فصلنامه بیماریهای گیاهی
سال پنجاه و چهارم شماره 4 (زمستان 1397)

Strictosidine synthase is a key enzyme in the biosynthesis of plant alkaloids. The homologous of the strictosidine synthase domain has been found in different organisms such as Arabidopsis thaliana. Bioinformatics and expression studies on one of the strictosidine synthase-like gene (SSL6) in Arabidopsis plants showed that gene responded to the signaling molecules, fungal and viral pathogens. The functional role of SSL6 has been further studied using an Arabidopsis knockout mutant with a T-DNA inserted into exon 1. The plants were inoculated with Alternaria brassicicola, which had incompatible interaction with A. thaliana. The fungal biomass was quantified by quantitative real-time PCR and spore count techniques. The assays indicated that T-DNA mediated ssl6 mutant was more susceptible than Col-0 genotype. The chlorophyll content and the size of necrotic lesions were significantly smaller in the ssl6 mutant compared with the Col-0. This is the first report with reference to the functional analysis of SSL6 suggesting that might be SSL6 plays an important role, among other factors, in plant defense against A. brassicicola.

Pyricularia oryzae is rice and wheat blast causal agent and can occurs leaf spot on some grass species. Blast disease is one of the most important diseases in rice areas cultivated in Iran, annually it cause economic damage to rice. Sampling was conducted from rice, maize, foxtail millet, and weeds of wheat and rice cultivation regions, citrus orchards, and jungles in southern of Caspian Sea and from rice fields in Khorasan-razavi province during summers of 2013 and 2015. Phylogenetic analysis with partial regions of Actin (ACT), Calmodulin (CAL), and RNA polymerase II largest subunit genes (Rpb1) allowed to assign the strains from different hosts to Pyricularia oryzae. Pathogenicity test of P. oryzae species was applied on rice, foxtail millet, maize, barnyard grass, and wild foxtail millet in control condition. Based on pathogenicity, each isolate were highly pathogenic toward its host but not to the other hosts tested. In order to a determination of mating type, Multiplex PCR technique using primers L1 and L2 (for Mat1-1), T1, and T2 (for Mat1-2) was done. Under lab conditions, the sexual stage was conducted with isolates from different hosts on rice flour- agar medium. The mating type and sexual reproduction show that Mat1-1 is frequent in rice population and foxtail millet population and Mat1-2 is frequent in weeds populations and maize population.

Sophora yellow stunt-associated virus (SYSaV) (Nanovirus, Nanoviridae) is a new nanovirus that recently identified in Iran with wide distribution. In the present study, the SYSaV infection of chickpea (Cicer arietinum L.), lentil (Lens culinaris Medikus), liquorice (Glycyrrhiza glabra L.), esfand (Peganum harmala L.) and milk vetch (Astragalus sp.) showing typical nanovirus symptoms including dwarfing and yellowing was tested by PCR and full-length sequencing of selected genome components. Results indicated that these samples are infected with SYSaV. In transmission experiments, the capability of cowpea aphid (Aphis craccivora) and pea aphid (Acyrthosiphon pisum) to transmit SYSaV to healthy plants was evaluated under greenhouse conditions. While Aphis craccivora transmitted the virus from infected to healthy sophora plants, Acyrthosiphon pisum collected on naturally infected sophora plants transmitted the virus to sophora, chickpea and cowpea seedlings. Based on the results of this study, beside the main host (sophora), SYSaV is able to infect two other medicinal plants. In addition, the host range of the virus is not limited to the wild species and at least two legume crops are infected with SYSaV.

In order to investigate the host range of various populations of causal agent of wheat leaf rust, Puccinia. recondita sensu lato, during 2010-2016, fifty isolates of the pathogen were collected from different hosts of Poaceae in various parts of Iran including: Ardabil, Fars, Golestan, Ilam, Kerman, Khuzestan, Khorasan Razavi, Kurdistan, Mazandaran and West Azerbaijan. Pathogenicity of all isolates on seven hosts, including bread wheat (Triticum aestivum L., cv. Boolani), durum wheat (Triticum durum Desf., cv. Karkhe & cv. Yavaroos), barley (Hordeum vulgare L., cv. Afzal), oat (Avena sativa L.), rye (Secale montanum Guss.) and triticale (Triticosecale Wittm. Ex A. Camus) was examined. Results indicated that all isolates had high disease severity on bread wheat (cv. Boolani) and triticale. Bread wheat isolates were avirulent on all hosts except for triticale, which showed a hypersensitive reaction or small, dispersed pustules. Triticale isolates were only pathogenic on triticale and bread wheat. Durum wheat isolates were virulent on bread wheat, durum wheat, and triticale, and were avirulent on barley and rye plants. Oat isolates showed an avirulence response on barley, rye and various genotypes of durum wheat and rye. Barley isolates were also pathogenic on bread wheat, triticale and barley and avirulent on durum wheat and rye. Although wild barley isolates were virulent on bread wheat, durum wheat, and triticale, they were avirulent on other hosts. Oat is a non-host for all leaf rust isolates, except for its own isolates. The findings indicate that in the absence of wheat, leaf rust populations are able to survive on other members of the Poaceae family.

Phytophthora parsiana has been considered as a unique and important pathogen in Iranian pistachio orchards. The description of novel and closely related species to this phylogenetic taxon in Clade 9 of Phytophthora spp. phylogenetic trees, including P. hydropathica, P. hydrogena and P. virginiana, as well as extremely heterogeneous morphological, physiological and host rang of the assigned isolates, necessitates a comparative study of the isolates as a complex species. Isolates that have been assigned to this taxon during the last 25 years, along with the isolates which have been isolated in 2014-2015 were studied using single-strand-conformation polymorphism (SSCP) of ribosomal DNA. The results of the patterns showed that the isolates assigned to P. parsiana were classified into four distinct groups. Phylogenetic analysis of cytochrome C oxidase subunit I based on maximum-likelihood inference also confirmed the results and the isolates grouped in four distinct groups along with other members of the Phytophthora spp. of clade 9. Morphology and physiology characteristics and pathogenicity tests revealed some differences between these four groups. Unlike other groups, the isolate of the third group was not pathogenic to pistachio seedlings, and the same as isolates of groups one and four it was not able to grow at 40 ° C. Additionally the micrometric characteristics of sporangia were significantly different from those of other groups. The evidence from this grouping confirms the existence of a significant intra-species variation as well as the need for a revision of the initial description of this complex species.

In the summer of 2013, some bacterial isolates were obtained from walnut tissues with the symptoms of shallow bark canker in the Alborz province of Iran. Based on the phenotype and genotype features, the causal agent was identified as Brenneria nigrifluens. It was the first report of B. nigrifluens causing shallow-bark canker in walnuts in the Alborz province of Iran. The existence of this disease in the Alborz province can pose a latent threat to many walnut orchards in that province.

Oxalis triangularis A. St.-Hil. (Oxalidaceae) known as “False Shamrock”, is a perennial ornamental plant native to Brazil. The plant is used as indoor pot plant in Iran. In June 2018, rust-infected leaves were sampled from an indoor pot plant in University of Maragheh, located in Maragheh, East Azarbaijan. The following morphological features were observed on infected leaves:

Phytolasmas are important phloem-restricted plant pathogens which are classified into prokaryotes kingdom and mollicutes class and annually cause considerable loss to crops, ornamentals and trees