فصلنامه گیاه پزشکی
سال چهل و دوم شماره 3 (پاییز 1398)

Background and Objectives The Botryosphaeriaceae (Botryosphaeriales, Ascomycetes) is a family of fungi that have a cosmopolitan distribution and occur on a wide range of woody plants. A field survey was conducted on trunk diseases of hazelnut (Corylus avellana L.) trees in Babol (Mazandaran province) during spring and summer of 2016. Symptoms typical of infection by the Botryosphaeriaceae species such as canker and wedge-shaped wood necrosis have been recorded in some trees. Therefore, the objectives of this study were to identify and pathogenicity of the Botryosphaeriaceaeisolates associated with wood necrosis of hazelnut trees in this region of Iran. Materials and Methods Wood samples were collected from branches of trees showing canker and wood necrosis symptoms. Fungal isolation was made from the margin between healthy and necrotic wood tissues. Wood pieces were cut from the affected tissues, surface-disinfected for 1 min in a 0.5 % sodium hypochlorite solution, and washed twice with sterile distilled water. Wood segments were plated on potato dextrose agar (PDA), and incubated at 25 °C in the dark. Single spore cultures were derived from all isolate prior to morphological and molecular identification. Fungal isolates were identified based on morphology, culture characteristics and sequence analysis of the translation elongation factor 1-alpha (tef-1α) region. Pathogenicity test was conducted for representative isolates on detached shoots of hazelnut under greenhouse conditions. Results In this study 31 isolates resembling of the Botryosphaeriaceae in colony and culture (fast growing, greyish to dark cultures) were obtained. According to morphological characters, as well as phylogenetic analyses of tef-1α gene, all isolated were identified as Botryosphaeria dothidea. Selected isolates used in pathogenicity test caused wood discoloration on inoculated branches after 45 days. Our results showed a variation in wood lesion lengths and re-isolation frequencies of inoculated isolates. Discussion This study represents the first attempt to identify and test the pathogenicity of Botryosphaeriaceae associated with canker disease of hazelnut trees in Iran. Some species of Botryosphaeriaceae had previously been found in declining hazelnut trees. However, this is the first report of occurrence and pathogenicity of B. dothidea on hazelnut in the world.

Background and Objectives The two-spotted spider mite Tetranychus urticae Koch(Acari: Tetranychidae) is one of the key pests that can damage a wide range of crops. Materials and Methods In this study, sublethal effects of thiamethoxam (Actara®) in three concentrations including LC5, LC10 and LC20 on biological parameters of two-spotted spider mite was assessed at 25±2 ºC, 60±5 % RH, and a photoperiod of 16:8 (L:D) hr. The life table, reproductive and population growth parameters of T. urticae were also studied. The raw data were analyzed based on two-sex life table analysis. Results Based on the results, sublethal concentrations of thiamethoxam significantly reduced the mean fecundity and lifespan from 61.1 eggs/individual and 23.71 days, respectively in control treatment to 45.89 eggs/individual and 20.89 day in LC20 treatment. The intrinsic and finite rate of increase (r, λ) was not affected by the increase of concentration. The net reproductive rate (R0) reached its lowest level (36.71 offspring/individual) in LC20 treatment. Discussion The results of this study showed that the sublethal concentrations of thiamethoxam affected some biological parameters of T. urticae. The results of this research can be used to design management plans for two-spotted spider mite.

Background and objectives Understanding the functional response of a predator to its prey and its parameters including attack rate and handling time, are one of the basic methods in applied biological control for evaluation of the efficiency of a predator. Nephus arcuatus is one of the most important biological control agents of Nipaecoccus viridis. Material and Methods In this study, a laboratory study has been conducted to evaluate the stage-specific functional response of larval stages and adult females and males of N. arcuatus to varying densities of N. viridis 2nd instar nymph. Experimental conditions were based on optimal temperature for N. arcuatus activities, 30±1ºC, 65±5% RH, and 14L:10D photoperiod. Results and Discussion The shape of functional response curve and the functional response parameters were determined respectively by logistic regression and nonlinear least square regression. The 1st instar, 2nd instar larvae, adult males as well as adult females exhibited a type II functional response. Attack rate (a) and handling time (Th) were estimated to be 0.1139 h-1 and 11.4117 h for the 1st instar, 0.3237 h-1 and 4.7013 h for 2nd instar larvae, 0.2233h-1 and 1.4711 h for adult males, and 0.2836h-1 and 1.0198 h for adult females, respectively. In contrast, the 3rd instar and 4th instar larvae of N. arcuatus exhibited a type III functional response. Constant b and handling time were estimated to be 0.0195 and 1.7396 h for the 3rd instar, and 0.00774 and 0.4912 h for 4th instar larvae, respectively. Our results indicated that estimated attack rates did not change significantly between different stages of N. arcuatus with similar functional response curve. In contrast, the handling times of N. arcuatus to its prey increased as the larval age of this predator increased, also females had longer handling time than adult males. Based on the maximum predation rate (T/Th), the 4th instar larva was the most voracious stage (48.56 prey/d) followed by the adult female (23.53 pey/d) and male (16.32 egg/d) N. arcuatus. These findings suggest that the voracity of all stages of N. arcuatus toward N. viridis hold good promises for a use of especially simultaneously 4th instar larvae, and adult males and females of N. arcuatus in a biological control program against N. viridis in orchards and on ornamental plants.

Background and Objectives Aphids are one of the major pests in ornamental plants may cause damage to plants directly by sucking their sap, and indirectly by injecting toxic salivary secretions, transmitting pathogens, attracting ants and favoring the development of sooty-mold. Crapemyrtle aphid, Tinocallis kahawaluokalani Kirkaldy, currently is considered the most serious pest of ornamental woody plant, Lagerstroemia spp. and produce large amounts of honeydew while feeding. T. kahawaluokalani causes premature drop of leaves, decline of summer flowering and reduces the commercial market. The multicolored Asian ladybird, Harmonia axyridis Pallas, is capable of eliminating T. kahawaluokalani populations on crape myrtle plants. There is no data about the predatory behavior of H. axyridis on T. kahawaluokalani. So, functional response of third and fourth larval instars, and females and males of H. axyridis to T. kahawaluokalani was studied in the laboratory condition. Materials and Methods Adults of H. axyridis and nymphs of T. kahawaluokalani were collected from Crapemyrtle plants in Mazandaran province (North of Iran). They were reared together on the Crapemyrtle leaves in the laboratory conditions (25± 2 °C, 60%± 10% RH and a photoperiod of 16:8 h L: D) h. Prey densities were 5, 10, 20, 30, 60, 80 and 120 aphids for third and fourth larval instars, and adult females and males. The number of prey consumed by each stage of the predator was recorded at each density after 24 hours. The type of the functional response was determined by logistic regression analysis (SAS/STAT, CATMOD pro cedure) of the proportion of prey killed (Ne) in relation to initial prey density (N0). The handling times and attack coefficients were estimated using Holling’s disk equation. Statistical analysis of the functional response was performed using the SAS software. Results In all the predator stages, according to the logistic regressions results, linear parameter, P1 was negative that shows a type II functional response. The response curve rises in a negatively accelerating manner to a plateau and the proportion of preys consumed by a predator decreases exponentially as the prey density increases. In highest densities, mean number of consumed aphids by third, fourth, and male and female adults were determined 50.5, 69.2, 75 and 83.9 aphids, respectively. Based on Rogers’s random equation, the lowest (0.0560 h-1) and the highest (0.1370 h-1) attack rates were obtained for third larval instar and adult female, respectively. Handling time was shortest (0.1821 h) in third larval instar and longest (0.2870 h) in female adult. Discussion Based on positive predatory characteristics including voracity and high searching efficiency of females, H. axyridis has high predation capacity and can be important in suppressing the T. kahawaluokalani populations.

Background and Objectives Bacterial leaf blight of rice, caused by Xanthomonas oryzae pv. Oryzae, is a destructive bacterial disease of rice in growing regions of this plant worldwide. Although the application of chemicals significantly reduces plant diseases, planting resistant cultivars remains the most effective strategy to control crop diseases. This study aims to evaluate the resistance of four rice cultivars Hashemi, Lenjan, Firuzan and Gilane to bacterial blight, under growth chamber conditions. Materials and Methods The population growth and symptom development were monitored after introduction of bacterial suspensions (107 cfu ml–1) into leaf intercellular spaces. In this investigation, the effects of Xanthomonas oryzae pv. oryzae stress on the activity of superoxide dismutase, catalase and peroxidase in different rice leaves were evaluated. Antioxidant assays were performed with leaf samples collected on 4th day after infection (4th DAI), 8th DAI and 12th DAI. Results After infiltration of different cultivars with the bacterium, the highest populations were detected in Hashemi cultivar, followed by Gilane and Firuzan cultivars 14 and 16 days after infiltration. At 12th DAI, the higher peroxidase activity was observed in Lenjan cultivar. At 12th DAI, the activity of superoxide dismutase was increased 33.3, 23.5, 15.5 and 33.3 percent, respectively, in Lenjan, Gilane, Hashemi and Firuzan cultivars compared to the control. Discussion The present study showed that based on the population dynamics of Xanthomonas oryzae pv. oryzae in different rice leaves, pathogenicity (percentage of necrotic area per leaf) and antioxidant activity, Hashemi was the most susceptible cultivar and Lenjan was the most resistant cultivar to bacterial blight.

Background and Objectives Phenacoccus solenopsis (Tinsley) (Hemiptera: Pseudococcidae) is an invasive polyphagous and rapid spread pest attacking cotton, vegetables, ornamentals and other plants. Plant essential oils may be a secure alternative approach than synthetic pesticides for P. solenopsis control because of their effectiveness and versatility. This study was directed to assess the biological effects of essential oils of 14 plants species including peppermint, poleigamander, rosemary, catmint, wild mint, sweet basil, spearmint, moldavian balm, marzeh khuzestani, oregano, myrtle, river redgum, weeping bottle-brush and ribbed cachrys against P. solenopsis under laboratory conditions. Materials and Methods Plants were collected from different areas. Their essential oils were extracted via steam distillation using a Clevenger apparatus. P. solenopsis adult females were fed on potato Solanum tuberosum (L.) buds. The toxicity of essential oils for first instar nymphs and adults of P. solenopsis were assayed by the leaf-dip method. Bioassay tests were conducted under laboratory conditions in petri dishes. Leaves of Chinese hibiscus of approximately the same size were dipped in desired concentrations for 15s and air-dried for 30 min. Control leaves were dipped only in Methanol (70%). Control and treated leaves were placed on a layer of agar in the petri dishes, then ten P. solenopsis first instar nymphs and ten adults were released at the center of leaf discs in the petri dishes. For each treatment, we applied four different concentrations in three replicates. After 48 h, mortality percentages of nymphs and adults were recorded. Repellency experiments were carried out with two treatments; the leaf discs were cut to two equal parts. Half of the leaf was dipped in desired concentrations and the other half was dipped only in Methanol. The dried treated leaf discs were laid on a layer of agar in the center of petri dishes and twenty adults were released in the petri dishes. Each treatment was repeated three times. Mortality was evaluated after 24 h. For persistency experiments, leaf discs of Chinese hibiscus of approximately the same size were dipped in desired concentrations and after drying the treated leaf discs were placed on a layer of agar in the petri dishes. Three days later, ten P. solenopsis first instar nymphs and ten adults were released at the center of leaf discs in the petri dishes. Mortality was evaluated after 24 h. The same experiment continued for 5, 7 and 9 days later. Results The most efficacious essential oils against first instar nymphs came from Mentha longifolia, Mentha piperita, Mentha spicata, and Nepeta cataria, with LC50s of 113.49, 129.74, 163.04 and 193.05 ppm, respectively.  Essential oils from Mentha longifolia, Mentha piperita, Prangos ferulacea, and Satureja khuzistanica, with LC50s of 370.12, 400.58, 413.87 and 430.81 ppm, respectively, were the most efficacious against adult mealybugs. The essential oil of M. longifolia showed the highest persistence and repellency on P. solenopsis. Discussion The results clearly indicated that essential oils possessed many useful properties to control insect pests. Also, the essential oil of Mentha longifolia might be used as either a safe compound or a model in construction of new synthetic compounds against P. solenopsis.