Iranian Journal of Plant Protection Science
Year:2019 | Volume:50 | Issue:1|Papers Count:7

Citrus exocortis viroid (CEVd) is the causal agent of exocortis disease, the economically important viroid disease of citrus. In this research, sequence polymorphism and population structure of CEVd were investigated in CEVd tolerant and sensitive hosts (sour orange (Citrus aurantium L. ) and citrange (Poncirus trifoliata (L. ) Raf. × C. sinensis (L. ), respectively) seedlings. Full-length in vitro transcript of single sequence CEVd-S1 isolate was used for mechanical inoculation. The genetic diversity of CEVd populations was estimated in two citrus hosts by single-strand conformation polymorphism (SSCP) and sequencing. The analysis of cloned DNAs recovered from infected hosts by this isolate demonstrated that host species was effective on the variability within a single CEVd isolate. The amount and composition of the genetic diversity were different among the two hosts, and was higher in the tolerant host compared with the sensitive one. Furthermore, the analysis of thermodynamic secondary structures illustrated that nucleotide changes identified in this study did not induce major modifications in the viroid rod-like secondary structure.

In order to study molecular identification and genetic diversity of Prunus necrotic ringspot virus (PNRSV), 149 leaf samples from 37 orchards of pome and stone fruit trees of Kurdistan province were collected and tested by RT-PCR using a PNRSV-F3/PNRS-R3 specific primer pair. Results showed that 20. 8% of the samples were infected by PNRSV. In the next stage of the study, 13 isolates were selected based on the host and geographic region and their amplified fragments were ligated into the pTG19-T plasmid, transformed to E. coli DH5α , and sequenced. Phylogenetic analysis showed that PNRSV isolates formed three clades PV96, PV32, and PE5, and all new-sequences from Kurdistan (in this research) were categorized in PV96 phylogenetic clade, which is close to other Iranian isolates. The new isolates shared 99 ± 0. 002 identities together and 94/9 ± 0. 005 with other previously PNRSV reported isolates at the nucleotide level. Pairwise comparisons of sequences showed that isolates peach from Kamyaran (KH10), pear from Sanandaj (SZ93), and peach from Dehgolan (D7) had the highest nucleotide similarity (98%) with Iranian isolate nectarine (KX353935) whereas isolate pear from Sanandaj (SZ26) had the lowest nucleotide identity with isolate plum from Poland (DQ983499). The low dN/dS ratio in all populations of the virus showed that negative selection plays important role in PNRSV-CP evolution and recombination. There is no recombination event in this domain of PNRSV genome of these isolates.

In this research, the influence of eggplant monoculture (E), soybean monoculture (S), and three intercropping systems including two rows of eggplant with four rows of soybean (2E: 4S), two rows of eggplant with two rows of soybean (2E: 2S) and four rows of eggplant with two rows of soybean (4E: 2S) were studied on population densities of Tetranychus urticae Koch, diversity and abundance of its predators, and yield of both crops in an experimental field based on a randomized block design with four blocks during two cropping seasons (2016-2017). In both years, the densities of T. urticae eggs and mobile forms on eggplant and soybean were significantly lower in the three intercrops compared to monoculture systems (P < 0. 05). Moreover, the densities of T. urticae eggs and mobile forms were significantly higher on the soybean than the eggplant in each monoculture and intercrop system. The Shannon’ s diversity indexes (H') for T. urticae predators on eggplants were significantly higher in the three intercrops compared to the monoculture. Furthermore, the values of this index were greater in soybean monoculture and 2E: 4S intercrop than 2E: 2S and 4E: 2S systems (P < 0. 05). Values of the land equivalent ratio (LER) were higher in 2E: 4S relative to other intercrop systems in both years. Therefore, it could be concluded that 2E: 4S intercrop is the most suitable cropping system for using in integrated management of T. urticae in eggplant and soybean fields.

Sugarcane Mosaic Virus (SCMV) is one of the important diseases of the sugarcane. In this study, the infection of sugarcane mosaic virus in imported and existing cultivars was screened based on nucleic acid-based molecular methods. During 2014– 15, samples showing disease symptoms were collected from 90 different cultivars grown in six sugarcane agro-industries and their partial blades were separated. The samples were freeze-dried and powdered in liquid nitrogen. Suitable primers were designed to amplify 1040 bp from the nuclear inclusion B and coat protein gene sequences using the RT-PCR method. Ten out of 90 surveyed samples were SCMV-infected and produced expected-size fragments. These samples belonged to the cultivars of IRC99-06, V58-4, and Q58 from Sugarcane Research and Training Institute for the Development of Industries in Khuzestan, IRC99-09, IRC00-21, and 4380-3 from Salman Farsi agro-industry, CP80-1557 and V68-74 from Imam Khomeini agro-industry and two uncertain cultivars. Four out of 10 detected samples were directly sequenced and deposited in GenBank. A BLASTn search of the four detected isolates, including Kh10, Kh41, Kh44, and Kh28, showed the highest identity to isolates from Iran and Argentina. Phylogenetic tree constructed using the maximum likelihood algorithm showed that the Iranian isolates were probably originated from Argentina and China.

Early blight disease is one of the most common foliar diseases of tomato, which causes a great reduction in the quantity and quality of its yield. Regarding the use of fungicides in controlling this disease, identification of plant defense mechanism against the pathogen can be useful in introducing resistant cultivars and controlling the damage of the pathogen. In this research, several biochemical changes and expression patterns of PR1b1 and WRKY33 genes were investigated by qRT-PCR in a resistant cultivar Super 2270 and a susceptible cultivar CH Flat infected with the fungus Alternaria solani. Sampling was done during five intervals with three replications. The hydrogen peroxide accumulation, activity of defense enzymes Guacul peroxidase, Catalase and Superoxide dismutase enzymes, and the number of transcripts of genes was found to be increased in a challenge with the pathogen. The activity of these enzymes and genes were higher in the resistant cultivar. H2O2 accumulated rapidly in the resistant cultivar leaf tissues and peaked during the early stages of infection, whereas accumulation was stronger and more intense in the susceptible cultivar tissues in later stages. These results indicated that the induction of oxidant/antioxidant responses and the activity of genes in this study are a part of the tomato defense mechanism against the necrotrophic fungus A. solani.

During survey of rice fields in Fars and Khuzestan provinces at mature grain stage, 42 seed samples were collected. Fusarium isolates were obtained from these samples by planting seeds on selective Fusarium medium (Pepton-PCNB-Agar, PPA) by two methods i. e.; surface sterilization by sodium hypochlorite (NaClO 1%) and without disinfection. Cultivated samples were kept in incubator at 25± 1° C and intermittent light (12 hours of light and 12 hours of darkness). Morphological identification of 26 purified Fusarium isolates was performed on the WA, PDA, CLA and SNA. Phylogenetic relationships of 18 isolates on the basis of TEF1-α gene region and ITS1-5. 8S-ITS2 region sequences were investigated. The results revealed that Fusarium isolates belonged to two species complexes FIESC (Fusarium incarnatum-equiseti species complex, 50%) and GFSC (Gibberella fujikuroi species complex, 46%). Fusarium fujikuroi species in Fars and F. semitectum species in Khuzestan were most frequent. Two species F. fujikuroi and F. andiyazi belonging to the GFSC species complex were identified in two separate clades in phylogentic tree based on TEF1-α . On the basis of TEF1-α gene, F. merismoides was not identified, but the ITS region sequence was identified as Fusicolla acetilerea and differentiated this species from Fusarium species in the phylogenetic tree.

Take-all disease, caused by Gaeumannomyces graminis var. tritici (Ggt), is the most devastating root disease of cereals throughout the world. The disease has been reported from different regions of Iran, including Kermanshah province. To evaluate current wheat cultivars for resistance or tolerance to take-all disease, 17 wheat cultivars were inoculated by a mixture of four selected isolates of Ggt and their resistance was evaluated under field conditions. In the spring of 2012, these cultivars were sown in microplots with 100×50 cm dimensions. The inoculum, prepared on autoclaved oat seeds, were added to every row of sowing and then covered with soil. Different traits including grain yield, biological yield, thousand grain weight, root fresh weight, shoot fresh weight, total fresh weight, root dry weight, shoot dry weight, percent of diseased rootlets, number of tillers, number of grains in the spike, weight of grains in 1 m rows, average weight of grains in the spike, total dry weight, harvest index, and grain yield in 1 m2 were recorded and analyzed. In this study, different stress indices including stress susceptibility index (SSI), stress tolerance index (STI), yield index (YI), and Harmonic mean (HAM) were calculated. Based on the RS parameter, which includes all the indices, Marvdasht, Parsi, and Aflak were introduced as tolerant cultivars. Moreover, Sardari, Sivand, Shiraz, and Alvand were identified as susceptible cultivars.