فصلنامه گیاه پزشکی
سال چهل و پنجم شماره 3 (پاییز 1401)

Citrus yellow vein clearing virus (CYVCV), is the causal agent of a significant and devastating disease that has spread in Iran and a number of countries in the region in recent years. In order to identify susceptible and tolerant cultivars for disease management, the reaction of a number of commercial citrus cultivars from the groups of orange, mandarin, grapefruit, citron, tangelo, pomelo, kumquat, lime and lemons was investigated after inoculation in the greenhouse conditions. The relative susceptibility of the cultivars was then determined according to the severity of the symptoms.

The buds of 19 commercial citrus cultivars of the country including Thomson navel orange, Valencia sweet orange, Moro blood orange, Siavaraz local orange, Clementine mandarin, Ponkan mandarin, Page mandarin, Satsuma mandarin, Sour orange, Sweet lime, Eureka lemon, Persian lime, Mexican lime, Flame grapefruit, Redblush grapefruit, Mineola tangelo, Etrog citron, Pummelo and Kumquat were propagated on sour orange rootstocks and the plants were simultaneously graft inoculated with a CYVCV isolate (Gene Bank number: KX902488). In order to confirm the infection, the total RNA of the symptomatic plants was extracted by 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. The reaction of the inoculated plants was monitored under greenhouse conditions with controlled temperature.

14 cultivars susceptible to citrus yellow vein clearing were detected based on the appearance of four types of symptoms in the inoculated plants including yellowing of the lateral veins on the upper surface of young leaves (symptoms type A), corresponding water soaked areas under the young leaves (symptoms type B), wrinkling of the old leaves (symptoms type C) and leaf spots on the old leaves (symptoms type D). These cultivars were classified into three groups with high, medium and low susceptibility according to the symptom severity. No symptoms were found in tolerant cultivars of Sweet lime, Mexican lime, Page mandarin and two grapefruit cultivars up to one year after inoculation. Descriptive grouping of frequency, severity and stability of symptoms was consistent with cluster analysis based on Euclidean Ward distance coefficient.

The management of citrus yellow vein clearing disease is based on preventive methods and the cultivation of resistant or tolerant cultivars instead of susceptible varieties. The results of the present study showed that Citrus yellow vein clearing virus has a wide host range and can infect different citrus species or groups. Sour orange, Eureka Lemon and Persian lime are the most susceptible hosts of the virus. Monitoring of four typical symptoms of the disease is recommended for disease management in citrus nurseries and orchards.

Iran’s Khuzestan province ranks first in wheat production. Root-lesion nematodes (RLN) are a group of plant parasitic nematodes that includes several closely related species of economically significant cereals. There have been eight species of RLN recorded for small grains. Four species (P. thornei, P. crenatus, P. neglectus and P. penetrans) are found worldwide, particularly in temperate zones. P. neglectus, P. thornei, P. pseudopratensis and P. penetrans prevalent in Iranian wheat fields. However, there is insufficient information regarding the status of RLN in the province of Khuzestan’s cereal fields. The objective of this study was to determine the occurrence, distribution and population density of RLN in wheat and barley fields in Khuzestan province.

A survey was conducted over three years (2008-2011), where 169 wheat and 31 barley fields were inspected and sampled in 21 regions during the grain filling and harvesting periods in the Khuzestan province of Iran. A stereomicroscope was used to examine the root tissue of 10 wheat and barley plant samples for disease symptoms. The Whitehead tray method was employed to process 250 cm3 of soil from each collected soil sample. The RLN species were identified using morphological and morphometric characteristics. ArcGIS 9.3 software was utilized to map the distribution of RLN on the map of Khuzestan.

Results indicated that 37% of wheat fields in the regions of Ahvaz, Andika, Andimeshk, Baghmalek, Behbahan, Dasht-e Azadegan, Dezful, Gotvand, Hoveyzeh, Izeh, Lali, Omidiyeh, Ramshir, Ramhormoz, Shadegan, Shushtar, and Shush were infested with P. thornei and P. neglectus, with mean population densities of 39 and 101 nematodes per gram of root and 250 cm3 of soil, respectively. In addition, 42% of barley fields in Andika, Baghmalek, Izeh, Lali, Omidiyeh, and Ramhormoz were infested with the nematode, with mean population densities of 9 and 72 nematodes per gram of root and 250 cm3 of soil, respectively. The regions with the highest and lowest nematode populations were Shush, Shusthar, Baghmalek, and Hendijan, with densities of 1,334, 904, 11, and 100 per 250 cm3 of soil, respectively. Ten percent of the surviving fields exhibited nematode populations exceeding 1-2 per gram of soil, which is extremely likely to cause cereal crop damage.

Pratylenchus thornei, P. neglectus, and a mix of the two species were observed in 62, 18, and 20% of the surveyed fields in Khuzestan, respectively. In both wheat and barley fields, P. thornei was the dominant species. Globally, P. thornei is deemed more dangerous than P. neglectus. This is the first report of the presence of root lesion nematodes in wheat and barley fields in Khuzestan province, with contamination rates of 37 and 42%, respectively. Disease incidence was higher in irrigated fields than in rain-fed fields, indicating that soil moisture and nutrients positively influence the nematode population. The nematode population density was higher in wheat fields than in barley fields, confirming that barley is a poor host for RLN. The economic damage thresholds for P. thornei and P. neglectus on wheat have been reported to be 1-2 nematodes per gram of soil in various parts of the world. The most important management practice is the use of resistant and tolerant wheat varieties to RLN.

Trialeurodes vaporarium (Westwood) is a polyphagous pest that causes economic damage to the quantity and quality of many crops around the world. In recent years, using plant compounds as low-risk insecticides to replace chemical pesticides has increased significantly. This research aimed to investigate the chemical composition of methanolic extracts of Mentha longifolia L. and Thymus pubescens Boiss. and their insecticidal and repellent effects on greenhouse whiteflies in a completely randomized design in laboratory conditions.

A contact toxicity test was performed using the two methanolic extracts, each in three concentrations (1000, 1500, and 2000 ppm) and after three durations (24, 48, and 72 hours). Filter papers impregnated with different concentrations of plant extracts were used to determine the percentage of repellency. Each filter paper was cut into equal halves, and one half was impregnated separately with concentrations of 1000, 1500, and 2000 ppm. The other half was impregnated with only methanol solvent as a control. The two paper halves were then glued together and placed in Petri dishes (with a diameter of 8 cm). In each petri dish, 20 adult whitefly (T. vaporarium) insects were placed in the middle of the filter paper, and the total number of insects on each half of the filter paper was checked after 24, 48, and 72 hours.

 The results showed a significant difference in the percentage of toxicity at different concentrations after each studied duration. Based on the contact toxicity tests, the mortality rate increased with increasing the concentration and duration of exposure to the extracts. The LC50 levels of oregano and thyme extracts were 11148 and 13980 mg/L, respectively. According to the results, the mortality rate increased with increasing concentration and time. The highest mortality rate was observed in M. longiflora extract with a concentration of 2000 ppm after 72 hours (96.25 %), and the lowest mortality in T. pubescens extract with a concentration of 1000 ppm after 24 hours (17.5 %). The repellent effect increased with the higher concentration of extracts. The repellency test showed that M. longiflora extract had a significantly high repellent power. The highest and lowest repellency effects were observed in M. longiflora extract (90 %) and T. pubescens extract (23.12 %), respectively. The chemical compounds of the methanolic extracts were identified using a GC-MS, and their diagrams were drawn. The analysis of chemical compounds found that most of the identified compounds of the two plant extracts studied were terpenoid compounds, monoterpenes, and Cesciue terpenes, and thymol (38-42 %) was the highest composition of the extracts.

The results of the present study indicated that these extracts have favorable insecticidal and repellent properties against T. vaporarium, and their use in controlling this pest is recommended.

In many parts of the world, medicinal plants have been used as an alternative medicine to promote human health and longevity since ancient times. Microbes residing within plant tissues are known as endophytes. The compounds produced by these microbes have the potential to be employed in modern medicine, agriculture, and other industries. Endophytic bacteria isolated from medicinal plants are valuable sources of novel bioactive compounds with diverse activities, including antimicrobial, anticancer, and antiviral properties. This study aimed to isolate, identify, and screen endophyte bacteria with antimicrobial activity against plant pathogenic bacteria. Aromatic plants such as Satureja khuzestanica are utilized in traditional medicine due to their secondary metabolites, but data regarding its naturally occurring bacterial endophytes is limited.

In the current study, 17 strains of bacterial endophytes were isolated in a Tryptic Soy Agar medium from the medicinal plant Satureja khuzestanica. Based on sequencing the 16S rRNA encoding gene, researchers isolated bacterial strains from the Bacillus, Streptomyces, and Pseudomonas genera with the highest activity against plant pathogenic bacteria. Under standard conditions, these endophytic bacteria’s bioactive secondary metabolites were extracted with ethyl acetate and analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). The mass spectra of the compounds were compared to the National Institute of Standards and Technology (NIST) library’s database. Moreover, microbroth dilution techniques were used to determine the minimum inhibitory concentration (MIC) values for five different bacteria species.

The GC-MS analysis revealed the presence of a number of compounds, including dibutyl phthalate (DBP), eicosane, octadecanoic acid, hexadecanoic acid, and hexadecane 1,4- dicyclohexylbutane. Four of the selected bacterial endophytes exhibited antimicrobial activity against three plant pathogens: Ralstonia solanacearum, Pectobacterium carotovorum subsp., carotovorum, and Clavibacter insidiosus. Data analysis revealed significant differences in antimicrobial activity, with the minimum inhibitor concentration ranging from 0.312 mg/ml to 2. 5 mg/ml. Furthermore, we identified bioactive secondary metabolites with reported biological activities in antimicrobial, anti-inflammatory, and antioxidant properties with biotechnological applications in medicine, agriculture, and other industries based on an endophytic crude extract data analysis.

Our findings shed new light on the antimicrobial properties of naturally occurring bacterial endophytes in S. khuzestanica.

The widespread Mediterranean flour moth, Ephestia kuehniella (Zeller), causes economic damage by feeding on stored products, particularly cereal flour. Pyriproxyfen is one of the most significant insect growth regulators widely used in controlling stored-product insect pests due to its low toxicity to mammals and lack of dangerous residues in food. By imitating the action of juvenile hormone, pyriproxyfen causes insect pests to experience prolonged larval development, failure to emerge as pupae or malformed pupae, absence of embryo development, and in some cases, a reduction in fecundity.
This study examined the toxicity of pyriproxyfen on E. kuehniella fifth instar larvae at 25 ± 1°C, 65 ± 5% relative humidity, and a photoperiod of 16:8 (L:D) h. The 50% lethal concentration (LC50) of the insecticide was calculated as 7.39 and 5.68 ppm at 72 and 96 h post-treatment, respectively. After preparing the desired concentrations based on the preliminary test using acetone solvent, the effect of sublethal concentrations (LC20 = 2.87, LC30 = 4.10, and LC40 = 5.56 ppm) of pyriproxyfen on mortality and survival period of fifth instar larvae was investigated.
The results of this study demonstrated that the survival period of larvae treated with LC20 (35.05 days) was significantly longer than the control group (18.85 days). One week after exposure to sublethal concentrations of pyriproxyfen, the larvae's survival rate was significantly lower than the control group. However, the survival percentage of larvae at two- and three-weeks post-treatment was not significantly different from the control.
One of the possible explanations for the shorter survival period of larvae treated with LC30 and LC40 is the greater toxicity of these concentrations against the pest and, consequently, the increase in the percentage of larval mortality in the second- and third-weeks following treatment. This study found that sublethal concentrations of pyriproxyfen could be used to control the Mediterranean flour moth under storage conditions.

Tomato (Solanum lycopersicum L.) belongs to the Solanaceae family and is economically one of the most important vegetable crops in Iran after the potato, cultivated all year but threatened by a large number of plant pathogens. One of the most significant diseases affecting this plant is tomato early blight, caused by various species of Alternaria. To date, chemical fungicides have been the only effective method of controlling this disease. Given the damaging effects of chemical pesticides on human and environmental health, as well as food safety, this study aimed to compare the inhibitory effects of savory, garlic, thyme, fennel, and rosemary essential oils on tomato early blight disease to that of a fungicide, Mancozeb+Metalaxy, under laboratory and greenhouse conditions.

Plant essential oils were extracted using a Clevenger apparatus and, after dehydration, utilized at 50, 150, and 250 μL/L concentrations by mixing with cultural media in Petri dishes. The growth inhibitory effect of plant essential oils was assessed by measuring the fungal colony’s growth diameter and calculating the amount of Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC) associated with each essential oil. Moreover, the effect of plant essential oils on tomato early blight control was evaluated at a 750 μL/L concentration by spraying tomato plants with 3 to 5 leaves under greenhouse conditions. A chemical mixture containing Mancozeb and Metalaxyl was used as a positive control to compare its antifungal effects versus plant essential oils.

Statistical analysis using Duncan’s multiple-range test revealed a significant difference in all treatments at the 5 percent level. A. alternata growth diameter measurements showed that the lowest colony growth diameter was associated with 250 μL/L of savory essential oil with 100% inhibition. At a concentration of 50 μL/L, rosemary essential oil inhibited fungus growth by 6.35%, resulting in the highest average growth diameter. Accordingly, among the studied essential oils, savory exhibited the strongest inhibitory effect, while rosemary yielded the weakest. However, MFC determination revealed that garlic essential oil demonstrated the highest fungicidal properties and the lowest amount of MFC (700 μL/L). On the other hand, fennel essential oil yielded the highest amount of MFC (2000 μL/L). In general, all essential oils were able to deteriorate and disrupt the structure and morphology of A. alternata mycelium, leading to sedimentation and granulation of cytoplasmic contents and its organelles. This fungus showed the least and most sporulation in the savory and rosemary treatments, respectively, compared to the control. In greenhouse studies, unlike laboratory tests, the highest control rate of tomato early blight was related to the application of a fungicide with an average leaf surface contamination of 1.6%, which demonstrated the highest control rate in greenhouse conditions compared to other essential oil treatments. Compared to the infected control, savory essential oil and rosemary essential oil, with disease severity of 16.66% and 35.0%, respectively, had the greatest effect on the appearance of symptoms following fungicide application.

Numerous plant compounds have been studied for their antifungal and antibacterial properties thus far. Using the antifungal effect of plant essential oils is undoubtedly one of the newest techniques for controlling plant pathogens. The current study compares plant essential oils to a chemical fungicide for controlling tomato early blight in vitro and under greenhouse conditions and demonstrates that plant essential oils are more effective than chemical fungicides. Consistent with this finding, previous research has demonstrated the potential of plant essential oils to control early blight in tomatoes.

Trichogramma wasp is one of the most successful parasitic species in the world, mainly used to control many pests. The effects of field (RC) and half recommended concentrations (half RC) of four insecticides: 1. Tetraniliprole, 2. Chlorantraniliprole 3. Lufenuron, and 4. Thiocyclam was studied in different preimaginal stages of 1. Trichogramma brassicae Bezdenko and 2. Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). Parasitized eggs of the angoumois grain moth Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae) were treated by 1. The dipping method at the larval, 2. Prepupal, and 3. Pupal stages of the parasitoid. For persistence evaluation, the insecticides were applied at the recommended concentration on tomato plants in a pot by a hand sprayer till the Runoff point. Plants were maintained under a transparent polyethylene rain cover in the field. Leaves of the treated tomato plants were sampled and transferred to the laboratory at time intervals of 3, 5, 16, and 31 days after application. In this experiment were adults (< 24 hours old) of T. brassicae and T. evanescens. Based on our results, thiocyclam at both RC and half RC was the most harmful insecticide for immature stages of both parasitoids. This insecticide at the prepupal stage (at both RC and half RC) had more adverse effects than in pupal or larval stages. Tetraniliprole, with 23.33% and 21.11% mortality in less than five days, was classified as the short-lived insecticide for T. brassicae and T. evanescens, respectively. The same result was obtained in the chlorantraniliprole treatment. That caused 25% and 26.11% mortality to the parasitoids, T. brassicae, and T. evanescens. Lufenuron, with 30.55% and 30.00% mortality in less than five days, was short-lived. However, thiocyclam, with 14.44% and 16.67% mortality in less than 30 days and 65.55% and 69.44% mortality in less than five days, was classified as moderately persistent for those two species. Therefore, according to the results, 1. tetraniliprole, 2. chlorantraniliprole, and 3. lufenuron can control lepidopteran pests by observing the appropriate spraying distance to release Trichogramma wasps. Thiocyclam, on the other hand, should be employed with extreme caution.

Adult insects of many parasitoids use carbohydrates to supply their energy. A high-carbohydrate diet increases the efficiency and other biological properties of parasitoids. Bracon hebetor Say (Hym: Braconidae) is one of the most important biological control factors on farms, orchards, and forests of the country, widely perceived to be found in nature, and can be effective in controlling larvae of leprose winged pests at an acceptable economic cost.

Materials and Methods:

 In this study, the effect of four sugar treatments [10% concentration of fructose, glucose, honey, and a mixture of fructose, glucose, and honey (1:1:1)] and distilled water (as a control for sugar treatments) was examined on the biological properties of B. hebetor male and female adults. B. hebetor was reared on fifth instars of Ephestia kuehniella Zeller (Lep: Pyralidae) in a growth chamber at 26±2 ºC‚ 60±5 %RH‚ and photoperiod of 16:8 (L: D) h. Daily observations and records were made for the development period and survival rate. The data were analyzed based on two-sex life table analysis using TWO SEX-MS Chart.

The present study showed a significant improvement in the biological reproductive and stable population parameters in sugar treatment groups compared with the distilled water treatment. The highest value of adult longevity and life expectancy (ex) of the B. hebetor occurred in fructose treatment. Moreover, the highest net reproduction rate(R0), finite rate of increase(λ), and lowest doubling time (DT) were observed in the mixed sugar treatment. On the other hand, the highest gross reproduction rate (GRR) and mean generation time (T) were found in glucose and fructose treatments. The results of study revealed that intrinsic rate of increase (rm) values for distilled water, fructose, glucose, honey, and mixed sugar were 0.257 ± 0.001, 0.272 ± .0011, 0.267 ± 0.033, 0.264 ± 0.007, and 0.291 ± 0.004 (day-1), respectively.

According to the results of the present study, B. hebetor was positively affected by the sugar treatments, and the suitability of sugar diets was ordered as mixed sugar > fructose > glucose and honey. In conclusion, sugar feeding is recommended for the mass rearing program of B. hebetor because suing them could increase the ability of this parasitoid in pest control. The highest rm value for the mixture of the three sugars indicated the importance of sugar-feeding quality in the mass-rearing program of natural enemies.

Honey is a healing compound produced by the Apidae bees. So far, the only genus of Apis with 9 known species worldwide is a honey bee. But species of paper wasps in the Vespidae can also produce honey. This research was conducted to study and identify the species of paper wasp honey producer in the South of Kerman. For this purpose, the activity areas of this wasp were identified, and specimens of this paper wasp were collected for species identification. The specimens were identified by keys and related articles and Confirmed by Dr. James M. Carpenter at the American Museum of natural history. Parapolybia escalerae (Meado-Waldo) was described by Mead-Waldo in the London British Museum in 1911 as a single female specimen from southwestern Iran. The World distribution of this paper wasp is in Pakistan, Turkey, and Iran. According to the results of this study, the species Parapolybia escalerae (Meado-Waldo, 1911) was identified for the first time in southeastern Iran (south of Kerman). This species was distributed south of Kerman from the tropical foothills of Jabalbarz Mountains (southern Jabalbarz to Mohammadabad) and Bahraseman. Parapolybia escalerae is introduced in the world as a paper wasp species of a honey producer. The paper wasp is known as dry or chocolate honey and has medicinal use. In this study, the male and queen specimens were collected and identified for the first time. This study found that this species of paper wasp, like the Apis florea, produces wild honey. A. florea has open nests and small colonies of a single comb, but P. escalerae is in the dark space of mountains and cliffs and produces many combs. The activity of this species was mostly observed on the Ziziphus sp. and Pistacia terebinthus trees. This paper wasp has a social life and includes three forms of queens, workers, and males. So far, only two species of Honey producing paper wasps have been reported in South America, including Brachygastra mellifica (Say, 1837), known as the Mexican Honey Wasp and Brachygastra lecheguana (Latreille, 1824), which are paper wasps belonging to the subfamily Polistinae. These two species have round nests and build their nests on tall trees and the ground in open spaces. Their honey has medicinal use in different regions of South America and is collected by local people. The paper wasp species P. escalerae works in the crevices of the rocks and has several flat combs. In Iran, the local people of the southern regions of Iran use this honey as medicine to treat respiratory diseases.

Root-knot nematodes (Meloidogyne spp.) are considered among the most important pathogens leading to great damage to agricultural products. So far, different practices such as crop rotation, resistant cultivars, and chemical compounds have been used for controlling these nematodes. High cost of chemical compounds and their environmental problems has attracted the researchers’ attention for using non-chemical methods for nematode management. The exploitation of resistant varieties is one of the most important approaches to managing plant-parasitic nematodes. The present study aims to evaluate the reaction of 15 different varieties of pomegranate to RKN, M. incognita race 2.

The morphological characters of isolated nematodes were evaluated after sampling, along with identifying the nematode species. The experiment was conducted in greenhouse conditions with a temperature ranging from 22-26°C based on the completely randomized design with factorial arrangement. First, pomegranate cuttings were rooted and inoculated with 2000 eggs and second-stage juveniles of the nematode per kg of soil. Then, host plant growth traits such as length, fresh and dry weight of stems, and roots, as well as developmental stages of the nematodes including the number of galls, egg mass, and reproduction factor were evaluated in different cultivars of pomegranate 90 days after inoculation. The final rating was conducted based on the Canto-Saenz system (1985). Finally, the data were analyzed by using SPSS 24 software, and Duncan test and t-test were used for comparing the means.

Based on the results, Malas-e Torsh cultivar was tolerant (GI≤2, RF>1), Malas-e Shirin and Tabestani were hypersusceptible (GI>2, RF≤1), and Agha Mohammad Ali, Alak-e Torsh, Bahabadi, Berit-e Poust Ghermez, Golnar, Naderi, Bihasteh-e Ravar, Pous Sefeed-e Shirin, Bihasteh-e Shomal, Poust siah, Souski-e Taft and Shahsavavar-e Yazdi were evaluated as susceptible (GI>2, RF>1).

Based on the results,tolerance of only one cultivar against root-knot nematodes should be considered by experts and farmers.