فصلنامه بیماریهای گیاهی
سال پنجاه و سوم شماره 4 (زمستان 1396)

During 2007-2012 surveys, pear decline (PD) symptoms was observed in different pear orchards in Mashhad andChenaran (Khorasan-e-Razavi province), and 11 areas in Fars province. In nested PCR assays using P1/P7 primer pair in the first round and R16F2n/R16R2 and fO1/rO1 primer pairs in the second round, expected fragments of 1250 and 1050 bp, respectively, were amplified from symptomatic naturally infected pear trees, pear psyllid (Cacopsylla pyricola) insects collected on PD affected trees and experimentally inoculated plants. Real and virtual RFLP analyses showed that phytoplasmas detected in naturally decline affected pear trees, inoculated plants and psyllid insects were identical and belonged to 'Candidatus Phytoplasma pyri'. Phylogenetic analysis also confirmed that the detected phytoplasmas are closely related to 'Ca. Phytoplasma pyri'. As representatives of PD phytoplasmas detected in Fars and Khorasan-e-Razavi provinces, respectively, pear decline agents from Bajgah and National orchard were transmitted from PD affected trees to pear and quince young trees by grafting and to periwinkle via dodder inoculation. This is the first report of association of 'Ca. Phytoplasma pyri' with PD disease and psylla insects in Khorasan-e-Razavi and some areas in Fars province, Iran.

Interaction between nematode Meloidogyne javanica and fungus Verticillium dahliae on tomato in greenhouses were investigated.Nematode and the fungus inoculated in different time intervals, nematode two weeks before the fungus, nematode and the fungus at the same time, fungus two weeks before the nematode, nematode alone and the fungus alone and the interaction of the pathogen agents were tested.The results showed that the presence of the both of the pathogens in the soil can lead to the greatest reduction in growth factors and the reduction in nematode two weeks before the fungus and nematode fungus (simultaneous) treatments was more significant.The highest disease severity index was observed after 90 days in the nematode two weeks before the fungus treatment, that was significantly different with fungus alone treatment and in all fungus received treatments disease severity index was more than two.Presence of the nematode M. javanica increased severity and rate of wilting caused by V. dahliae on tomato while the presence of fungus, reduced nematode pathogenicity and population indices.The least amount of vascular tissue browning index and stem colonization percent was observed in treatment with fungus alone inoculated and in other words, nematode increases vascular tissue browning index and stem colonization percent.The highest plant height reduction observed in the treatments where both of the pathogens were present.The interaction between pathogen agents with reduction in growth factors indices and increase in tomato wilt disease increases the damage to the plant

A field experiment was conducted in the 2 × 3 m plots to determine the effect of different initial population densities of Meloidogyne javanica on growth parameters and yield of okra (Abelmoschus esculentus; cv. Soltani) in 2013. This research was carried out based on completely randomized design (CRD) with five replications using a geometric series of 14 nematode population densities (0 to 512 eggs or second stage juveniles (J2) / cm3 soil). The plants died at high levels of nematode population (> 256). The relative shoot fresh and dry weight and relative yield fitted the Seinhorst damage model and the tolerance limit for those traits was 0.34, 0.33 and 0.28 eggs or J2 / cm3 soil, respectively. The maximum multiplication rate was 749 and the equilibrium density was 159 eggs or J2 / cm3 soil. Nematode reproduction factor was negatively correlated with the initial populations as the highest multiplication was occurred at the lowest initial population densities. Damage threshold (10% yield loss) of okra to M. javanica was estimated as 0.85 eggs or J2 / cm3 soil which represented the susceptibility of okra plant to M. javanica.

Viroids are pathogenic RNAs in plants without protein encoding capacity. Seven viroids belonging to four genera in the Pospiviroidae family have been reported from citrus species. By constructing the infectious clones of citrus viroids, it was possible to carried out their pathogenicity test. Full-length genome of CEVd, HSVd, CBCVd, CDVd, CVdV and CBLVd was separately amplified in RT-PCR using total RNA extracted from a Moro blood orange plant and resulting PCR products were sequenced. The full-length genome of each viroid was inserted under the control of cauliflower mosaic virus 35S promoter in a pBin62SK binary vector. Pathogenicity of viroids was tested by agroinoculation of their infectious clones to cucumber (Cucumis sativus), tomato (Solanum lycopersicum) and trifoliate orange (Poncirus trifoliata). Three weeks after inoculation, viroids were detected in newly grown leaves of inoculated plants by RT-PCR using specific primers and by dot blot hybridization using viroid specific probes. Five weeks after inoculation, symptoms including little leaf, mottling and epinasty by CVdV and CBCVd, mottling by CDVd, and epinasty and leaf deformation by CEVd, HSVd and CBLVd in tomato leaves were observed. Mechanical inoculation of infected sap of infected tomato plants induced similar symptoms in healthy tomato plants. Identification of the viroids in newly grown leaves of inoculated plants indicated the infectiousness of the generated constructs. Infectious clones of CEVd, HSVd and CBCVd were previously made, but it is the first report of the construction of the infectious clone for CDVd, CBLVd and CVdV.

Beet curly top Iran virus (BCTIV, genus Becurtovirus) and the severe strain of Beet curly top virus (BCTV-Svr, genus Curtovirus) are known as the causal agents of curly top disease in sugar beet and several other dicotyledonous plants in Iran. In addition to sugar beet, tomato and pepper are also economically important hosts of these viruses. Tomato leaf curl disease, one of the most important viral diseases of this crop, is caused by several species of the genus Begomovirus including the Iranian isolate of Tomato yellow leaf curl virus (TYLCV-[Ab]) that is a severe strain of TYLCV. TYLCV-[Ab] is a major component of tomato leaf curl disease in southern Iran. In this study, the interaction of BCTIV and BCTV-Svr with TYLCV-[Ab] in tomato plants was studied under greenhouse conditions. Analysis of the Real-time PCR data showed antagonistic interaction in simultaneous infection of BCTV-Svr or BCTIV with TYLCV-[Ab] as evidenced by decreasing in concentration of each virus involved in mixed infection in comparison to single infections. In general, in mixed infections, TYLCV-[Ab] was dominant and seemed more adaptive to tomato compared to BCTIV and BCTV-Svr.

Members of the genus Orthotospovirus cause serious diseases in a variety of economically important crops, including ornamentals and vegetables, worldwide. To detect the orthotospoviruses infecting different crops and ornamental plants in Markazi province, Iran, about 160 suspected samples with viral-like symptoms were collected. Totally 106 of the specimens showed positive reaction in DAS-LEISA test using polyclonal antibodies raised against N proteins of Tomato yellow ring virus (TYRV), Iris yellow spot virus (IYSV) and Groundnut bud necrosis virus (GBNV). Sequence analysis of the obtained fragments from RT-PCR using generic primers of Asian and Eurasian clades of tospoviruses and nucleocapsid gene specific primers confirmed the occurrence of TYRV on alstroemeria, tobacco, tomato and nasturtium; IYSV on onion and leek and Capsicum chlorosis virus (CaCV) on black-eyed susan (Rudbeckia sp.). Biological analysis of selected isolates of orthotospoviruses on Nicotiana benthamiana, Capsicum annuum and Vigna unguiculata showed that TYRV isolates were differentiated from each other. Phylogenetic analysis based on amino acid sequences of nucleocapsid protein indicated that TYRV isolates belong to TYRV-t strain and IYSV isolates belong to Eurasia-IYSV cluster. In addition, CaCV isolates were grouped into Watermelon silver mottle virus (WSMoV) clade with close relationship with the United State CaCV isolate.

Efficiency of the application of two species from arbuscular mycorrhizal fungi, Glomus mosseae and G. versiforme, and four plant growth promoting Rhizobacteria Pseudomonas fluorescens, Pseudomonas striata, Bacillus subtilis and Paenibacillus polymyxa on the control of root-knot nematode, Meloidogyne javanica, was studied. Based on our results arbuscular mycorrhizal fungi and plant growth promoting rhizobacteria stimulated the growth of tomato plants and also reduced the severity of the disease caused by M. javanica. Combined application of the tested biocontrol agents was more effective than their single usage. P. polymyxa was more efficient in controlling M. javanica than other implemented biological agents so that this bacterium could decrease egg number in the egg mass of M. javanica as 52% compared with nematode alone control treatment. Likewise, the combined application of G. mosseae and P. polymyxa had the best effect to suppress nematode, so that in this treatment J2 population decreased as 59% compared with nematode alone treatment.