IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2000 | Volume:36 | Issue:3-4|Papers Count:22

The citrus root nematode Tylenchulus semipenetran, is widespread in the citrus orchards of the northern parts of Iran. Seedlings of different rootstocks: trifoliate orange (Poncirus trifoliata), Swingle citrumelo (P. trifoliata × Citrus paradisi), troyer citrange (P. trifoliata ×C. sinensis), sour orange (Citrus aurantium), Taiwanica (Citrus taiwanica), yuzu (Citrus ichanjensis × Citrus reticulata) and a number of Iranian natural citrus hybrids were evaluated for resistance to the citrus nematode. The experiments were carried out under pot and orchard conditions. The rootstock seedlings, five months old, were tansplanted into pot with 20 J2/g soil as well as in the naturally infested soil in a citrus orchard. The root of seedlingsgrownin pots were evaluated for nematode infestation after 5.5 months. The root of seedlings were also scored for nematode infestation4.5 and 15 months after being transplanted into an infested field. The susceptibility of rootstocks to citrus nematode was evaluated according to the number of embeded females per gram feeder roots. Results confirmed resistance of P. trifoliate and Swingle citrumelo to the citrus nematode, whereas the other rootstocks supported a high population of the nematode. The biotype of the citrus nematode used in this study was identical with or closely similar to the citrus biotype.

A total of 68 strains comprising 12 standard strains of pathotypes, A, B, C, D and E of Xanthomonas axonopodis and 56 strains isolated from affected citrus trees in southern Iran were characterized byFAMEs analysis. The most important fatty acids which were characteristic for the tested strains included: 11:0 iso, 13:0 iso 3OH, 15:0 iso, 15:0 anteiso, 16:0 16:1 cis 9, 17:0 and 17:1 iso F. The representatives of the five standard pathotype strains were separated into three groups including group A; group B, C and D; group E. Strains from group B, C and D could not be differentiated by FAMEs analysis. An atypical strain of pathotype E formed a separate group.All Iranian strains (except two strains which were clustered with strains of pathotype E) were similar to strains of pathotype A and were grouped with strains of this pathotypes in a main cluster.

In September 1996, various sunflower fields in Mazandaran and Golestan provinces were surveyed and 18 samples of diseased plants were collected from the area. Immediatly after transferring samples to the lab., seedlings of universally susceptible line, "S37-388" and widely grown cultivar, "Record" were inoculated with spores of each isolate for multiplication and purification purposes. To identify physiological races of the pathogen, freshly harvested urediniospores of each isolate were inoculated on Canadian differential lines including S37-388 (with no known resitance gene), CM-90RR (with R1 resistance gene), 29-3 (with R2 resistance gene) and a single USA inbred line, HA-R5 (with R4 resistance gene) using dusting method (dispersed urediniospores in talcum powder). After 14 days reactions of differential lines were recorded according to Yang (1986)scale. The results showed that, race 3 was present in the region. Development process of the disease in the susceptible line S37-388 was also studied. Germination of spores was observed 2h after inoculation and reached a maximum in 8h. The first appressorium was formed by 6h after inoculation, the maximum was reached by 14h. The mean diameter of rust colonies within the leaf 8 days after inoculation was approximathy 1000 µ.m.

A survey of sixtysoil and root samples collected from the rhizosphere of citrus and kiwifruit orchards; tea plantations and cultivated plants from different regions of Gilan and Mazandaran provinces revealed that isolates of P. penetrans group activelyexist in the north of Iran and naturally parasitizea number of plant parasitic nematodes. Three different isolates of this group of bacteria were found on the basis of host, eproduction and size of spores. The first isolate type was observed on Helicotylenchus pseudorobustus, H. dihystera and H. digonichus in which some specimens were infected over eighty percent and the body fully occupied by endospores of the bacterium. The diameter and the central core in this isolate were 4-5 m µ(4.7) and 2-2.1 (2) mµ, respectively, and were lager in comparison with the other isolates. The diameter and the central core of the second isolate observed on Boleodorus thylactus and Paratylenchus sp. were 2.2-3(2.88) m µ and O.9-1.2( 1) mµ which was as large as the citrus nematode isolate except for its developmental stages. The latter complets its developmental stages in male and secod stage juveniles of citrus nematode but not in adult female. The third group of siolates which were obtained from Meloidogyne incognita race 2 and M. arenaria races 1and 2 reproduced on these species, possessed an endospores 3-4(3.85) mµ and central core of 1-1.2(1.16) mµ in diameter. The host ranges of the isolates from the root knot and the citrus nematods were tested on a number of plant parasitic nematodes. In either spore infested soil or water suspension (Oostendrop et aL 1990,Stirling& Watchel 1980),none of the isolate scould attach to the males or second stage juveniles of the citrus nematode. The isolate obtained from M. arenaria race 1 in water suspension attached to all Meloidogyne and Pratylenchus zeae tested and showed the widest host range. The tested isolates did not attach to second stage juveniles of Heterodera schachtii, P. loosi or Ditylenchus dipsaci.

Samples of potato and tomato plants with yellowing and sudden wilting symptoms were collected from fields in Hamedan and Fars provinces. The bacterial ooze extracted from stem and/or from vasular bundles of diseased potato tubers were streaked on sucrose peptone agar (SPA) and triphenyl tetrazolium chloride (TZC) media. Agram neative bacterium with irregular, slimy white colonies, were isolated from plants and some potato tubers from Esfahan, Shahrekord and Zanjan. All strains were identified as biovar II of Ralstonia solanacearum, using standard biochemical and physiological assays. In order to evaluate resistance of potato and tomato plants to bacterial wilt, different methods of inoculation such as stem puncture (SP), wounding the roots of plant and soil infestation were used. The susceptibility of plants was increased with stem puncture method and incubation at 28 to 35°C. A latent infection developed, when plant inoculated with stem puncture method were incubated at low tempature. In the other inoculation methods such as wounding the roots and soil infestation no latent infection at low temprature was observed. Environmental factors (e. g. temprature, moisture) increasingly affected the development of disease and susceptibility or resistance of the hosts. Potato cultivars Granulla, Vancokh, Marfona, Caezer, Strix and Draga had the greatest susceptibility to bacterial wilt. Premiere, Cosima, Ajax, Casmos, Moren, Concord, Vital and Cardinal were fairly susceptible and Feresia, Diamant and Mondial CVs were relatively resistant. In tomato, L-612, was susceptible, L-293, Peto Early, GS-12 and CLN-2915 were fairly susceptible and L-528 was fairly resistant to bacterial wilt.

Wound healing on sweet lime fruits was evaluated using warm air (35°C at 80± 1 RH, and 20°C at atmospheric RH as control) and warm water (25, 45, 55°C) treatements. Four wounds were made on fruit and each inoculated with 500 spores (1O/µl )of Penicillium italicum. In warm air treatment, superficial (2mm) and deep (5 mm) wounds were inoculated before or after 24-72hr exposure to warm air. In warm water treatment, deep wound inoculated fruits were kept at room temperature for 4-5h, and dipped in water bath at 25, 45 and 55°C for 2 and 5 min. Inoculated and non-inoculated heat treated fruits were placed in plastic bags (with 24 holes) and stored at 9°C and 86%± RH. After 10 weeks storage, decay was not observed in fruits inoculated with superficial wound before or after warm air treatment or in deep wound inoculated fruits before warm air treatment. Heat treatment using warm water at 25 and 45°C for 5 min also reduced decay significantly during storage. According to the present results, it is recommended to substitude heat treatment for chemical treatment to control post harvest decay of sweet lime fruit during storage.

In present investigation, vegetative compatibility groups (VCGs) of39 isolates of Fusarium graminearum collected from four provinces(Golestan, Mazandaran, Kerman, and Hormozgan) were determined using nitrate non-utilizing(nit) mutants. Results showed that with the exception of a single isolate (Fg-196)all the remaining isolates were forced to produce nit mutants on MMC and PDC media containing potassium chlorate. In total, 375 nit mutants were obtained of which, 72.5% were synthesized on MMC and 27.5% on PDC medium. On the basis of colony characteristics on basal medium containing one of the five nitrogen sources (sodium nitrate, sodium nitrite, ammonium tartarate, uric acid, and hypoxanthine) three nit mutant phenotypic classes were determined. Of these, 33.2% belonged to nit I, 28.2% to nit3, and 38.6% to nit M. To determine VCGs and complementation tests, pairing were made between all nit M and nit 1and I or nit3. In a compatible reaction between nit M and two other nit mutants, a dense growth at the line of contact between two colonies was formed after 5-14 days. But a much weaker similar phenomenon taking more than 14 days was observed, when nit 1and nit3 mutants were paired. All isolates examined in this study, were grouped nito 24 VCGs of which 14isolates, all from Goleston and Mazandarn provinces belonged to VCG 1, two isolates to VCG2 and each of the 22 remaining isolates (with various geographic origins) were classified in a separate VCGs. None of 39 isolates tested exhibited vegetative self-incompatibility reaction. In addition, no correlation was found between VCG2 and relative virulecnce of isolates.

Rice black-gall dwarf has been found in some rice fields of Firouzabad and Mamasani in the Fars province. Major symptoms of the disease are severe stunting and formation of elongated vein galls on the lower surface of leaves. The galls are green at first but turn dark and finally black. The causal agent of the disease was transmitted from infected rice to rice and certain other plant species with Laodelphax striatellus and Unkanodes tanasijevici under greenhouse conditions. L striatellus also proved to be the natural vector of the disease agent when planthoppers captured from rice fields were tested for transmission in the greenhouse. Electron microscopy of crude extracts and thin sections of infected leaves, as well as thin sections of inoculative planthoppers showed presence of isometric reovirus- like particles of ca. 60 nm diameter. Parallel host range studies of the rice black-gall dwarf associated virus (RBGDA V) and maize rough dwarf virus (MRDV) showed that both viruses infected rice, wheat barley, maize, rye, Setaria italicum, and Echinochloa crus-galli, inducing similar symptoms in most cases. MRDV however, did not cause formation of gallson barley leaves while RBGDAV did. In immunoelecron microscopy tests, RBGDA V was not decorated with a MRDV antiserum from Italy. RBGDAV appears to be a Fijivirus biologically close to MRDV.

Tilletia indica Mitra, causal agent of Karnal bunt or partial bunt of wheat, is heterothallic and no solopathogenic line has been found yet. Although incompatibility in some smut fungi can be determined in vitro by fusion of monosporidial lines, followed by the formation or non-formation of dikaryotic mycelia, this is not the case in T. indica, since no dikaryotic-infective mycelia develop on artificial media, even when paris of monosporidial lines known to be pathogenic in artificial inoculation, are paired on a wide variety of media. Fuentes-Davila and Duran (1986), for the first time, isolated a complex of vegetative and sporogenous hyphae from infected caryopses cultured on axenic media.In this investigation, for the isolation of sporogenous mycelia and the formation of teliospores in artificial media, susceptible wheat cultivar WL711, were inoculated in booting stage with suspension of 2 ×105 sporidia per ml. Ten to 15 days after inoculation, the young caryopses were excised from the inoculated spikes, surface strillized in 0.5% sodium hypochlorite, and sectioned in half transeversely, and the halves with embryos were placed on potato-dextrose agar (PDA) and incubated at 200C and 12h light period. The mycelial isolates were kept on laboratory benches or in incubator, and periodically subcultured.Two kinds of fungal colonies were isolated in axenic cultures including a complex of sporidiogenous and teliosporogenous mycelia, and the pure colonies of teliosporogenous mycelia. In the subsequent studies, pure colonies were used. In spite of repeated subculturing, teliospore formation has been continuing for ten months. Mean growth rates of teliosporognous colinies on water agar, PDA, and Czapecks agar, in a completely randomized design (CRD) with four replications at 200Cand 12h light period, were 1.22, 1.8and 3.08 mm/day, respectively. To study the rate of teliospore formation in culture media, in a CRD with three replications, a 7 mm block of PDA containing the teliosporognous mycelia was placed in the center of Petri dish (9 cm in diameter) containing culture media and incubated at 200C and 12h light period. After 4 weeks, each treatment was mixed in a blender with little water, filtered through two folded muslin cloth, and then passed through a 500-meshsieve (25µm). The residue on the sieve was resuspended in 50ml water. Teliospore number wrer enumerated on three replications. Each time, lml of this suspension was added to a small 2×2×2 cm dish. Teliospores were counted by means of a binocular (×50). Mean teliospore number produced in the above mentioned culture media were counted 24.66, 100, and 128.1 teliospores per each petri dish, respectively. Using CRD by Duncans multiple range test, the results indicated that there are significant differences in the teliospore formation in these media. Pathogenicity tests using dikariotic mycelia failed to initiate disease development. Teliospores produced in media were germinated typically 11.4-14.3%, and study on the effect of susceptible and resistant seed extracts on teliospore formation showed that there were no effect of seed extracts on teliospore formation .

During spring and fall of 1997-1998, general surveys were made in vineyards in Fars, Kohgiluyeh and Boyreahmad provinces. Thirty one Agrobacterium strains were isolated from gall and sap of infected grapes and soils, using Roy and Sasser (RS), 1A and 2E media. On the basis of standard biochemical and physiological tests, the strains were identified as Agrobacterium vitis and Agrobacterium tumefaciens biovar 1. Sixteen isolates of A. vitis -and one isolate of A. temefaciens biovar 1 caused crown gall on grapevine, whereas some isolates of both species did not. Inoculation to different cultivars of Vitis vinifera with two pathogenic strains of A. vitis, showed that all cultivars were susceptible to the isolates and produced bacterial galls. Resultus of biochemical and physiological tests showed that isolates of the two species were variable in some of their characteristics.

Bacterial speck of tomato, cused by Pseudomonas syringae pv. tomato, was reported from Varamin in 1994. Subsequent surveys of tomato fields in Varamin during the spring and summer months in 1995-96 revealed variabilitis in symptoms type and severity of infection among plants within and between farms. Disease symptoms appeared as regular or irregular brown to black lesions on leaf, sepal, peduncle, branches and stems. Specks, with or without chlorotic haloes, appeared on fruits. Fifty three strains were isolated from affected tomato plants and their phenotypic features and electrophoretic patterns of cell proteins were compared. Two pathovars of Pseudomonas syringae were found to be involved. One group was identified as P. syringae pv. tomato (Pst) (causing bacterial speck of tomato). Their phenotypic features were very similar too but different from the type strain with respect to hydrolysis of esculine, tolerance to 5% NaCI, tyrosinase activity, utilization of lactate, L-histidine and adenine and production of mucoid growth on yeast dextrose calcium carbonate agar (YDC). Their electrophoretic profiles of cell proteins were similar but the strains could be differentiated into two groups, based on the relative mobility and intensity of a few protein bands. The second group of strains were indentified as syringom deficient strains of P. syringae pv. syringae (Pss) causing syringae leaf spot. The electrophoretic profiles of cell proteins of the two Pss strains were identical and very similar to that of a Pss strain isolated from peach (prunus persica)

Lime witches broom Phytoplasma from Iranian provinces of Sistan-Baluchistan and Hormozgan was transmitted to time by grafting and from time to periwinkle and periwinkle to lime by dodder. The disease agent was transmitted to eggplant, ornamental eggplant, Jimson weed, two species of tobacco, nightshade and tomato by grafting and dodder. Disease symptoms consisted of yellowing, small leaves, in ternode shortening, virescence, phyllody, witches broom, stunting, wilting and plant death. The type of symptoms differed from that of other phytoplasmas in several cases. Broadbean, cotton, prosopis (syrian mesquite), sugarbeet, camelthorn, pigweed, potato, hemp, physalis, pepper, chrysanthemum, sesame, marigold, paper-flower,  Mirabilis , carrot and alfalfa were not infected via dodder or graft inoculation.