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Aflatoxin contamination of food products is recognised as a major food safety concern throughout the world because of its carcinogenic, mutagenic, and immunosuppressive effects on human health. Of the various types of aflatoxins, aflatoxin B1 (AFB1) is the ubiquitous and most threatening foodborne mycotoxin to humans. A wide range of detoxification methods is used to reduce the toxic effects of AFB1. In the present work, the ability of probiotics isolated from yoghurt (produced by bacterial fermentation of milk), “laban” (fermented milk beverage), and “idli” batter (fermented rice and black gram) in the detoxification of AFB1 was investigated under laboratory conditions. Among the four isolates from fermented foods evaluated, the isolate YGT1 from yoghurt showed the maximum (83.8%) degradation of AFB1 in Luria-Bertani (LB) liquid medium after 48 h of incubation at 30°C. The degradation of AFB1 by the probiotic isolate was further confirmed by liquid chromatography/mass spectrometry analysis. On the basis of 16S rRNA gene sequence analysis, the bacterial isolate YGT1 was identified as Bacillus subtilis. The culture supernatant and heat-treated culture supernatant (boiled for 30 min) of B. subtilis YGT1 also exhibited degradation of AFB1, thus suggesting the involvement of thermostable bioactive compound(s) in the degradation of AFB1. These results suggested that B. subtilis YGT1 isolated from yoghurt may be a promising candidate for exploitation in food and feed industries for the removal of AFB1.

Strawberry fruits are vulnerable to infection by a broad range of fungal pathogens before and after harvest. In this study, Alternaria spp. strains associated with fruit rot of strawberry were isolated and characterized and the potential of the antagonistic yeast Meyerozyma guilliermondii strain SQUCC-33Y for the control of fruit rot of strawberry was evaluated. A total of seven isolates of Alternaria (STR2-STR8) were isolated from strawberry fruits showing symptoms of rot. On the basis of internal transcribed spacer (ITS) ribosomal RNA (rRNA) sequences, these fungal isolates were identified as Alternaria alternata. Pathogenicity tests revealed that most of the strains of A. alternata were pathogenic to strawberry. The measurement of disease severity on strawberry fruits revealed significant differences in the virulence between A. alternata strains. M. guilliermondii restricted the growth of all the strains of A. alternata in dual culture assay. Postharvest treatment of strawberry fruits with M. guilliermondii significantly reduced the fruit rot lesion size caused by A. alternata. This antagonistic yeast has the potential for use as a biofungicide for the control of A. alternata-induced postharvest fruit rot of strawberry.

The production of antifungal compound(s) by an indigenous Pseudomonas resinovorans strain B11, showing antagonistic activity against Monosporascus cannonballus, the causal fungus of muskmelon Monosporascus root rot and vine decline disease was studied. The crude antibiotics were extracted from the cell-free culture filtrate of P. resinovorans B11 by solvent extraction. Analysis of the antibiotics preparation by thin layer chromatography revealed a prominent band with an Rf of 0.23 under ultraviolet light. Results of the gas chromatography–mass spectrometry analysis revealed that two compounds with retention time (RT) of 4.25 min and 10.58 min were present in the fluorescent band eluted at Rf 0.23. By comparing the mass spectra of these compounds with those found in the NIST/ Wiley database, these compounds were identified as 5-hydroxy-2-pentanone (RT: 4.25 min) and 4-hydroxy-4-methyl-2-pentanone (RT: 10.58 min) with molecular weights of 102.13 and 116.16, respectively. The compound 4-hydroxy-4-methyl-2-pentanone has been described as one of the components of antibiotics produced by other soil bacteria. However, this is the first report of production of 4-hydroxy-4-methyl-2-pentanone by P. resinovorans B11.

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Bacterial endophytes were isolated from the leaves of Bougainvillea spectabilis Willd. and screened for their in vitro antagonistic activity against three important phytopathogenic fungi viz., Neoc...

The efficacy of bacterial isolates obtained from the rhizosphere soil samples collected from cucumber fields of Muscat Governorate of Oman was assessed against Pythium aphanidermatum, the causal agent of damping-off of cucumber. Of the 58 isolates screened in a dual culture assay, only four isolates (B11, B9, AT3 and 4A) inhibited the growth of P. aphanidermatum and produced inhibition zones of above 5 mm. Among the four isolates, B11 was the most effective followed by B9, AT3 and 4A, which recorded inhibition zones of 14 mm, 13 mm, 11 mm and 6.8 mm, respectively. Scanning electron micrographs of hyphae of P. aphanidermatum grown in the presence of antagonists showed morphological abnormalities. These antagonistic bacteria were identified based on sequence analysis of 16S rDNA gene. The potential of the promising antagonists, Pseudomonas resinovorans (B11) and Pseudomonas aeruginosa (AT3) was evaluated either individually or in combination with a commercial formulation of Trichoderma viride against damping-off of cucumber under greenhouse conditions. Among the biocontrol treatments, soil application of P. resinovorans (B11) was the most effective, which resulted in a significantly lower damping-off incidence (24 to 30%) compared with Pythium-infected control (82 to 84%). To our knowledge, this is the first report on biological control of P. aphanidermatum with P. resinovorans.

The potential of antagonistic bacteria isolated from tomato rhizosphere soils of Oman in the control of damping-off disease of tomato was investigated. A total of 27 bacterial isolates were isolated from 18 soil samples collected from the rhizosphere of tomato from Al-Batinah South, Al-Sharqia North and Muscat Governorate. These bacterial isolates were tested in vitro for their antagonistic activity against Pythium aphanidermatum using a dual culture technique. Of the 27 bacterial isolates tested, four isolates designated D1/3, D1/8, D1/17 and D1/18 were effective in inhibiting the mycelial growth of P. aphanidermatum, by inducing an inhibition zone of 32.3, 10.3, 6.3 and 9.9 mm, respectively. Compatibility tests using a cross-streak assay on nutrient agar medium indicated that these four bacterial isolates were compatible with one another. The bacterial isolates were identified as Klebsiella oxytoca (D1/3), Exiguobacterium indicum (D1/8) and Bacillus cereus (D1/17 and D1/18), on the basis of the rRNA gene sequences. Among the isolates tested for in vitro plant growth promoting activity, D1/8 induced the maximum shoot length and seedling vigor. The potential of bacterial antagonists either individually or in combination in the control of damping-off disease of tomato was tested under greenhouse conditions. Among the biocontrol treatments, the combined application of D1/8 and D1/17 was the most effective, where damping-off incidence was reduced by 27% relative to the infected control. These bacterial antagonists appear to be potential candidates to be developed as bio-inoculants for the ecofriendly management of damping-off of tomato under desert farming ecosystem.

A study was conducted on the possible in vitro production of phytotoxins by the melon root rot pathogen, Monosporascus cannonballus. The culture filtrate of a highly virulent isolate of the fungus was tested for its phytotoxic activity on cucumber by detached leaf assay, electrolyte leakage assay and seedling vigour test. In detached leaf bioassay, necrotic symptoms developed on cucumber leaves 5–7 days after application of the culture filtrate. The culture filtrate of M. cannonballus caused substantial reduction in seed germination, vigor of cucumber seedlings and an increase in electrolyte leakage from leaf tissues compared to the control. Studies on the effect of heat and dialysis on the phytotoxic activity of the culture filtrate revealed that the toxic metabolites are thermostable and have low molecular weight (

For decades, the production of acid lime (Citrus aurantifolia) in Oman has been affected by diseases caused by phytoplasmas, notably witches’ broom disease of lime (WBDL). In recent years, a new phytoplasma strain in Oman has been observed that promotes the sudden decline of lime (SDL). The molecular mechanisms behind its pathogenicity and mode of interaction with citrus host plants is still completely unknown. In this study, we evaluated the differential expression of genes in symptomatic and asymptomatic lime trees in Oman using a real-time quantitative PCR assay. Among 27 regulatory and biosynthesis-related genes tested in Citrus aurantifolia plants during phytoplasma infection, we verified the presence of 14 responsive genes in plants showing SDL symptoms, revealing a specific set of SDL-responsive genes. Quantification data of endogenous 3-indoleacetic acid and jasmonic acid show an unbalanced hormonal content in symptomatic lime trees, corroborating the gene expression data. The identification of regulatory genes differentially expressed in plant-phytoplasma interactions during SDL will help to elucidate the mechanisms possibly involved in defense responses, development and death-triggered signals in infected citrus plants.

Witches’ broom disease (WBD), caused by ‘Candidatus Phytoplasma aurantifolia’, is a serious disease of acid lime (Citrus aurantifolia L.) in Oman and UAE. However, little is known about the distribution of phytoplasma and the expression of WBD symptoms in different geographical locations. A survey was carried out in 18 districts in Oman and the UAE covering 143 orchards and 5823 acid lime trees. ‘Ca. P. aurantifolia’ was detected in acid lime in all the 18 surveyed districts. However, the development of typical symptoms of WBD was only observed in 12 districts. Districts in which the phytoplasma was present but symptoms were not expressed were located either in desert areas or in areas characterized by semi-tropical conditions. Phylogenetic analysis of 16 phytoplasma isolates from trees developing WBD symptoms and six phytoplasma isolates from trees with no WBD symptoms showed that all isolates share an identical 16S rRNA sequence, belonging to subgroup II-B. Quantitative real time PCR analysis showed that the concentration of phytoplasma is significantly higher (8,800-801,000 copies) in leaves developing WBD symptoms compared to 2-268 copies in asymptomatic leaves from the same trees and 8 to 874 copies in acid lime trees from areas where disease symptoms were not expressed. The lack of expression of WBD symptoms under certain environmental conditions may suggest that symptom development and phytoplasma are affected by certain unfavorable environmental conditions. These findings could provide a basis for managing witches’ broom disease through encouraging lime cultivation under climatic conditions less conducive to WBD symptom expression. This article is protected by copyright. All rights reserved.

Spent mushroom substrate (SMS) is widely used as fertilizer and to control plant diseases. The microorganisms surviving in SMS play a crucial role in plant growth promotion and biocontrol properties of SMS. In this study, an effort was made to isolate and characterize the bacterial species present in the SMS of Agaricus bisporus and to study their antagonistic potential, plant growth-promoting ability and indole-3-acetic acid (IAA) producing trait. Six different bacterial isolates exhibiting morphological variabilities were obtained from the SMS by serial dilution technique. On the basis of 16S rRNA gene sequences, these isolates were identified as Staphylococcus epidermidis (Sh1 and Sh3), S. aureus (Sh2), Bacillus albus (Sh4), Delftia lacustris (Sh6) and Comamonas aquatica (Sh7). These bacterial strains were assayed for their antagonism against Pythium aphanidermatum , a phytopathogenic oomycete. The results of in vitro dual culture assay revealed that all the 6 bacterial isolates showed low levels of suppression of P. aphanidermatum and recorded less than 5 mm inhibition zone. Among the bacterial isolates, S. epidermidis Sh3 recorded the maximum inhibition zone of 4.2 mm. Plant growth promotion test using roll paper towel method revealed that C. aquatica Sh7, B. albus Sh4, D. lacustris Sh6 and S. epidermidis Sh3 caused a significant increase in seedling vigour of cucumber compared to control. The seeds treated with the bacterial isolate C. aquatica Sh7 showed the maximum seedling vigor. Assessment of in vitro production of IAA by the bacterial isolates revealed that the bacterial isolates highly varied (ranging from 0.28 to 9.25 mg L -1 ) in their potential for production of IAA. The maximum amount of IAA was produced by C. aquatica Sh7 (9.25 mg L -1 ), while the minimum was produced by S. epidermidis Sh1 (0.28 mg L -1 ).

Euphorbia larica Boiss. (Arabic = Isbaq) is a dominant and common component of the native desert flora of northern Oman. Traditional ethnobotanical uses have included use of the latex for treating camels with parasites. In February 2011, E. larica plants showing stem lesions up to several cm long and in many cases with stem dieback were collected from Al-Khoudh 50 km west of Muscat. The disease appeared widespread within the location where several dead specimens were also recorded, although the cause was unclear. Sections (5 mm) of five diseased branches taken from different plants and placed on potato dextrose agar (PDA) in all cases yielded Fusarium-like colonies. Colonies recovered were initially white becoming rose to medium red in color with abundant aerial mycelium. Macroconidia were scarce and scattered (mean of 20 spores: 26.83 × 4.73 μm) with three to four septa per spore; microconidia were slightly curved, ovoid, and fusiform (mean of 20 spores: 11.64 × 4.03 μm) with zero to two septa per spore. Spherical chlamydospores (mean of 20 spores: 11.05 μm) were terminal and intercalary, single, and in chains. In vitro characters and spores measurements conformed to previously described features of Fusarium brachygibbosum Padwick (1). Mycelial plugs (5 mm) were taken from 7-day-old cultures of the fungus grown on 2.5% PDA and applied to a small incision (3 mm) on the stems of healthy E. larica grown in situ and protected with wet cotton and Parafilm. The residual agar, mycelium, cotton, and Parafilm were removed after 7 days and symptoms were recorded. Control stems were inoculated using PDA (5 mm) plugs alone and inoculations were repeated twice. Artificial inoculations resulted in dieback of all stems within 11 days and fungal colonies identical to initial isolations were recovered from artificially infected surface-sterilized stem pieces. Identification of F. brachygibbosum was confirmed by comparing sequences generated from the internal transcribed spacer (ITS) region of the ribosomal DNA (ITS1 and ITS4 primers) and the intron region of translation elongation factor alpha (EF1-α) (EF-1-986 and EF-728 primers). The ITS and EF1-α sequences were found to share 100% and 99% nucleotide similarity to previously published sequences of the ITS (HQ443206) and EF1-α (JQ429370) regions of F. brachygibbosum in GenBank. The accession number of ITS sequence of one isolate assigned to EMBL-Bank was HF562936. The EF sequence was assigned to EMBL-Bank accession (submission number Hx2000027017; number will be sent later). This pathogen has previously been reported on date palm (2) in Oman but, to our knowledge, this is the first report of this pathogen on E. larica. References: (1) A. M. Al-Sadi et al. Crop Prot. 37:1, 2012. (2) G. W. Padwick. Mycol. Pap. 12:11, 1945.

In March 2013, 90% of mature bean plants (Phaseolus vulgaris L. cv. Kendo) grown on a commercial farm in the north of Oman (Barka) developed symptoms of root rot and necrotic streaks on the crown area of the stem and wilted. A Pythium spp. was isolated consistently from roots and basal stems on 2.5% potato dextrose agar (PDA) and V8 (100% vegetable juice) plus 1.5% agar technical. Colonies of Pythium spp. on PDA and V8 plus agar developed abundant aerial mycelia, with the main hyphae being up to 10 μm wide. Zoosporangia were made up of terminal complexes of swollen hyphal branches of different lengths and up to 22 μm wide. Oogonia were terminal, globose, and smooth with a 26-μm diameter (average of 20). Antheridia were mostly intercalary, sometimes terminal, and broadly sac-shaped, 15 μm long and 11 μm wide (average of 20). Oospores were aplerotic, 23 μm in diameter (average of 24), with walls 1 to 2 μm thick at 25°C (ambient temperature). The internal transcribed spacer of the ribosomal DNA (ITS1 and ITS4) sequence of the isolates matched the sequence of Pythium aphanidermatum (Edson) Fitzp. in GenBank. The sequence of isolate Py1 was deposited in GenBank as Accession No. KM102739. This isolate was identified as P. aphanidermatum on the basis of morphological and cultural characteristics (1) and the ITS rDNA sequence. The ITS was found to share 100% nucleotide similarity to previously published sequences of the ITS (KJ755088). To fulfill Koch's postulate, a 5-mm plug of 5-day-old mycelium of isolate Py1 grown on 2.5% PDA was used to inoculate healthy seedlings of beans cv. Kendo. The plug was placed adjacent to the bean stem; PDA served as a control. Five replicate plants were used for the treatment and the control. The plants were maintained in a glasshouse at a temperature of 23 to 25°C. The plants were watered every day. The irrigation water had an electrical conductivity value of 0.2 dSm−1. Eleven days after inoculation, 90% of the plants developed root rot, crown necrosis, and wilt symptoms similar to those observed in the field. On the other hand, control plants did not show any symptoms. The pathogen was re-isolated from roots and basal stems of symptomatic plants. To our knowledge, this is the first report of P. aphanidermatum as the causal agent of root and crown necrosis of mature bean plants in Oman. Future studies should focus on evaluating management options for this disease to avoid possible losses in a crop that has a high export value in Oman. Reference: (1) Y. Serrano et al. Plant Dis. 92:174, 2008.

A study was conducted to characterize the common Pythium spp. in greenhouses in Oman and their level of resistance to hymexazol, a widely used fungicide in the country. Pythium isolates were obtained from soil samples, cocopeat bags, and cucumber roots collected from seven regions in the country. Identification of 80 Pythium isolates to the species level using sequences of the internal transcribed spacer region of the ribosomal RNA showed that they belong to four species: Pythium aphanidermatum (77 isolates), P. spinosum (1 isolate), P. myriotylum (1 isolate), and P. catenulatum (1 isolate). Investigating the aggressiveness of three Pythium spp. on cucumber showed that P. aphanidermatum, P. myriotylum, and P. spinosum are pathogenic. Phylogenetic analysis of P. aphanidermatum isolates showed that most of the isolates obtained from cocopeat clustered separately from isolates obtained from soil and roots. This may indicate a difference in the origin of the cocopeat isolates. Evaluating the resistance of 27 P. aphanidermatum isolates to hymexazol showed that most isolates were sensitive (0.9 to 31.2 mg liter−1) whereas one isolate was resistant (142.9 mg liter−1). This study is the first to report P. myriotylum and P. catenulatum in Oman. It is also the first to report the development of resistance to hymexazol among P. aphanidermatum populations from greenhouses. Growers should use integrated disease management strategies to avoid further development of resistance to hymexazol.

The purpose of this study was to characterize fungal and oomycete species associated with root diseases ofPhaseolus vulgaris,Vigna unguiculata,V. radiataandVicia fabain Oman. Root samples were collected from plants suffering from weakened growth and yellowing symptoms. Fungal species were isolated on 2.5% potato dextrose agar amended with 10 mg l−1rifampicin and 200 mg l−1of ampicillin and identification was based on sequences of the internal transcribed spacer region of the ribosomal RNA gene (ITS rRNA), glycerol-3-phosphate dehydrogenase (GPDH), translation elongation factor-1 alpha (TEF), beta-tubulin (TUB), calmodulin (CMD), actin (ACT). Isolations yielded 204 fungal isolates belonging to nine different genera, with most isolates belonging toAlternariaandFusarium. Molecular identification revealed that the isolates belong to 20 fungal species, the most dominant of which wasAlternaria alternata. Pathogenicity tests were conducted on each plant species. The inoculations onP. vulgarisrevealed thatPythium aphanidermatuminduced rotting, damping-off and wilt symptoms whileFusarium equisetiinduced yellowing symptoms on the leaves.Rhizoctonia solaniproduced lesions and root rot onVigna unguiculatawhileCurvularia muehlenbeckiaeandCurvularia caricae-papayaeproduced root lesions on the roots ofV. unguiculataandV. radiata, respectively.Alternaria alternataproduced brown symptoms on the tap root ofVicia faba.P. aphanidermatumresulted in a significant reduction in the fresh weight, dry weight and shoot length ofPhaseolus vulgaris. The study shows that several fungal species can be found associated with the roots of beans andVigna unguiculatain Oman and can result in varying disease symptoms. This is the first report of root lesions produced byCurvularia muehlenbeckiaeon the roots ofV. unguiculataand byC. caricae-papayaeonV. radiataworldwide.

Ceratocystis wilt is among the most important diseases on mango (Mangifera indica) in Brazil, Oman, and Pakistan. The causal agent was originally identified in Brazil as Ceratocystis fimbriata, which is considered by some as a complex of many cryptic species, and four new species on mango trees were distinguished from C. fimbriata based on variation in internal transcribed spacer sequences. In the present study, phylogenetic analyses using DNA sequences of mating type genes, TEF-1α, and β-tubulin failed to identify lineages corresponding to the four new species names. Further, mating experiments found that the mango isolates representing the new species were interfertile with each other and a tester strain from sweet potato (Ipomoea batatas), on which the name C. fimbriata is based, and there was little morphological variation among the mango isolates. Microsatellite markers found substantial differentiation among mango isolates at the regional and population levels, but certain microsatellite genotypes were commonly found in multiple populations, suggesting that these genotypes had been disseminated in infected nursery stock. The most common microsatellite genotypes corresponded to the four recently named species (C. manginecans, C. acaciivora, C. mangicola, and C. mangivora), which are considered synonyms of C. fimbriata. This study points to the potential problems of naming new species based on introduced genotypes of a pathogen, the value of an understanding of natural variation within and among populations, and the importance of phenotype in delimiting species.

A study was conducted to investigate genetic diversity and sensitivity to hymexazol among 80 isolates of Fusarium solani complex obtained from date palm (30), citrus (31) and cucumber (19). Characterization based on sequences of the EF1α and ITS rRNA showed that isolates belong to F. solani complex MLST type 3 + 4. AFLP analysis produced 980 polymorphic loci, 80 AFLP genotypes and moderate levels of genetic diversity (H = 0.2494). Clustering of the isolates was not related to the host or the geographical origin of the isolates. Analysis of molecular variance (amova) indicated the existence of a low level of genetic differentiation among populations obtained from different hosts (Fst = 0.0162) and regions (Fst = 0.0066). This may provide evidence for frequent movement of inoculum among hosts and regions in Oman, which could be attributed to cultural practices employed by farmers. Isolates of F. solani displayed variation in sensitivity to hymexazol, with EC50 values ranging from 2 to 5745 μg/ml (mean = 878 μg/ml); 19% of the isolates have an EC50 value of more than 1000 μg/ml. Findings are discussed in terms of the factors that affect diversity in F. solani isolates. The study reports for the first time the development of resistance to hymexazol among F. solani isolates from date palm, citrus and cucumber.

“CandidatusPhytoplasma aurantifolia” is associated with witches’ broom disease of lime in Oman and the UAE. A previous study showed that an infection by phytoplasma may not necessarily result in the physical appearance of witches’ broom symptoms in some locations in Oman and the UAE. This study investigated whether phytoplasma strains belonging to “Ca.P. aurantifolia” (based on the 16S rRNA gene analysis) in locations where disease symptoms are expressed are different from phytoplasma in locations where disease symptoms are not expressed. About 21 phytoplasma strains (15 from areas and trees with disease symptoms and six from areas and trees without disease symptoms) were included in the analysis. The study utilized sequences of the imp and SAP11 genes to characterize the 21 strains. Phylogenetic analysis of both genes showed that the 21 strains are similar to each other and to reference strains in GenBank. The study shows that there is a low level of diversity among all phytoplasma strains. In addition, it shows that phytoplasma in places where witches’ broom symptoms are not expressed are similar to phytoplasma in places where disease symptoms are expressed. This may suggest that disease expression is not linked to the presence of different phytoplasma strains, but may be due to other factors such as weather conditions.

Lasiodiplodia is a common pathogen causing dieback, gummosis, or root necrosis on the three most important fruit crops in Oman and the United Arab Emirates (UAE): date palm (Phoenix dactylifera), Citrus spp., and mango (Mangifera indica). A study was conducted to examine diversity in 64 Lasiodiplodia isolates infecting date palm (24), Citrus (11), and mango (29) in Oman and the UAE. Identification based on sequences of the internal transcribed spacer (ITS) rDNA and EF1α gene showed that date palm isolates belonged to L. hormozganensis (75% of isolates) and L. theobromae (25%); Citrus isolates belonged to L. hormozganensis (45%), L. theobromae (45%), and L. iraniensis (10%); and mango isolates belonged to L. theobromae (59%), L. iraniensis (34%), and L. hormozganensis (7%). Amplified fragment length polymorphism (AFLP) fingerprinting of the 64 isolates using four primer pair combinations produced 64 genotypes and 972 polymorphic alleles. Cluster analysis separated the isolates into four clusters representing the three species. A higher level of genetic diversity was observed in L. iraniensis (0.3105) compared to L. hormozganensis (0.2503) and L. theobromae (0.2331) in Oman. Analysis of molecular variance (AMOVA) indicated the existence of low levels of genetic differentiation among date palm populations of L. hormozganensis obtained from Oman and the UAE (FST = 0.025) and among populations of L. hormozganensis (0.0485) and L. theobromae (0.0703) from date palm, Citrus, and mango. These findings imply a high rate of movement of L. hormozganensis and L. theobromae isolates among date palm, Citrus, and mango and between the two countries. Findings from the pathogenicity test supported the AMOVA analysis and suggested a lack of host specialization in L. hormozganensis, L. iraniensis, and L. theobromae on date palm, acid lime, and mango. Although this is the first record of L. hormozganensis and L. iraniensis in Oman, the relatively moderate level of genetic diversity in the two species compared to L. theobromae suggests that the two species have been in Oman for a long time but misidentified by morphology and ITS rDNA sequences as L. theobromae. This study is also the first record of date palm and acid lime as natural hosts for L. hormozganensis and the first record of L. hormozganensis in the UAE. The diversity in Lasiodiplodia species affecting date palm, Citrus, and mango in Oman and the UAE should be taken into consideration when planning future management programs for diseases caused by these pathogens.

Stemphylium lycopersici is an important pathogen causing leaf spot of tomatoes worldwide. Although much information is available about the pathogen, little is known about dynamics of S. lycopersici in tomato fields. Seventy-nine symptomatic leaf samples were collected from two tomato cultivars grown in a farm (Miral and Inbred line). Fungal species associated with the disease were isolated on potato dextrose agar. Seventy-nine isolates were obtained and identified as S. lycopersici based on sequence analysis of combined dataset of the internal transcribed spacer and glyceraldehyde-3-phosphate dehydrogenase regions. The 79 isolates were subjected to amplified fragment length polymorphism analysis using three primer combinations. The Stemphylium lycopersici population from the two cultivars was found to have a very low level of genetic diversity (H = 0.0948). Cluster analysis showed intermixing of isolates from the two cultivars. In addition, analysis of molecular variance showed the presence of a very low level of genetic differentiation between populations obtained from the two cultivars (Fst = 0.0206). These findings indicate the presence of a high rate of gene flow between the two populations and may suggest that the two populations originated from the same inoculum source. The implications of these findings on the management of Stemphylium-induced leaf spot of tomatoes are discussed.

Date palm is the most important crop in Oman and the Arabian Peninsula. A study was conducted to investigate fungal and oomycete pathogens associated with root diseases of date palms in Oman. Isolations were done from date palm roots showing root rot/necrosis symptoms. The root samples were collected from 111 date palm trees representing 29 different date palm cultivars. Morphological and molecular identification of the isolated fungi and oomycetes showed that they belong to 34 different fungal and oomycete species. Fusarium solani (27%), Ceratocystis radicicola (25%) and Lasiodiplodia theobromae (19%) were found to be the most common pathogens associated with root diseases of date palms. Pathogenicity tests on seedlings of date palm cv. Khalas showed that 21 fungal and oomycete species are pathogenic on date palm seedlings. The pathogenic species produced root rot, root necrosis or wilt symptoms upon inoculation on date palm seedlings. A total of 1, 7, 13 and 10 fungal and oomycete pathogens were found to be aggressive, moderately aggressive, weak and non-pathogenic on date palm seedlings, respectively, with C. radicicola being the most aggressive. Among the 21 pathogenic species, 13 are reported in this study for the first time as new root pathogens of date palm on a global basis. These include Ceratocystis omanensis, Cochliobolus hawaiiensis, Exserohilum rostratum, Corynascus kuwaitiensis, Fusarium brachygibbosum, Fusarium acuminatum, Fusarium redolens, Fusarium thapsinum, Nigrospora sphaerica, Phoma multirostrata, Pythium indigoferae, Pythium spinosum and Pythium ultimum var. ultimum. In addition, this study reports for the first time the occurrence of 22 fungal and oomycete species in Oman.

A study was conducted to characterize occurrence, molecular variability and potential sources of Citrus tristeza virus (CTV) in Oman. A survey during 2009 and 2010 showed that CTV occurs in most (91%) of the surveyed districts. Moderate to high levels of infection with CTV in lime were detected in northern Oman (15–63%) compared to the south (0–12%). This could be related to the continuous introduction of infected citrus germplasm in the north from abroad, where CTV was detected in 45% of citrus seedlings imported from Syria, Lebanon, India, Pakistan and Egypt. CTV was detected for the first time in sweet lime, sweet lemon, citron, mandarin, sweet orange and sour orange and was found to be associated with stem pitting, stunting, leaf curling and vein clearing symptoms in many of the infected trees and seedlings in Oman. Bi-directional reverse transcription-PCR analysis of the coat protein (CP) gene of 22 randomly selected CTV-positive samples provided evidence that severe strains of CTV exist in Oman. Cloning and sequencing the CP gene of six isolates showed that they have 91–100% nucleotide identity with each other and 96–99% with representative isolates from other parts of the world. Phylogenetic analysis of the CTV isolates showed that four belong to CTV Group 4. However, two isolates formed a separate clade with 100% bootstrap support for separation from Group 5. Phylogenetic analysis and coefficient of differentiation values suggest that the two isolates from Oman constitute a new CTV phylogenetic group.

A long-term study was conducted between 2000 and 2009 to characterize the incidence, progress and causal agents of cucumber vine decline in Oman. A survey in 175 different greenhouses showed that disease incidence levels range from 0 to 50%, with the highest levels of mortality being in the hotter seasons. Detailed temporal disease increase data from 24 different greenhouses showed mortality progress consists of two phases. The first phase is characterized by attack of young seedlings (

Potting mixtures, which are imported from overseas, as well as local and imported organic fertilizers are commonly used by growers in Oman for vegetable production. However, there is a lack of information about pathogens that might be introduced into farms along with potting mixtures and organic fertilizers. The purpose of this study was therefore to investigate the most common fungal pathogens introduced into farms in Oman via potting mixtures and organic fertilizers. Forty eight samples of potting mixtures and organic fertilizer samples were screened for their contamination with fungal pathogens using different methods. Fungal pathogens were identified using morphological characteristics and sequences of the internal transcribed spacer region of the ribosomal DNA (ITS rDNA). Penicillium, Rhizopus, Aspergillus, Helminthosporium, Alternaria, Trichoderma, Acrospira, Fusarium spp., and three human fungi were isolated from potting mixtures and organic fertilizers. Investigating sensitivity of different Fusarium species to hymexazole revealed high variation among isolates. Three isolates showed resistance to this fungicide. This appears to be the first report of occurrence resistance to hymexazole fungicide among Fusarium spp.

Potting media are commonly used by growers in different parts of the world for potted plants, raising seedlings and for improving soil characteristics. This study was conducted to characterize bacterial communities occurring in 13 commercial potting media products originating from seven countries. Bacteria were isolated using serial dilution. Identification to the species level was based on phylogenetic analysis of the 16S rRNA gene. The analysis showed the association of 13 bacterial species with the different potting media samples, namely Arthrobacter livingstonensis, Kocuria flava, Leifsonia lichenia, Bacillus vallismortis, Bacillus pumilus, Staphylococcus warneri, Burkholderia phenazinium, Burkholderia sp., Ralstonia pickettii, Rhodanobacter spathiphylli, Rhodanobacter sp., Pseudomonas thivervalensis and Chryseobacterium gallinarum. Bacterial densities in the samples ranged from 8 × 107 to 1.2 × 109 colony forming units per gram of substrate. The study shows the isolation of some potential plant and human bacterial pathogens. However, most of the isolated species were either biocontrol species or saprophytes. The study questions the ways by which these bacterial species were introduced into potting media. To the best of our knowledge, this appears to be the first report of most of the isolated bacteria from potting media, except B. pumilus.

Cucumber (Cucumis sativus) is a widely cultivated plant in the family Cucurbitaceae that is grown as greenhouse crop in Oman. During a recent survey for begomoviruses, whitefly infestation was observed in two greenhouses of cucumber in the Barka region. Plants were exhibiting a foliar yellow mosaic and crumpling, symptoms typical of begomovirus infection (Supplementary Figure 1), with an incidence of 50-60 %. Leaves from four symptomatic plants were collected, two plants from each greenhouse, as well as leaves from two apparently healthy (symptomless) plants, one from each greenhouse. Electron microscopy analysis of negatively stained sap samples showed the presence of geminate (twinned quasi-icosahedral) particles of ~18-20x30 nm in samples from symptomatic but not non-symptomatic plants, suggesting the presence of a geminivirus. Nucleic acids were extracted from leaf samples (Porebski and Bailey 1997) and used in PCR with primers to the conserved domain of the coat protein of begomoviruses (Brown et al....

A study was conducted to investigate the most common fungal and oomycete pathogens introduced into farms in Oman via potting mixtures and organic manures. A total of 37 commercial types of potting mixtures (2 local and 35 imported from overseas), 4 commercial types of organic manures and 11 non-commercial types of organic manures were included in the study. Identification of the isolated species was based on morphological characteristics, except for the most common species which were further identified using sequences of the internal transcribed spacer region of the ribosomal DNA (ITS rDNA). Fusarium spp. (14%), Pythium aphanidermatum (3%), Alternaria spp. (5%), Helminthosporium spp. (5%) and Cladosporium spp. (3%) were recovered at different frequencies from samples of potting mixtures. Fusarium solani (40%) and Fusarium equiseti (47%) were recovered at high frequencies from samples of organic manures. Isolations from organic manures also yielded Pythium periplocum (7%), Rhizoctonia solani (7%), Fusarium lichenicola (7%), Helminthosporium spp. (27%) and Alternaria spp. (27%). Trichoderma spp., Penicillium spp., Aspergillus spp. and Rhizopus spp. were found to be common in samples of potting mixtures and organic manures. Investigating sensitivity to hymexazol among 9 isolates of F. equiseti and 13 isolates of F. solani revealed variations among different isolates. The EC50 values ranged from 1 to over 1200 (avg. 192 μg ml−1) for F. equiseti isolates and from 135 to 789 (avg. 324 μg ml−1) for F. solani isolates, indicating presence of resistance to this important fungicide among some Fusarium isolates. This appears to be the first report of contamination with R. solani, P. periplocum, F. solani, F. equiseti and F. lichenicola of organic manures. This study appears to report for the first time F. lichenicola in Oman and appears to be the first report of occurrence of resistance to hymexazol among F. equiseti and F. solani isolates.

Witches’ broom disease of lime is a devastating disease in the Sultanate of Oman. In recent years a new disease has been observed, which promotes a sudden decline in Citrus aurantifolia (acid lime). The etiological agent of this new disease has not yet been determined. In this study the presence of phytoplasmas and RNAs was evaluated in plants showing the sudden decline symptomatology. The results reveal the presence of a complex of at least three different pathogens: 16SrII phytoplasmas, Citrus tristeza virus and Citrus exocortis viroid.