نشریه دانش بیماری شناسی گیاهی
سال یازدهم شماره 1 (پیاپی 21، پاییز و زمستان 1400)

Grapevine fanleaf virus (GFLV) is a major grapevine infecting virus in the world.

Grapes showing GFLV signs were sampled from the suburbs of the city of Khorramabad in Lorestan Province of Iran in spring 2020 and RT-PCR test was performed to amplify their GFLV-CP gene and the product was sequenced.

Specific primers were able to amplify a 1515 bp fragment of the CP gene. Based on the nucleotide sequence of this fragment, GFLV was first identified in this region. The nucleotide sequence similarity of this isolate was detected at 89.14-95.64% with other isolates in the NCBI library. Also, the phylogenetic tree of these isolates, based on the genomic CP region, grouped GFLV isolates into two groups I and II. The Lorestan GFLV isolate was placed in a subgroup in Group I together with GFLV isolates from the northwestern part of Iran and the Takestan isolate, and isolates from other countries were grouped in a separate subgroup of this group. Also in the phylogenetic tree, the Northeast isolates and the Fars and Kohgiloyeh & Boyer-Ahmad province isolates were classified in Group II.

The results of this research indicate that the virus is endemic and that its likely origin was in Iran and then spread to other parts of the world. The impact of geographic segregation on the evolution of GFLV can also be deduced.

The province of Kohgiluyeh and Boyer-Ahmad in southwestern Iran is an important rice-growing area. Seed-borne fungi can cause harmful diseases, so identifying them is important to prevent these diseases.

Thirty seed samples of four rice varieties were collected from different regions of the province. Seed-borne fungi were isolated by using the potato-dextrose-agar plate, blotter, and deep freezing blotter methods and after purification, their morphological characteristics were studied and they were identified. The total frequency of seeds infected with fungi and the frequency of seeds infected with each fungus were calculated. The effect of these fungi on seed germination and root growth of four cultivars Champa, Shamim, Gerdeh, and Lenjan was tested by placing them between wet sterile filter papers.

Twenty-eight fungi of 11 genera vs. Alternaria, Aspergillus, Bipolaris, Cladosporium, Curvularia, Epicoccum, Fusarium, Penicillium, Pyrenophora, Rhizopus, and Ulocladium were identified in these thirty samples. These fungi did not significantly affect seed germination of these varieties, but caused root rot in them. The average infestation of the Champa variety was lower than the others.

The Champa variety is relatively resistant to these fungi, followed by Shamim, Lenjan, and Gerdeh respectively.

Blast caused by Pyricularia oryzae is the most important fungal disease of rice in the world. The best method of disease management is to identify and cultivate resistant cultivars.

In this study, the response of 109 promising lines from the Iranian Rice Research Institute along with three control cultivars (susceptible and resistant) to blast disease was evaluated. Seeds of each line were sown in an upland nursery to assess leaf blast in early July. In order to inoculate the desired lines, leaves infected with the blast were collected from different areas of Guilan Province and placed on the surface of the rice blast nursery. In all stages, the necessary humidity to cause disease was provided by sprinkler irrigation. The severity of the disease was rated from zero to nine using the standard method of the International Rice Research Institute. Seedlings were grown in large pots in the greenhouse and inoculated by injection into the panicle neck to assess panicle burst.

Seven and 14 lines with grades 2 and 3 showed resistance to leaf blast. Other lines ranged from relatively susceptible to very susceptible to the disease. Three lines TH1, TH2, and TH3 with a degree of contamination of 5 were susceptible to panicle blast disease.

Twenty-one known blast-resistant lines can be used in the rice cultivars breeding program.

Legumes are the most important source of human food after cereals. More than 70 species of plant-parasitic nematodes have been reported from legumes of the world. Some of these nematodes cause great damage to these plants. Pratylenchoides ritteri is widespread in Iran on various plants such as legumes.

The number of P. ritteri nematodes per kg of soil in an infected field soil was counted and this soil was used for a greenhouse experiment. Nematode reproductive factor and some plant growth traits in six plants including; Broad bean, soybean, lentil, bean, mung bean, and Chickpea were studied under greenhouse and field conditions. Tests were performed in randomized complete block designs and the data were analyzed using SPSS 22 software.

All the plants were hosts for the nematode and the reproductive factor of the nematode was higher than one. The highest reproductive factor was found in soybean and the lowest in mung bean. Under greenhouse conditions, a decrease in most plant growth indices was observed in all infected plants. Among these plants, beans showed the largest decrease and mung bean the smallest decrease in growth indices.

Broad bean, soybean, lentil, bean, mung bean, and chickpea are hosts for P. ritteri and this nematode can cause decreases in most plant growth indices.

Cucumber mosaic virus (CMV) is one of the most common pathogens of cucurbits plants in the world. The best way to manage the disease is to identify and cultivate resistant cultivars.

Reaction of 40 genotypes or cultivars of cucurbits plants including Cantaloupe, cucumber, melon, squash and watermelon were evaluated for a CMV isolate from subgroup IB under greenhouse conditions in a completely randomized design with 10 replications per treatment. The plants were inoculated with CMV-infected tobacco extract at the cotyledon leaf stage. Up to four weeks after inoculation, their reaction was determined based on symptom severity index and absorption index in ELISA test (OD405).

Genotypes were classified into five groups: highly sensitive, sensitive, relatively resistant, resistant and completely resistant.

Cultivation of completely resistant or resistant genotypes for disease management can be recommended.

Verticillium wilt, caused by Verticillium dahliae, is one of the most important soil-borne diseases of stone-fruit trees.

Samples showing evidence of Verticillium wilt were collected from stone fruit orchards in the suburbs of Shahroud and Damavand and four isolates of V. dahliae were obtained. The fungal inoculum was prepared on sterile wheat grains and the response of 13 peach and nectarine cultivars propagated by grafting on GF305 (almond-peach hybrid) rootstock was inoculated with it in the canopy area in the garden in early spring. Sixteen weeks after inoculation, disease severity was recorded on a three-point scale.

All peach and nectarine cultivars were classified as very susceptible, susceptible, or semi-susceptible and none of them showed resistance. The Nectarine Independence cultivar was highly susceptible to disease, while the peach cultivar had the lowest disease severity index and was therefore classified as semi-susceptible.

Among these cultivars, the Romestar peach cultivar is less susceptible to the disease.

Green mold (Penicillium digitatum) is one of the most important post-harvest pathogens of citrus fruits. Tens of thousands of citrus fruits are often destroyed by green mold in Iran every year. The use of chemical toxins to control the disease, in addition to negative environmental effects, leads to the selection of fungal-resistant populations and also endangers consumer health, so non-chemical control of the pathogen has become an important goal of researchers in recent years.

The essential oil components of myrtle (Myrtus communis L.) were extracted with a Clevenger apparatus and their compounds were identified with a gas chromatography apparatus with a mass spectrometer. The inhibitory effect of myrtle essential oil and the fungicides chitosan and thiabendazole on spore germination and colony growth was investigated by mixing with PDA and PDB under laboratory conditions and by impregnating the fruit surface during storage.

Thirteen compounds were identified in myrtle essential oil, which was quantitatively the highest compound 1-8 cineole. Myrtle essential oil at a concentration of 1700 ppm and chitosan at a concentration of 500 ppm inhibited 100% of fungal colony growth, as did the fungicide thiabendazole.

It is possible to use myrtle essential oil or chitosan as an alternative to the fungicide thiabendazole to control citrus green mold.

The aim of this study was to collect and identify entomopathogenic nematodes native to Iran and to evaluate their pathogenicity on honeycomb moth larvae (Galleria mellonella).

Thirteen isolates of entomopathogenic nematodes were collected from different provinces of Iran and identified based on morphological characters. The percentage mortality of G. mellonella larvae infected with these isolates at 25 ± 1 and 32 ± 1 °C was determined in a one-to-one assay, and the ability of the isolates to find a target and the mortality of the insect in the sand column test were determined.

Seven isolates of Heterorhabditis bacteriophora, two isolates of Steinernema feltiae, and five isolates of S. carpocapsae were identified. The ability of isolates of all three nematode species to penetrate the insect's body has been shown to be up to 93% within 48-72 hours post-infection at 25 ± 1°C. The optimum temperature for the biological activity of the identified isolates was 25±1°C. S. carpocapsae found a target faster than the other two species in the sand column test.

Isolates of S. carpocapsae have higher potential in targeting and pathogenicity of honeycomb moth larvae than the other two nematode species.

Plant diseases usually cause economic damage and reduce growth and crop yield.  Treatment of plant diseases with chemical toxins can result in environmental side effects, the emergence of resistance in pathogens, and loss of beneficial soil microorganisms, so the search for alternative methods such as identification and use of antagonistic microorganisms for disease treatment has been considered by researchers. A set of endophyte fungi that grow without damage or symptoms in host plant tissues and are known to be biological control agents of some plant diseases. Endophyte fungi with different mechanisms such as the production of antibiotic metabolites, competition, induction of resistance, and hyperparasitism of the pathogen weaken or eliminate the pathogens. These fungi can also help increase the growth and resistance of host plants to various stresses by producing antioxidant and antitumor compounds, as well as various growth hormones.

The use of essential oils and extracts of medicinal plants is one of the environmentally friendly methods in the management of plant diseases caused by fungi and bacteria. The antimicrobial effect of essential oils and extracts of various medicinal plants such as thyme, cloves, savory, garlic, licorice and fennel has been proven and their active ingredient has also been identified. Based on these studies, the possibility of introducing, formulating and using essential oils and extracts of medicinal plants or any of their components with antimicrobial properties, as an alternative method of using chemical toxins in the management of fungal and bacterial diseases of plants can be provided.

Acute oak decline with signs of canker and colored discharge on the trunks of old trees has been reported in northern Iran for the past two decades. Several bacteria of the order Enterobacterales, the family Pectobacteriaceae and the genus Brenneria were isolated and identified from diseased trees. Although oak possesses several genes whose products are responsible for plant resistance to fungal pathogens, bio-trophic pathogens, hemibiotrophic pathogens, and water stress, it does not show resistance to these necrotrophic pathogenic bacteria. The mechanism of the occurrence and epidemic of acute oak decay is the predisposition of trees to successive droughts, the outbreak of some pests, and the relatively low rate of development of oak defense genes against the high rate of evolution of pathogenic genes of necrotrophic bacteria such as Brenneria species. Due to the many climate changes in recent years, there may be an epidemic of the disease in the forests of other parts of the country in the future. This article describes research into the disease to pave the way for an appropriate method of disease management.

Autophagy plays an important role in the process of plant development and interaction with pathogens such as fungi, bacteria, and plant viruses. Autophagy is linked to immunity and disease resistance through inhibition of programmed cell death (PCD) and is recognized as an important defense component in plants. Autophagy also helps selectively eliminate pathogens through specific interactions. A number of pathogens have acquired the ability to cope with or evade autophagy and use it to develop the disease. Some other pathogens also use the autophagy system as pathogenic factors. Therefore, understanding cellular processes such as responses related to autophagy genes are very important for studying pathological physiology and plant immunity. The role of autophagy in the immune system and the plant's defense response to pathogens is described in this article.