نشریه مهار زیستی در گیاه پزشکی
سال یکم شماره 2 (پاییز و زمستان 1392)

Crown and root rot diseases of wheat caused mainly by Fusarium culmorum and F. pseudograminearum are important diseases of wheat world wide including Iran. In this study, 60 strains of pseudomonad fluorescent bacteria were obtained and isolated from wheat rhizosphere in Tehran, Ghazvin, Golestan, Ardebil, Zanjan, Markazi and Esfahan provinces and their efficacy in biological control of F. culmorum was investigated. According to biochemical, physiological and morphological characteristics of the bacteria, the strains were very similar to biovars І, ІІІ and V of Pseudomonas fluorescence and P. protegens. Antagonistic activities of pseudomonad fluorescent strains against F. culmorum were then evaluatedResults showed that 11 isolates along with CHA0 were the most effective strains. In order to determine competition and colonization abilities of the selected stains in the soil and wheat rhizosphere, the strains were tested on four wheat cultivars for three continuous growth cycles, each which was 42 days long. The results indicated that Niknejad cv. had the highest bacterial population density after three cycles, followed by Zagross cv. The over all results of this study showed that the bacterial strains 19 and 27 (both belonging to P. progegens) had a very good antagonistic ability and have the potential for biological control of F. culmorum.

Bacillus thuringiensis bacteria because of many advantages such as specific effect on pest insects larvae, no adverse effects on the environment and non-target organisms and also easy combination with other methods of pest control, has an important role in pest management programs. The first step as a basis for doing research on this bacteria is to study virulence of different isolates and strains of the pathogen in the control of the target pest. In this research, the virulence of three native isolates and a commercial product (Dipel®) was evaluated on the larvae of cotton bollworm, Helicoverpa armigera and diamondback moth, Plutella xylostella at 27oC, a relative humidity of 65% and 16L:8D photoperiod. Based on the calculated results, 50% lethal concentration (LC50) of three native isolates of KD2, 20, 6R and commercial product of Dipel on the 2nd larval instars of H. armigera were obtained as 1.21×107, 8.8×107, 1.39×107 and 6.91×107 spore ml-1, respectively and KD2 isolate was the best strain among others. Results of 50% lethal concentration (LC50) bioassay of three native isolates and commercial sample of Dipel on the 2nd larval instars of P. xylostella were calculated as 6.1×104, 3.4×103, 2. 9×105 and 8.8×104 spore ml-1, respectively and isolate of 20 was the best strain among others. The molecular analysis of the isolates revealed that isolates cry genes are not identical.

The antibacterial activities of aqueous, acetonous and methanol extracts of galls caused by Aphelonyx persica on Quercus persica were compared on some gram positive and gram negative plant pathogenic bacteria including: Xanthomonas translucens pv. cerealis (cause of bacterial leaf streak of wheat), Ralstonia solanacearum (cause of bacterial wilt of potato), Rathayibacter tritici (cause of wheat gum) and Clavibacter michiganensis subsp. michiganensis (cause of bacterial canker of tomato). Oak galls were collected in Zagros forests of Iran. Antibacterial properties of extracts at concentrations of 10, 50 and 100 mg/ml were studied as inhibition zone using two methods including agar well diffusion assay and disc diffusion assay. The results showed that gram-positive bacteria including Clavibacter michiganensis subsp. michiganensis and Rathayibacter tritici were more sensitive to the gall extracts compared with gram-negative bacteria such as Xanthomonas translucens pv. cerealis and Ralstonia solanacearum at different concentrations of all three solvents extract (aqueous, acetone and methanol).

Cotton thistles, Onopordum spp. (Asteraceae), are native plants belong to Mediterranean basin, southwest and central Asia. Their reproduction is entirely by seed and the plants are biennial. The biology of cotton thistles stem-boring weevil, Lixus cardui Olivier, was studied on Onopordum acanthium and O. leptolepis in fields and rangelands in Urmia. The results of this study showed that, the stem-boring weevil has a single generation per year and overwinters as adult whithin the dried stems of host plants. The adults emerge from the dead stems, in late April. After emerging, they start to feed on the leaf tissues of host plants and mate from time to time. Then females chew holes into the stem, and lay eggs either singly or in batches of up to 5 in a row the each hole. Females cover their eggs with plant fiber that had been chewed away to make the hole for protection. Each female laid a mean of 35±3.63 eggs during her life span. Eggs hatch 6-8 days after oviposition and the young larvae bore into the stem and feed on the tissue. The full grown larvae produce pupal cell in the stem and eventually pupate. After 9-13 days, pupa develops into a new generation of adults within the stems in summer. These adults remain inactive in the dried stems until the following spring. The total life cycle from egg to adult ranges from 37 to 48 days under natural conditions.

Gray mold caused by Botrytis cinerea is the most important disease of strawberry in the greenhouse and in the field worldwide. The disease is also a serious problem during storage, transit and marketing stages. Nowadays, fungicide application is the most common strategy to control this disease. Consequently, strawberries are among the crops which may be contaminated with pesticide residues. Public concern about such residues in edible products and the environment, augmented by the practical problems arising from fungicide resistance in pathogen, has accelerated the search for the safe and effective alternative disease control strategies. One of the alternative strategies for the replacement of chemical methods could be biological control. Trichoderma species are ubiquitous fungi in soil with antagonistic activity against several plant pathogens. This study aimed to evaluate potential of indigenous Trichoderma strains against B. cinerea in in vitro and in the greenhouse. In dual culture tests, the majority of Trichoderma strains overgrew on B. cinerea colony with a high sporulation. More than 66% of strains were considered to be antagonists against B. cinerea. Furthermore, most strains were more or less capable of lysing sclerotia of the pathogen. The volatile metabolites of all Trichoderma strains significantly reduced the mycelial growth of the pathogen but, the inhibition rate was not above 55%. Culture filtrates of all strains at two concentrations significantly prevented the mycelial growth with maximum rate of 71% and 85% for 1 and 6 ml concentrations, respectively. The results obtained in the greenhouse experiments showed that disease infection was decreased in all treatments comparing to contro. Meanwhile, lowest and highest disease incidence (53.5 and 70.7%) was recorded for T. harzianum MS6-2 and TRICHO-MIX HV, respectively.

Temperature-dependent development of the common green lacewing, Chrysoperla carnea was studied at four constant temperatures, 20, 25, 27 and 30ºC, 50 - 60% RH and a photoperiod of 16L: 8D h in growth chamber. Developmental rate of incubation period (egg), larval instars, pupal period and overall immature stages of the common green lacewing increased linearly in relation to temperature. Two mathematical models, including common and Ikemoto and Takai linear models, were used to describe temperature-dependent development of the common green lacewing. Based on the statistical criteria, whereas the common linear model had shown an acceptable fit to data, Ikemoto and Takai linear model estimated thermal indices more precisely than common linear model. Estimated values for thermal requirement for incubation period, 1st. 2nd, and 3rd larval instars, total larval period, pupal period and overall immature stages of the common green lacewing were 56.821, 52.719, 28.979, 33.199, 115.470, 120.432 and 290.986 degree-days, respectively, and the values of the lower temperature threshold for the mentioned above developmental stages were 10.848, 9.572, 13.307, 12.514, 11.487, 12.004 and 11.624°C, respectively, by using Ikemoto and Takaei linear model. Moreover, mathematical models for description of temperature-dependent development of the common green lacewing developmental stages were presented.

Pistachio psylla, Agonoscena pistaciae Burckharat & Lauterer (Hem.: Psyllidae), is the most important pest of pistachio orchards and reduce the quantity and quality of product. Several different insecticides have been used to control psylla. In the present study, for reduction of chemical insecticides using, the application of red pepper extract (Tondexir® EC85%), garlic extract (Sirinol® EC80%), cocunat botanical soap (Palizin® SL70%) and acetamipride (Mospilan®, SP 20%,) were tested in the fields of Kashmar region, during 2012. The botanical insecticides (2000 ppm concentration) and acetamipride insecticide (250 ppm) were sprayed over the whole canopy three times at 4–5-week intervals during May to July. The treatments were compared considering psylla population before and after treatment. Based on the field studies, red pepper extract application reduced more than acetamipride insecticide the psylla nymphs population in the first, second and third generations in pistachio trees. The rate of efficacy percentage for psylla nymph control, in 3 days after spraying were 86.7, 85.4, 77.3 and 78.2 and in 14 days after spraying were 69.4, 62.3, 59.3 and 49.3 for red pepper extract, acetamipride insecticide, garlic extract and cocunat soap treatments, respectively. Therefore, red pepper extract (Tondexir® Ec) spraying with 2000 ppm concentration, over the whole canopy of pistachio trees, were effective in decreasing pistachio psylla damage.

Among Anuras, Pelophylax (=Rana) ridibunda has great interest in living in farms and fields. This species can always be seen in the vast areas of rice fields, particularly in North of Iran. Therefore, they have always been important because of their close relationship with crops there is a debate as whether these animals can be used as biological pest control in the fields. So that, the type and method of their nutrition is specifically important from the perspective of agriculture and conservation of natural resources. This study is an attempt to investigate the diet of P. ridibundas around Caspian Sea and its effect on pest control in rice fields. For achieving this aim, 90 samples were collected from 14 stations in the North of Iran between 2009- 2012. After being hunted, they were anesthetized and got an injection of formalin in their stomachs. Then all the samples were transferred to laboratory, and after being coded, they were fixed. Their stomach contents were dissected and identified. The results indicated that the frequency of these animals is the only factor determining their nutrition kind. It is also indicated that females eat more plants and have a stronger tendency toward cannibalism. These characteristics of P. ridibunda leave no doubt that they are one of the natural pest controls that can regulate the frequency of pests in the fields.

Entomopathogenic nematodes are obligatory parasites of insects, which are used in many integrated pest management programs. Two genera Steinernema and Heterorhabditis belong to the order Rhabditida include the most important species of entomopathogenic nematodes. The effect of a native isolate of Steinernema feltiae (Filipjev, 1934)on different larval instars of tomato leafminer Tuta absoluta were investigated. The isolate of S. feltiae were collected from the soil of alfaalfa farm located in Firoozkouh city by using Galleria bait method. Obtained nematodes from Galleria baits, were reared on the last larval instars of G. mellonella to provide sufficient population of the studied entomopathogenic nematode. The infected tomato plants by T. absoluta were collected from the infected greenhouses of Varamin, and different larval instars of the mentioned pest were isolated. 10 different larval instars of tomato leafminer were placed individually in each petri dishe by five replicates were considerd for theme. The larvae in each petri dish were infected with 1000, 3rd instar larvae of the entomopathogenic nematode and kept up to 96 hours at laboratory temperature. In addition a check treatment was considered without entomopathogenic nematodes. Examining treated larvae by the evaluated nematode, that the S. feltiae was succeed to infect all the pest larvae cleared within 48 hours and causing their mortality. Infected larvae were inactive accumulation of the nematodes on the larval body, became visible after 72 hours. Third infectious larvae, and gradually the second generation of male and female nematodes appeared after 96 hours. This is the first report about the parasitism of the tomato leafminer by S. feltiae.

In order to determine the parasitoid insects (Hymenoptera) associating with cabbage fields, a sampling was perfomed at southern part of Tehran in 2011. Five species of parasitoid wasps belonging to three families including, Oomyzus sokolowskii (Kurdjumov, 1912) (Eulophidae), Pteromalus sp. (Pteromalidae), Cotesia plutellae (Kurdjumov, 1912) (Braconidae), Diadegma anurum (Thomson, 1877) and Syrphophilus bizonarius (Gravenhorst, 1829) (Ichenumonidae) were collected and identified. S. bizonarius (Ichneumonidae: Diplazontinae) representing a new genus and species record for the fauna of Iran.