Virulence factors of Fusarium spp., causing wheat crown and root rot in Iran

Crown and root rot of wheat, caused by Fusarium spp., limit crop yields worldwide, from rotting of seeds, seedlings, crowns, roots and basal plant stems. Virulence factors and virulence and aggressiveness of Fusarium spp. were investigated for isolates from Iran, obtained from wheat plants with crown and root rot symptoms. Forty isolates of Fusarium were used in this research. Among the isolates, nivalenol (NIV) was detected as the dominant trichothecene chemotype produced. Production of trichothecenes and zearalenone (ZEA) in autoclaved rice cultures of Fusarium isolates was analyzed using high performance liquid chromatography. The levels of NIV ranged from 258 to 1246 μg kg−1, of deoxynivalenol (DON) from 45 to 1411 μg kg−1, and of ZEA from 53 to 3220 μg kg−1. All Fusarium isolates produced cellulase and pectinase enzymes. Positive correlation was observed between activity of cell wall degrading enzymes (CWDEs) produced by the isolates and their pathogenicity on wheat leaf segments. Virulence of trichothecene-producing isolates was greater than that of non-trichothecene-producing isolates. Considerable association was detected between the capability of Fusarium spp. isolates to produce virulence factors (such as mycotoxins and CWDEs) and their pathogenicity on wheat

Studies on variation within races and competion and genetical recombination between races in Puccina hordei

Brown rust of barley Puccinia hordei Otth is an importantfoliage disease in the warm season in Southern Britain, causing considerable losses. A sexual stage is known for this fungus, but the appearance of new races is not apparently due to sexual hybridization, because the aecidial stage is very rare in Britain. Changes in virulence are more likely to arise by mutation and asexual recombination. Whether a newly developed race is capable of competing with other races in the field population depends upon its virulence and aggressiveness under the prevailing environmental condition: In order to obtain a colour mutant for recombination andcompetition studies, uredospores of race A were treated with ultra-violet radiation or Ethyl Methane Sulphonate. Following UV radiation one yellow coloured pustule appeared, but attempts to multiply it failed. The use of EMS resulted in production of three orange isolates all with the same pathogenicity as the parent race. After a time those orange isolates designated as A1 started segregating somatically, producing brown pustules and it proved imposible to obtain a completely stable line. To study vegetative recombination as a possible mechanism for the appearance of new races, the orange race (A1) was mixed successively with races F,J,K, and D and cultured on a susceptible host. A total of 564 cultures were screened but no detectable change in pathogenicity was observed. A population study was carried out; again the orange race was paired with races F, J, D and K in equal proportions and inoculated on to a range of susceptible barley cultivars at both the seedling and adult stages using two temperatures and two levels of inoculum density, heavy and light infection. A separate experiment with races F and A1 was carried out in the field. The effects of density of initial inoculum, time interval of successive spore collection, and location of the leaf on competition were also studied. In this experiment the predominating race at low temperatures with heavy inoculation was different from that at lower inoculation or higher temperature. In the majority of cases the race with the wider host range became the prevalent race regardless of its initial ratio in the mixture; contrary to expectation on current the cry. Histological studies provided a reason for the failure to detect asexual recombination and the prevalence of one race rather than another in mixed populations. Puccinia hordei has a very limited rate of mycelium spread, a small sporulation zone, a short latent period and secondary pustule formation does not occur after heavy inoculation. The collective effect of these factors is that opportunities for the production of new variants as the result of asexual recombination are few. The rates of spore germination, approssorium formation andpenetration were affected differentially by temperature in differentraces, and the race germinating rapidly under specific environmental conditions came to predominate in the population in heavy infection where there is competition for stomatal entry. Following light infection, the race which had higher spore viability, a larger number of spores per pustule, larger pustule size and higher infectivity became-the prevalent race. The relavance of these factors in relation to the competitive ability of a race in the field is discussed.</p

Evaluation of resistance and the role of some defense responses in wheat cultivars to Fusarium head blight

Fusarium graminearum and F. culmorum are the causal agents of Fusarium head blight (FHB) in cereal crops worldwide. Application of resistant cultivars is the most effective and economic method for management of FHB and reducing mycotoxin production in wheat. Understanding the physiological and biochemical mechanisms involved in basal resistance of wheat to FHB disease is limited. In this research, after screening resistance levels of eighteen wheat cultivars planted in Iran, Gaskozhen and Falat were identified as partially resistant and susceptible wheat cultivars against Fusarium spp., respectively. Also, we investigated the role of hydroxyl radical (OH−), nitric oxide (NO), callose deposition, lipid peroxidation and protein content in basal resistance of wheat to the hemi-biotrophic and necrotrophic Fusarium species causing FHB. Nitric oxide as a signaling molecule may be involved in physiological and defensive processes in plants. Our results showed that NO generation increased in seedlings and spikes of wheat cultivars after inoculation with Fusarium species. We observed earlier and stronger callose deposition at early time points after infection by Fusarium spp. isolates than in non-infected plants, which was positively related to the resistance levels in wheat cultivars. Higher levels of OH− and malondialdehyde (MDA) accumulation (as a marker of lipid peroxidation) were observed in the Falat than in the Gaskozhen cultivar, under non-infected and infected conditions. So, estimation of lipid peroxidation could be useful to evaluate cultivars’ susceptibility. These findings can provide novel insights for better recognition of physiological and biochemical markers of FHB resistance, which could be used for rapid screening of resistance levels in wheat cultivars against this destructive fungal disease

Characterization of Aspergillus section Flavi from pistachio soils in Iran

Abstract: During 2012, soil samples from commercial pistachio orchards in three major production regions include Rafsanjan (Ker-man Province, center of Iran), Damghan (Semnan Province, north-central Iran) and Feyz-Abad (Khorasan-e Razavi Province, north-eastern Iran), were assayed on Dichloran Rose-Bengal Chloramphenicol agar (DRBC) and Aspergillus flavus-parasiticus agar media to quantify populations of Aspergillus species from the section Flavi. The mean propagule density of Aspergillus species from the Flavi section [log10 (CFU/g soil)] was higher in Feyz-Abad (3.06, 2.88–3.24), compared to Damghan (2.55, 2.44–2.65) and Rafsanjan (2.40, 2.26–2.54). A. flavus (69.7, 65.3 and 57.9%), A. parasiticus (19.6, 25.4, and 29.3%), and A. nomius (10.7, 9.3, and 12.8%) were the predomi-nant species in the regions of Rafsanjan, Damghan, and Feyz-Abad, respectively. There were significant differences among sclerotia producing isolates of A. flavus in the sampling regions (p &lt; 0.05). The percentage of sclerotium-producing isolates of A. flavus from Raf-sanjan (14.5%) was much lower than Damghan (39.5%) and Feyz-Abad (41.4%). The A. flavus isolates from Damghan, Rafsanjan, and Feyz-Abad were toxigenic at 53.7%, 61.6%, and 60.4%, respectively. In Rafsanjan, aflatoxin B1 (AFB1), and AFB1 + AFB2 (aflatoxin B2

Characterization of Aspergillus section Flavi from pistachio soils in Iran

During 2012, soil samples from commercial pistachio orchards in three major production regions include Rafsanjan (Kerman Province, center of Iran), Damghan (Semnan Province, north-central Iran) and Feyz-Abad (Khorasan-e Razavi Province, northeastern Iran), were assayed on Dichloran Rose-Bengal Chloramphenicol agar (DRBC) and Aspergillus flavus-parasiticus agar media to quantify populations of Aspergillus species from the section Flavi. The mean propagule density of Aspergillus species from the Flavi section [log10 (CFU/g soil)] was higher in Feyz-Abad (3.06, 2.88–3.24), compared to Damghan (2.55, 2.44–2.65) and Rafsanjan (2.40, 2.26–2.54). A. flavus (69.7, 65.3 and 57.9%), A. parasiticus (19.6, 25.4, and 29.3%), and A. nomius (10.7, 9.3, and 12.8%) were the predominant species in the regions of Rafsanjan, Damghan, and Feyz-Abad, respectively. There were significant differences among sclerotia producing isolates of A. flavus in the sampling regions (p < 0.05). The percentage of sclerotium-producing isolates of A. flavus from Rafsanjan (14.5%) was much lower than Damghan (39.5%) and Feyz-Abad (41.4%). The A. flavus isolates from Damghan, Rafsanjan, and Feyz-Abad were toxigenic at 53.7%, 61.6%, and 60.4%, respectively. In Rafsanjan, aflatoxin B1 (AFB1), and AFB1 + AFB2 (aflatoxin B2) ranged from 274 to 553 ppb (393±17.11) and 394 to 3745 ppb, respectively, while AFB1, and AFB1 + AFB2 ranged from 257 to 392 ppb (285±13.18) and 415 to 1658 ppb, respectively, in Damghan. We found 16 and 20 vegetative compatibility groups (VCGs) for 41 and 37 nit mutant producing isolates of A. flavus from Rafsanjan and Damghan, respectively. From Damghan the VCG diversity for A. flavus isolates was greater (54%) than from Rafsanjan (39%). Because there were a few number of sclerotium-producing isolates of A. flavus, we did not determine the relationships between sclerotium production with VCGs and/or geographical distribution in the three pistachio production regions. This study was the first to determine the strain and VCG diversity of A. flavus soil isolates from Iranian pistachio orchards

Studies on Aspergillus Flavus Link. Isolated From Maize in Iran

The Aspergillus flavus population structure from maize kernels was examined. During 2011, samples were collected from two main grain maize production areas in Iran (Fars and Ardebil provinces), shortly before harvest. One-hundred nine A. flavus isolates were recovered on Dichloran Rose Bengal Chloramphenicole (DRBC) agar and Aspergillus flavus/parasiticus medium (AFPA) and grouped into morphotypes and Vegetative Compatibility Groups (VCGs) based on morphological (e.g. sclerotia production), physiological (e.g. aflatoxin-producing ability) and genetic criteria (e.g. heterokaryosis). In general, morphotype and VCG composition were highly dissimilar in both provinces. In total, 43.8% and 44.3% of A. flavus isolates from Ardebil and Fars, respectively, produced sclerotia. Sclerotia producers were identified as A. flavus L and S strain morphotypes in Ardebil (66.7% and 33.3%, respectively) and Fars (29.6% and 70.4%, respectively). Furthermore, 71 isolates (65.1%) were able to produce aflatoxin (Ardebil 40.8%, Fars 59.2%). The aflatoxin values were categorized into four different classes ( 1,000 ppb). In total, 51 aflatoxin producing isolates of A. flavus (Ardebil n = 22, Fars n = 29) were assigned into 26 VCGs by complementation of nit auxotrophs on nitrate medium. None of the A. flavus isolates from Ardebil complemented with any isolates from Fars. Genetic diversity of A. flavus isolates was 59.1% and 41.8% for Ardebil and Fars, respectively. The different geographical adaptation and genetic make-up of A. flavus isolates may be due to different climatic conditions, soil types and crop sequences in both maize production areas