فصلنامه گیاه پزشکی
سال چهل و سوم شماره 4 (زمستان 1399)

Fire blight, caused by Erwinia amylovora, is one of the important bacterial diseases of pome fruit trees. It causes the blight of different organs of the tree (blossoms, shoots, leaves, fruits, and limbs) and exudates' production. The main symptoms of fire blight infection are the burnt-like appearance of infected tissues, bacterial ooze released from the infected tissues, shepherd’s crook, wilting, and water-soaked appearance. Recently, it has been included in the top 10 plant pathogenic bacteria. This study aimed to collect, identify and characterize E. amylovora isolates from provinces of Semnan in Iran and determine their pathogenicity factor and the current situation of fire blight disease in this province.

In the present study, 68 strains isolated from pear, quince, and apple hosts were identified in Semnan Provinces. Phenotypic, nutritional, and biochemical tests were performed on strains. The molecular identification of isolates was conducted using specific primers A and B of the plasmid pEA29. A pathogenicity test of the bacterial isolates on the immature pear fruit of the Spadona pear cultivar was performed, and the most pathogenic bacterium isolate was selected for further evaluation. Pathogenicity test was carried out on immature fruits and blooms of eight pear cultivars. Pathogenicity characteristics such as amylovoran, biofilm, and siderophore were studied in most virulence isolates.

The isolates were gram and oxidase negative, catalase-positive, and anaerobic. The isolates were able to produce a hypersensitive response in tobacco and levan production, but none of them could produce fluorescent pigment on King B medium and growth at 39 °C. The results suggested that of 68 strains collected, 52 isolates belong to Erwinia amylovora bacteria. The virulent isolate (D 43) was collected from Dibaj city. All 52 isolates under study proliferated 1000 base pairs. These tests, along with sequencing of PCR products, proved they were Erwinia amylovora species. Studying pathogenicity factors showed an almost direct relationship between all pathogenicity factors (other than biofilm production) and the severity of disease symptoms on tissues. The most resistant blooms tissues to D 43 isolate were shown to be related to Dargazi and Spadona pear cultivars; Duchess and Chini Hesar pear cultivars had the most resistant immature fruits tissues to D 43. It is therefore concluded that the susceptibility tissues to isolates of Erwinia amylovora were different in various cultivars. This point could help control fire blight disease and programs of breeding cultivars in the future.

One of the most destructive diseases of pome fruit species which causes irreparable damage to gardening products worldwide is fire blight disease caused by Erwinia amylovora. In Iran, it was first observed in pear trees in Alborz province and then spread across fruit orchards in the country. One of the main problems in fire blight management is evaluating causal agent genotypic characteristics. Thus, the present research was conducted to characterize genotypic features of E. amylovora as the cause of fire blight disease in pome fruit species in Hamadan province, Iran.

In this study, the samples with symptoms of canker on shoots and blight blossoms were observed and collected from the orchards in Hamadan province located in the west of Iran. After isolation, the isolates were purified for further studies. Phenotypic, biochemical, and pathogenicity tests were performed due to standard bacterial criteria. Phenotypic and biochemical tests of strains were examined by Ntsys-pc 2.02 software. A total of 15 representative isolates were selected and analyzed due to the size of amplified DNA using primers Ea71 and genetic features of the rep-PCR test using primers ERIC and BOX. For more accuracy and higher reliability of the specific primers results, the 16S rDNA_ gene of two representative isolates was amplified and subjected to sequencing.

Based on the biochemical, pathogenicity and molecular tests, a total of 34 isolates were identified as E. amylovora. Due to the numerical analysis, the data obtained by phenotypic and biochemical tests were similar at 89% level. Therefore, the isolates obtained from a specific host or region was grouped very close to each other. In the PCR tests survey, the isolates amplified 187 base pair expected fragments. The results of determining sequences indicated that both isolates were similar to E. amylovora showing 97% identity to the type of strains in the NCBI database. Due to data from the rep-PCR analysis, the isolates were divided into three groups at the similarity level of 77%.

The results of genetic diversity using rep-PCR showed that there is no significant difference among E. amylovora bacterial isolates from different regions of Hamadan Province. Moreover, they showed high similarity to each other and placed close to each other. Our results confirm other studies regarding phenotypic characteristics of E. amylovora. Our results confirm that the isolates are homogenous in Hamadan province of Iran. To summary, these findings can be applied to breeding programs to better management of the bacterial disease.

Development, reproduction, and life table parameters of the parasitoid Eretmocerus delhiensis Mani (Hymenoptera: Aphelinidae)parasitizing sugarcane whitefly, Neomaskellia andropogonis Corbett (Hemiptera: Aleyrodidae)were studied at 20, 25, 30 and 32°C, 45±5% RH, and 12: 12 h (L: D). The developmental time of egg to adult stage, decreased from 24.2±0.46 days at 20°C to 10.7±0.33 days at 32°C. An average of 250 degree-days was required to complete development above the lower threshold temperature (11.25°C). Preimaginal survivorship was 77.76±0.41, 82.33±0.38, 74.99 ±0.37, and 59.45±1.07% at 20, 25, 30, and 32°C, respectively. The mean fecundity of E. delhiensis was 65.66±1.48, 82.80±3.24, 18.93±0.60, and 8.46±0.49 eggs at 20, 25, 30, and 32°C, respectively, and had a mean longevity of 23.80±0.55, 17.33±0.54, 6.66±0.28, and 4.43±0.22 days at the same four temperatures. The intrinsic rate of population increase (rm) ranged from 0.156±0.01 to 0.234±0.02, with the highest value recorded at 25°C. Our results revealed that 25°C is the optimum temperature for development and reproduction of E. delhiensis. These data can be used in supplementary studies to maximize the production of E. delhiensis from mass rearing facilities and to develop computer simulation models to predict E. delhiensis development plus population dynamics for release programs.

Chickpea is cultivated in the rotation with wheat and barley which plays an important role in the sustainable agriculture in the western provinces of Iran. The production of chickpea is strictly limited due to some devastating fungal diseases such as Aschochyta blight disease.

During 2017-2018, chickpea fields were monitored for the suspicious samples. Then, they were transferred to the laboratory. 100 samples were recovered from 20 local areas, and all isolates were categorized into 20 groups based on the geographical regions. From each group, one representative was selected for further studies. To investigate the pathogenicity and morphological diversity, three different chickpea varieties were selected for this study. This investigation was performed in the completely randomized block with three replications, and some resistant and production-related features were measured. To determine disease severity, a 0–9 rating scale was applied.

In this investigation, 100 isolates from 20 local areas were selected. Subsequently, one representative from each group was selected. Based on the analytical results, the isolates were different in the pathogenicity and morphological at one percent probability level. Analytical approaches showed that interaction between isolates and varieties were different at all measured features at one percent probability. Among the varieties, for features such as the weight of 100 seeds, the number of sheet in each plant, number of shoots in each plant, plant height, wet and dry weight of root and upper parts were different at five percent similarity level. The variety of ILC482 was the most proficient with an average of 35 grams in 100 seed weight. 100 seed weight and the number of pods were affected by the disease more than other parameters. The evaluation of disease showed the variation among pathogenicity and morphological traits among isolates. In surveying the morphological parameters of isolates on CSMDA media, considerable differences were observed in colony color, pycnidium shape, and pycnidiospore. The isolates were divided into three groups: highly aggressive, medium aggressive and least aggressive based on the pathogenicity results. The isolates IL8, IL9, and IL10 had the highest pathogenicity on all cultivars. The isolate IL10 had the highest effect on morphological characteristics.

Resistant variety is the best method of control Ascochyta blight due to the high price of fungicides and their harms to the environment. Unfortunately, resistance is not durable for a long time because of the fungal population's diversity. The interaction of differential chickpea varieties and fungal isolates showed different virulence (p < /em><0.01).It indicates that varieties are in different levels of resistance level. These variations are necessary for the identification and classification of virulence levels among the isolates. Differential varieties should contain different resistant genes. Analytical results showed that probable differences exist between varieties and isolates at one percent probability. Our results revealed that the functional features of chickpea are affected by Ascochyta blight.

Biology and life table parameters of the jasmine whitefly, Aleuroclava jasmini (Takahashi) were studied at five constant temperatures (20, 25, 27, 30 and 32 °C) under laboratory conditions. Egg-to-adult developmental time of female ranged from 53.22 at 20 °C to 26.70 days at 32 °C. Immature mortality decreased from 41.77 to 16.07 % with increasing temperature from 20 to 30 °C. The threshold temperatures of egg, first, second, third and fourth nymphal stage (prepupa+ pupa) and a generation were 14.87, 9.33, 10, 14.44, 10.50 and 13 °C whereas the degree-day requirement at each stage was 105.208, 143.688, 75.95, 37.523, 134.904 and 465.61 DD, respectively. The mean total fecundity of A. jasmine was 18.24, 22.19, 25.53, 38.28 and 29.93 eggs at 20, 25, 27, 30 and 32 °C, respectively. Also, the mean adult longevity was 12.41, 7.35, 3.40, 2.64 and 2.12 days at the same five temperatures. The intrinsic rate of increase was 0.042, 0.061, 0.089, 0.127 and 0.114 female/ female/ day at 20, 25, 27, 30 and 32 °C, respectively. Optimal temperature for development, survival, and reproduction, within the range examined, was 30 °C.

Canola Brassica napus L. (Brassicaceae) is a plant with oil-rich seeds; grown worldwide. The cabbage aphid, Brevicoryne brassicae L. is one of the most important pests of Canola crops. Considering the importance of human health and environmental protection, the reduction of using the chemical pesticides in the pest control program is essential. Therefore, the sub-lethal effect of Palizine® and Tandaxir® plant insecticides on the life table parameters of cabbage aphid was investigated using the aphid leaf immersion method Besides, the toxicity of insecticides was studied on the first nymphal instar of cabbage aphid.

First, preliminary experiments were conducted to determine the concentration range. After determining the highest and lowest concentrations, the middle concentration was selected. Six concentrations and one control were selected for each insecticide. After determining the concentration in the preliminary experiment, the leaf discs (5 cm in diameter) including aphids (first nymphal stage) were immersed in the different concentrations of insecticides for 5 seconds. The leaf discs to be treated were then dried, covered with an organza net, and placed under natural laboratory conditions for one hour. Distilled water and Tween 80 were used as control treatments. To investigate the sub-lethal effect of insecticides on aphids, the concentrations of 1843.99, and 1627.02 mg / L (LC30) were used for Tandaxir® and Palizin®, respectively. The experiments were performed at 25±5oC, 60%±5% RH and 16: 8 (L: D) photoperiod on canola seedlings, B. napus.

The levels of LC50, Tondaxir®, and Palizine® were estimated to be 2331.52 and 2190.60 mg / L, respectively. The intrinsic rate of increased population (r) were 0.27±0.003 for control, 0.21±0.008 for Palizin® and 0.2±0.007b for Tondexir®. Net fecundity rate of decreased population in both insecticide.Net reproduction rate and intrinsic reproduction rate decreased in both insecticide treatments compared to the control treatment. A relative increase in the intrinsic mortality rate of insecticide-treated aphids was observed. The mean production time and doubling time were also lower in the population treated with the insecticides than the control group. There was a significant decrease in the average number of nymphs produced per female aphid; compared to control group. The mean lifespan of adult females in control group was significantly different from the insecticide treatments. All LC30 aphid-treated table statistics were negatively affected compared to control group.

Conclusion  :                                               

Due to the results, these two insecticides are toxic to cabbage wax aphids even at low concentrations and suppress the population of this pest. The present study can be a step towards the practical use of plant compounds and as a suitable alternative to chemical insecticides. By conducting the additional experiments, these plant compounds can be used to control cabbage wax aphids in the field.

Low temperatures have significant effects on the biological aspects of stored-product pests; thus, those can be used as a control method. Due to the delayed effects of low temperatures, the lethal and sublethal effects of 4˚C temperature were investigated, alone and combined to the eucalyptus essential oil, on mortality and some reproductive aspects of Mediterranean flour moth, Ephestia kuehniella Zeller (Lep.: Pyralidae) for probable elimination of this limitation.

All experiments were carried out at the Entomological Research Lab., Department of Plant Protection, Gorgan University of Agricultural Sciences and Natural Resources. The insect reared on wheat flour under laboratory conditions (25 ± 2 °C, 70 ± 5% R.H., 16:8 L:D). Adult's mortality due to the continuous exposure to low temperature, the effects of adults exposure to low temperature on their longevity, fecundity and percentage egg hatch, and finally, the effects of low temperature combined to different concentrations of eucalyptus essential oil on mortality, daily oviposition and percentage egg hatch of survived adults were recorded, and synergistic or antagonistic effects were determined. The chemical composition of essential oil was analyzed using a Varian CP-3800 gas chromatograph equipped with a Varian Saturn 2200 ion trap mass spectrometer and Helium as the carrier gas.

Continuous exposure to low temperature prolonged the lifespan of adult insects (some of them lived more than 33 days). Estimated LT50 and LT95 values for male adults of the Mediterranean flour moth exposed to 4 °C were 14.87 and 45.17 days, respectively; for female adults were 10.77 and 39.38 days, respectively; and as total were 12.67 and 42.28 days, respectively. Adult exposure to low temperature decreased the longevity, fecundity and percentage of the egg hatch of survived ones. By increasing exposure interval and essential oil concentration, fecundity decreased at a higher rate but percentage egg hatch did not affect. The interactions between low temperature and different plant essential oil concentrations were antagonistic. Among 16 identified constituents in the eucalyptus essential oil, 1,8-cineol (Eucalyptol) was the major oil component (30.48%).

Long-time exposure of stored-products moths to 4˚C temperature reduces the activity and mobility of these pests which has negative effects on their reproductive aspects. Hence, it could be effective as a control method. Antagonistic effect between low temperature and plant essential oil indicates that before selecting two insecticide agents for using in the combination, it is necessary that their synergistic interaction would be confirmed by carrying out the appropriate experiments.