Macrophomina phaseolina associated with grapevine decline in Iran

Grapevines exhibiting general decline symptoms were observed in July 2012 in Arbatan, a region in Marand county, north-western Iran. Leaf necrosis symptoms were also observed in affected grapevines. Dark brown necrotic lesions and wood discoloration were observed in the vascular tissues of affected cordons. Fungal isolates, all with similar cultural and morphological features, were obtained from symptomatic tissues. Morphological characteristics indicated that the isolates were Macrophomina phaseolina. Sequence analysis of the elongation factor (EF-1α) gene from isolates confirmed this identification, with 100% similarity to the reference M. phaseolina sequences obtained from GenBank. Pathogenicity assays of two M. phaseolina isolates on 2-year-old potted vines (cv. ‘Keshmeshi’) demonstrated that M. phaseolina was pathogenic on grapevine. This study confirmed the association of M. phaseolina with grapevine decline symptoms, and represents the first report of this fungus associated with grapevine trunk diseases in Iran

Effect of silicon on rice blast disease

Silicon is the second most plentiful element in soil and is beneficial for a large variety of plants. It is concentrated in plant tissues in quantities similar to that of macronutrients. Considerable damages to plants caused by abiotic stresses such as drought stress, salinity stress, heavy metal stress and nutrient imbalance, as well as biotic stresses like insect pests and pathogens and even herbivorous attacks, have been reported to be reduced significantly by silicon application. Among rice diseases, blast is recognized as the most devastating one. Silicon fertilization has been reported to be efficacious in controlling and mitigating rice blast severity. Two different hypotheses are proposed for the ability of silicon to lessen disease severity. The first hypothesis emphasizes on silicon function as a mechanical barrier against appressorial penetration, while the second hypothesis is based upon the belief that silicon has some physiological roles in disease resistance

Plant tonic, a plant-derived bioactive natural product, exhibits antifungal activity against rice blast disease

The tendency towards application of natural products and botanical extracts as safer antimicrobial agents against plant pathogens has recently been increased. Plant Tonic9 (EOX-SOV) is an environmentally friendly product and by its application there is no concern of resistance as it is with conventional pesticides. The goal of the present research was to determine the effect of application of this product against Magnaporthe oryzae, the causal agent of rice blast. The efficacy of plant tonic against M. oryzae was evaluated through in vitro and in vivo experiments. Under in vitro conditions, application of plant tonic at all rates (2, 3, and 4 mL/L) could significantly inhibit the mycelial growth and conidial germination of fungus with the highest inhibition (83.63% and 95.15%, respectively) recorded by the rate of 4 mL. Plant tonic treatment (3 and 4 mL) was more effective than fungicide treatment (propiconazole 25% EC (0.1%); 250 ppm) to inhibit mycelial growth and conidial germination of M. oryzae. Under in vivo conditions, plant tonic application (4 mL) was also the most effective treatment and resulted in a significant reduction (57.12%) of the area under the disease progress curve (AUDPC) value as compared with the control. Application of plant tonic also caused increased accumulation of phenolic compounds and higher activity of peroxidase and polyphenol oxidase enzymes than the control. The maximum amount of phenolic compounds (0.49 mg Gallic acid equivalent/g leaf fresh weight) and the highest activity of the enzymes (1.24 and 7.85 Units/mL for peroxidase and polyphenol oxidase, respectively) were observed in plants treated with plant tonic (4 mL) and challenged with M. oryzae as compared with other treatments. No phytotoxicity was observed in plant tonic treated rice plants when compared with the control. Results of the present study confirmed the beneficial effects of plant tonic in controlling rice blast disease. Therefore, its application may help to develop appropriate management strategies and provide with the opportunity to have cleaner and safer environment for agriculture

An outbreak of leaf spot caused by Stemphylium solani on eggplant in Malaysia.

In 2011, a severe gray leaf spot was observed on aubergine (Solanum melongena) in major aubergine growing areas in Malaysia, including the Pahang, Johor and Selangor states. Disease incidence was >70% in severely infected areas of approximately 150 ha of aubergine greenhouses and fields examined. Symptoms initially appeared as small (1-5 mm in diameter), brownish-black specks with concentric circles on the lower leaves. The specks then coalesced and developed into greyish-brown, necrotic lesions, which also appeared on the upper leaves. Eventually, the leaves senesced and were shed. Fungal colonies were greyish green to light brown, and produced a yellow pigment. Single, muriform, brown, oblong conidia formed at the terminal end of each conidiophore. The conidiophores were tan to light brown and ≤220 µm long. Based on these morphological criteria, 25 isolates of the fungus were identified as Stemphylium solani. Further confirmation of the identification was obtained by molecular characterization. A BLAST search in the NCBI database revealed that the sequence was 99% identical with published ITS sequences for two isolates of Stemphylium solani (Accession Nos. AF203451 and HQ840713). This is thought to be the first report of Stemphylium solani on aubergine in Malaysia

Characterisation of Magnaporthe oryzae isolates from rice in peninsular Malaysia

The genus Pyricularia (anamorph)/Magnaporthe (teleomorph) includes important destructive pathogens causing blast disease on various species from the family Poaceae. Thirty-five Magnaporthe isolates were collected from diseased rice plants (variety MR219) in different rice-growing regions of Malaysia, including the five states of Selangor,Penang, Kedah, Kelantan, and Perak between 2010 and 2014. DNA sequence analyses of the internal transcribed spacer (ITS), actin, β-tubulin and calmodulin gene regions, random amplified polymorphic DNA (RAPD) and intersimple sequence repeat (ISSR) analyses were conducted to analyse 35 Magnaporthe isolates. Phylogenetic analysis of the combined dataset confirmed the identification of all isolates as M. oryzae with a high distance from other Magnaporthe (Pyricularia) species. RAPD and ISSR analyses indicated the existence of a relatively low similarity index value among M. oryzae isolates through identification of four main clades. The clustering of RAPD and ISSR analyses demonstrated that there was a correlation between the isolates and their geographical origins

Leaf spot on lettuce (Lactuca sativa) caused by Stemphylium solani, a new disease in Malaysia.

In June 2011, lettuce (Lactuca sativa) plants cultivated in major lettuce growing areas in Malaysia, including the Pahang and Johor states, had extensive leaf spots. In severe cases, disease incidence was recorded to be more than 80%. Symptoms on 50 plants were initially water-soaked spots (1-2 mm in diameter) on leaves, which then became circular spots spreading over much of the leaves. Main lettuce growing areas infected by the pathogen in the aforementioned states were investigated and the pathogen was isolated onto potato dextrose agar. Fourteen isolates were identified as Stemphylium solani based on morphological criteria. To confirm morphological characterization, the DNA of the fungus was extracted from mycelium and PCR was conducted using universal primers ITS5 (5′-GGAAGTAAAAGTCGTAACAAGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′), which amplified the internal transcribed spacer (ITS) region of rDNA. The sequencing result was subjected to BLAST analysis, revealing a 99% similarity to other published sequences in the GenBank database (GenBank accession nos. AF203451 and HQ840713). This is thought to be the first report of Stemphylium solani on lettuce in Malaysia

Identification of Pithomyces chartarum causing leaf spot of cabbage in Malaysia

A leaf spot disease was observed on cabbage (Brassica oleracea L. var. capitata) affecting 80% of plants growing in greenhouses and fields in Serdang, Selangor, Malaysia. Symptomatic leaf samples were collected from infected plants and isolations made on agar medium. Single-spore isolates from resulting colonies were identified based on cultural and morphological characteristics as Pithomyces chartarum. Morphological identification was confirmed by sequence analysis of the internal transcribed spacer (ITS) regions 1 and 2, including 5.8S rDNA (ITS1-5.8S-ITS2). Pathogenicity tests indicated that P. chartarum causes leaf spot on cabbage. This is the first report of leaf spot caused by P. chartarum on cabbage in Malaysia

Analysis of genetic and virulence variability of Stemphylium lycopersici associated with leaf spot of vegetable crops

Stemphylium lycopersici (Enjoji) W. Yamam was initially described from tomato and has been reported to infect different hosts worldwide. Sequence analyses of the internal transcribed spacer (ITS) regions 1 and 2, including 5.8S rDNA (ITS-5.8S rDNA) and glyceraldehyde-3-phosphate dehydrogenase (gpd) gene, random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR), as well as virulence studies were conducted to analyze 46 S. lycopersici isolates. Stemphylium lycopersici isolates used in this study were obtained from diseased tomato (Solanum lycopersicum L.), eggplant (Solanum melongena L.), pepper (Capsicum annuum L.) and lettuce (Lactuca sativa L.) from major vegetable growing regions of Malaysia, including the three states of Pahang, Johor and Selangor between 2011 and 2012. Phylogenetic analysis of a combined dataset of the ITS-5.8S rDNA and gpd regions indicated that all isolates were clustered in the sub-cluster that comprised S. lycopersici, and were distinguished from other Stemphylium species. Cluster analyses using the UPGMA method for both RAPD and ISSR markers grouped S. lycopersici isolates into three main clusters with similarity index values of 67 and 68 %. The genetic diversity data confirmed that isolates of S. lycopersici are in concordance to host plants, and not geographical origin of the isolates. All S. lycopersici isolates were pathogenic on their original host plants and showed leaf spot symptoms; however, virulence variability was observed among the isolates. In cross-inoculation assays, the representative isolates were able to cause leaf spot symptoms on eggplant, pepper, lettuce and tomato, but not on cabbage

Alternaria capsicicola sp. nov., a new species causing leaf spot of pepper (Capsicum annuum) in Malaysia

A new species of Alternaria causing leaf spot of pepper (Capsicum annuum) obtained from the Cameron highlands, Pahang, Malaysia, was determined based on phylogenetic analyses, morphological characteristics, and pathogenicity assays. Phylogenetic analyses of combined dataset of the glyceraldehyde-3-phosphate dehydrogenase (gpd), Alternaria allergen a 1 (Alt a1) and calmodulin genes revealed that the new isolates clustered into a subclade distinct from the closely related Alternaria species A. tomato and A. burnsii. The solitary or short chains of conidia resemble those of A. burnsii. However, conidia with long beaks are morphologically similar to A. tomato. Hence, the pathogenic fungus is proposed as Alternaria capsicicola sp. nov. Pathogenicity assays indicated that A. capsicicola causes leaf spot on pepper

Effects of foliar and root application of silicon on rice blast fungus in MR219 rice

Rice blast caused by fungus Magnaporthe grisea (Hebert) Barr [teleomorph]Pyricularia oryzae Cavara is among the most devastating diseases of rice worldwide. In modern agricultural practices it is highly important to manage diseases and pests using efficient methods with minimum harm to the environment. Although silicon has been reported to significantly reduce foliar diseases in crops, its application has not been widely adopted in Malaysia. Hence studies were conducted to determine the effects of silicon on Pyricularia oryzae. Rice variety MR219 was grown in the glasshouse and the function of silica gel and sodium silicate in conferring resistance against blast was investigated. Silica gel was applied to soil prior to planting (0, 60, 120, 180 g/5 kg of soil) while sodium silicate was used as foliar spray (0, 1,2, 3 mL/L). The treatments were arranged in a completely randomized design with three replications. The severity of disease and silicon content of leaves were compared between the non-amended controls and rice plants receiving the different rates and sources of silicon. Silicon at all rates of application significantly (α=0.05) reduced the severity of disease with the highest reduction (75%) recorded in treatments receiving 120 g of silica gel. The relationship between leaf blast severity (Y) and amount of silicon applied to the plants (X) could be explained by the exponential decay curve using equation y=Ae-bx indicating that leaf blast severity was lower with higher rates of silicon application. Scanning Electron Microscopic observations showed that there were two types of silicified cells on the adaxial surface of rice leaves which included dumbbell-shaped and small scattered silica cells. The X-ray spectra analysis demonstrated a significant difference in weight concentration of silicon in silica cells on the leaf epidermis between silicon treated (25.79%) and non treated plants (7.87%) as well as among plants treated with different rates of silica gel and sodium silicate, indicating that silicon-fertilization resulted in higher deposition of silicon in both kinds of silica cells. Application of silicon also led to a significant increase (25.3 g/kg) in silicon content of leaves compared to nontreated plants (6.28 g/kg). The rate of photosynthesis of silicon treated plants (11.98 μmolm-2s-1) was significantly higher than plants in the control group (6.36 μmolm-2s-1). Shoot dry weight of rice plants increased significantly (1.50 g) with silicon fertilization as compared to non-treated plants (0.90 g). Contrast procedures indicated higher efficiency of silica gel in comparison to sodium silicate in almost all parameters assessed. The results suggest that mitigated levels of disease were associated with fortification of rice leaf epidermal cells through silicon fertilization. Although both foliar and root application of silicon were effective in decreasing the intensity of blast,greater effectiveness was achieved through root application. In conclusion,the study supports the hypothesis that silicon is able to confer resistance against blast disease. This could make silicon a useful tool for managing rice diseases, possibly in conjunction with reduced rate of fungicide, and may provide alternative to rice growers in areas where blast resistant cultivars have become susceptible