فصلنامه بیماریهای گیاهی
سال پنجاه و نهم شماره 3 (پاییز 1402)

Among the oilseed plants, safflower has a special place, for production under climate change conditions. One of the main problems of safflower cultivation is fungal attack, which ultimately reduces crop yield. Studies have shown that Fusarium solani is the cause of the disease. Fifty six safflower genotypes were evaluated for their response to Fusarium root rot in a completely randomized block design with three replications in greenhouse conditions. The response was assessed by measuring traits such as mortality rate, length of necrosis zone in roots, number of viable plants, dry root weight, and dry weight of aerial area, stem height and stem diameter. The results showed that there is a high negative correlation between the mean necrosis length on the root and the number of live plants in the greenhouse. Genotypes were divided into 5 groups (resistant, relatively resistant, tolerant, sensitive, and relatively sensitive). The most resistant genotypes were Padideh, Golmehr, and P. Kose was evaluated as susceptible genotype. Since the wild species of C. palaestinus (P) and some genotypes resulting from its interspecies had the highest survival rate and the lowest necrosis length and mortality rate and on the other hand, this species is the most similar in terms of agronomic traits to the domestic species, the use of this species and the lines resulting from its interspecies to create disease-resistant cultivars could be recommended.

Grapevine decline disease (GDD) complex is a major global viticulture problem associated with a multi-year decrease in plant productivity and an increase in vine mortality, resulting in important economic losses to the viticulture industry. More than 35 fungal genera have been involved in the GDD complex, and the genus Cytospora has also been reported as one of the genera included in the disease-causing complex. This study aimed to identify Cytospora species involved in GDD complex in the vineyards of Miyandoab (West Azarbaijan province) and Malekan (East Azarbaijan province) Counties. So, during the summer and autumn of 2020-2021, sampling was done from the diseased plants showing symptoms of shoot wilting and die-back, bark and wood discoloration, brown to black discoloration of vascular tissues, and wood canker. The fungal isolation was done based on common phytopathological methods, and 78 isolates with the common characteristics of the genus Cytospora were isolated and purified. Based on the results combining morphological characteristics and sequence data obtained from three genomic regions, ITS-rDNA, TUB2, and RPB2, four species viz., C. chrysosperma (15 isolates), C. ershadii (24 isolates), C. salicina (28 isolates), and C. viticola (11 isolates) were identified. Cytospora viticola is a new species for the fungal biota of Iran, and grapevine is reported as a new host (matrix nova) for C. ershadii in Iran and the world. Pathogenicity of the selected fungal isolates from the identified species was confirmed on shoots of the Thompson seedless cultivar based on Koch's postulates.

Citrus canker is one of the most destructive citrus diseases caused by Xanthomonas citri subsp. citri (Xcc) Following the pathogen's attack on the plant, plant hormones and the induction of resistance genes play crucial roles in plant defense. This study explored the antibacterial effects of linalool and citral components against Xcc bacteria. Subsequently, we examined the expression patterns of the FLS2, RAR1, and PR1 genes in C. aurantifolia seedlings under different treatments, including citral, linalool, citral+Xcc bacteria (strain KVXCC1), and linalool+Xcc bacteria (strain KVXCC1), at 0-, 1-, and 4-days post-inoculation with Xcc bacteria using real-time PCR. The antimicrobial activity of linalool and citral essential oils revealed significant inhibitory effects on Xcc bacterial growth (P < 0.01). The minimum inhibitory concentration results showed that citral essential oil, with a concentration of 0.37 μg/ml, exhibited relatively high inhibitory power on this pathogen. Gene expression results indicated that the expression of FLS2, RAR1, and PR1 genes increased in response to citral, linalool, bacterial citral, and bacterial linalool treatments within one day after inoculation. However, the expression levels of these genes differed four days after inoculation. The findings of this study demonstrated that the linalool+bacteria treatment effectively enhanced the expression of defense genes and induced disease resistance in C. aurantifolia seedlings, thereby significantly reducing the pathogenic damage caused by citrus canker.

In March-April of 2020-2022, round and water-soaked spots surrounded by a brown border were observed on the green bean pods delivered to the markets of Isfahan from the southern provinces of the country. A bacterium with a fluorescent appearance and a spindle-shaped structure with irregular edges was routinely isolated from the 81 specimens collected. The genetic fingerprinting employing rep-PCR revealed a resemblance between the PCR product profiles of the isolates, which is consistent with their pathogenic and biochemical characteristics. The PCR reaction of representative isolates produced the expected-size fragments of 16Sr DNA through genus-specific primer sets. Subsequent analysis of the sequences of the fragments confirmed the affiliation of the isolates with Pseudomonas spp. The expected-sized amplicons were amplified and sequenced in nested-PCR tests using phaseolotoxin gene based primer pairs. The results showed that the nucleotide sequences were 99% homologous to Pseudomonas savastanoi pv. phaseolicola (Psp). By conducting a phylogenetic analysis with sequences of housekeeping genes gyrB and rpoD, the isolates were clustered with reference strains of Psp, confirming their identity. Considering the isolates’ morphological, biochemical and molecular characteristics, Psp was identified as the cause of halo blight disease in beans imported to Isfahan from the southern regions. In laboratory conditions, the persistence of the pathogen on seed was evaluated for more than one year. The long-term viability of Psp on seeds may lead to the ongoing prevalence of bean halo blight disease in the country in the forthcoming years, due to the cool and moist conditions resulting from spring rains.

Oaks (Quercus) are among the most important trees found in forests Iran and rest of the world. Over the last decade, oak charcoal disease (OCD) has become more common in numerous forest areas in the Zagros and Hyrcanian regions, largely due to reduced rainfall and multiple droughts. This disease causes local or systemic necrosis, wilting, and even death of infected oak trees within one or more years. In addition, there is a complex interaction between trees and biotic and abiotic environmental factors. This study was conducted in 2020-2021 on oak trees in seven provinces of the country, namely Khuzestan, Ilam, Lorestan, Kurdistan, Khuzestan, Isfahan and Golestan, to analyze and determine the current status of oak trees in terms of OCD and the causative fungal pathogens. For this purpose, samples of infected oak trees were collected and then the causal agents of the disease isolated and identified morphologically. Detection of the samples was confirmed by sequencing the fungal ITS1-5.8S-ITS2 and ß-tubulin gene. The results showed that the most prevalent fungal pathogens of OCD in the samples were Biscogniauxia mediterranea and Obolarina persica. The prevalence of these fungi in the studied provinces varied, with the highest prevalence of B. mediterranea in Lorestan and the highest prevalence of O. persica in Ilam. The results of this study complemented the existing relatively limited data on the prevalence of each fungal pathogen of OCD in different provinces. In addition, the current status of oak infection in each of the studied regions was clarified.

Corn (Zea mays) is from the cereal category and the large wheat family; it is the third crop after wheat and rice cultivated areas worldwide. This research aims to investigate the detection and identification of the pathogenic bacterium Pantoea dispersa in Iran using biochemical and molecular identification methods and the host range of this bacterial species. For this purpose, in two consecutive years, sampling was done from the corn fields of different provinces of Iran, which have symptoms such as leaf spots and wilting. Standard plant bacteriology methods were used to isolate bacteria with the mentioned symptoms, and isolates were identified using biochemical characteristics and primers related to housekeeping genes. In the investigation of pathogenicity and host range of 20 bacterial isolates obtained from different corn fields, six isolates were identified as P. dispersa. This is the first report of the presence of the bacterium in Iran. In examining the host range of the mentioned isolates millet and sourghum are introduced as new hosts of this species in Iran.