فصلنامه بیماریهای گیاهی
سال پنجاه و پنجم شماره 2 (پاییز 1398)

During 2010-2017, samples of different plants grown in greenhouses and crops with sprinkler irrigation systems, in Chaharmahal va Bakhtiary province, showing symptoms of necrotic spots, marginal leaf blight, fruit rot, and wilting were collected and tested for the presence of bacteria associated with those symptoms. The isolated bacteria were identified based on standard methods for the identification of plant pathogenic bacteria. Pathogenicity of strains was tested on appropriate hosts under greenhouse conditions. Although various genera of bacteria were isolated, isolation frequency of fluorescent pseudomonads was more than other genera of bacteria. Fifty-three and a half percent of pseudomonads was identified as Pseudomonas marginalis and 18.2% as P. syringae pv syringae. The isolates of P. marginalis from cucumber, potato, tomato, pepper, wheat, beet, and dieffenbachia and strains of P. syringae pv syringae from cucumber, sugar beet, wheat, and tomato were pathogenic on their respective hosts. Polymerase chain reaction with universal primers 16Sf / 16Sr and R1378 / PO27F, designed for detection of γ-Proteobacteria, confirmed the identity of the isolated bacteria based on biochemical and physiological tests by the alignment of nucleotide sequences in the GeneBank. Phylogenetic analysis based on 16SrDNA gene sequences of 10 isolates of  P. marginalis were differentiated from each other. This investigation showed that strains of P. marginalis can  bepotential pathogens for greenhouse plants and field crops  with sprinkler irrigation.

In spite of existing of several methods for detection of viruses, time consuming is major limitation of them. So, developing faster and real time method is important to certificate the plant materials in quarantine stations and virus management. In the recent research, nanotechnology was employed to detect Potato virus S (PVS) using gold nanoparticles (AuNPs). Colloidal AuNPs were prepared through citrate reduction and conjugated to a specific antibody against PVS coat protein. Conjugation was optimized by changing the pH of AuNPs and antibody concentration. Antibody coated nanoparticles were used to detect different concentrations of antigen using spectrophotometry. After binding the antibody to the gold nanoparticles which cause an increase in particle size, the SPR peak was displaced in range of 4-5 nm and shifted from 524 to 530 nm. The binding of the antigen to the nanoparticle also caused a change in the particle size and an increase maximum absorbance from 530 to 539 nm. No spectral change were seen when PVY and CMV used as controls. This study is the first attempt of nanoparticle usage in quick and easy detection of PVS

The charcoal root disease caused by Macrophomina phaseolina is necrotroph pathogen with wide host range and showed various phenotipic intraspecies variabiity. Considering the difficult identification of intraspecies heterogeneity on the basis of phenotypic factors, compatible mycelium groups were introduced as an appropriate tool for classification and intraspecies heterogeneity distinction. In the present study, mycelial compatibility groups (MCGs) were investigated among a total of 112 isolates of M. phaseolina from different hosts in different regions of Iran. A total of 33 different MCGs were identified, showing the existence of high genetic diversity among the fungal isolates. There was no relationship between mycelial compatibility grouping, geographic distributions and host origins of the isolates. This is the first report on the compatible mycelium groups of M. phaseolina isolats in Iran.

Phytochemicals of some plants are suppressive to the root-knot nematodes (Meloidogyne spp.). In this study, effects of aqueous extract or dry powder of several plants on the activity of M. incognita and M. javanica were investigated. Treatment of second stage juveniles (J2s) of the nematodes with aquatic extracts of 25 plant species under laboratory conditions showed that after 48 hours, extracts of eruca, ornamental chili pepper, tarragon, caster bean, sesame, thistle, chinaberry and dyer's crotoncaused more than 50% mortality of the J2s of both nematodes. In pasteurized‏ soil, extracts of scarlet sage and safflower seed with 78.9% and 46.9% reduction of reproduction factors (RFs) of M. incognita and M. javanica, respectively, were the most effective plants in treatment of tomato plants (cv. Early Urbana) with 13 different plant extracts. In addition, eruca and creeping thistle extracts reduced RFs of both species. None of the treatments affected fresh and dry shoot weight of tomato. In field soil, extracts of eruca and caster bean with 57.2% and 51.0% reduction of RFs of M. incognita and M. javanica in tomato plants, respectively, were the most effective extracts among eruca, caster bean, tarragonand creeping thistle plants. All treatments significantly increased the fresh shoot weight of infected tomato. In pasteurized‏ soil, scarlet sage powder with 70.3% and creeping thistle with 49.7% had the highest effect on RF reduction of M. incognita as compared to ornamental chili pepper, castor bean, chinaberry and safflower seed.

In recent years, non-chemical control of common species of the root-knot nematodes (Meloidogyne spp.), including soil enrichments by organic matters, animal manures and chemical fertilizers has received considerable attention. In 2014, in an experiment, effects of two levels (10 and 25 mg/kg) of sulfur fertilizers viz. ammonium sulfate, calcium sulfate, potassium sulfate, magnesium sulfate and zinc sulfate, and the levels of 25 and 50 mg/kg of elemental sulfur on the activity of the root-knot nematode M. incognita, in pasteurized soil were studied in greenhouse. Seedlings of cucumber cv. Negin at three or four-leaf stages were inoculated with two eggs or second stage juveniles of the nematode/g of soil. The results of two trials showed that magnesium sulfate 10 mg/kg caused 179% increase in the yield on average. The highest reduction was recorded in the number of eggs/g of root and reproductive factor in 25 mg/kg level of calcium sulfate with 71.6% and 58.6%, decrease followed by 25 mg/kg sulfur with 69.1% and 57.0% decrease respectively. The treatment of 50 mg/kg of sulfur was also in the next rank.

Faba bean necrotic yellows virus (FBNYV) causes severe yield losses and crop failure in legumes in the north African, south Asian and European countries. Following nucleotide sequencing of DNA-M segment of 17 host and geographical FBNYV isolates in Iran, different molecular analysis were performed based on all available DNA-M sequences of FBNYV. Based on constructed phylogenetic tree using nucleotide sequence of DNA-M component, FBNYV isolates were grouped into three clades, including isolates from Iran and Azerbaijan as a distinct clade. Genetic distance studies of FBNYV host subpopulations revealed some evidences of host adaptation in FBNYV natural selection. High gene flow was found among Iran – Azerbaijan and Spain – Africa subpopulations, indicating the relationship of their origins. Maximum genetic diversity of DNA-M was estimated in the central subpopulation of Iran. The dN/dS (Ѡ) value less than 1 represented the negative selection pressure on the movement protein of the virus. Seven out of nine recombination events were detected in DNA-M of Iranian FBNYV isolates. This is the first report of the FBNYV infection on pea from Iran. In the current study, the complete DNA-M nucleotide sequences of French bean and pea isolates of FBNYV were determined for the first time in the world.