JOURNAL OF CROP PROTECTION
Year:2013 | Volume:2 | Issue:4|Papers Count:13

Cotton bollworm, Helicoverpa armigera (Hubner) is one of the most destructive insect pests on many crops in the world that has been found to develop resistance against conventional insecticides. Using insecticides with different modes of action may result in appropriate control of the pest and delay insecticide resistance development. In this study, lethal and sublethal effects of emamectin benzoate and cypermethrin insecticides were investigated on third instar larvae of H. armigera by residue contact methods at 26±1oC, 70±5% RH and a photoperiod of 16:8h (L: D) under laboratory conditions. LC50 values, on larval stage of the pest, of emamectin benzoate and cypermethrin were 1.75 and 127.74 mg a.i./ml, respectively. According to the findings, the larvae that were exposed to the LC30 of emamectin benzoate and cypermethrin exhibited lower pupal weight and increased larval and pupal developmental times compared with control. The longevity and fecundity of adults were significantly affected by the insecticides. Emamectin benzoate and cypermethrin reduced fecundity by 53.1% and 50.5%, respectively compared to control. The LC30 values of emamectin benzoate and cypermethrin reduced egg hatching by 62.06% and 37.9%, respectively. It is predicted that these insecticides, especially emamectin benzoate, may induce significant lethal and sublethal effects on population parameters of H. armigera.

Citrus tristeza virus (CTV) is among the most destructive pathogens of citrus and causes substantial economic losses to citrus industry worldwide. Considering recent distribution of this pathogen and its capability of transmission by existing aphid vectors in Iran, detection of this virus should be mandatory for controlling the damage caused by this pathogen in Iran, as one of the major citrus producing countries. Toward this aim, developing a reliable and sensitive detection method such as enzyme- linked immunosorbant assay (ELISA) would be the first step to detect CTV in large scale screenings of field samples. As the serological method requires great amounts of specific antibody, consequently preparation of a large scale antigen source for immunization process would be necessary. In this study the coat protein gene of CTV (CP25) was amplified by polymerase chain reaction from a cloned CP25 gene in pTZ57R/T and subcloned in pET26b expression vector and named pET-CP25. Two Escherichia coli strains of BL21 and Rosetta Gami (DE3) were transformed by pET-CP25. Expression of recombinant protein was induced by IPTG. The authenticity of recombinant protein was confirmed by western immunoblot analysis using a polyclonal antiserum against CTV particles. The results indicated that CTV coat protein gene was expressed in E. coli. This recombinant protein could be used as a source of antigen for immunization process.

To evaluate the effects of presence of insect pollinators on quantity and quality of seeds of two common cultivars of onion (Allium cepa L.), namely Red Azar Shahr and Yellow Sweet Spanish, an experiment in a factorial randomized complete block design was carried out at two sites. Bulbs of equal size were planted with plant to plant 35 cm and row to row 50 cm spacing. At each site, experimental groups differed only in pollination method. About a week before flowering start, at each site 3 groups of 10 individual inflorescences as block replications of each treatment combination (pollination × cultivar) were selected randomly and marked. For each onion cultivar, half of the plants were left uncovered (free pollination), whereas the other ones were isolated from insect pollinators by using wooden cages covered with cloth net. When about 10 percent of black seeds were visibly exposed in the umbels, harvest was done. After drying, the number and weight of seeds produced per inflorescence as well as 1000 seed weight was measured for each treatment combination. Four weeks after the harvesting date the germination test of seeds produced in each treatment combination was evaluated. Non availability of insect pollinators during the flowering period of onion caused substantial reduction on seed number and seed weight per umbel. Also, seeds from free pollination flowers showed higher germination capacity than those obtained in the absence of insect visitors. However, varieties as well as experimental sites did not show significant influences on seed setting of onion.

The potato tuber moth (PTM), Phthorimaea operculella (Zeller) is one of the important pests of potato in tropical regions. In this research, the toxicity of two insecticides, abamectin and deltamethrin on P. operculella was studied at 26±1 oC, 65±5% RH and photoperiod of 16:8 h (L: D). The concentrations were determined by preliminary dose setting experiments. Distilled water was used as control. LC50 values for egg, first instar larvae and adult stage for abamectin were 0.92, 0.014 and 0.46 mg ai/l and for deltamethrin were 0.09, 0.024 and 0.29 mg ai/l, respectively. The sublethal effects of abamectin and deltamethrin on population growth parameters of P. operculella were determined at mentioned conditions. Four hundred 1 day old eggs of the pest were dipped in insecticides solutions (LC30). After egg hatching, the first instar larvae were transferred on potato tubers and placed in transparent plastic dishes. After adults' emergence, 20 females were used for each treatment in life table experiments. Intrinsic rates of increase were estimated to be 0.060, 0.042 and 0.141 day-1 In control, abamectin and deltamethrin treatments, respectively. Statistical analyses showed that deltamethrin caused higher toxicity to egg and adult stages of PTM while abamectin caused higher toxicity to its first instar larvae. Since deltamethrin increased the stable population parameters of P. operculella specially its intrinsic rate of increase, thus it might not be recommended for control of PTM. However based on lethal and sublethal effects, abamectin could be suitable for management of this pest.

The effect of host diet on developmental time, fecundity and life table parameters of Bracon hebetor (Say) (Hymenoptera: Braconidae), parasitoid of the Mediterranean flour moth Ephestia kuehniella (Zeller) was studied in the laboratory condition at 26±1 °C, 65±5% relative humidity and a photoperiod of 16L: 8D h. The diets used were rice, barley, corn and wheat flours. The developmental time (egg to adult) of the first and second generations of the parasitoid ranged from 9.00 to 14.00 days on barley flour and wheat flour. The survival of immature stages in 1st and 2nd generations ranged from 27 to 63%. The sex ratio of wasp progeny (females/total) ranged from 36.72 to 57.83% on wheat flour and rice flour. In the first and second generations, the fecundity of B. hebetor reared on barley and rice flours was greatest. Life table parameters varied significantly with host diets. In 2nd generation, larvae of B. hebetor that were reared on rice flour showed the highest net reproduction rate (R0= 106.13) and the highest intrinsic rate of increase (rm= 0.269). Based on the life table analyses, rice flour was found to be the best diet for rearing the parasitoid. The results of this study can be used to improve mass-rearing programs of B. hebetor.

The cypress family, Cupressaceae, has a global dispersion. Currently, endophytic microorganisms from plants are being investigated for their diversity and bioactivities. Here, we aimed at exploration and characterization of cultivable endophytic fungi from foliar tissues of Cupressaceae, i.e. Cupressus arizonica, C. sempervirens var. cereiformis, C. sempervirens var. fastigiata, Juniperus excelsa, Juniperus sp. and Thuja orientalis. Asymptomatic fresh foliar tissues, collected from mature healthy plants, were sterilized and the inner layers were plated on culture media at 26-28oC for 2-12 weeks, until fungal colonies emerged and were purified. Endophytic Penicillia i.e. Penicillium aurantiogriseum, P. chrysogenum, P. commune, P. echinulatum, P. expansum and P. viridicatum were the dominant fungi recovered. Results indicated that both host plant and geographical location of sampling affected the biodiversity and bioactivity of endophytic Penicillia. Results also indicated that those endophytic Penicillia had significant bioactivities. According to our results, both intra-and extra-cellular secondary metabolites from all isolated Penicillia had significant cytotoxic and antifungal effects against the model fungus Pyricularia oryzae and cypress fungal phytopathogens Diplodia seriata, Phaeobotryon cupressi and Spencermartinsia viticola. Further studies indicated the significant antimicrobial bioactivities of superior Penicillia against model bacteria. Altogether, this study highlights, for the first time, the biodiversity of endophytic Penicillia from Cupressaceae plants and documents their significance for agrochemical/drug discovery and for plant disease biocontrol.

Application of Trichoderma species is a harmless method of controlling soil borne plant diseases thus reducing hazardous pesticide use and environmental pollution. Some Trichoderma isolates with good inhibitory effect against Fusarium oxysporum f. sp. tuberosi under laboratory and green house conditions were tested against wilt disease of potato caused by this pathogen under field condition in Shahrood Agricultural Research Center, Iran, during 2009-2010. Results of two years of field study indicated that T. virens (T7) followed by T. asperellum (T2) were superior to others in reducing the disease. In comparison to control plots, yield was higher in all plots treated with Trichoderma, but significantly higher yields were obtained from plots in which T. virens (T7) and T. asperellum (T2) were involved. It may be concluded that isolates of T. virens and T. asperellum have the required efficacy as biocontrol agents against Fusarium wilt disease of potato and can be used as formulated biofungicides for reducing this disease.

Ozone is a powerful oxidant capable of killing insects and microorganisms and has been used in the food processing industry in the gaseous and aqueous states. In a laboratory study, the susceptibility of immature stages of an important stored-product pest, the Indian meal moth, Plodia interpunctella Hubner to ozonated water was investigated. Ozone was applied in aqueous form at four concentrations (0, 2, 3 and 5 ppm) for four different periods (30, 60, 90 and 120 min) on eggs, larvae and pupae of, P. interpunctella. The results indicated that in all tested stages, the rate of mortality increased as concentration and exposure time increased. This study showed that 5-day old larvae were more susceptible than other stages (12-, 17-day old larvae, pupae and eggs) when exposed to 5 ppm ozone for 120 min. Following 5-day old larvae, 12-day old larvae, 17-day old larvae and pupae had the highest sensitivity to ozonation. At the highest concentration of ozone for the longest time, the lowest mortality was recorded for one day old eggs. According to these preliminary results, ozonated water has potential of reducing population density of P. interpunctella, one of the most important pests of dried fruits such as date, almond and pistachio in storage.

The present checklist is a compilation of the eupodoid mites of Iran using published records and original data from recent researches. It contains 19 species belonging to 13 genera and five families. Family Cocceupodidae Jesionowska, 2010 (because of moving the genera to a new family) and two species i.e. Foveacheles (Foveacheles) cegetensis Zacharda, 1983 and Linopodes antennaepes Banks, 1894 are new records for Iranian mite fauna. In addition to some corrections to specific identities which have been previously reported in Iranian literature, we report here the known geographical distribution and habitats in Iran and distribution in the world as well.

Mulberry pyralid, Glyphodes pyloalis Walker is an important pest on mulberry. The essential oil of Rosemary Rosemarinus officinalis L. (Lamiales: Lamiaceae) has been investigated on toxicity and physiological characteristics of this moth under controlled conditions. The major compounds of the oil were analyzed as 1, 8-Cineol (20.021%), Borneol (7.17%), Camphor (6.541%), Geraniol (6.281%), Camphene (5.623%), Linalool (4.993%) a-fenchyl acetate (4.222%) and Verbenone (4.147%). Sublethal and lethal concentrations (LC10, LC30 and LC50) were estimated at 0.77%, 1.18% and 1.59% (v/v) respectively. The essential oil affected the nutritional indices of fourth instar larvae of G. pyloalis, such that efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD), relative consumption rate (RCR) and relative growth rate (RGR) were reduced in the treated larvae while approximate digestibility (AD) was significantly increased compared with the control. The essential oil affected the insect's some key metabolic compounds such as; lipid, protein and carbohydrates. Similarly this effect was also significant in the activities of certain key enzymes like; a-amylase, lipase, protease, glutathione-s-transferase and esterases.

Fusarium graminearum is one of the most important causes of FHB or wheat scab in different part of the world. This fungus is able to produce diffrent Trichothecene mycotoxins such as Nivalenol (NIV) and Deoxynivalenol (DON) which are harmful for both human and animals. To determine chemotypes of Trichothecene, a total of 100 isolates from different fields of Golestan province in Iran including Gorgan, Kordkuy, Bandaregaz, Gonbad, Minodasht, Kalaleh and Azadshahr were identified as F. graminearum using morphological features. The identity of 96 isolates was confirmed by polymerase chain reaction (PCR) assay using F. graminearum species-specific primers (Fg16F/Fg16R). Based on sequences of Tri13 gene involved in the mycotoxin biosynthetic pathway, PCR assays were used to detect Nivalenol (NIV) and Deoxynivalenol (DON) chemotypes. Of the 96 tested isolates in Tri13 PCR assays, 70 classified as NIV chemotype and the remaining 26 isolates as DON producers. These results indicated that NIV chemotype was the most dominant chemotype in studied region. A greater proportion of NIV chemotype was found in Gorgan fields (P<0.05, P<0.0001), whereas greater proportion of DON was detected in Gonbad fields (P<0.05, P<0.0001). PCR assay-based chemotyping was confirmed by HPLC method. These results demonstrated that PCR assay and HPLC could be used as rapid, reliable and cost-effective methods for the detection and identification of mycotoxin-producing Fusarium-species and may thus help to develop strategies to avoid or reduce mycotoxin contamination of cereals.

Rice blast, caused by Pyricularia grisea, is one of the most important diseases of this crop in Iran and all over the world. To evaluate the relationship between spore population (SP) and meteorological factors, SP was measured daily using spore trap during growing seasons of 2006-2008 in Rasht and Lahijan regions (Guilan province, Iran). Weather data including precipitation, daily maximum and minimum temperatures, daily maximum and minimum relative humidity and duration of sunny hours were obtained from weather stations which were five kilometers away from the fields. The relationship between spore population and metrological factors was evaluated by Neurosolution 5.0 software. Weather data and spore population were considered as input and output data, respectively. In this study, multilayer perceptron neural network, regression model and Log (x+1) transformation were performed. To evaluate the model efficiency, correlation coefficient and mean square error were used. The results showed that the correlation coefficient (r) and mean square error (MSE) parameters were 0.55 and 0.03 in Rasht and 0.1 and 0.03 in Lahijan, respectively. The results also showed the potential of this model for modeling SP using meteorological factors; however more data is needed for validation of this model. There has been no previous report on modeling the relationship between SP and meteorological data using artificial neural network in Guilan province (Iran).