IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2013 | Volume:49 | Issue:3 (195)|Papers Count:15

Pistachio gummosis is the most important disease of pistachio trees in Iran. The fungus-like oomycetous pathogen, Phytophthora pistaciae, is a major cause of the disease. In order to investigate the reaction of different pistachio cultivars, P. pistaciae was isolated from infected pistachio trees in Yazd and Kerman Provinces of Iran during 2009 and 2010. These isolates were identified based on morphological and ribosomal genome characteristics, and their pathogenicity confirmed. In this study, five-month-old seedlings of various pistachio cultivars including Sarakhs, Badami-Rize-Zarand, Ghazvini, Kaleh Ghochi, Ahmad Aghaiy, Ohadi, Khanjari-Damghan, and Fandoghi were challenge inoculated using different isolates of P. pistaciae. The disease symptoms in infected cultivars were monitored for six months and the percentage of dead trees, the fresh and dry weight of roots and shoots, height of the plants and percentage of the root colonization were determined. The trial was performed as a two-factor factorial experiment with 3 replications for each combination, the factors being cultivars and isolates at 7 and 3 levels, respectively, in a completely randomized design. No significant differences were observed among pathogenicity of the pathogen isolates. A comparison of mortality showed that the Sarakhs had the highest percentage of deaths (80%) and the Badami-Rize-Zarand had the lowest percentage of deaths (15%), while in Ghazvini no mortality was observed. The results of root colonization by pathogen varied in various cultivars, with the Sarakhs and Ghazvini giving the maximum and minimum root colonization, respectively. Sarakhs had the most height reduction (45%), with the Badami-Rize-Zarand (12%) and Ghazvini (8%) cultivars having the least. Studies on fresh and dry weight of shoots and roots of plants also showed some reduction in infected plant tissues, with the Sarakhs cultivar having the highest weight reduction in comparison with the control. On the whole, using the investigated criteria, Ghazvini and Badami-Rize-Zarand seemed to be more resistant than other cultivars, with Sarakhs being the most susceptible one. Although 30oC was calculated as the optimal temperature for pathogenicity in Sarakhs cultivar, the results showed that the range of 25 to 30oC could be extensively effective in development of the disease.

The genus Helicotylenchus with about 250 described species is one the largest genera in order Tylenchida or infraorder Tylenchomorpha. In order to identify the species of Helicotylenchus, over 500 soil and root samples collected from rhizosphere of different plants and localities of Iran, during 2009-2010. Soil samples were collected and its nematodes extracted, killed and processed to glycerin. Then the nematodes examined by light microscope, equipped with drawing tube and digital camera. In this study, in addition to 15 species of 26 previously reported species of the genus Helicotylenchus, a number of other known species were isolated and identified. Among the identified species, due to morphological and morphometric similarities, H. indicus, H. insignis, H. falcatus and H. egyptiensis are discussed in two groups. The ventral tail projection in the first three species usually is shorter than two body annuls width, and in H. egyptiensis is as long as two body annuls width or longer. The morphometric characters of the first three species are very similar and for this reason H. insignis and some other species were synonymized with H. indicus by several authors. However the shape of stylet knobs is different among these species. Stylet knobs are sloping backward in H. indicus, but indented forward in H. insignis. H. egyptiensis has a usually pointed tail tip. H. insignis and H. falcatus, as new records for Iranian nematode fauna are described. Also the descriptions of H. indicus and H. egyptiensis which has already been reported form Iran, presented in more details.

Sclerotium rolfsii is a soilborne fungal pathogen that causes southern blight disease on a wide range of agricultural crops. This study was performed to evaluate genetic diversity of the fungus based on mycelial compatibility groups (MCGs) in Guilan province. MCG for 92 pure isolates collected from 12 host species were assessed according to the mycelial-barrage response on PDA. Mycelia of isolates in the same MCG intermingled (a compatible reaction), whereas mycelia of isolates from different MCG formed a cleared antagonism zone in the area of mycelial contact (incompatible reaction). Sclerotia formed on either side of this zone for most incompatible pairings. The width of antagonism zone between incompatible isolates was different from 1-5 mm. The results showed that S. rolfsii population can be divided into six MCGs, designated as MCG1, MCG2, MCG3, MCG4, MCG5 and MCG6. MCG1 was the prevalent group and had the most number of isolates in these areas; also MCG3 had the widest host range. According to the results, bean had the highest Shanon diversity index and all six groups were found on this host. Knowledge about the genetic and virulence diversity in local populations of S. rolfsii associated with different crops is a key component for the management of sclerotium root rot diseases, particularly through the use of host resistance and crop rotation in a given region.

During the study on the Alternaria species from potato fields of West Azerbaijan province, foliage and stems that had suspected infections with Alternaria fungi were collected. Totally, 141 isolates belonging to the genus Alternaria were isolated and purified. Based on macro and micomorphological characters of the isolates, 9 species viz.: A. alternata, A. broussonetiae, A. destruens, A. dumosa, A. interrupta, A. rhadina, A. solani, A. soliaegyptiacae and A. tenuissima were identified. Among the identified species, 5 species: A. alternata, A. dumosa, A. interrupta, A. solani and A. tenuissima were reported previously from potato, but three species: A. broussonetiae, A. rhadina and A. soliaegyptiaca are new to mycoflora of Iran and are reported for the first time from potato plants (matrix nova). Also, potato is matrix nova for A. destruens. Pathogenicity studies on isolates of identified species were done on potato cultivar Agria and their pathogenicity were confirmed based on Koch’s postulates. All the studied isolates were pathogenic, although the degree of pathogenicity based on diameter of necrotic area varied among different species. A. tenuissima had the highest frequency and A. solani and A. tenuissima had the highest degree of pathogenicity among the studied Alternaria isolates.

Trichoderma species are used in plant disease control due to secretion of some chitinase enzymes as a strong factor involves in biological control. In recent years, application of microelements fertilizers has been a common practice that can impact on biological control efficacy of microorganisms. In this study, the specific activity of the chitinase enzyme of Trichoderma species was evaluated in SM liquid medium containing 100 ppm of manganese, copper micronutrients and 100 and 500 ppm of iron micronutrient. The results revealed that all Trichoderma species were able to produce chitinase and chitinase activity significantly varied in different species grown on media containing different micronutrients. The highest specific activity of the enzyme was found in isolates belonging to T. brevicompactum and T. koningiopsis grown in medium containing manganese micronutrient equivalent to 0.0048 U/mg protein and 0.0045 U/mg protein, respectively. The lowest activity was found in isolate belonging to T. arundinaceum in medium containing 500 ppm iron micronutrient with 0.0018 U/mg protein and in isolate belonging to T. atroviride in medium containing 500 ppm iron micronutrient and isolate belonging to T. brevicompactum in medium containing copper micronutrient. As a result, manganese micronutrient increased the production of chitinase in some Trichoderma species and can be used in biological control application. Conversely, iron and copper micronutrients showed a negative effect on the activity of the enzyme.

The formation of chlamydospores of Phytophthora parsiana, a newly described high temperature tolerant pathogen of woody plants, were investigated in culture media and in infected roots of susceptible host plants. Different solid agar media and cleared V-8 juice broth were inoculated with different isolates of P. parsiana and incubated for four days at room temperature before they were transferred to 4oC in the dark. Chlamydospore formation was monitored during twelve months. Infected almond and pistachio roots inoculated with the pathogen under greenhouse conditions were removed from soil, washed thoroughly and incubated within moist sterilized sand in plastic bags at 4oC for twelve months and examined monthly using light microscope. Chlamydospores were observed only on carrot agar two weeks after incubation and after four months in infected pistachio and almond roots. No chlamydospores were produced on other solid media and in CV8 juice during 12 months incubation. The average diameter of chlamydospore in culture and in roots were 29.7 and 32.47mmm with wall thickness 1.7 and 2.07 mm, respectively. Frozen culture medium and root containing chlamydospores at - 20oC for 72 hours resumed growth after thawing on Phytophthora selective medium. Sterilized non inoculated root segments colonized internally by the pathogen did not resume growth after freezing. The isolates did not produce oospores in single or dual cultures with P. capsici mating types. It is concluded that under natural conditions chlamydospore is a survival propagule of the pathogen.

In the framework of national project of Collection and Identification of Fungi of Iran some new findings about powdery mildews (Erysiphaceae) are reported here. The identity of causal agent of Lagerstroemia indica powdery mildew in Iran is discussed. Some new host species is reported for Leveillula taurica in Iran. Three Erysiphe species viz. Erysiphe deutziae on Deutzia gracilis; E. sesbaniae on Sesbania punicea and E. castaneigena on Quercus macranthera are also reported here as new members for Iranian mycobiota.Enumeration of taxa - Pseudoidium yenii (U. Braun) U. Braun & R.T.A. Cook, Taxonomic Manual of the Erysiphales (PowderyMildews) (2012) On Lagerstroemia indica L.- Leveillula taurica (Lev.) G. Arnaud, Annls Epiphyt.7: 92 (1921), emend. Braun & Cook 2012.On Datisca cannabina L. and Cerinthe minor L.- Leveillula rutae (Jacz.) U. Braun, Taxonomic Manual of the Erysiphales (Powdery Mildews) (2012) On Haplophyllum acutifolium G. Don - Erysiphe deutziae (Bunkina) U. Braun & S. Takam., Schlechtendalia 4: 7 (2000) Deutzia gracilis Siebold & Zucc.- Erysiphe sesbaniae Wolcan & U. Braun, in Braun, Kruse, Wolcan & Murace, Mycotaxon 112: 181 (2010) On Sesbania punicea Benth.- Erysiphe castaneigena U. Braun & Cunningt., in Braune, Delhey, Dianese & Hosagoudar, Schlechtendalia 14: 85 (2006) On Quercus macranthera Fisch. & C.A.Mey.

In the framework of study on rust fungi of Iran six species belong to different genera are newly reported from Iran. All voucher specimens are preserved at the Fungal Reference Collection of the Ministry of Jihad-e Agriculture (IRAN) located at the Iranian Research Institute of Plant Protection, Tehran.

During April 2013, branches of oak (Quercus brantii Lindl.) with fungal infection were collected from Kohkiluyeh and Buyer Ahmad province of Iran. Laboratory survey indicated acervuli on the samples of oak dead twigs (3mm diameter). Acervuli immersed in bark, were scattered, small (500mm), flat to subconical, 3- 4 angled gray to black, hymenium labyrinthiform, pale grey, finally smeared over with golden yellow startum of spores. Conidiophores were crowded, branched, acicular, nearly straight, about as long as the conidia. Spores abundant, slender, and strongly arcuate, 20-42 (35.6)×0.6-0.8 (0.7) mm. According to Barnett and Hunter (1998) and Grove (1937), this fungus was identified as Libertella quercina Tul. Saccardo (1906) described Cytosporina quercina (Tul.) Traverso (basionym: Libertella quercina) on branches of Quercus and Castanea in Italy, France, and Germany. It is the anamorphic state of Diatrypella quercina (Pers.) Cooke. Teleomorphic state was not found on our samples. This is the first report of Libertella quercina for mycobiota of Iran.

Pilidiella granati has been recognized as the agent of pomegranate fruit rot disease which is reported as crown rot pathogen in recent years.In order to identify the causal agent of pomegranate crown rot, samples were collected from infected pomegranate trees in Lorestan province. Fungal isolates were purified and identified morphologically. Based on morphological and cultural characteristics, the fungus was identified as Pilidiella granati. This is the first report of P. granati pomegranate crown rot in Lorestan province.

Cabbage (Brassica oleracea var. capitata) is an economically important and widely cultivated vegetable in Urmia region, West Azerbaijan, Iran. During the surveys of cabbage diseases in the years 2009-2012, mature plants of both white cabbage (B. o. var. capitata f. alba) and red cabbage (B. o. var. capitata f. rubra) with yellowing and detaching of lower leaves, watersoaking, browning and softening of leaf petioles and head outer parts, formation of white cottony mycelium and numerous large and black sclerotia on diseased parts, characteristics of Sclerotinia head rot of cabbage, was observed (Fig.1 in Persian section). Infected heads or petiols and sclerotia were collected, surface sterilized and grown on PDA medium. Isolated fungi were purified by hyphal tip culture method and were kept in PCA slants for further studies. Apothecia were produced from sclerotia based on the method of Mylchreest and Wheeler (1987). Based on morphological characters of isolated fungi, Sclerotinia sclerotiorum (Lib.) de Bary was identified (Purdy, 1979; Saharan and Mehta, 2008). Pathogenicity tests were performed both on detached leaves and on container-grown healthy, 3 months old cabbage stems. Healthy cabbage leaves were washed under tap water, and then surface sterilized with 10% ethanol and inoculated at the center with a 5 mm2 PDA plug from 5 days old mycelial cultures.The inoculated leaves were kept in plastic containers equipped with wet filter paper and incubated at room temperature for 10 days. Cabbage stems were first surface sterilized and then inoculated as leaf assays without any wounding. Plants were incubated in a growth chamber and maintained at 25oC, 95% relative humidity on a 12-h fluorescent light/dark conditions for 7 days. Leaves and stems only inoculated with PDA plugs served as controls. Inoculated leaves and stems showed brown, water soaked and softened lesions several centimeters around the inoculated area (Fig.2 in Persian section). No symptoms were observed on control plants. Inoculated fungi reisolated from symptomatic parts, so Kochs postulates were completed. This is the first report of cabbage head rot on white and red cabbages caused by Sclerotinia sclerotiorum from Iran. in Iran.

True myrtle, Myrtus communis L belonging to Myrtaceae family is an important medicinal herb in traditional medicine and Pharmaceutical industries in Iran. Moreover because of being evergreen, having dense foliage and ease of pruning, it is planted at steep slopes, grasslands, boulevards and sidelines of parks as an ornamental shrub or hedge of green. It is distributed in southern Europe, Asia, Iran and particularly Zagros mountains in humid and semihumid regions. In a survey of a twoyear old field of true myrtle of approximately two hectares located at Kashkan, Sarab Doureh, 60 km from Khoram Abad, signs of decline, chlorosis and stunting was observed in some plants as irregular patches. Roots showed swellings as small galls singly or in groups. Upon dissection of galls under a stereomicroscope, egg masses and mature female of Meloidogye were found inside the infected tissues indicating the infection of the roots by root knot nematode. Second stage juveniles of Meloidogyne were recovered from soil samples collected from the rhizospher of infected plants. Nearly 1500 second stage juveniles / 250 cm3 were counted. Based on the morphological characters of mature females and juveniles, the species was identified as M. javanica which was further confirmed by PCR using specific primers of Fjav and Rjav designed for this species, generating one single fragment of ca.670 bp. Occurrence of root knot nematode on true myrtle was also observed in a greenhouse of M. communis close to Khoram Abad. There are several references concerning the nematicidal effects of essential oil, leaf powder and plant extracts of M. communis against root knot nematodes, but there is no known report on true myrtle as a host of root knot nematode species. To our knowledge, this is the first record of the occurrence of M. javanica on M. communis in the world.