 and 200 p.p.m.-h, respectively. Reduction in the percentage infection after spore inoculation of berries required a larger dosage ( 100 p.p.m.-h) than that which controlled mycelial growth ( 50 p.p.m.-h). For initial fumigation of grapes after harvest, where control of spores on the surface of grapes is required, 100 p.p.m.-h should be sufficient; for subsequent storage fumigations where control of mycelial growth from latent infections is required, 50 p.p.m.-h should be sufficient. Colorimetric dosimeters have been developed to quantify exposures of humans to SO2 rapidly and inexpensively for safety purposes. They consist of a sealed glass tube containing a colour-indicating substrate that reacts with SO2 to produce a coloured product. One end of the tube is opened before use, and the length of the colour change indicates the accumulated dosage in units of p.p.m.-h. They should be placed inside grape packages before fumigation and examined promptly after fumigation. Their accuracy was sufficient for determination of adequacy of SO2 dosages to control decay.  相似文献   

15.
Anthracnose disease of papaya, caused by Colletotrichum gloeosporioides Penz, can cause extensive postharvest losses. The goal of this research was to use pre-harvest calcium applications to reduce anthracnose disease. Six pre-harvest foliar calcium sprays were applied biweekly to papaya trees in experimental orchards at Universiti Putra Malaysia. Additional in vitro and in vivo tests were carried out to test the effect of calcium on fruit calcium content, spore germination, mycelial growth and disease severity. Calcium chloride at 1%, 1.5% and 2.0% concentrations significantly decreased spore germination. Calcium content of papaya fruit was significantly increased by calcium sprays at a concentration of 2.0% in 2012 and 2013. In vivo studies showed that increasing calcium content in fruit by calcium sprays at 1.5 and 2.0% concentrations significantly reduced anthracnose incidence of fruits during five weeks storage at 12 ± 2 °C, and delayed initiation of disease symptoms by four weeks.  相似文献   

16.
Three substances that show antifungal activity against Blumeria graminis f. sp. hordei were isolated from roots of Rumex crispus and identified as chrysophanol, parietin, and nepodin. The substances were tested for plant disease control activity in vivo against six plant pathogenic fungi. All specifically reduced the development of barley powdery mildew. The concentrations required for 50% disease control were 4.7 μg/ml for chrysophanol, 0.48 μg/ml for parietin, and 20 μg/ml for nepodin. These agents showed both curative and protective activity against barley powdery mildew. Chrysophanol (100 μg/ml) and nepodin (400 μg/ml) were more effective than the fungicides fenarimol (30 μg/ml) and polyoxin B (100 μg/ml), under glasshouse conditions, against cucumber powdery mildew, which is caused by Podosphaera xanthii. Parietin (30 and 10 μg/ml) reduced the development of cucumber powdery mildew as efficiently as fenarimol (30 μg/ml) and more effectively than polyoxin B (100 μg/ml).  相似文献   

17.
The many recent dry-grind plants that convert corn to ethanol are a potential source of substantial amounts of corn oil, if an economical method of separating it can be developed. Oil separation from corn germ by aqueous extraction (AE) was studied. Batches of 5–20% germ in a buffer solution were preheated in a pressure cooker, ground in a blender or colloid mill, churned in an incubator/shaker and centrifuged to separate a free oil fraction. The highest oil yields were obtained when the germ mass fraction was between 0.1 and 0.16. Addition of an enzyme solution to the ground germ suspension prior to churning, aqueous enzymatic extraction (AEE) gave an oil yield twice as high as the AE yield, carried out using similar conditions. Both types of extraction produced the most oil after a 122 °C cook followed by churning at 160 rpm and 70 °C. Oil yield increased linearly with dispersion loading, from 0.5 up to 1.0 g/cm2 based on beaker cross-section (0.09–0.12 germ mass fraction). Over a several month period the germ used for the extractions became more difficult to extract, despite storage at 4 °C.  相似文献   

18.
为探究韭菜根系分泌物对苦瓜枯萎病菌的化感作用,本研究以‘山东雪韭6号’韭菜和苦瓜枯萎病菌为试验材料,水培法收集韭菜根系分泌物,采用菌丝生长速率和孢子萌发法研究韭菜根系分泌物对苦瓜枯萎病菌的化感作用;利用气相色谱-质谱联用技术（GC-MS）鉴定根系分泌物组成成分,筛选可能的主效化感物质,进一步通过体外抑菌试验验证其化感作用,明确主效化感物质。结果表明,随着韭菜根系分泌物浓度的升高,苦瓜枯萎病菌的菌落直径和孢子萌发数均呈先降后升的趋势,当分泌物浓度为3.22 mg/mL时,抑制作用最大,满足化感作用低浓度促进、高浓度抑制的特性。通过GC-MS鉴定出韭菜根系分泌物中的主要成分为酚类、酯类、烷烃类、醇类、烯类、芳香类,可能的化感物质为邻苯二甲酸二丁酯、2,4-二叔丁基苯酚、2,2°-亚甲基双-(4-甲基-6-叔丁基苯酚)。通过体外抑菌试验证实这3种物质对苦瓜枯萎病菌菌丝生长和孢子萌发都有不同程度的化感抑制作用,且抑菌效果为2,4-二叔丁基苯酚>邻苯二甲酸二丁酯>2,2°-亚甲基双-(4-甲基-6-叔丁基苯酚),明确其为化感物质。由此可知,韭菜根系分泌的主效化感物质对苦瓜枯萎病菌有显著的化感抑制作用,这为苦瓜间套轮作韭菜防控苦瓜枯萎病和研制植物源抑菌剂提供了理论依据和技术支撑。  相似文献   

19.
Field trials were conducted at Samaru in the northern Guinea and at Bakuta and Kadawa in the Sudan Savanna ecological zones of Nigeria to identify suitable herbicides for weed control in irrigated onion. The herbicides tested were chlorthal-dimethyl, fluorodifen and oxadiazon. In the trials each herbicide treatment was compared with an identical treatment which received supplementary hand-weeding. The results of these experiments show that oxadiazon at 1·0–2·0 kg a.i./ha, with or without supplementary hoe-weeding at 6 weeks after transplanting, combined effective weed control with high bulb yields in irrigated dry season onions. While fluorodifen at 1·5 kg a.i./ha followed by supplementary hoe-weeding may be effective at sites with low weed infestation, a higher rate (3·0 kg/ha) may be desirable at sites with a higher broad-leaved weed infestation. Chlorthaldimethyl at 10·0 kg a.i./ha effectively controlled weeds at all the sites and gave high onion yields at sites with 6–12% clay; the selectivity was, however, lower at Bakura with very light soil. Uncontrolled weed growth caused 49–86% reduction in the bulb yields compared with the best herbicide treatments.  相似文献   

20.
Alternaria alternata is the predominant fungal pathogen responsible for moldy-core in red delicious strains of apple. In this study, we report on the effects of the polyoxin B compound Polar, the strobilurin fungicides, azoxystrobin and trifloxystrobin, and the sterol inhibitor difenoconazole on spore germination, mycelial growth and fruit decay on detached fruits caused by A. alternata. Germination was most sensitive to polyoxin B and trifloxystrobin among the tested compounds. The 50% and 95% effective concentration (EC50, and EC95), values for in vitro inhibition of conidial germination of the fungus were lowest for polyoxin B and trifloxystrobin, ranging from <0.01 to 0.15 μg/ml and 180 μg/ml, respectively. Germination was least sensitive to difenoconazole and azoxystrobin (EC50 and EC95 values ranging from 25 to 72 μg/ml and 720 μg/ml, respectively). Mycelial growth in vitro of A. alternata was most sensitive to difenoconazole (EC50 and EC95 values of 0.8 and 12 μg/ml, respectively) and least sensitive to both strobilurin fungicides (EC95>1000 μg/ml). Decay formation by A. alternata on mature detached fruits was most affected by trifloxystrobin and azoxystrobin (EC50 and EC95 values of 0.015–0.087 μg/ml and 8 μg/ml, respectively), intermidiate in sensitivity to Polyoxin B (EC50 and EC95 from 1 to 33 μg/ml, respectively), and difenoconazole was the least effective (EC50 and EC95 from 20 to 490 μg/ml, respectively). Polyoxin B applied at 24 or 48 h post-inoculation inhibited fruit decay development. Difenoconazole and trifloxystrobin were less effective and azoxystrobin was ineffective when applied at 48 h post inoculation. The activity of azoxystrobin, difenoconazole, Polyoxin B and trifloxystrobin on one or more stages of the life cycle of A. alternata and on decay development in fruits suggests that these compounds potentially could provide control of moldy-core disease in apple.  相似文献   

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