فصلنامه بیماریهای گیاهی
سال پنجاه و هشتم شماره 1 (پاییز 1401)

Aflatoxins are toxic secondary metabolites produced by speices of Aspergillus including A. flavus and A. parasiticus. Mycotoxins are potential carcinogens and reduce global trade of agricultural products. Soil and peanuts were sampled across fields located in seven important peanut production villages of Astaneh Ashrafieh to investigate the frequency of toxigenic and atoxigenic strains of A. flavus and A. parasiticus. Toxigenicity of the Flavi section strains was evaluated according to change in color of the back of colonies on coconut agar in contact with ammonium hydroxide vapor. 48 isolates of Flavi section were identified, including 20 isolates of A. flavus and 28 isolates of A. parasiticus with nine atoxigenic and 39 toxigenic isolates. Risk maps were developed based on mean toxigenicity where Lakujdeh, Mohsenabad, and Noghredeh respectively with mean toxigenicity of 2.50, 2.25 and 2.10 had the highest risk scores for peanut cultivation while parkaposht, Nubijarmahale and Nabi dehka with mean toxigenicity of 1.00, had the lowest risk scores. Peanut fields located in Dehsar with a mean toxigenicity of 1.50 were classified with moderate risk scores. The outlook of this study was based on identification of atoxigenic isolates of the fungus with potential future application in biological control of toxigenic strains of Flavi section and emphasize on their competitive ability to colonize peanuts as well as developing risk maps to plan for reducing the risk of aflatoxin production on peanuts, an important product of Guilan province, and to pave the way for increased production and export of this product.

Iris yellow spot virus (IYSV) is a member of the Eurasian phylogenetic group of the genus Orthotospovirus. Similar to other species in the genus, the viral particles contain three genomic fragments: small (S), medium (M), and large (L) RNAs. In the present study, the complete nucleotide sequence of the small fragment (S) RNA of two IYSV isolates from leek (Allium ampeloprasum ) (IYSV-Le1M) and onion (A. cepa) (IYSV-O2K) and the non-structural gene of the M RNA of the IYSV-Le1M isolate were determined. The results showed that based on nucleocapsid (N), small (NSs), and medium (NSm) RNA fragment non-structural genes, the isolates of Markazi Province are more closely related to each other than other IYSV isolates. However, the intergenic region (IGR) of the two isolates showed significant structural differences compared to other sequenced IYSV isolates. The IGR of the IYSV-Le1M isolate was longer than those of other IYSV isolates studied, while, for IYSV-O2K isolate, it was 440 nucleotides shorter. It was also found that for Indian and Dutch IYSV isolates, the IGR was 31 and 22 nucleotides shorter than that in the IYSV-Le1M isolate. These findings provide new information about the genetic diversity and phylogeny of IYSV isolates.

Barley yellow dwarf virus (BYDV) causes a significant yield reduction and crop loss in cereal and grasses worldwide. Studies revealed that barley yellow dwarf virus is present in most regions of Iran. Wheat and barley plants showing the infection symptoms were collected from cereal fields in Hamedan Province during the springs of 2020 and 2021. Samples were tested for BYDV infection by Indirect ELISA. Positive reactions to BYDV antibody in most samples were detected. After total RNA extraction, RT-PCR was performed to amplify polymerase gene using specific BYDV-PAV primers. BYDV-PAV is the most prevalent species of BYDVs in Iran. Results confirmed BYDV infection. For molecular and phylogenetic comparison, two samples from Hamedan and Asadabad were selected and their polymerase genes were sequenced. The sequencing results revealed that Hamedan isolate had maximum homology with Kahnouj, Karaj, Yazd and Arak isolates (with 95% - 96% identity). The isolates in this group proposed as a distinct species due to their low similarity with other isolates in GenBank. Asadabad isolate had maximum homology with Estonia and America BYDV-PAS with more than 92% homology. The results of phylogenetic analysis revealed that Iranian isolates of BYDV clustered in three distinct groups which shows the presence of a high diversity in the polymerase gene of this virus. This study is the first report of BYDV-PAS species in Iran.

The movement of plant-parasitic nematodes in soil is influenced by the soil environment and the microorganisms present in it, and soil conditions affect disease incident. The objective of this study was to investigate the movement of second-stage juveniles of the root-knot nematode Meloidogyne incognita 18 weeks after incubation with vermicompost, under constant saturation flow 24 and 72 hours after addition of the nematodes. The test was conducted as a factorial experiment with a randomized complete block design in three replicates. The nematodes were extracted by the tray method and then counted. The results showed that 24 hours after nematode injection into the control soil, the highest population of nematodes was observed at the injection site and the nematodes moved more toward the water flow. At 72 hours after injection, a higher percentage of them moved and the nematode population decreased at the injection site (1.52%). Also, in the soil treated with vermicompost for 18 weeks, nematodes moved both in and against the direction of water flow 24 hours after injection and were distributed in all points of the column. The highest rate of nematode movement was observed at point (-4) at 14%. At 72 hours after injection, the nematodes were also very evenly distributed throughout the column and the number of nematodes that entered the wastewater was higher.

During visiting the alfalfa fields in Sahneh county of Kermanshah province, the symptoms of a disease were observed in the form of galls with variable sizes in the crown part of the plants, which had caused a severe decrease in the growth in the alfalfa fields. The size of the galls varied from a few millimeters to several centimeters and were observed only in the crown. After transfer to the laboratory and microscopic examinations, a species of fungus with the characteristics of Physoderma alfalfae (Pat & Lagerh.) Karling Syn: Urophlyctis alfalfae (Pat & Lagerh.) Magnus was observed with chambers containing numerous resting spores and turbinate cells (Figure 1), which are prominent features of alfalfa crown wart disease cause. The resting spores had a depressed part and their size was 40-55 micrometers in the longer diameter and 22.5-35 micrometers in the shorter diameter. According to the classification of Hibett et al. (2007), this species is placed in the Blastocladiomycota phylum, Blastocladiomycetes order and Blastocladiales order. The fungus was first reported by Viennot-Bourgin et al. in 1970 from Karaj on alfalfa plant, but afterward there has been no other report of the disease or the fungus in Iran. Considering the damage caused by this disease, it is important to pay attention to its monitoring and to study its biological and pathogenic aspects.

Emerging plant diseases accounts for serious treats to agricultural crop yields, and food security. Tomato torrado virus (ToTV) for the first time was reported in canary island (Spain) from greenhouse-grown tomato plants expressing yellowing areas at the base of the leaflets which later turn into necrotic spots or large necrotic area covering leaves, stem and fruit (Verbeek et al., 2007). During a field survey carried out during spring 2021, a total number of 14 tomato plant samples showing severe necrosis symptoms on tomato leaves and fruits, similar to those described for ToTV (Moodley et al., 2019), were collected from an open tomato field in vicinity of Shiraz. , Total RNA was extracted from leaf and fruit tissues of 14 symptomatic samples using Trizol reagent, and for the presence of ToTV was subjected to reverse transcription polymerase chain reaction (RT-PCR) using a set of specific primer pair (3Avp/35seq R and 3Avp/35seq F) targeting approximately a 275 nucleotide fragment in the coat protein gene (Wieczoreck et al. 2020). Eleven symptomatic tomato samples yielded an amplicon of the expected size ( about 275 bp) in RT-PCR assay, Multiple alignment of the obtained nucleotide sequences showed that the Iranian ToTV isolates have the highest similarity of 98.2% (IRSHZ1) and 97.3% (IRSHZ3) with ToTV strain TEN-03 and the lowest similarity of 96.8% (IRSHZ1) and 95.4% (IRSHZ3) with ToTV strain GNC-06, both of which were reported from Spain