The gene encoding RNA-dependent RNA polymerase 1 (RDR1) is involved in basal resistance to several viruses. Expression of the RDR1 gene also is induced in resistance to Tobacco mosaic virus (TMV) mediated by the N gene in tobacco (Nicotiana tabacum cv. Samsun NN) in an incompatible hypersensitive response, as well as in a compatible response against Potato virus Y (PVY). Reducing the accumulation of NtRDR1 transcripts by RNA inhibition mediated by transgenic expression of a double-stranded RNA hairpin corresponding to part of the RDR1 gene resulted in little or no induction of accumulation of RDR1 transcripts after infection by PVY. Plants with lower accumulation of RDR1 transcripts showed much higher accumulation levels of PVY. Reduced accumulation of NtRDR1 transcripts also resulted in lower or no induced expression of three other antiviral, defense-related genes after infection by PVY. These genes encoded a mitochondrial alternative oxidase, an inhibitor of virus replication (IVR), and a transcription factor, ERF5, all involved in resistance to infection by TMV, as well as RDR6, involved in RNA silencing. The extent of the effect on the induced NtIVR and NtERF5 genes correlated with the extent of suppression of the NtRDR1 gene.

The incidence and distribution of Tobacco mosaic virus (TMV) and related tobamoviruses was determined using an enzyme-linked immunosorbent assay on 1,926 symptomatic horticultural crops and 107 asymptomatic weed samples collected from 78 highly infected fields in the major horticultural crop-producing areas in 17 provinces throughout Iran. The results were confirmed by host range studies and reverse transcription-polymerase chain reaction. The overall incidence of infection by these viruses in symptomatic plants was 11.3%. The coat protein (CP) gene sequences of a number of isolates were determined and disclosed to be a high identity (up to 100%) among the Iranian isolates. Phylogenetic analysis of all known TMV CP genes showed three clades on the basis of nucleotide sequences with all Iranian isolates distinctly clustered in clade II. Analysis using the complete CP amino acid sequence showed one clade with two subgroups, IA and IB, with Iranian isolates in both subgroups. The nucleotide diversity within each sub-group was very low, but higher between the two clades. No correlation was found between genetic distance and geographical origin or host species of isolation. Statistical analyses suggested a negative selection and demonstrated the occurrence of gene flow from the isolates in other clades to the Iranian population.

During 2009–2010, a survey was conducted in gardens and commercial fig orchards throughout Iran to determine the prevalence of Fig leaf mottle‐associated virus 1 (FLMaV‐1), Fig leaf mottle‐associated virus 2 (FLMaV‐2), Fig mild mottle‐associated virus (FMMaV), Fig latent virus 1 (FLV‐1) and Fig mosaic virus (FMV). Reverse transcription‐polymerase chain reaction and dot immunobinding assay (DIBA) were conducted on 104 fig samples collected from seven provinces. FLV‐1, FLMaV‐1 and FMV were found in 14.5, 11.5 and 8.6% of the samples, respectively, but FLMaV‐2 and FMMaV were absent. The overall average of infection reached 18.3%, with a peak of 42.9% in Semnan Province, followed by Golestan (40%), Tehran (32.3%), Lorestan (28.6%) and Mazandaran (25%) provinces. No infection was found in Fars and Gilan provinces. Fig samples from Varamin and Khorramabad districts showed high levels of mixed infections, 35.7 and 28.6%, respectively. The presence of FMV and FLV‐1 in the sap of symptomatic fig leaves was also ascertained by DIBA. Sequence analysis of amplified DNA from the partial RNA‐dependent RNA polymerase gene of two FMV isolates from Iran showed a low level of nucleotide variability (5%). The Iranian isolates shared a common phylogeny with other Mediterranean FMV isolates and in particular with those originating from Turkey already reported in GenBank. This is the first report on the presence of FLMaV‐1 and FLV‐1 in Iran and offers a preliminary insight into the unsatisfactory health status of fig in this country.

ABSTRACT:The purpose of this study was to evaluate the effectiveness of a commercial biofungicide such as Trichomix-HV in controlling damping-off disease in cucumber seedlings of greenhouses. In this regard, 504 fungal isolates were collected from greenhouses at 31 districts in city of Jiroft in Iran. Pythium aphanidermatum, P.ultimum, P. irregulare, Phytophthora drechsleri, and Ph. melonis accounted for 9.9 %, 8.3 %, 4.5 %, 4.9 %, and 21 % of total isolates collected, respectively. Isolates of P. aphanidermatum obtained from commercial cucumber in greenhouses were tested in vitro and under greenhouse conditions for sensitivity to chemical and biological treatments. To this aim, Trichomix-HV a commercial formulation of Trichoderma harzianum strain T969 and the fungicides Metalaxyl and Metalaxyl MZ were amended into the culture medium as well as into sterilized or non-sterilized greenhouse soils inoculated by the pathogen and containing plants at the seedling stage. Trichomix-HV significantly (P < 0.001) reduced seedling infection at a rate of 82 % when applied into soil medium at a concentration of 10 7 conidia ml/L and reduced vegetative growth of Pythium aphanidermatum in vitro. The result from this study shows that Trichomix-HV can be effectively used as a biocontrol agent for controlling damping-off cucumber seedlings and having the potential to replace chemical fungicides as a mean of disease control.

We have studied how simultaneously elevated temperature and CO levels [climate change-related conditions (CCC) of 30°C, 970 parts-per-million (ppm) of CO vs. standard conditions (SC) of 25°C, ~ 405ppm CO] affect physiochemical properties of Nicotiana benthamiana leaves, and also its infection by several positive-sense RNA viruses. In previous works we had studied effects of elevated temperature, CO levels separately. Under CCC, leaves of healthy plants almost doubled their area relative to SC but contained less protein/unit-of-area, similarly to what we had found under conditions of elevated CO alone. CCC also affected the sizes/numbers of different foliar cell types differently. Under CCC, infection outcomes in titers and symptoms were virus type-specific, broadly similar to those observed under elevated temperature alone. Under either condition, infections did not significantly alter the protein content of leaf discs. Therefore, effects of elevated temperature and CO combined on properties of the pathosystems studied were overall cumulative.