Effect of different strains of Saccharomyces cerevisiae on reduction of aflatoxin B1, B2, G1 and G2

Saccharomyces cerevisiae is one of the major microorganisms widely used in food fermentation, and the ability of its strains to reduce the level of aflatoxins has been reported. The aim of this study was to test the capability of S. cerevisiae strains on reduction of aflatoxin B1, B2, G1 and G2 levels. For this reason, standard strains of PTCC 5052 and PTCC 5269 were cultivated on Yeast Mold Agar. Afterwards, cell suspension containing 107 cell/ml was spiked into PBS (pH= 7.2) containing 20 ng/ml of each B1, B2, G2 and G1 aflatoxins. Aflatoxin levels were determined using HPLC and immunoaffinity columns. The results show that different strains of S. cerevisiae reduced the aflatoxin levels in a different rate and various durations. At the time 320 min the PTCC 5052 strain reduced the aflatoxin B1, B2, G1 and G2 levels to 11.2 , 13.9, 8.0 and 8.1%, respectively; meanwhile, these results for the PTCC 5269  strain 9.5, 8.0, 2.3 and 16.2%, respectively. Results suggested that different strains of S. cerevisiae had a different reduction rate on aflatoxins. Moreover, the strains need to have sufficient time to absorb the maximum amounts of aflatoxin

First report of Pilidiella granati causing dieback and fruit rot of pomegranate (Punica granatum) in Iran

Iran is the largest producer of pomegranate (Punica granatum) in the world, with more than 60,000 ha currently in production. In the spring of 2011, a decline and dieback of young pomegranate trees (7 to 10 years old) were observed in the Kheir area of Fars Province. Dieback and twig blight developed toward the lower part of the stem, resulting in death of aerial tree parts and growing suckers from roots. Surface-disinfected tissues of diseased plants were plated on potato dextrose agar (PDA) and malt extract agar media. Isolates were separated into two groups that had either pale green or white aerial mycelia and sporulated after 5 to 7 days at 25°C. Pycnidia were globose and black with thin, membranous, pseudoparenchymatic walls, 80 to 140 µm in diameter. Conidia were hyaline, one-celled, elongate to fusiform, straight, and 11 to 17 × 4 to 6 µm (average 14 × 4.7 µm). Cardinal minimum growth temperatures were 8 to 10°C, optimum at 27 to 30°C, and maximum at 35°C. Radial growth rate at 30°C was 8 to 9 mm per day. Representative isolates were deposited in the CBS-KNAW Fungal Biodiversity Centre, the Netherlands (CPC 19625 = CBS 130974 and CPC 19626 = CBS 130975; GenBank JN815312 and JN815313, respectively). Genomic DNA was extracted with the UltraClean Microbial DNA Isolation Kit (MoBio Laboratories, Inc., Solana Beach, CA) and the internal transcribed spacer (ITS) region of the nrDNA operon of two isolates were sequenced as described previously (1). On the basis of morphology (3), the causal organism was identified as Pilidiella granati Sacc. This identification was corroborated by the ITS sequence data, which was identical for both colony types to GenBank HQ166057 (identities = 614 of 614 [100%]). Pathogenicity tests were conducted using two representative isolates from each group on 5-month-old P. granatum trees with 10 replicates under greenhouse conditions; 5-mm mycelial plugs from the edge of 7-day-old colonies on PDA were placed under the bark of twig wounds. Uncolonized PDA plugs were used as noninoculated controls. Pathogenicity was also tested on nonwounded fruit by placing colonized 5-mm-diameter mycelial plugs on surface-disinfected pomegranate fruits; noncolonized PDA plugs were used as controls. All treated fruit were placed in plastic bags and maintained at 25°C for 10 days. Isolates were found to be pathogenic on twigs after 2 months, giving rise to brown lesions that were 2 to 5 cm long. No lesions were observed on the controls. Furthermore, the fungus was reisolated from all infected tissues, satisfying Koch's postulates. On pomegranate fruit, the fungus colonized the fruit after 5 to 8 days, followed by the appearance of fruit rot symptoms leading to the formation of abundant pycnidia covering the skin after 10 days. No decay was observed in control inoculations. Pilidiella granati has previously been reported as a pathogen of P. granatum fruit from Europe, Asia, and the United States (2). To our knowledge, this is the first report of this pathogen causing dieback and fruit rot of pomegranate in Iran

The Occurrence of Charcoal Disease Caused by Biscogniauxia mediterranea on Chestnut-Leaved Oak (Quercus castaneifolia) in the Golestan Forests of Iran

The chestnut-leaved oak (Quercus castaneifolia) is native to the Alborz Mountains, including the Golestan Forests, in northern Iran. Trees grow up to 35 (-50) m tall with a trunk up to 2.5 (-3.5) m in diameter. During 2010, we received reports of a decline of oak trees in the Ghorogh Region of the Golestan Forests. The decline began with discolorations and browning of the leaves, resulting in drying of the foliage. Viscous liquid exudates were observed on the trunks, resulting in a brown-black discoloration of phloem and bark. In January 2011, all infected trees were dead and exhibited symptoms of charcoal disease with carbonaceous, perithecial stromata erupting from the bark on stems. Perithecia were obovoid, containing short-stipitate, amyloid asci with dark brown, ellipsoid ascospores, 14 to 19 × 7 to 9 µm, with straight germ slits along the spore length. On the basis of these morphological characteristics, the fungus was identified as Biscogniauxia mediterranea. Blast searches of the NCBI GenBank nucleotide database were done using ITS sequences derived from three cultures (CBS 129072 to 129074). GenBank Accession Nos. JF295127 to JF295129 of the isolated fungus differed by one nucleotide from B. mediterranea (GenBank Accession No. AF280624) (1,3). Pathogenicity tests were conducted using an isolate of B. mediterranea under greenhouse conditions. Six-month-old Q. castaneifolia seedlings were inoculated by means of stem wounds with a mycelial plug of colonized potato dextrose agar. After 6 months, typical decline disease symptoms associated with charcoal disease were observed and the same fungus was reisolated. Perithecia were observed on the surface of black carbonaceous stromata, which usually developed on stems of inoculated plants. The decline is known as charcoal disease because fungal growth induces a typical charcoal-black surface on diseased branches and trunks. The pathogen can easily spread through large cavity vessels, colonize bark and woody tissues, and is able to kill the host in a single, growing season. B. mediterranea causes necrosis on stems and branches of Quercus spp., including Q. suber, Q. cerris, Q. frainetto, Q. pubescens (4), Q. alba, Q. ilex, Q. imbricaria, Q. lusitanica, Q. palustris, and Q. pyrenaica (2) in Europe, North America, Africa, New Zealand, and Asia (China and India). On the basis of our current knowledge, Q. castaneifolia represents a new host of B. mediterranea, and this is the first report of this fungal pathogen from Iran causing charcoal disease on Q. castaneifolia trees in the Golestan Forest. Given its new introduction into Iran, it is highly likely that it will spread to species of Fagus, Zelkova, and other woody hosts in the area. References: (1) J. Collado et al. Mycologia 93:875, 2001. (2) D.

Change in biochemical parameters of Persian oak (Quercus brantii Lindl.) seedlings inoculated by pathogens of charcoal disease under water deficit conditions

Drought alone or in combination with charcoal disease pathogens led to modifications in some biochemical characteristics of Persian oak seedlings. Drought conditions enhances the effects of charcoal fungus with effects at biochemical level.AbstractCharcoal disease is one of the common diseases in oak forest of Zagros in western Iran that has increased in the recent years. The disease is associated with abiotic stress, especially drought, and contributes to the decline of Persian oak (Quercus brantii Lindl.), the major oak species in this forest association. Persian oak seedlings were exposed to a factorial combination of two irrigation levels and inoculation with either Biscogniauxia mediterranea or Obolarina persica (agents of charcoal disease). Proline, total soluble sugar and soluble protein contents in seedling foliage were increased in response to charcoal pathogen inoculation, especially when combined with water stress, while starch, chlorophyll a+b and carotenoid contents strongly declined. Pathogen inoculation stimulated malondialdehyde content, electrolyte leakage, and hydrogen peroxide and superoxide radical contents in oak leaves, and were increased by water stress. The combination of charcoal disease agents and water stress increased peroxidase and superoxide dismutase activity while, for catalase and ascorbate peroxidase activities, the interaction between the two factors of variability was not significantly increased. Ascorbate peroxidase activity was at maximum level in seedlings infected with O. persica independently of water stress. Glutathione reductase had the highest activity in inoculated seedlings under soil moisture stress while those under higher soil moisture levels, the enzyme was increased only when inoculated with O. persica. Contents of non-enzymatic antioxidants including ascorbic acid and glutathione increased in response to combined pathogen inoculation and water stress and was higher when seedlings were inoculated with O. persica than with B. mediterranea. Chitinase activity significantly increased because of pathogen inoculation. Furthermore, foliar phenylalanine ammonia lyase activity was higher under all treatment combinations, as compared to the controls. The effects of B. mediterranea or O. persica pathogens on foliar biochemical responses of Q. brantii seedlings were more severe under water-stress and it was more sensitive to B. mediterranea than O. persica