نشریه تحقیقات بیماری های گیاهی
سال یکم شماره 3 (پاییز 1392)

Weeds always cause serious problems in pome fruit orchards. These plant species are primary، secondary and epiphytic hosts of some major plant bacteria which upon transmission to fruit trees may result in bacterial infection and crop loss. These weeds include annuals and perennials. The most prevalent perennial and spring annual weeds that serve as secondary hosts were collected during two years of study (2011-2012). Samples were examined for determining incidence of bacteria via conventional bacteriological methods. The more frequent bacteria were identified and checked for pathogenicity and epiphytic phases. Results showed that Xanthomonas spp.، Pseudomonas spp. and Erwinia spp. were found on Avena fatua، Sorghum halepense، Cynodoun dactylon‍‍، Agropyron repense، Hordeum vulgare and Poa sp. as epiphytes. These bacteria could be isolated during spring. Pseudomonas syringae pv. syringae was isolated from some Poaceae species. Erwinia amylovora، the causal agent of fire blight، was isolated from Cynodon dactylon‍‍ and Agropyron repense.

The symptoms of brown patch or Rhizoctonia blight of bristle basket grass (Oplismenus hirtellus) were observed in the summer of 2004 in a citrus orchard in Babolkenar region، South of Babol، Mazandaran province. The individual plant symptoms consisted of blighted spots، which gradually expanded to encompass the entire surface of the leaf. Patches of affected grass had a diameter of approximately 20 to 100 cm. Dark brown sclerotia were abundantly produced on the diseased plants and in soil. Plants started to recover and resumed growth from the centre of the patch outward at the end of summer (because of the cooling of the air)، producing a ring pattern in the affected area. A multinucleate Rhizoctonia sp. was consistently isolated from blighted tissues. Based on colony and mycelial characteristics، the fungus was identified as Rhizoctonia solani، and the anastomosis group (AG) for most of these isolates was determined as AG 1 by anastomosis testing. On the basis of cultural and sclerotial characteristics، subset of the isolates was determined as AG 1- IA. The hyphal diameter of the isolates was 7. 0 µm، and the mean number of nuclei was 6. 4 per hyphal cell. The colony was light brown on potato dextrose agar after 2 weeks of growth، and dark brown sclerotia measuring 0. 7 to 4 × 1 to 4. 5 mm were abundantly produced on the medium. Cardinal temperatures for growth of this isolate were 10، 28، and 35°C. The linear growth rate at the optimum temperature was 34 mm per day. Pathogenicity of the AG 1-IA isolate was confirmed by placing 8-mm disks from the margins of an actively growing colony on the leaves and sheaths of the host plant. Symptoms observed were the same as those in the field، and the fungus was reisolated from the blighted tissue. To our knowledge، this is the first report on the occurrence of brown patch disease of O. hirtellus in Iran. The bristle basket grass is introduced as a new host for R. soloni in Iran.

Potato virus Y (PVY) is the type species of the genus Potyvirus in Potyviridae، and is one of the most important potato infecting viruses which can cause severe crop loss in epidemics. This damage and reduction of yield depends on several factors including potato cultivar، time of infection and virus strain. Currently all tobacco and potato fields are sensitive to PVY and its infection is widespread in many potato fields in Golestan province. Use of resistant varieties is considered as the most effective and economic، and safest method to reduce damages of plant viruses. This study was performed to determine the reaction against PVYO of four prevalentpotato varieties cultivated in the potato fields of Golestan، including Banba، Boren، Marla and Satina، and to identify possible sources of resistance. Eight leaved plants from each cultivar were inoculated mechanically with extract of tobacco leaves infected by PVYO. Plants were kept in greenhouse and symptoms evaluated for four weeks. Statistical analysis was performed using the recorded ratings of the symptoms. Inoculated plants were tested by DAS-ELISA. PVY symptoms، with different severities، were observed in all varieties. Satina was the only variety which its symptom ratings was significantly lower than the total mean، but the maximum titer of virus was observed in DAS-ELISA experiments for Boren variety.

Use of some essential oils as antimicrobial agents has increased during the past decade. In this study the antifungal activity of essential oils of peppermint (Mentha piperita)، fennel (Foeniculum vulgare) and thyme (Thymus vulgaris) was examined for inhibition of mycelia growrh of Sclerotinia sclerotiorum on PDA amended with ethanolic extracts of the 3 medicinal plants at five concentrations (75، 150،300، 600 and 1200 microliter/l.). Results showed that the essential oil of peppermint did not have sufficient effects on mycelial growth of Sclerotinia sclerotiorum because it exhibited no significant difference with control at 99% confidence level. The essential oil of fennel had high antifungal activity and suppressed fungal growth at minimum inhibitory concentration of 150 µl/l. Thyme oil reduced mycelial growth at relatively higher concentration. Findings from this study showed that essential oils of fennel could be considered as a candidate for further investigations towards its application as natural fungicide to control S. sclerotiorum. Results suggest that the kind and concentration of essential oil can affect pathogenic fungi differently.

Sclerotinia stem rot (SSR)، caused by Sclerotinia sclerotiorum، is the most important disease of canola (Brassica napus). This disease has been observed in different regions of Golestan province since the first years of canola planting. In order to study of infection situation of the fields in the province، disease evaluating was carried out in 80 fields in four locations (Gorgan، Ali Abad، Kalaleh and Gonbad) during 2006 and 2007. Statistical analyses of disease data were performed based on disease incidence (I) and mean severity (S) of the fields. The results revealed that the incidence (P=0. 05) and severity (P=0. 02) are significantly different in the four locations. Minimum and maximum of average incidence was observed in Kalaleh (10. 7%) and AliAbad (22. 11%)، respectively، but Minimum and maximum of mean severity was recorded in Gonbad (5. 6%) and Ali Abad (17. 2%)، respectively. Minimum and maximum of disease incidence was observed in Gorgan in 2006 (1%) and Ali Abad in 2006 (81. 5%)، respectively، that were equivalent to 0. 6% and 66. 75% disease severity.

Root lesion nematode (Pratylenchus loosi Loof، 1960) is among the most damaging agents on tea plant in Iran. The nematode causes quality and quantity losses on tea crop. Most of tea plantations in Iran are under rain-fed conditions. In this research the impact of irrigation intervals (and consequently drought stress) and two types of soil texture، loamy-sandy and loamy-clay، on the population density of root lesion nematode and the growth indices of tea sapling were studied. Tea saplings of clone 100 were planted in pots 6000 cm3 containing either loamy-sandy or loamy-clay soil with population density of one nematode per g of soil. The pots were irrigated at 7، 14، 21 and 28 days intervals and some were left without irrigation as control. Pots were kept in the Tea-Research Station of Fashaalam for 8 months، during this period the required agronomic practices were done according to the routine of the region. After this period the saplings were harvested and in each experimental unit the growth indices such as height، total weight، root fresh weight، aerial fresh weight، aerial dry weight and root volume were measured. The nematode population density in soil and root were determined as well. The results of analysis of variance showed that all treatments had significant differences with each other. P. loosi could multiply well in treatments of 7 and 14 day irrigation intervals compared to treatments of 21 and 28 day and without irrigation. Nematode populations in root showed positive correlation with root volume and root weight at different irrigation intervals. Nematode population in soil and root were related too. The results of this survey showed that tea saplings with 7 and 14 day irrigation intervals could better tolerate the damage caused by P. loosi، in comparison to longer irrigation intervals and the treatment without irrigation. The nematode population density was higher in root and soil in loamy-sandy texture soil compared to loamy-clay soil This research revealed that in the treatments with 7 and 14 day irrigation intervals the water requirements of tea plants are met، consequently showing less damage in comparison with the other treatments with less water supply.

Root knot nematodes are one of the most important plant parasitic nematodes that damage many crops، particularly vegetables. Increasing use of pesticides has caused environmental concern and the use of eco-friendly natural substances to control pests and plant diseases has become a priority. Nematicidal effects of the water extracts of different parts of two medicinal plants، namely Ferulago angulata (Schlecht.) Boiss and Zataria multiflora Boiss on root knot nematode، Meloidogyne javanica، were determined under laboratory condition. Concentrations of extract from plant parts were 0. 04%، 0. 2% and 0. 4% (w/w) of leaves، stem and flower and distilled water was used as control. Each treatment was replicated 4 times. All plant parts and concentrations from both tested plants، significantly (P>0. 01) increased the larval mortality and decreased the egg hatching of M. javanica، in comparison with controls. In case of larval mortality، the best treatments were flower extract of F. angulata (0. 4%) and leaf extract of F. angulata (0. 2% and 0. 4%) which caused more than 90% mortality in J2s، as compared to leaf extract of Z. multiflora (0. 4%) with 72% larval mortality. Although the larval mortality in control was 4. 33%، flower extract of F. angulata at the rate of 0. 4% killed 97. 33% of J2s. At the same rate، mortality of larva was 61. 67%، when stem extract of Z. multiflora was applied. Aqueous extract of the both tested plant materials 69-91% inhibited the egg hatching. Flower extract of F. angulata (0. 4%) was the best treatment with 90. 11% inhibition in egg hatch. Phytochemical analysis of plant extracts revealed the presence of flavonoid and tannin. Only stem extract of F. angulata had no steroid and there was no saponin in any of the tested plant extracts.

Bacterial blight of cotton caused by Xanthomonas citri pv. malvacearum is an important quarantine disease in the country. To date، no official report exists on the susceptibility or resistance assessments of different cotton varieties to the disease in greenhouse conditions. To achieve this aim، disease incidence and severity in the three growth stages of cotyledonary، flowering and boll formation for 8 cotton varieties under greenhouse conditions (mean T. 38/31; d/n and RH% 58/65 d/n.) were evaluated using a completely randomized design with six replicates. Bacterial inoculum was prepared by mixing the inocula of 5 X. citri pv. malvacearum isolates that was adjusted at concentration of 106 cfu/ml. The leaves were pricked with sterile needle and sprayed with bacterial inoculum for three successive days at the flowering stage. Three weeks old bolls were pricked with needle at 2 points and inoculated with cotton plugs soaked in bacterial suspension. Distilled water was used as control. An in vitro (moist chamber) experiment on cotton bolls was also carried out in a completely randomized design with six replications. Hunter،1986 and Hillocks، 1988 evaluation systems were used for leaf and boll susceptibility or resistance assessments respectively. Results indicated that the local cultivar Bomi (G. herbaceum) was the most susceptible among the eight cultivars studied here. In contrast، the three cultivars، Siokra، Syndose and Bakhtegan were considered as the most resistant ones in both (vivo & vitro) experiments. Reactions of the varieties to inoculation at the flowering stage were similar to those at boll formation stage. Mean comparison of the data revealed significant differences among all varieties، except the 3 most resistant ones mentioned above. Inoculation of young plants at seedling stage did not show any disease symptoms.