Effects of temperature on the latent period of the rose powdery mildew pathogen, Sphaerotheca pannosa

The effects of temperature on the length of the latent period of rose powdery mildew, caused by Sphaerotheca pannosa var . rosae , were studied. At constant temperatures over the range of 10–28°C, the length of the latent period ranged from 4 to 10 days. The relationship between temperature and the rate of fungal development during the latent period (expressed as the reciprocal of the latent period) was described by a nonlinear (thermodynamic) model. The resulting curve was asymmetrically bell-shaped with an optimum temperature of about 22°C. The latent period was further subdivided into two periods: incubation period (from inoculation to visible colonies) and postincubation period (from visible colonies to the first sign of conidiophores). The relationship between temperature and the rate of fungal development during the incubation period (expressed as the reciprocal of the incubation period) was also well described by a thermodynamic model. In contrast, the relationship between temperature and the rate of fungal development during the postincubation period (expressed as the reciprocal of the postincubation period) was approximately linear. The latent period under fluctuating temperatures was predicted using a two-stage integration scheme at a step of 24 min by first integrating the incubation rate and then the postincubation rate. The predicted length of the latent period agreed well with the observed values.     

Evaluation of different types of compost tea to control rose powdery mildew (Sphaerotheca pannosa var. rosae)

Powdery mildew (Sphaerotheca pannosa var. rosae) is an important foliar disease which is found in all rose-producing greenhouses. An experiment was carried out in a commercial greenhouse in Hashtgerd, Iran, in 2014 to investigate whether compost teas can be used to control this disease. Taguchi's design of experiment (Taguchi's DOE) method was used to plan a minimum number of experiments and optimization to control rose powdery mildew. The test included three factors, namely the different types of compost tea (aerated and non-aerated compost tea, aerated and non-aerated vermicompost tea), the dosage (1:8 and 1:16, compost:water), and the number of spray applications (once and twice per week). The experiment was set up as an orthogonal array L₈ with three replicates. Based on the experimental results, the optimum treatment combination for controlling rose powdery mildew was found to be aerated compost tea with 1:8 dilution with an application of twice per week.     

Effects of temperature on the incubation and latent periods of hawthorn powdery mildew (Podosphaera clandestina)

The effects of temperature on the length of the incubation and latent periods of hawthorn powdery mildew, caused by Podosphaera clandestina , were studied. At constant temperatures over the range 10–28°C, the incubation period ranged from 5 to 14 days and the latent period from 5 to 16 days; no visible colonies had developed at 30°C after 15 days. The relationships between temperature and the rates of fungus development within the incubation and latent periods were well described by a nonlinear model. The resulting curves were asymmetrically bell-shaped with an optimum temperature of approximately 23°C. The lengths of the incubation and latent periods under fluctuating temperatures were also determined, and were used to evaluate the models developed from constant temperature experiments for their accuracy of prediction. The incubation and latent periods under fluctuating temperature regimes were predicted using a rate-summation scheme with a time step of 24 min, by integrating the respective incubation and latent rate functions obtained under constant temperatures. The predicted incubation or latent periods agreed well with the observed values. Under constant temperature the interval between the times when symptoms and sporulation on the same leaflet were first observed was very short, on average <1 day, and was not significantly correlated with temperature. However, this interval was negatively correlated with mean temperature under fluctuating regimes.     

Effect of Film-forming Polymers on Infection of Barley with the Powdery Mildew Fungus, Blumeria graminis f. sp. hordei

The effects of three film-forming compounds, Ethokem, Bond and Vapor Gard, on infection of barley by the powdery mildew fungus Blumeria graminis f. sp. hordei were examined in glasshouse and field experiments. The three compounds provided significant control of powdery mildew infection when applied as pre- or post-inoculation treatments in the glasshouse. Such treatment had no effect on plant growth. Bond and Vapor Gard reduced the germination of conidia of B. graminis by 78% and 85% respectively, and reduced the subsequent formation of appressoria (73% and 85% respectively) and haustoria (75% and 79% respectively). The three compounds were less effective in field experiments, although they provided significant control of mildew infection and had no impact on plant growth and grain yield.     

Assessment of Partial Resistance to Powdery Mildew (Podosphaera pannosa) in a Tetraploid Rose Population Using a Spore-suspension Inoculation Method

Powdery mildew (Podosphaera pannosa) is the most important fungal disease in greenhouse roses and is in practice controlled by fungicides. The creation of novel cultivars with durable resistance to powdery mildew is highly desirable. To understand the inheritance of mildew resistance, a tetraploid rose population with a size of 181 seedlings was obtained by crossing two tetraploid genotypes each having partial resistance. The population and its parents were tested under greenhouse conditions with two well-defined monospore isolates (2 and F1) using artificial inoculation with spore suspensions. Disease score at 11 days post-inoculation, latent period and rate of symptom development were used to describe seedling resistance. The tests for both isolates exhibited a wide and significant variation among genotypes for resistance. The distribution of the genotypic means of the disease scores was continuous and showed a considerable transgression. Statistical analysis, scatter plot of disease scores for the isolates, and correlation analyses indicated that the two isolates differed in pathogenicity. The outcome of the tests showed that the inoculation assay with spore suspensions was a reliable and effective way to screen large numbers of genotypes under greenhouse conditions for genetic and breeding studies. This is the first report on spore-suspension inoculation to be used successfully in rose.     

Effects of Temperature and Wetness Duration on Infection of Oilseed Rape Leaves by Ascospores of Leptosphaeria maculans (Stem Canker)

In controlled environment experiments, ascospores of Leptosphaeria maculans (stem canker) infected oilseed rape (cv. Nickel) leaves and caused phoma leaf spots at temperatures from 8°C to 24°C and leaf wetness durations from 8 h to 72 h. The conditions that produced the greatest numbers of leaf spot lesions were a leaf wetness duration of 48 h at 20°C; numbers of lesions decreased with decreasing leaf wetness duration and increasing or decreasing temperature. At 20°C with 48 h of leaf wetness, it was estimated that one out of four spores infected leaves to cause a lesion whereas with 8 h of leaf wetness only one out of 300 spores caused a lesion. As temperature increased from 8°C to 20°C, the time from inoculation to the appearance of the first lesions (a measure of the incubation period) decreased from 15 to 5 days but leaf wetness duration affected the length of the incubation period only at sub-optimal temperatures. Analyses suggested that, within the optimal ranges, there was little effect of temperature or wetness duration on incubation period expressed as degree-days; the time until appearance of 50% of the lesions was ca. 145 degree-days. A linear regression of % leaves with lesions (P_l) (square-root transformed) on % plants with lesions (P_p) accounted for 93% of the variance: P_l=1.31+0.061P_p. This relationship was also investigated in winter oilseed rape field experiments in unsprayed plots from October to April in 1995/96 (cv. Envol), 1996/97 (cv. Envol), 1997/98 (cvs Bristol and Capitol) and 1998/99 (cvs Apex, Bristol and Capitol) seasons. The linear regression of % leaves with lesions (square-root transformed) on % plants with lesions accounted for 90% of the variance and had a similar slope to the controlled environment relationship: P_l=0.81+0.051P_p. These results were used to examine relationships between the development of phoma leaf spot on plants in winter oilseed rape crops, the incubation period of L. maculans and the occurrence of infection criteria (temperature, rainfall) in the autumns of 1996, 1997 and 1998.     

Monitoring physiological races of<Emphasis Type="Italic">Podosphaera xanthii</Emphasis> (syn.<Emphasis Type="Italic">Sphaerotheca fuliginea</Emphasis>), the causal agent of powdery mildew in cucurbits: Factors affecting race identification and the importance for research and commerce

Identification of the physiological races ofPodosphaera xanthii (syn.Sphaerotheca fuliginea), the causal agent of powdery mildew in cucurbits, is based upon the differing responses of various melon cultigens to the pathogen. Eight races of the pathogen have been identified to date in the USA, Africa, Europe and around the Mediterranean Sea, and four new races were reported from greenhouse melons in the major growing area of Japan. Plant responses to powdery mildew may be affected by environmental factors such as light intensity, temperature and humidity, as well as by age and nutritional status of the plants. The same factors affect the accuracy and reliability of race identification. In an attempt to overcome those obstacles, the genetic diversity ofP. xanthii was studied using molecular markers. Unfortunately, no correlation was found between DNA polymorphism and the race of the pathogen as identified by biological tests. The usefulness of race identification as a guide for the grower in selecting appropriate cultivars is limited because changes or shifts in the pathogen population are common. Such changes may be found among growing seasons, geographic regions and hosts, and also within a single greenhouse during a single season. On the other hand, race identification is important for basic research and is especially important for the commercial seed industry, which requires accuracy in declaring the type and level of resistance to powdery mildew in its products. http://www.phytoparasitica.org posting March 2, 2004. Contribution from the Agricultural Research Organization. No. 501/04.     

Effects of adjuvants on the performance of a novel powdery mildew fungicide, 1-(4-chlorobenzyl)-4-phenylpiperidine

The effects of adjuvants on the performance of a dispersible concentrate formulation (DCI) of a novel powdery mildew fungicide, 1-(4-chlorobenzyl)-4-phenylpiperidine (I) were investigated. The method involved assessment, under glasshouse conditions, of the therapeutic (curative) control of infections of powdery mildew (Erysiphe graminis DC f.sp. hordei Marchal) on barley (Hordeum vulgare, L.) eight to nine days after spray application to plants that had been inoculated one day prior to spraying. The results from the first trial showed that marked improvements (∽five-fold) in the performance of DCI could be obtained by the spray tank addition of some types of surfactant adjuvants and a series of further trials investigating a wide range of adjuvants was conducted. Nonylphenol, alkylamine and alcohol ethoxylates varying in mean ethylene oxide content between 5 and 20 moles were highly effective. There were indications that optimum performance enhancements were obtained with these surfactants containing between 5 and 10 moles ethylene oxide. Lower enhancements, sometimes only marginal, were obtained from trisiloxane, phosphate ester, propylene oxide, alkylamine-propylene oxide and castor oil ethoxylates and also alkyl polyglucoside biosurfactants. Negligible adjuvant enhancements were observed with emulsifiable paraffinic/naphthenic and rape seed oils, though slightly better enhancements were seen with an emulsifiable transmethylated rape seed oil and, interestingly, larger enhancements with an emulsifiable lipophilic alcohol. A final trial identified the alcohol ethoxylate, ‘Dobanol’ 91-6, as the most effective adjuvant and that its optimum application rate under glasshouse conditions was 250 g ha^-1. This information will be used to guide the design of field trials. © 1997 SCI     

温度和湿度对B型烟粉虱发育、存活和生殖的影响

研究了采自北京市的B型烟粉虱种群在不同温、湿度条件下的生长、发育和繁殖力参数.结果表明,相对湿度是影响卵、1龄若虫、3龄若虫和成虫发育的主要因素,30%～70%RH是烟粉虱发育的适宜范围.在25℃组合90%、70%、50%和30%RH环境下的种群内禀增长率(rm)分别为0.0499、0.0596、0.064和0.0856.若虫的发育历期随温度的升高而缩短,20～30℃是烟粉虱发育的适宜范围.在1 5℃下从卵发育到成虫需要69.0天,但30℃下则减少到27.7天.当温度上升到35℃时,只有少数个体能发育到3龄.不同龄期对温度的要求有较大的区别,2龄若虫的发育起点温度最低(6.16℃),而卵期所需的有效积温最高(110.22日度).在80%RH配合30、25、20和15℃条件下的内禀增长率(rm)分别为0.0729、0.0673、0.0895和0.0486.     

盐分、温度对猪毛菜种子萌发的影响

通过对浆果猪毛菜和钠猪毛菜种子在不同盐分、温度环境下的萌发过程与对策研究,结果表明:2种猪毛菜种子萌发的最佳温度约为25 ℃.浆果猪毛菜在蒸馏水中的萌发速度低于钠猪毛菜.浓度低于0.2 mol/L的NaC1溶液对萌发的影响不大;随NaCl浓度增高,浆果猪毛菜和钠猪毛菜种子萌发率降低.一定的盐分胁迫不影响种子萌发潜力,其萌发恢复率随原处理溶液抑制程度的增加而增加.同时,讨论了2种猪毛菜种子萌发特性与环境的关系.     

温度对绿豆象种群增长的影响

在实验室条件下以绿豆为食料饲养绿豆象,在20、25、30和35℃等4个温度条件下,逐日观察记录绿豆象产卵量、卵孵化数和成虫羽化数等生物学参数。结果表明,随着温度的升高,绿豆象卵期、豆内期、未成熟期、雄虫历期及雌虫历期逐渐缩短,温度从20℃升至35℃时,卵历期从18.33d缩短为4.40d,豆内期从36.43d缩短为15.20d,未成熟期从54.76d缩短至19.60d,雄虫历期从43.93d缩短至8.07d,雌虫历期从25.33d缩短至8.07d。在20℃下,绿豆象卵、豆内期及未成熟期存活率均最低,且与其他3个温度差异显著。在20℃下,绿豆象产卵历期最长,为20.67d,但总产卵量及雌性比例均较其他3个温度低,分别为43.33粒和33.27%。绿豆象卵、豆内期、未成熟期及整个世代的发育起点温度分别为14.69、11.11、12.03和13.73℃,有效积温分别为82.63、342.87、427.94和565.59日·度。在35℃时,绿豆象内禀增长率和周限增长率均最大,分别为0.044 58和1.045 58。研究结果表明,在30~35℃条件下,最有利于种群增长,为绿豆象发育的最适宜温度。