IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2012 | Volume:48 | Issue:1 (189)|Papers Count:15

The two most important diseases of potato in Hamedan province are black-dot disease caused by Colletotrichum coccodesand bacterial wilt disease caused by Ralstonia solanacearum. In this study interactions between the two pathogens were surveyed on the three potato cultivars, Agria, Boren and Diamant using two inoculation methods. Data analysis revealed that co-inoculation of potato by both pathogens showed pathogenicity synergistic effect, and potato length and stems and roots weight were decreased. In Agria, R. solanacearum increased C. coccodes effectiveness on potato plants. Agria cultivar root colonization by C. coccodes sclerotia was more than other cultivars and was scored as 50-70%. In fact, this cultivar was more susceptible toC. coccodes than others. Pathogenicity of C. coccodes and R. solanacearum on Boren potato cultivar were almost equal and potato length and stems and roots weight were decreased in compare to control plants. At the presence of two pathogens plant parameters were more decreased. In this cultivar root colonization by C. coccodes sclerotia was scored as 50%. In most cases, Rs treatment on Diamant has no significant differences with control plants and there was relative resistance to the bacterial wilt in this cultivar. In compar to other cultivars, root colonization in Diamant was low and scored 30%. Diamant potato cultivar was more resistant than others to C. coccodes.

Root rot and vine decline of cantaloupe and muskmelon plants is an economically important disease in Iran caused by Monosporascus cannonballus. Regarding the recent detection of the disease in Iran, genetic diversity of the causal agent need further research. In this study, isolates of M. cannonballus were collected from Esfahan, Yazd, Tehran, Fars, Semnan, Markazi, Ghazvin, Sistan Baluchestan and Khorasan Razavi provinces. Genetic diversity between 50 isolates of the pathogen was studied using Rep-PCR markers; Box and ERIC. Reproducible fragments were between 100 and 1500bp and the genetic diversity amongst the isolates calculated 0.32. There was a correlation between genetic diversity, host and geographic origin of the isolates. M. cannonballus isolates were placed in two groups based on their host plant. Cluster analysis using UPGMA method and Dice's coefficient revealed 100% similarity between some isolates collected from different regions. There was a correlation between colony morphology in the culture media and genetic diversity where at 80% similarity level the isolates were placed in three different groups. The discriminatory power of rep-PCR was high, indicating that rep-PCR is a rapid, effective marker for genotyping M. cannonballus isolates.

To achieve a simple and sensitive Rosellinia necatrix detection method in soil, three detection methods including soil direct culture method, infected soil in culture media e.g. MEAR, MEAR+ penconazole and MEAS, Nested PCR method and bait twig method were compared. Direct DNA Extraction from soil was done. Two specific primer pairs R2, R8 and R7, R10 in Nested PCR were used and the extracted DNA was purified using PVPP column. Among used methods, the direct culture method from soil was not suitable and wasn’t sensitive for detection. However, bait twig method was capable to detect, the pathogen in soil and root but it is time consuming and laborious method. In conventional PCR, using primer pairs R2-R8, 10 pg ml−1 of fungal DNA was detected; however in Nested PCR using R7-R10 primer pairs, 1fg ml−1 of fungal DNA was detected. Among used methods, the Nested PCR was better in detection of the fungus. Nested PCR method of detection in soil and root is more sensitive and reliable.

Deoxynivalenol (DON) is a major mycotoxin produced by the fungus Fusarium graminearum during infection and is known to be harmful to both animal and human health. DON is believed to act as a virulence factor in fungal pathogenesis by inhibiting eukaryotic protein synthesis. The putative site of action of DON is 60s ribosomal protein L3 (RPL3). Previously, single amino acid changes in RPL3 conferring DON resistance have been described in yeast. Sequence characterization of six wheat genes encoding RPL3 has shown that there is no amino acid alteration between resistant and susceptible cultivars. The main goal of this study, was to determine any induced changes in transcriptional levels of RPL3 (A and B type) genes under stress conditions caused by Fusarium Head Blight (FHB) in wheat. In order to detect expression levels of RPL3 genes, we extracted RNA from both inoculated and non-inoculated spikes of sensitive and tolerant cultivars, during 1, 3 and 7 days post-infection. Quantitative RT-PCRs were performed with A and B type-specific RPL3 primers to detect the expression differences. Primary data indicated a decrease in the genes expression level in Sumai3 and Falat cultivars 24 hours post-infection. On the other hand, increased level of RPL3A transcript in Frontana 7 days post-infection may reveal the role of this specific protein in inducing the resistance in this cultivar.

A general surveys were conducted in Mazandaran citrus groves for the presence of Phytophthora species causing citrus gummosis. Soil samples and infected citrus tissues were collected and assayed using baiting and selective medium. Phytophthora citrophthora and P. nicotianae were detected in all of the citrus orchards and their distribution was mapped. The soil population of each species was also determined. Eighty two and 86% of the orchards were infested respectively with P. citrophthoraand P. nicotianae with average over 10 propagules /g soil. The virulence of five isolates of each species to root of 1-year-old citrange, citromelo, Shahsavar orange, and sweet lime was examined. Data analysis of fresh weight of root and stem, and disease index in citrange revealed three groups including control, P. nicotianae, and P. citrophthora isolates, which the that third group was significantly more virulent than the second group. Data analysis of fresh weight of root and stem in citromelo and Shahsavar orange did not show significant differences between P. nicotianae, and P. citrophthora isolates. On the basis of disease index data of citromelo and Shahsavar orange, P. citrophthora isolates were more virulent than P. nicotianae isolates. Data analysis of fresh weight of root and stem and disease index in sweet lime did not show significant differences betweenP. nicotianae, and P. citrophthora isolates.

Powdery mildew caused by an obligate biotrophic fungus Erysiphe necator (synonym Uncinula necator) is the most economically important disease of grapevines. Most widely grown grape cultivars are highly susceptible to E. necator, because they are derived from Vitis vinifera, a species which was not exposed to this pathogen during its evolution. In this study we investigated germinating of grapevine powdery mildew on two susceptible and resistant grapevine genotypes as well as ontogenic resistance in vegetative tissues of Cabernet sauvignon andArabidopsis thaliana with different age. Conidia germinated and appressorium and haustorium appeared during 2-12 hpi in both genotypes. The primary hypha developed 12 hpi in both genotypes however; yellow deposits could be seen surround epidermal cells 12 hpi just in resistant genotype. Development of primary hypha continued up to 24 hpi in susceptible Cabernet sauvignon, however, 24 hpi the hypersensitive reaction (HR) happened in resistant genotype and blocked secondary hypha development, but not in Cabernet sauvignon. By increased in physiological age related to ontogenic resistance the penetration efficiency of fungi in Cabernet sauvignon and Arabidopsis thaliana reduced.

Isolates of the yeasts Candida membranifaciens, Rhodotorula mucilaginosa and Pichia guilliermondii obtained from healthy apples were evaluated as potential bio. control agents for apple gray mold caused by Botrytis mali and B. cinerea. In-vitro volatile metabolites emitted from all yeast isolates inhibited the mycelial growth of B. mali and B. cinerea by 82.7 to 97.7 and 81.2 to 98.3 percent, respectively. Each of the yeasts significantly reduced the decay area in apples inoculated with the pathogens C. membranifaciens A2, A4, A5 and P. guilliermondii A6 had the greatest effect on decay reduction at 4oC, 20oC and 20±3oC. The populations of C. membranifaciens A2 and C. membranifaciens A5 during the experiment increased in apple wounds at 4oC.

The effect of rhizosphere bacteria on root-knot nematode (Meloidogyne javanica) was investigated on cucumber under greenhouse conditions. The bacteria were isolated from infected cucumber, tomato and cedar from Garmsar, Marvdasht and Shiraz, as well as cedar, grass and wheat from Bajgah. After sampling, purification, rearing on root of tomato and identification of M. javanica species, the effect of 40 isolates were investigated on hatching (in 3 and 8 days after bacteria inoculation) and the activity of second stage juvenile of the nematode (24, 48 and 72 hours after adding bacteria)in vitro condition. Then 10 best isolates were used on cucumber (Super Amelia) in greenhouse. All isolates increased growth of the plants and decreased the indices of the nematode. Pseudomonas fluorescens CHAO was the most effective isolate and caused about 55.31% and 55.72% reduction in the gall number and also respectively 91.13% and 82.84% reduction in reproduction factor (RF) in the first and second experiments. The second one was an isolate of Pantoeasp. Additionally the effects of P. fluorescens, Bacillus subtilis and Pantoea sp. on the infected cucumber (Super Amelia) to M. javanica, as single application and in combination was tested. The results indicated that using combination of three bacteria are more effective than application of single and combination of two bacteria on increasing growth of plant and reducing indices of the nematode.

Phytoplasmal lettuce phyllody (LP) disease previously was reported from Fars province is vectored by Neoaliturus fenestratus leafhopper. Transmission characteristics of LP phytoplasma with N. fenestratus including acquisition feeding, latency and inoculation feeding period were studied. The minimum acquisition access period (AAP) was four hours. Transmission increased with AAP. With an AAP of 48 hours, 88.88% of plants were infected. The minimum latent period (LP) in N. fenestratus was 14 days and transmission increased after this minimum LP. At 32 days postacquisition, 92.85% of plants were infected, but the rate of transmission gradually decreased. The minimum inoculation access period (IAP) was 4 hours. Transmission increased with IAP. At an IAP of 48 hours, 96.66% of the plants were infected. Results of this study indicate that the transmission processes of acquisition, latency and inoculation occur in much the same pattern as in other plant pathogenic mollicutes.

In order to evaluate the effect of sugar beet genotype and method of plant inoculation on resistance to Iranian isolate of Beet severe curly top virus (BSCTV-Ir), a completely randomized experimental design was performed using 18 sugar beet cultivars. Eighteen plants of each cultivar were grown in 6 pots. Two methods of inoculation, namely, agroinoculation using the infectious clone of BSCTVIr and inoculation by viruliferous leafhopper (Circulifer haematoceps) were used. The virus replication in inoculated plants was analyzed by PCR, 21 and 35 days post-inoculation (dpi) in the first experiment and 21 dpi in the second experiment. The severity of disease symptoms of inoculated plants was graded using a 0-3 scale (0, symptomless; 1, mild; 2, moderate and 3 severe symptoms). Data analysis of the first experiment indicated that the cv Brigita was the only cultivar in which all the inoculated plants were infected by the virus and all of them showed severe symptoms. Consequently, this cultivar was considered as a highly sensitive control cultivar and used in comparisons. Statistical analysis of the disease symptom severity index showed highly significant differences among cultivars when compared with the control cultivar. As a result, three distinct groups were identified. The first group including the cultivars BR1, FIMMA, HM1990, 7233, and H5505, and the second group including the cultivars Rasoul, Afshari, hybrid of Balk Shiraz, P.P.8, P.P.22, Dorothea, Zarghan, Rhizofouret, IC, Flores, Hilma and Polyrow were regarded as tolerant and sensitive groups, respectively. The third group included only Brigita cultivar which was regarded as very sensitive. Comparison of the data obtained from two inoculation methods indicated that in most cultivars, the virus infection rate was lower with vector inoculation than with agroinoculation.

Plane trees (Platanus orientalis) decline is prevalent in Shiraz and other parts of the country. From 50 plane trees with decline symptoms, forty one yielded several fungi such asCytospera (42.85%), Alternaria (18.9%), Aspergillus (12.7%), Nattrassia mangiferae (3.22%), Penicillium (3.05%), Rhizopus (0.7%), Helminthosporium (0.24%), Chaetomium (0.2%), Coniothyrium (0.2%) and Ulocladium (0.07%). The fungi were inoculated to detached stem of plane tree. Only N. mangiferae and few isolates of Cytospora were pathogenic. From 41 isolates of Cytospora recovered, only 8 isolates were mildly pathogenic to detached but not to intact plane tree. From ten isolates of Cytosporainoculated to detached stem of Acer pseudoplatanus, Platanus orientalis, Magnolia grandiflora, Morus alba, Citrus aurantium, Malus communis, Juglans regia, Cercis siliquastrum, Fraxinus excelserand Pinus sp. only 1 isolate was pathogenic on M. alba and 5 to C. siliquastrum. None of the 40 Cytospora isolates caused infection of stem the above plants under natural conditions. On the basis of morphological characteristics the fungus was identified as Cytospora theryana. There was no significant differences among soil samples collected around declining and healthy plane tree in Shiraz in respect to soil, EC, pH and soil texture. It is concluded that plane tree decline in Shiraz city is as the result of various environmental and nutritional stresses which predisposed trees to various opportunistic fungi.

Apple powdery mildew (Podosphaera leucotricha) is one of the most important diseases in this crop causing weakness and yield reduction in Semirom, Isfahan Province. In order to evaluate the reaction of 14 commercial cultivars budded trees (on apple rootstock) were planted in a completely randomised block design, with 3 replicates (3 plants in every plot) 2.5×1 m apart, at Kahangan village in Semirom. Sampling were carried out at the time of matimum lesion size. Relative resistance was assessed on the basis of lesion size in natural conditions.The results showed that all of the cultivars infected with different intensity. Fugi, Golden delicious, Gala, Azayesh, Braborn and Delbar Stival cultivars, with Severity Index (SI): 30.12, 37.92, 31.71, 33.2, 42.91 and 25.78 were susceptible. Janatan, Golab Isfahan, Golab Kermanshah, Golab Khorasan and Golab Kohanz cultivars with the SI: 54.96, 55.57, 58.71, 53.68 and 59.42 were highly susceptible while Red Delicious and Ingrid Mary with the SI: 9.04 and 11.44 were resistance respectively.

Pear fruits (Pyrus communis) with rotting symptoms and orange spore masses were collected in Guilan Province (Rasht), Iran in spring of 2009. Morphological characteristics including shape and size of conidia and appressoria, presence or absence of setae and sclerotia and color and growth rate of colony were studied. Moreover, total DNA was extracted with Chelex 5% method. The ITS1- 5.8S-ITS2 regions of rDNA were amplified and sequenced using ITS1 and ITS4 primers. According to morphological and molecular characteristics the fungus was identified as Colletotrichum acutatum. In pathogenicity test, the species caused fruit rot on wounded and unwounded pear fruits. Based on this study, pear is reported as a new host of C. acutatum for Iran and this is the first report of ITS regions of rDNA of this fungus from Iran on Pear.

Beet curly top is a disease of sugar beet which has been in the center of attention due to its unpredictable epidemics and its economic importance. It has been shown that due to short life cycle and high populations of the leafhopper vector, the disease often spreads very rapidly in a region. At least five virus species of the genus Curtovirus (Geminiviridae) are recognized as the cause of beet curly top disease. Two of these species, namely, Beet severe curly top virus (BSCTV) and Beet curly top Iran virus (BCTIV) have been reported from Iran. Two leafhopper species, Circulifer haematoceps and C. tenellus, have been reported as the vector of Beet curly top virus before recognition of different species (Fattahi et al., 2010). Therefore, it was not certain whether one or both viruses are transmitted by the leafhoppers. Recently, it was shown that C. haematoceps could transmit BSCTV from sugar beet plants infected via an infectious clone of the virus. In the present study, the possibility of transmission of BCTIV by C. haematoceps was examined. Leafhoppers were collected in sugar beet fields of northern Fars province using D-Vac. The dominant species was C. haematoceps. The leafhoppers were allowed to breed on healthy sugar beet in the greenhouse. The newly born nymphs were placed on sugar beet plants previously agroinoculated with an infectious clone of BCTIV (Zarghan isolate) for an acquisition access period of four days, and then transferred to healthy seedlings at 2-leaf stage (5 leafhoppers/3 seedlings). Typical symptoms of curly top appeared on all inoculated seedlings after two weeks. Presence of BCTIV in symptomatic test plants was verified by PCR using specific BCTIV primers. The experiment was repeated two more times with similar results. It is concluded that like BSCTV, BCTIV is transmitted by C. haematoceps under greenhouse condition.