IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2007 | Volume:43 | Issue:1 (169)|Papers Count:16

Sugarcane mosaic virus (SCMV) is a widespread cereal potyvirus in the world. Two SCMV isolates, KhzL66 and KhzQ86, from sugarcane plantation in Khuzistan were subjected to RT-PCR using potyviral degenerate and specific primers. Amplified segments were cloned and sequenced. The resulting sequences were assembled to yield segments of 1815 nt which included 3´-region of NIb gene, CP gene and 3´-UTR. Comparisons were made between these two isolates and a number of other cereal potyviruses available in GenBank using MegAlign (DNASTAR) and CLUSTAL X based on alignment of CP-UTR region. Maize dwarf mosaic virus (MDMV), Sorghum mosaic virus (SrMV), Johnson grass mosaic virus (JGMV), Iranian Johnson grass mosaic virus (IJMV) and Zea mosaic virus (ZeMV) were included in multiple alignment. Phylogenetic tree was constructed by Neighbor-joining majority- rule method. In phylogenetic analysis 41 sequences were differentiated into 7 groups (viruses): MDMV, SrMV, JGMV, IJMV, ZeMV and SCMV with two major subgroups I and II. Iranian isolates of SCMV were grouped with isolates of Egypt and South Africa in a subclade in group I. It is speculated that the Iranian isolates have been introduced into this country with sugarcane cuttings.

Fusarium oxysporum f. sp. melonis, the causal agent of Fusarium wilt of Cucumis melo was investigated for the presence of mycoviruses. Four dsRNA segments were identified in an isolate of F. oxysporum isolated from stems of Cucumis melo plants in Maharloo (east of Shiraz). DNase and RNase treatments confirmed the double-stranded nature of the RNA molecules. Mycelial mats were obtained in PD broth. The dsRNAs were extracted and purified using CF-11 cellulose chromatography. The dsRNA segments were approximately 0.7, 2.3, 2.5 and 3 kbp in size. Virus purification and electron microscopy revealed the presence of isometric virus-like particles (VLPs), ca 35 nm in diameter. The name Fusarium oxysporum f. sp. melonis virus (FuOMV) was suggested for this virus. Attempts to cure of dsRNA from the viruliferous culture by hyphal tip excision or using a range of cycloheximide concentrations, up to 200 mg ml-1, with or without incubation at 32°C were unsuccessful. Pathogenecity tests by root dip inoculation of susceptible C. melo cultivars with a suspension of 5x105 conidia per ml indicated the virulence of this isolate. The results implied that the isolated dsRNAs have no apparent effects on morphology and pathogenicity of the F. oxysporum f. sp. melonis. Molecular cloning and partial nucleotide sequencing of the largest dsRNA segment (dsRNA I) showed the significant sequence similarity of the deduced amino acid sequences to the RdRp encoded by Chrysoviruses. Collectively, the biological and molecular data imply the resemblance of this mycovirus with those of Chrysovirus genus.

Enzyme phenotypes of esterase, malate dehydrogenase and superoxide dismutase were used to identify 90 populations of Meloidogyne spp.( 62 M. javanica, 20 M. incognita, five M. arenaria and three unknown species) from different regions of Iran. Esterase was the most useful biochemical marker for identification of major species. Soluble proteins were extracted from young egg-laying females and resolved in polyacrylamid gel (%10) under nondenaturing electrophoresis conditions. Esterase profile in M. javanica populations were identified by a unique three banded pattern named J3, whereas M. incognita populations had a characteristic single banded pattern named I1. M. arenaria was identified with typically four superoxide dismutase bands named A4. The undescribed species Meloidogyne sp1, Meloidogyne sp2 and Meloidogyne sp3 were similar to M. incognita on perineal pattern but esterase pattern of the first species was J3, the second species had three bands but their rate of migration were different from M. javanica. Meloidogyne sp3 had two bands in esterase. The first two species were collected on Melissa officinalis in Ghazvin and the third species was collected from Beta vulgaris in Karaj.

Main potato growing areas were surveyed for the relative incidence of Potato virus A (PVA) in Kerman province, during April 2002 through September 2004. Totally 656 samples showing virus symptoms were collected and tested by DAS-ELISA using a PVA polyclonal antiserum. The results showed that PVA is widely distributed and the percentage of PVA infected plant samples was between 9 and 62.8. The virus was propagated in Nicotiana tabacum L. cv. Samsun NN and partially purified. This preparation was injected into a rabbit. The dilution of 1/512 of obtained antiserum reacted with PVA infected plant sap in indirect ELISA. Five plant species were identified to differentiate PVA from PVY. In RT-PCR, the main segment (1065bp) of coat protein (CP) gene was amplified using specific primers.

Cachexia is a viroid disease of citrus worldwide. Field symptoms of cachexia including stunting, chlorosis, decline, gumming of the bark and stem pitting have been observed on many Satsuma (Citrus unshiu) and Clementine (C. reticulata) and some sweet orange trees in Mazandaran. In 2004, eight Satsuma and Clementine samples were collected from symptomatic trees in eastern Mazandaran. Young leaves and bark tissues were used for RNA extraction. Reverse transcription-polymerase chain reaction was performed using viroid specific primer pairs of Hop stunt viroid, Citrus bent leaf viroid, Citrus exocortis viroid, Citrus viroid III, Citrus viroid IV and coat protein gene (CP25) of Citrus tristeza virus. The expected HSVd 300bp fragment was observed on 1.5% agarose gels following electrophoresis. Single-strand conformation polymorphism analysis differentiated the isolates into two groups. The amplified products from a representative of both groups were ligated into pBluescript SK and one clone of each was sequenced using M13 primers. Alignment of the nucleotide sequences of the isolates with those deposited in GenBank revealed their highest identities with other isolates of Hop stunt viroid. As the symptoms of citrus cachexia disease have been observed in almost all citrus trees sampled, it appears that the majority of citrus trees in northern Iran are infected with the HSVd. This is the first report on the molecular characterization of Hop stunt viroid in citrus cachexia disease from Iran.

Phytophthora blight, crown and root rots caused by P. capsici are important diseases on many crops. In this investigation the population genetic structure of 29 representative isolates of a total 79 Iranian isolates of P. capsici, which showed the highest morphological diversity was studied using RAPD and ISSR primers. Five of 12 decamer RAPD primers as well as a 27 bp ISSR primer, exhibited reproducible polymorphic banding patterns. Cluster analysis using UPGMA method and Jaccard's coefficient showed that the RAPD primers all together categorize the isolates into two groups at 55% similarity. These two groups contained the southern (tropical) isolates including Fars and Khuzestan, 24% and central and northern (temperate) isolates, 76%. Cluster analysis of ISSR marker, divided the isolates into four groups at 40% similarity. The first group contained 17.5% and each of the other groups included 27.5% of isolates. The first group encompassed Mazandaran and Golestan isolates, the second contained Fars and Khuzestan isolates, Ardebil and East Azarbayejan isolates categorized in the third group and the fourth group included Tehran and Qazvin isolates. The results of banding patterns of ISSR and RAPD markers were analyzed together and the isolates categorized into five groups at 55% similarity. Mazandaran and Golestan isolates were in the first group, Fars and Khuzestan isolates in the second group, an isolate from Qazvin in third group, East Azarbayejan and Ardebil isolates in the fourth group and Tehran and Qazvin isolates in the fifth group. The frequencies of isolates in these five groups were 17.5, 24, 3.5, 27.5 and 27.5, respectively. This is the first report on the genetic diversity of Iranian populations of P. capsici using RAPD and ISSR markers.

In the summer of 2004 and 2005, symptoms of a new disease were observed on sugarcane (Saccharum officinarum L.) sheaths as orange to red- colored blights in Mazandaran province (Babol, Babolsar and Sari regions) and in some fields up to 90 % of plants were infected. A multinucleate Rhizoctonia (3-10 nuclei) with orange hypha was isolated from the infected tissues and after two weeks, produced very tiny (0.3 X 0.35 mm) and red sclerotia under and over the culture medium. The cardinal temperature was 10, 32 and 40°C respectively. All isolates were capable to anastomose with WAG-Z. Accordingly, the causal fungus was identified as Rhizoctonia zeae Voorhees. The fungus was also isolated from soil of infected sugarcane fields and from sheath and culms tissues of Zea mays, Sorghum bicolor, S. vulgare var. sudanense, S. halepense, Cynodon dactylon, Saccharum ravennae, and Eragrostis barrelieri and their pathogenicity were approved on relevant hosts. This is the first report on the occurrence of R. zeae in Iran and all host plants, except corn and Johnson grass, are introduced as matrix nova for this fungus.

Biology and population dynamics of tea root lesion nematode, Pratylenchus loosi , as the most important crop loss agent of tea plant in Iran was investigated in natural conditions for five years in one of the infested tea gardens and also were studied in laboratory. According to this study, tea root lesion nematode, as migratory endoparasite, parasitises feeder and hairy roots of tea as soon as soil temperature reaches to 15°C or above. Juvenile stages and adult females are infectious agents, the overwintering is in form of egg in soil or in feeder roots, although can overwinter in form of Ju or adult stages. Laboratory studies in culture medium (carrot discs) showed that optimum temperature for reproduction in in vitro was 20-21°C and for egg hatching in 2 % water agar was 17°C. Complete life cycle of this species in lab was 46-49 days which hatching of egg was 15-17 days, Juvenile stages were 15-16 days and adult nematode was 16 days. Five years study of population dynamics showed that P. laosi has 3-4 population pick per year in May, July, September and November or March (depends on environmental condition). Regression analysis of population dynamics and mean soil temperature and rainfall for five years showed significant relationships between environmental factors and population densities. Soil temperature appears to have more important role than rainfall.