فصلنامه گیاه پزشکی
سال چهل و سوم شماره 2 (تابستان 1399)

Citrus, as a critical horticultural product, has a special place in our country's economy. Meanwhile, scale insects such as Planococcus citri and Pulvinaria aurantii are the most important pests of citrus in northern Iran and cause economic damage. To prevent the damage of these pests, various insecticides are recommended. Due to a waxy layer on their bodies, it is difficult to control them chemically. Excessive use of pesticides and repeated spraying can have adverse effects on non-target organisms. In the present study, the effect of three compounds was conducted on some biological and reproductive characteristics of a coccinellid predator, Cryptolaemus montrouzieri. Also, these compounds were grouped according to the criteria of the International Organization for Biological Control (IOBC).

The effect of three compounds at field recommended concentration and half dosage of them in 9 treatments, including: 1, 2: mineral oils, EC, at two concentrations of 5 ml/L and 10 ml/L, 3, 4: mineral oils mayonnaise, at two concentrations of 5 ml/L and 10 ml/L, 5, 6: insecticidal soap palizin 1.25 and 2.5 ml/L, 7, 8: buprofezin 0.25 and 0.5 ml/L and 9: water (control) were investigated on C. montrouzieri. Treatments were done on eggs via dipping method and on the fourth instar larvae and adults via direct spray on mealybug-infested citrus seedling after releasing the ladybeetle.

Mayonnaise oil (10 ml/L) caused a 43.4% reduction on egg hatching compared with that of control. Buprofezin treatment (0.5 ml/L) with 36.6, 35.5 and 40% mortalities on fourth instar larvae, male and female adult respectively, was significantly different compared to the control. In the treated females with buprofezin 0.5 ml/L, mean of longevity and fecundity were 30.9 days and 26.1 eggs compared to the control 87.8 days and 114 eggs, respectively. According to IOBC standard method, mayonnaise (5 ml/L) as harmless (E=24.6, class 1), buprofezin as moderately harmful (E=84.1, class 3), and other compounds as slightly harmful (class 2) were classified. Used compounds at half doses had a low adverse effect on tested parameters compared with field recommended concentration.

Many researchers emphasize the harmlessness of oils to pests' natural enemies. Also, the safety of palizin on them has been reported by some researchers. The use of buprofezin in the larval stage reduced the percentage of adult exit from the pupa, and in the maturing stage, reduced the number of ladybeetle eggs compared to other compounds, so its toxicity is observed to this predator. On the other hand, the effectiveness of mineral oils and palizin in reducing the population of citrus scales has been positively evaluated by researchers. Therefore, these compounds can be used as alternatives to chemical pesticides in the integrated management of citrus pest programs. Also, the mentioned compounds had a less adverse effect on the ladybeetle at the half dosage of the recommended concentrations, which can be used in combination with the ladybeetle to pest control.

The Fungus causing Ascochyta blight is one of the most important biological factors limiting chickpea cultivation and production in most parts of the world, including Iran.

The present study was conducted to evaluating genetic sources of resistance of 20 chickpea genotypes in three seedling, Flowering, and podding stages in greenhouse conditions at University of Mohaghegh Ardabili. Disease damage was recorded using a 9-degree scale after observing complete death in the sensitive control genotype. Analysis of variance of the studied traits of chickpea genotypes was conducted via factorial experiment in a completely randomized design at two levels for factor A (disease-free and disease-contaminated conditions) and 18 levels (genotypes) for factor B (Given that the 13 and 15 genotypes were lost due to high susceptibility to disease in the first stage of growth, Samples were taken from 18 genotypes). Kolmogorov-Smirnov test used to evaluate the normality of data distribution.

The results showed that the resistant and susceptible genotypes were more accurately distinguished from each other in the podding stage. At this stage, 9 genotypes with a degree of damage 1, 2, and 3 (less than five) showed high resistance to the causative agent of Ascochyta blight. Physiological and biochemical traits involved in disease resistance were measured. The results showed that all traits except chlorophyll a, chlorophyll b and polyphenol oxidase had significant differences at 1% probability level in terms of disease stress. Chlorophyll a, chlorophyll b and polyphenol oxidase traits were significantly different at 5% probability level. Genotypes were significantly different in terms of chlorophyll a and total chlorophyll traits. In interaction of disease × genotype, only catalase was significantly different among all studied traits. The amounts of peroxidase and polyphenol oxidase have been affected by the disease and their rates increased. The highest coefficient of variation for Content soluble protein was 74.1 and the lowest for soluble sugar was 16.5. Significant interaction of genotype in stress showed that the trend of genotypes for traits under normal and stress conditions was not the same and superior genotypes under normal conditions were not necessarily recommended for disease stress conditions.

A positive relationship between polyphenol oxidase level and pathogen resistance was observed in the plants. The amount of damage that stress inflicts on crops leads to further efforts to understand the effects of disease on different plant mechanisms and requires understanding of appropriate adaptive responses to this environmental factor.

The incidence of pests’ resistance to pesticides, adverse effects of pesticides on non-target species, and environmental hazards have increased the tendency of applying various pests control techniques. Nanopesticide formulations are thus considered as one of the recent techniques in controlling pests. Using this technology increases the effectiveness of pesticides under various environmental conditions, including light and hot situations. Indeed, it decreases the amount of pesticide use and ultimately decreases the chance of pests’ resistance to insecticides.

In the current study, the silica nanoparticles were prepared using the sol-gel method and loaded with deltamethrin, pyriproxyfen, and chlorpyrifos. The mosaic and galvanized steel surfaces were treated with either deltamethrin (0.0025 and 0.005 g(a.i.)/m2), pyriproxyfen (0.001, 0.01 and 0.1 g(a.i.)/m2) and chlorpyrifos (0.01 and 0.2 g(a.i.)/m2) alone or loaded in nanosilica. The experiments were carried out at 3 replicates, and 3 sub replicates. In each replicate, 10 small or large larvae of Trogoderma granarium Everts (Coleoptera: Dermestidae) were introduced, and 2 g wheat Chamran variety was utilized as food source. All experiments were conducted at 30±1 °C, 65±5 % RH, and darkness. The initial mortality of small and large larvae of T. granarium was counted 1, 3, and 7 days after exposure, and delayed mortality was assessed 7 days thereafter. For each larval group, the variance analysis of initial and delayed mortality was subjected to the factorial test (concentration and time as main effects). Means were separated by Tukey Kramer HSD test at p < /em> =0.05 using SPSS software version 16.

Results indicated that initial and delayed mortality increased by raising concentration levels and exposing time to each concentration in all experiments. In all cases, the small larvae of T. granarium were more sensitive than large larvae.  Deltamethrin, followed by chlorpyrifos, was the most toxic to the larvae of T. granarium. Due to our findings, the mortality was dramatically higher in galvanized steel than the mosaic one. It could be attributed to the steel's flat surface, reducing insecticide residues' absorbance within the surface. Moreover, the insecticidal efficacy of nanosilica loaded with insecticides was significantly greater than the application of insecticides without nanosilica. Utilizing nanoparticles, we found an increase in the ratio of surface area to volume of insecticides, resulting in more insect contact to insecticide particles and eventually improved the mortality rate of insecticide.

It is therefore concluded that the application of loaded insecticides in silica nanoparticles significantly increased T. granarium larvae's mortality rate. Furthermore, silica nanoparticles can be introduced as the carrier of insecticides to control T. granarium in the stored wheat efficiently. Besides, deltamethrin loaded SNPs is potentially recommended as one capable component that can be effectively conducted during pest management programs in terms of stored products pest control.

Citrus yellow vein clearing virus (CYVCV), a new member of the genus Mandarivirus (family Alfafelxiviridae), has been recently reported from Iran after being recognized in Pakistan, India, Turkey and China. Typical symptoms of infection on the leaves of sour orange, lemon and Persian lime, as local sensitive hosts, consist of yellowing lateral veins with corresponding water-soaked appearance on the lower surface of the leaves. Biological and molecular detection, some modes of transmission and phylogenetic analysis of CYVCV isolates of Mazandaran province have been investigated in the present study.

Typical induced symptoms by CYVCV infection; namely yellowing and water soaking of the lateral veins, was considered as the initial criterion for diagnosis of the disease within seedlings and trees of sour orange, lemon and Persian lime cultivars in nurseries and orchards in Mazandaran province.  Three isolates, out of 53 samples, were selected for more analysis from the region collected during the spring of 2016, 2017, and 2018. Inoculation of these isolates into bean plants, sour oranges and lemons were performed using mechanical and grafting methods under greenhouse conditions with controlled temperatures. In order to confirm the infection, total RNA of the collected samples and the inoculated plants were extracted by the SDS-Potassium acetate method. A two-step Reverse Transcription Polymerase chain reaction (RT-PCR) was carried out using a specific primer pair of the virus coat protein (CP) gene.

Characteristic symptoms of the disease were expressed after top-work grafting of the susceptible virus-free orchard cultivars on the trunks of diseased trees. Using specific primer pair in RT-PCR, an expected 614 bp fragment was amplified in symptomatic samples. The consensus sequences, obtained from direct sequencing the PCR products of the studied isolates based on forward and reverse specific primes, were similar to the sequences of other CYVCV isolates of China, India, Pakistan and Turkey at the level of 95.75 to 98.37%. A phylogenetic tree of this part of the genome, grouped Iranian isolates with two isolates from India and Turkey and two Pakistani isolates.

The present study confirmed the presence of Citrus yellow vein clearing virus in the north of the country. Lemon and Persian lime are the two most important susceptible hosts of the virus. These citrus varieties are also valuable cultivars in the south of the country and are considered tolerant genotypes to Witches' broom disease, which is prevalent in these areas. Preventing the spread of the yellow vein clearingdisease to the new infection foci by continuous monitoring of the citrus nurseries should be seriously considered.

Silicon is the most common soil element which has beneficial effects to enhance the tolerance to biotic and abiotic stresses in plants. The addition of silicon to plant nutrient solution decreases sodium concentration, increases plant growth, has positive effects on plant reproduction, and increases mechanical resistance.  Also, silicon affects absorption and translocation of several macro- as well as micronutrient elements and imposes the formation of precipitates under cuticle reduces plant transpiration, and causes resistance to stresses such as side effects of excessive phosphorus and heavy metals (high concentration of manganese and aluminum) or salinity. Furthermore, silicon salts can significantly reduce the diseases in broad bean by reducing the percentage of root colonization and plant death, as well as decreasing root rot compared to controls. Silicon salts such as sodium and potassium silicate cause significant reduction in growth, asexual organ reproduction, and dry weight of hyphae, and prevent cysts' germination in some plant pathogens such as Phytophthora species. The application of silicon salts before and after inoculation of sterilized soil with Phytophthora pistaciae significantly reduces the disease by reducing the percentage of colonized roots and the broad bean's mortality. In this study, in vivo activities of sodium and potassium silicate in controlling Rhizoctonia solani were evaluated.

Studying the effect of sodium silicate (0.5 mM) and potassium silicate (2 mM) to increase the resistance of broad bean against R. solani a factorial experiment in a completely randomized design with salt treatments before and after inoculation was conducted. The level of catalase, peroxidase, polyphenol oxidase, proline, total protein, and carbohydrates in plants, as well as pH and the electrical conductivity of soil were examined.

The results showed that silicon salts might enhance broad bean resistance to R. solani by increasing the level of catalase, peroxidase, polyphenol oxidase, and total protein and decreasing proline. None of the salts had any effects on the level of the plants' carbohydrate content and pH, and the electrical conductivity of soil. As a result, controlling the pathogen is not directly affected by soil pH.

Due to the results, it can be concluded that the role of silicon salts in promoting broad been tolerance could be due to increasing the activities of the antioxidant enzymes which in turn reduced the oxidative damages of reactive oxygen species produced under disease stress.

Detergents and soaps can be used as co-adjuvants (in the tank) for conventional or biological pesticides. Detergents and soaps can also be applied first to debilitate pest insects and mites, and later along with spraying insecticides and miticides. In both cases, a rate reduction occurs for conventional and more expensive and restricted products. The spirotetramat as an insecticide is used to control the sucking insect pests. Surfactants are used for increasing the insecticide's effect. Water pH is one of the most important factors influencing efficiency of insecticides against the common pistachio psyllid, Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Aphalaridae), as the most important pest found in Iran's pistachio orchards. Therefore, this study was conducted to investigate the effect of Jonobegan spraying soap, pH-reducing Citral soap ,and Thymol soap on the spirotetramat's efficiency in pistachio orchards and its effects on the parasitoid wasp, Psyllaephagus pistaciae (Hymenoptera: Encyrtidae).

In this study, the effect of insecticides including spirotetramat (Monvento® SC 100), Jonobegan spraying soap, and spirotetramat mixture (Jonobegan, Thymol® soap, and pH-reducing Citral® soap) was investigated on reduction of population density of nymphs of the common pistachio psyllid under field conditions. Experiment was carried out as randomized complete block design with four replications and six treatments. Sampling was done one day before and 3, 7, 14, and 21 days after application of the treatments. Efficiency percentage of treatments on A. pistaciae was calculated by Henderson-Tilton formula. Means were compared by Tukey's test at P = 0.5%.

The results showed a highly significant difference between the treatments including Jonobegan spraying soap, spirotetramat, spirotetramat + Thymolsoap, spirotetramat + Jonobegan spraying soap, and spirotetramat + pH-reducing Citral soap against A. pistaciae. According to the international organization for biological control (IOBC) indices, all the treatments were harmless for parasitoid wasp, p < /em>. pistaciae.

Two days after application of the treatments, a significant difference was observed in the spirotetramat plus additives of Thymol soap, and pH-reducing Citral soap compared to spirotetramat alone. Because, the spirotetramat has a delaying effect, on 7, 14, and 21 days after application of the treatments, there was no significant difference between spirotetramat and spirotetramat plus additives in terms of reducing population density of the nymphs of A. pistaciae. The results showed that additives of Jonobegan spraying soap , Thymol soap ,and pH-reducing pH Citral soap could not increase the effect of spirotetramat significantly on 7, 14 ,and 21 days after application of the treatments. On 7 and 14 days after the intervention, the effect of spirotetramat in combination with pH-reducing Citral soap was significantly more than spirotetramat combined with Thymol soap and Jonobegan spraying soap. Also, it should be mentioned that all the treatments were harmless for parasitoid wasp, p < /em>. pistaciae.