IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2004 | Volume:40 | Issue:1-2|Papers Count:11

Nematode species infected with Pasturia penetran were founed in 5 out of 55 root and soil samples coIlected from various regions of Iran. The bacterial isolates recovered from Meloidogyne javanica from Ahwas (isolate PA), M. javanica from Saravan (isolate PS), M. javanica from Varamin (isolate PV), Helicotylenchus pseudorobustus from Ardestan H. vulgans and Amplimerlinius macrurus from Golpayegan. They were on the basis of morphological features of endospores and characteristics of the vegetative stages identified as Pasturia penetrans.The efficacy of P. penetrans isolates PA and PNG (an isolate received from New Guinea) in controlIing M. javanica infection on tomato plants was evaluated under greenhouse conditions.PA and PNG at a density of 105 spores/g.soil and Nemacure (fenamifos, as check) at 4µg/g.Soil were added separately to 500 g soil in pots infested with 4000, eggs of M. javanica. One tomato cv. Rutgers seedling was trans planted in each pot. The isolates PA and PNG and Nemacure reduced population of M. javanica by 71%, 87.1% and 79.8% respectively. Difference between the treatments were not statistically significant.

During chickpea growing season of 1998-1999, on a time regulated schedule, several surveys were carried out in warm and cold chickpea growing areas in Fars province. Forty isolates of Ascochyta rabiei (Telemorph: Didymella rabiei ) were collected from symptomatic chickpea tissues in different parts of the province and used for cultural and morphological characters.Analysis of variance of morphological characters in asexual stage, (growth rate of colony, sprorulation, pycnidium and pucnidiospore size), and sexual stage (pseudothecium, asci and ascospore size) showed that there were significant variations among isolates. On the basis of the above features, they could be differentiated into several groups.The interaction of forty isolates of the pathogen with standard tester isolates (MAT-1 & MAT-2), showed that 38 isolates (%95) belonged to MAT-1 and two isolates (%5) to MAT-2. Microscopic studies of naturally infected tissues and tissues inoculated with standard isolates (MAT-1 &MAT-2), which had been kept for two years under natural conditions, showed that the sexual stage (pedudothecium) of the fungus was developed. This is the first report of the occurrence of sexual stage under natural conditions in Fars province.On the basis of host pathogen interactions on ten differential chickpea cultivars under greenhouse conditions and data anlaysis, four pathogenicity groups (A-D) were identified among isolates of Ascochyta rabiei. According to the present results, the use of race for the isolates of the causal agent was not suggested.

Some 500 isolates belonging to Altemaria species were obtained from seeds and plant parts from various localities of Iran. Prior to morphological examination, pure cultures were obtained by single conidium and single chain methods. Descriptions for each taxon are based on cultures developed on potato carrot agar. Inoculated plates were incubated at 23-25°C under a cool-white fluorescent light/dark cycle of ca. 8/l6 hrs. Microscopic examinations were carried out after 5-7 days and 90% lactic acid was used as mountant. Conidiophores, conidia and sporulation patterns were studied and recorded. Eight species of Altemaria are introduced and described in the present investigation, three of which (A. dauci, A. radicina and A. triticina) are being reported for the first time from Iran. Other five species,A.altemata, A. brassicicola, A.nobilis, A. macrospora and A. ziniae, that have been reported from Iran previously, are described here based on the current species concept.

The prevalence of Phytophthora species, the causal agents of pistachio gummosis and root rot was investigated in Kerman and Fars provinces.From 65 isolates of Phytophthora recovered in Rafsanjan region, found to be P. drechsleri which were isolated from crown, root, water and soil at the frequency of 24, 7,5 and 4 respectively which were mostly homothallic.Twenty isolates of P. cryptogea were recovered in Rafsanjan and Neirez Fars at the rate of 6, 10 and 4 respectively from water, crown and soil. This species had two types of hyphl swelling, either irregular in chain or round, irregular and botryose. This species was heterothallic mostly of A1 compibility types. P. citrophthora was recovered less frequently at the rate of 3,4 and 1 respectively form crown, root and soil.The virulence of the species on pistachio seedling cultivars Sarakhs in descending order was P. citrophthora, P. drechsleri and P. cryptogea.The reaction of crown and root of 9-month - old Pistacia vera cultivars Sarakhs, Badami and Ghazvini to Phytophtora citrophthora (Pc) and P. drechsleri (Pd).was performed under greenhouse conditions. Plant height, dry weight of root and foliage, disease progress, seedling mortality and root colonization were determined. The results indicated that cultivars Ghazvini and Sarakhs were the most tolerant and susceptible respetively.Comparative reaction of crown and root of various pistachio rootstocks to Pc and Pd showed that crown of the cultivars was more resistant than root to Pd but root of Sarakhs and Ghazvini and crown of Bad ami showed higher resistance to Pc.

Tomato leaf curl virus (TLCY, Family Geminiviridae, genus Begomovirus) is a whitefly (Bemisia tabaci) transmitted geminivirus (WTG) causing a destructive disease of tomato in many regions of India, East Asia and Australia. While TLCY isolates from Australia, Bangalore (India) and Taiwan and Tomato yellow leaf curl virus (TYLCY) isolates from different regions of Asia, Europe and America have a single genomic component (designated DNA A), those from Northern India and Thailand have two components (DNA A and DNA B). Previously, TYLCY-like geminiviruses have been identified from southern provinces of Iran causing leaf curling, stunting, and severe reduction in fruits of tomato plants in the fields. We have used degenerate DNA A specific PCR primers to clone part of the genome of an Iranian isolate of TLCY (TLCY-Ir) from field-infected tomato plants growing in Iranshahr, Sistan-Baluchestan Province. Degenerate DNA B-specific PCR primers did not amplify a putative DNA B from infected tomato under conditions that DNA B fragments were amplified from plants infected with Tomato golden mosaic virus, a known bipartite begomovirus. The full-length 2763 nucleotide DNA A genome of TLCY-Ir was sequenced and compared to Iranian isolate of TYLCY (TYLCY-Ir, previously sequenced by Bananej et al., (GcnBank accession No. AJ 132711) isolated from tomato in the same region.As other monopartite TLCV and TYLCV isolates, both TLCV-Ir and TYLCV-Ir genomes contain six open reading frames, two on the virion-sense strand and four on the complementary-sense strand. Sequence comparisons indicated that TLCV-Ir is substantially different from TYLCV-Ir with only 79% nucleotide sequence identity. Phylogenetic analysis showed while the TYLCV-Ir represents an isolate of TYLCV-Israel (TYLCV-Is) group, the TLCV-Ir is closer to TLCV isolates from southern India (TLCVs-Bangalore 2-5) which are most similar to other WTGs infecting tomato and cotton in Pakistan, India and East Asia and differ substantially from T(Y)LCVs of the Middle East, America, Europe and Australia.Presence of two tomato - infecting begomoviruses in the same area provides a favorable environment for recombination of these viruses.

During growing season 1997-98 several non-host plants including weeds and field crops were collected in cotton growing region of Estahban (Khir fields) in wheat, sugarbeet and cotton fields and brought to the laboratory. Roots and stems were washed, surface sterilized with 0.5% NaOCl and plated on selective alcohol agar medium. From 48 non-hosts species, mostly weeds, Verticillium dahliae was recovered from stem of Hibiscus sp. and roots of Datura stramonium, Solanum nigrum and Anthium sp. grown under natural condition. Certain weed species grown in artificially infested soil with microsclerotia of cotton isolate of V. dahliae, showed that the pathogen could colonize stem of Solanum letum, S.nigrum, Medicago lupulina and Hibiscus sp. and roots of Amaranthus sp., Datura stramonium, Xanthium sp. and Chenopodium quinoa.

The role of alternate hosts in cucurbits fields in relation to the activity and survival of Phytophthora drechsleri was investigated in some regions of Fars province. Due to interference by Pythium spp., isolation of P. drechsleri from roots of various weeds on CMA supplemented with pimarcin (10 ppm) and ampicillin (500 ppm) (CMAPA) was not successful. Addition of hymexazol (50 ppm) to CMAPA resulted in exclusion of Pythium spp and isolation of P. drechsleri from the following prennial and annual weeds. Alhagi persarum, Chenopodium album, C. amaranticolor, Glycyrrhiza glabra, Melilotus officinalis and Rhaphanus raphinstrum. Only M. officinalis had visual field symptoms of wilting and root rot.The pathogen was not detected in roots of Amaranhus retroflexus, Carthamus oxyacantha, Convolovolus arvensis, Cynodon dactylon, Euphorbia petiolata, Helintropium europeum, Lepidium draba, Malva rothundifolia, Physalis lanceifolia, Portulaca oleracea, Rumex acetosella, Solanum nigrum and Turgenia latifolia. The fungus could not be isolated also from roots of rotational crops such as barley, wheat, potato, alfalfa, com and pepper. All isolates of P. drechsleri from weeds grew at 37°C and were pathogenic on cantaloupes. Most of the weeds grown in autoclaved or non autoclaved virgin soils became infected after inoculation with zoospores of P. dreehsleri. Propopis stephaniana. P.laneeifolia, L. draba. C. oxyanatha and M. rotundifolia were not infected by zoospores of the pathogen. Inoculation of zoos pores to non cucurbit plants resulted in the appearance of disease symptoms within 2-3 weeks in Cieer arietinum, Lens eseulenta. Lepidium sativum, Medicago sativa and 3-4 weeks in Lathyrus ocloraus and Phaseolus areus. No chlamydospores were observed in roots of inoculated plants. zoospores were formed in root of inoculated plants if both mating types of the pathogen were present.

Epidemiological studies were conducted during two consecutive growing seasons (1999-2000 and 2000-2001), to find the best model that describe disease progress curve of wheat Fusarium head blight (FHB) caused by Fusarium graminearum. Progression of FHB on three cultivars: Falat, Tajan and Zagros and one resistant line (SHA3/SERI/Nanjing 833// Lira) was dctermined in a complete randomized design with four replicates at Araghi Mahalleh Research Station in Gorgan. Experiments were performed under mist and no mist system with and without artificial inoculation. The plants were inoculated weekly for five times and the disease severity recorded at least five times every three days. Various epidemiological models including Monomolecular, Logistic, Gompertz, Log-logistic and Weibull were used to evaluate temporal analysis of the disease. The goodness-of-fit for each model was tested by calculating the corrc1ation coefficient (R2) and mean square of errors. The correlation coefficient values for all modc1s in 1999-2000 growing season were low indicating that the disease progression could not be precisely determined. In spite of this, according to R2 and error the log logistic model for Falat and Tajan, and the Gompertz model for Zagros were considered as the preferred model. In 2000-2001 experiments under mist and artificial inoculation, the disease progression on Falat and Tajan was best possible using monomolecular model with R2 of 0.966 and 0.828, respectively. However, on Zagros the Weibull (c=2) with R2 of 0.744 was considered as the preferred model. In the experiments under mist with no inoculation, on Falat the log logistic and on Tajan the monomolecular with R2 of 0.774 and 0.597, respectively were evaluated as the most suitable model. Under the same condition on Zagros, the Logistic (R2= 0.679) exhibited high efficiency. In the experiments with no mist but artificial inoculation, the Gompertz model with R2 of 0.679 was the best fitted model for Falat. On Tajan cultivar, the R2 values were very low in all models and none of them was suitable. In spite of this, the Weibull (c=2) model was better than the others. For Zagros cultivar, the log-Logistic (R2=0.667) was considered to be the best fitted model. Resistant line showed little infection and naturally none of these models were fitted to its data.