Plant Pathology Science

Report of nine species of criconematide nematodes from forests of the Mazandaran Province, Iran

Farahnaz Jahanshahi Afshar

The Mazandaran Province occupies more than half of the area of Hyrcanian forests in the north of Iran and has a very diverse vegetation. In order to be aware of the entry of important plant parasite nematodes into these forests and to prevent their spread to downstream farms and gardens, continuous monitoring and determination of the density of important plant parasite nematodes in this area was necessary. Ninety rhizosphere samples of forest trees, including maple, birch, oak, raspberry, alder, walnut, and hornbeam, were collected from this province in 2020. Nematodes were extracted from the samples by wet sieving and centrifugation method, and after fixing, permanent slides were prepared from them and their morphological indices were measured and identified using valid keys. Also their frequency in the samples and their population density in 200 cm³ rhizosphere were determined. Nine nematode species from the superfamily Criconematoidea were identified from the rhizosphere of these trees under the following names: Criconemoides informis, Criconemoides parvus, Mesocriconema solivagum, Mesocriconema xenoplax, Crossonema civellae, Crossonema menzeli, Ogma fagini, Xenocriconemella macrodora, and Paratylenchus straeleni. Among these nematodes, C. parvus had the highest frequency, and population density in the rhizosphere of alder trees in the Dohaz forest of this province. Some of these plant parasitic nematodes in high populations, in addition to direct damage to the roots, cause the spread of some plant diseases and exacerbate the effects of frostbite.

Evaluation of the possibility of determining genetic diversity of Mauginiella scaettae isolates using UP-PCR

Hamid Alvanipour

The fungus Mauginiella scaettae is the causative agent of the destructive Khamej disease (inflorescence rot) common in various date palm cultivation areas. UP-PCR is one of the DNA fingerprinting methods with high reproducibility and specificity. The aim of this study was to investigate the possibility of DNA amplification with UP-PCR primers and the feasibility of studying the genetic diversity of M. scaettae isolates using this marker. Date palm inflorescences with Khamej disease symptoms were sampled in Khuzestan and Fars provinces. The purified isolates were identified based on morphological characteristics and confirmed by amplification and sequencing of the ITS-nrDNA genomic region. Three primer pairs UP-15/19, UP-21 and UP-45 were used to investigate the possibility of amplification and determine the genetic diversity among the fungal isolates. Five isolates of M. scaettae were obtained from three cities: Abadan, Karun and Behbahan in Khuzestan province and one sample from Kazerun in Fars province. The isolates were obtained from four date palm cultivars: Sayer, Khazravi, Khasi and Zahedi. Constructing of phylogenetic tree based on ITS sequences confirmed that the isolate belonged to M. scaettae fungus with 100% bootstrap values. Examination of the UP-PCR marker amplification results showed that the highest number of observed bands was related to the UP15 primer and the lowest number of bands was related to the UP45 primer. Band diversity was observed between the UP-PCR primers used, but genetic diversity was not observed among the five M. scaettae isolates in any of the three UP-PCR primers and the banding pattern of the isolates was similar for each primer. The reason for the failure to detect genetic diversity between isolates of this pathogen using these primers and the marker could be due to their close genetic relationship.

Effect of Salvia mirzayanii and Mentha piperita essential oils on toxigenicity and aflatoxin gene expression in Aspergillus flavus

Sedigheh Mohammadi

Aflatoxins are toxic metabolites produced by certain Aspergillus species. They cause disease and contaminate food, so reducing and controlling these toxins is extremely important. Due to their antifungal properties, essential oils and extracts from medicinal plants are increasingly used. As part of this study, the medicinal plants Salvia mirzayanii and Mentha piperita were harvested from their original habitat in Hormozgan Province and essential oils were extracted. Subsequently, the toxin-producing fungus A. flavus was isolated and purified from maize kernels, and the effect of the essential oil of both plants on the toxigenicity of A. flavus and the expression of the aflatoxin-encoding gene was investigated using real-time PCR. The antifungal properties were assessed using the disk diffusion method and a mixed evaluation, and then the effective concentration of the essential oil in both plants was determined. The essential oils of both plants effectively inhibited the growth of A. flavus at concentrations of 1000 and 2000 ppm. However, peppermint essential oil significantly reduced toxin production and had a stronger effect on the expression of the gene encoding aflatoxin at a concentration of 2000 ppm. Considering the effectiveness of peppermint essential oil at a concentration of 2000 ppm on the expression of the gene encoding aflatoxin, this essential oil can be introduced as a biological and safe method for the biological control of aflatoxin.

Reaction of four Iranian rice cultivars to bacterial leaf blight disease

Rasool Rezaei

Rice is an important food crop in the world. Bacterial leaf blight, caused by Xanthomonas oryzae pv. oryzae, is one of the important diseases of rice that is prevalent in different cultivars in the world. Identifying and planting resistant or semi-resistant cultivars is the most effective method of disease management. This study aimed to investigate the reaction of four Iranian rice cultivars; Shiroodi, Setayesh, Fajr, and Hashemi, to the disease under field conditions. Rice plants with the disease symptoms were sampled from different regions of Kohgiluyeh and Boyer-Ahmad province in southwestern Iran, during 2012-2013. The pathogen was isolated from infected leaves after their surface disinfection, on Yeast extract-dextrose-CaCO₃(YDC) medium. The isolated bacterium was rod-shaped, gram-negative, obligate aerobic, oxidase negative, catalase positive, levan and lecithinase positive. It induced a hypersensitivity reaction in tobacco leaves and could not hydrolyze starch, but it hydrolyzed gelatin, ascoline, and Tween 80. Based on a comprehensive analysis of morphological, biochemical, pathogenicity, and genotypic traits, the pathogen was identified as X. oryzae pv. oryzae. The reaction of these four Iranian rice cultivars to the disease was evaluated by inoculating them with the pathogen, monitoring the progression of disease symptoms, and measuring the growth of the bacterial population in each cultivar. There was a significant difference among the cultivars in terms of the length of leaf necrosis and the bacterial population within the tissue, with the Hashemi cultivar exhibiting the highest sensitivity and the Shiroodi cultivar showing the lowest sensitivity to the disease. The occurrence of bacterial leaf blight disease in Kohgiluyeh and Boyer-Ahmad province, as well as the reaction of these cultivars to the disease, are being reported for the first time.

The effect of three Trichoderma species and organic sulfur on root-knot nematode of cucumber

Leila Kashi

Today, with the increase in cucumber cultivation in greenhouses and fields, their contamination with root-knot nematodes is observed in some areas. The effect of three Trichoderma species (T. crassum, T. harzianum and T. afroharzianum) with liquid organic sulfur of Raskood company on the control of root-knot nematode (Meloidogyne javanica) on cucumber (Nagin variety) was investigated with two separeted tests under greenhouse conditions, in this research. Both tests were done with eight treatments (the use of each of the mushrooms together with sulfur, each of the fungi alone and sulfur alone and the infected control) in five repetitions and the form of Completely Randomized Design with Duncan's test at 5% level. In order to infect the plants, 2500 second-stage larvae and nematode eggs were added to each kilogram of potting soil containing cucumber seedlings at the four-leaf stage. Then, depending on the type of treatment, one milliliter of Trichoderma suspension (10⁶ spores per milliliter) and sulfur were added to each seedling, and the pots were investigated after 45 and 60 days for the first and second tests, respectively. Data analysis was done using SAS 9.4 software. The results of this study showed that in both tests, the use of sulfur with each of the fungi and sulfur alone led to significant differences between the plant growth indicators of tretments (fresh and dry weight of aerial organs, lenght of the root and aerial organs) and control. Also, nematode pathogenicity factors (the number of second stage larvae in the soil, the number of female nematodes in each gall, the number of female nematodes in the whole root, the number of galls in the whole root, the number of egg mass in each gall, the number of egg mass in the whole The root and reproduction factor) of the treatments that with both of Tricoderma and sulfur together, as well as the treatment using sulfur alone showed a significant difference compared to the control. However, in the both of tests, the most effective treatments were related to the use of T. crassum together with sulfur.

The impact of four commercial biological products on Rhizoctonia root rot disease in bean

Mehdi Sadravi

Rhizoctonia root rot, caused by the soil-borne fungus Rhizoctonia solani, is an important disease of beans, which has been reported from different parts of Iran. The disease has been reported to cause damage to up to 60% of the crop worldwide. Biological control can be a healthy and environmentally friendly method for managing plant diseases. This study was conducted to investigate the effect of four commercial biological products available in the Iranian market on growth indices and severity of Rhizoctonia root rot in beans to find a suitable method for biological control of the disease. The effect of three biological products of arbuscular mycorrhizal fungi including Funeliformis mosseae, Rhizoglomus intraradices and Mycopersica (a mixture of several mycorrhizal fungi) and the bacterium Bradyrhizobium japonicum on growth indices and severity of Rhizoctonia root rot in Kosha pinto-bean cultivar was tested under greenhouse conditions. Statistical analysis of the data from this experiment showed that these treatments had a significant effect on reducing disease severity and plant growth indices, and among them, F. mosseae and Mycopersica caused the greatest reduction in disease severity and improved plant growth indices, respectively. Therefore, the biological product of F. mosseae and Mycopersica can be used to reduce the severity of Rhizoctonia root rot disease in beans and improve its growth indices.

The effect of Funeliformis mosseae and Trichoderma harzianum on early blight disease in tomato

Khadijeh Abbasi

Early blight, caused by Alternaria alternata, is a major tomato disease that leads to significant economic losses. This study aimed to evaluate the effectiveness of two fungi, Funeliformis mosseae and Trichoderma harzianum, as potential biological control agents against the disease. Initially, the inhibitory effect of T. harzianum on the pathogen's colony growth was assessed under laboratory conditions using the dual-culture method, where T. harzianum reduced pathogen colony growth by 70%. Subsequently, the efficacy of F. mosseae and T. harzianum, applied individually and in combination, was tested against A. alternata in greenhouse conditions using a completely randomized design with three replications per treatment. Various parameters were measured, including chlorophyll a, b, and total content; total phenol; activities of catalase and peroxidase enzymes; and plant growth traits such as stem number, stem height, fresh and dry weight of aerial parts, root length, and fresh and dry weight of roots. Statistical analysis revealed that the application of T. harzianum and F. mosseae enhanced antioxidant enzyme activity (catalase and peroxidase) and phenolic compound levels, leading to improved growth and increased dry matter content in tomatoes under pathogen infection conditions.

Application of secondary metabolites of Streptomyces species in plant disease management

Fatemeh Shahryari

The genus Streptomyces belongs to the actinomycetes, which is an aerobic, gram-positive and multicellular bacterium. The members of this genus are mostly known as soil-dwelling bacteria. However, they are found in various environments such as marine sediments, freshwater ecosystems, symbiotic with insects and sponges, and plant endophytes. In particular, only a few pathogenic species of this genus have been identified that cause disease in plants and humans. Beyond the range of distribution, specific genomic features, unusual mushroom-like growth mode, impressive metabolic capabilities, including the ability to produce diverse antibiotics and other bioactive natural products, have made members of this genus attractive organisms for study. They are also among the most promising microorganisms for improving the overall health of the soil and increasing agricultural productivity. Approximately two-thirds of all known actinomycete antibiotics are produced primarily by members of this genus. The metabolites of this genus have a wide spectrum including cyclic and linear peptides, terpenoids, macrolactams, macrolides, glycosides, polyaromatics and linear polyketides. The discovery of numerous and different compounds shows the high potential of Streptomyces as a source of new and interesting natural products.

Morphological and molecular characteristics of two species of Psilnchus (Nematoda: Psilenchidae) from the Taf region of Lorestan province, Iran

Arezoo Naghavi

The species of the genus Psilenchus are weak parasites of plants and mosses that feed on hairy roots and epidermal cells of root. Previously, the members of the genus were placed in the family Tylenchidae because of having weak stylet and elongate tail, but because of the didelphys uterus and the presence of phasmid on the tail, they were more similar to the members of the supper family Dolichodoroidea, so “Psilenchidae”, as a new family with two subfamilies Antarctenchinae (Stylet knobbed and vulva with lateral membranes and epiptygma) and Psilenchinae (Stylet not knobbed and vulva without lateral membranes and epiptygma) was established. The genus Psilenchus currently has 21 valid species (only four species have been sequenced), of which 10 species have been recorded from Iran. About 100 samples were collected from the rhizosphere of fruit and forest trees in Taf region of Khoramabad county in 2022 and 2023. The nematodes were extracted using tray method and after fixation, permanent slides were prepared. The morphological and morphometric characteristics of the samples were examined, then a molecular study was performed using the D2-D3 28S rDNA marker. Two species, Psilenchus curcumerus and P. vinciguerrae, were identified with one and two sequences, respectively. This is the first report of these two species from the region. These two species were confirmed based on morphometric and morphological characteristics and phylogeny studies.