IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2008 | Volume:44 | Issue:1 (173)|Papers Count:9

Potato (Solanum tuberosum L.) covers 22 million hec. of the cultivable l& s of the world, producing more than 300 million tons of tuber & is considered to be a major diet ranking fourth after wheat, barley & rice. One hundred twenty strains of bacteria were recovered from potato rhizospheres & purified on NA & King’B media. Of these, 27 strains exhibited high antagonistic effects using dual-culture tests. Antagonistic potential of the selected bacteria were evaluated by their ability to produce antibiotics, volatile metabolites & siderophore. Of the 27 isolates tested, eight strains including two mutants exhibited higher antagonistic effects & were selected for greenhouse experiments. These were Pseudomonas fluorescens biov. III DA1, DA1m, DA3, Bacillus subtilis DM1, DM1m, DP1, B. brevis B1 & P. fluorescens CHAO (A model strain). Biocontrol test on potato tubers was performed by two methods of seed coating & soil drenching, in a completely r& omized design experiment with 37 treatments & 3 replicates. P. fluorescens biov. III DA1 showed the greatest effect on reduction of disease severity, while B. brevis B1 had the greatest effect on growth parameters. Results of antagonist & pathogen population counts to rifampicin & nalidixic acid during greenhouse tests showed a negative correlation (r=-64.3%) between these two parameters.

Sheath blight caused by Rhizoctonia solani is one of the most important diseases of rice in Iran and almost in all rice-producing countries. R. solani AG1-IA is the causal agent of sheath blight in rice. It is believed that R. solani could use plant material by secretion of pectolytic enzyme such as pectinase. In this study samples were obtained during two years from diseased rice in from diseased rice in Golestan province of Iran. Seventy five isolates were identified as AG1-IA, based on the number of nuclei per cell and anastomosis reaction. The identified isolates of R. solani AG1-IA were used for pectic zymogram analyses. The pectic enzyme electrophoretic patterns were interpreted in terms of loci coding for polygalacturonase (PG) and pectic esterase (PE). Presence or absence of a band with a particular Rf value was scord as "1" and "0", respectively. The obtained zymogram electrophoretic patterns (ZPs) were divided into six groups: ZP1-ZP6. PG and PE bands were observed for all isolates tested. A total of 18 bands (15 PG and 3 PE) were identified, one PG and one PE appeared as cathodic bands. Inter-group relationships were deduced from the similarity matrices. The genetic similarity among zymogram electrophoretic phenotypes, ranged from 62% to 88% based on band frequency. The cluster analysis showed two main branches. ZP3 was clustered separately on a single branch, and the other branch was divided into two subbranches, one containing ZP5, and the other ZP1, ZP4. ZP2 and ZP6. The results indicated that there is a distinguishable diversity among different R. solani isolates of rice fields of Golestan province, and that could be detected by isozymes but not by anastomosis group. We concluded that the pectic enzyme electrophoresis could be a suitable technique to study genetic variation of AG1-IA isolates.

In recent years, anthracnose disease of citrus trees in Mazandaran province causes heavy loss in some citrus commercial varieties. The disease has spread out in the citrus orchards of this Province. In order to isolate and identify the causal agent(s) of the disease, infected areas and susceptible of important and introduced citrus varieties in north of Iran, sampling was done from infected orchards at random during 2004-2005. In laboratory, disease samples tested were cultured on PDA medium. Of 119 samples, 96 Colletotrichum isolates were recovered. Based on morphological and some physiological characters and optimal temperature, all isolates were identified as C. gloeosporioides. The sexual stage were identified as Glomerella cingulata. Among the isolates, only one isolate produced perithecium in YPSS medium. Pathogenicity tests were conducted with some isolates of C. gloeosporioides in laboratory and greenhouse. The pathogenicity of these isolates were different they produced on the branches loxon and on the fruites brown rots. In laboratory, detached branches were inoculated by a disc of PDA culture containing mycelia of the fungus, leaves and fruits were sprayed with spore suspension of fungi. In greenhouse, leaves and branches of two-year old seedlings were inoculated as above. The rate of infection of citrus trees in Mazandaran province to anthracnose was about 23-74 % (49% average). The effect of various temperatures on radial growth of the isolates was different. It can be as a specific character of isolates. The rates of temperature for growth were 5-10oC (minimum), 25-27oC (optimum) and 35-37oC (maximum) on PDA medium in dark condition. Overwintering studies indicate that the fungus persists at least for one year by hypha and acervulus in infected plant residues.

Phytophthora species are the main fungal plant pathogens in cucurbits in Iran. The two species namely P. melonis and P. drechsleri have been considered to be the major causal agent of cucurbit root rot. Based on morphological features available, the two species can not be easily identified. The two species were discriminated by use of the reaction to safflower seedling, potato pink rot and host range. Additionally in this work, the causal agent of cucurbit root rot was investigated in several provinces. Forty seven isolates (45 isolates from cucumber and 2 isolates from melon) of Phytophthora collected from root and crown of cucurbits from various parts of Fars, Kerman, Yazd, Khuzestan, Kuhgiloyeh and Boyer- Ahmad and Bushehr provinces between April and September, were identified as P. melonis. Unlike the isolates of P. drechsleri and P. cryptogea, the isolates of P. melonis neither infected safflowers nor induced pink rot symptoms in potato tubers. It is concluded that the main causal agent of cucurbit root rot in Iran is P. melonis. Host range of P. melonis and P. drechsleri was examined using several plant species including cucurbits, sugar beet, lentil, vetch, bean, broad bean, okra, sesame, rapeseed, sunflower, eggplant, pepper, tomato, carrot and tobacco. All cucurbits and lentil showed disease symptoms when inoculated by P. melonis (D45 from cucumber). While bean and rapeseed showed symptoms when inoculated by P. drechsleri (Kv3 from sugarbeet). Water melon showed disease symptom when inoculated by both species.

Gray mold of rose flowers caused by Botrytis cinerea is considered to be one of the major problem in greenhouse rose production all over the world including in Iran. Three hydroponic experiments were conducted to elucidate the effect of nitrate to ammonium ratio and calcium concentration on susceptibility of rose flowers to gray mold at Safi Abad Agricultural Research Center. On the basis of results from the first and second experiments, a moderately virulent isolate with proper conidial concentration (104 spore/ml) was selected for inoculation of rose flowers. The third experiment was carried out as factorial in a randomized complete block design with four replicates. In this experiment, rose plants were grown with three nitrate to ammonium ratios (100/0, 75/25 and 50/50) in combination with Ca two levels (1.6 and 4.8 mM). Rose flowers from two consecutive harvesting dates were sprayed with the conidial suspension (104 spore/ml) of the selected B. cinerea isolate. At the end of experiment, the disease severity was recorded and analyzed. The results revealed that increased NHH+ concentration up to 50% of applied nitrogen led to a meaningful increase (32%) of disease severity of petals (P<0.01). This was due to decreased Ca concentration in the rose petals. How ever, at Ca, levels of 1.6 to 4.8 mM, a 29-23.2% day-1 deeline in descaae severslty was observed. Also, a significantly negative correlation (P<0.05) was found between petal Ca concentration and the disease severity of gray mold (r2=0.78). From the results reported herein, it can be concluded that the use of nutrient solution with higher ratio of nitrate to ammonium (100/0) and 4.8 mM Ca could lead to the reduction of disease severity of rose gray rose flower.

This study investigated genetic polymorphism of Puccinia striiformis f. sp. Tritici populations in Iran during 2005-2006. Eighty six isolates were analyzed for their amplified fragment length polymorphism (AFLP) pattern. DNA extraction was performed according to phenol-chloroform method. Digestion was carried out by EcoRI and MseI restriction enzymes. After ligation of adapters to DNA fragment a preamplification PCR was done. Selective PCR amplification was performed using four primer combinations. PCR products were analyzed on polyacrylamid gel and stainined by silver staining method. 97 markers were revealed. Polymorphic bands were recorded and analyzed by Popgene 32 software using UPGMA method and Nei coefficient. In average genetic variation was 38%. The populations of Golestan and Mazandaran had more than 90% similarity. This suggest that they were a clonal lineage. On the other hand the Karaj population is not similar to these. High similarity of west/NWest population with the all other populations, may be because of gene flow between these regions.

Root knot nematodes (Meloidogyne spp.) ranked among the top five major plant pathogens because of their world wide distribution, extensive host ranges and involvement with fungi and bacteria in disease complexes. The previous studies on the host ranges of Meloidogyne species, on some of the medicinal plants indicated that the plants such as plantain, hemp, parsley, ash, spearmint and coriander are the hosts of several species of rootknot nematodes in Iran and Esfahan province (AKHIANI et al, 1984. Iran. J. Plant Path 20) In order to determine the specific hosts of each species on medicinal plants ,130 soil and root samples were collected from the various research stations in Esfahan, including, Dastgerd, Najafabab, and Kashan during 1999-2002.