Aggressiveness of Small-Spored Alternaria spp. and Their Sensitivity to Succinate Dehydrogenase Inhibitor Fungicides

Brown leaf spot of potato is caused by a number of small-spored Alternaria spp. Alternaria alternata sensu stricto, Alternaria arborescens, and Alternaria tenuissima have been reported with increasing frequency in commercial potato fields. Potato cultivars with resistance to small-spored Alternaria spp. have yet to be developed; therefore, the application of foliar fungicides is a primary management strategy. Greenhouse inoculation assays demonstrated that isolates of these three small-spored Alternaria spp. were pathogenic to potato. Significant differences in aggressiveness were observed across isolates; however, there was no trend in aggressiveness based on species. Significant fungicide by isolate interactions in in vitro fungicide sensitivity and significant differences between baseline and non-baseline isolates were observed in all three small-spored Alternaria spp. The ranges of in vitro sensitivity of A. alternata baseline isolates to boscalid (EC50 <0.010 to 0.89 µg/ml), fluopyram (<0.010 to 1.14 µg/ml) and solatenol (<0.010 to 1.14 µg/ml) were relatively wide when compared to adepidyn (<0.010 to 0.023 µg/ml). The baseline sensitivity of A. arborescens and A. tenuissima isolates to all four fungicides were less than 0.065 µg/ml. Between 10 and 21% of non-baseline A. alternata isolates fell outside the baseline range established for the four SDHI fungicides evaluated. In A. arborescens, 10 to 80% of non-baseline isolates had higher sensitivities than the baseline. A. tenuissima isolates fell outside the baseline for boscalid (55%), fluopyram (14%), and solatenol (14%) but none fell outside the baseline range for adepidyn. Evaluations of in vivo fungicide efficacy demonstrated that most isolates were equally controlled by the four SDHI fungicides. However, reduced boscalid efficacy was observed for four isolates (two each of A. arborescens and A. tenuissima) and reduced fluopyram control was observed in one A. alternata isolate. Results of these studies demonstrate that isolates of all three species could be contributing to the brown leaf spot pathogen complex and that monitoring both species diversity and fungicide sensitivity could be advantageous for the management of brown leaf spot in potatoes with SDHI fungicides.

Heterologous expression of a polyketide synthase ACRTS2 in Aspregillus oryzae produces host selective ACR-toxins: Co-production of minor metabolites

Previously, we succeeded to produce the core structure of the host-selective ACR-toxin (1) on brown leaf spot on rough lemon when the polyketide synthase ACRTS2 gene was heterologously expressed in Aspergillus oryzae (AO). To confirm the production of 1 in AO, the detection limit and suppressing decarboxylation were improved, and these efforts led us to conclude the direct production of 1 instead of its decarboxylation product. During this examination, minor ACR-toxin-related metabolites were found. Their structure determination enabled us to propose a decarboxylation mechanism and novel branching route forming byproducts from the coupling of the dihydropyrone moiety of 1 with the acetaldehyde and kojic acid abundant in AO. The involvement of putative cyclase ACRTS3 in the chain release of linear polyketide was excluded by the co-expression analysis of ACRTS2 and ACRTS3. Taken together, we concluded the production of 1 in AO is solely responsible for ACRTS2.

First Report of Brown Leaf Spot of Rice (Oryza sativa L.) Caused by Bipolaris sorokiniana in Pakistan

Brown leaf spot of rice is one of the major seed-borne diseases and can diminish grain production up to 52% (Barnwal et al. 2013). In 2018, infected leaf samples showing the typical symptoms of brown spots were collected from the vicinity of the University of Agriculture, Faisalabad (31°26'10.3"N 73°03'35.1"E). The symptoms were brown-dark spots, with gray-light gray or brown centers surrounded by dark margins and with chlorotic halos and of oval or cylindrical shapes (5 to 9 mm in diameter). Disease incidence averaged 61% across the seven fields observed. Leaves were collected from the seven infected fields and symptomatic leaf tissues of 5 mm2 were excised from representative necrotic spots in each. These tissues were surface disinfected with 70% ethanol, rinsed with sterile distilled water (SDW), dried by blotting on paper, and placed on potato dextrose agar medium. For pathogen growth, the plates were placed at 25oC (±2oC) with a 12-hour photoperiod for 5 days. Five samples from each of the infected fields were taken for pathogen isolation and among them ten isolates were sub-cultured and purified by using the single spore method. The resulting fungal colonies were fluffy and ranged in color from grayish black/black to light brown. Fifteen conidia were measured that are olivaceous-brown to dark brown in color, elliptical to oblong with narrow (tapered) ends, with 3-10 septa and 35.6-65.4 µm in length x 13.1-25.7 µm in width. Conidiophores were yellowish-brown, geniculate, and solitary (Pratt 2003). For molecular studies, rDNA of the internal transcribed spacer (ITS) region, translation elongation factor (tef), RNA polymerase II second largest subunit (rpb2) and glyceraldehyde-3-phosphate dehydrogenase (gpd) gene were amplified by using the primers ITS1F/ITS4R (White et al. 1990), EF1-983F/EF1-2218R (Rehner and Buckley 2005), 5F2/7CR (O’Donnell et al. 2007), and GPD1/GPD2 (Berbee et al. 1999) respectively. The sequence of all the amplified gene regions of one SUL-1 isolate was deposited into GenBank with accession numbers MN314844 (ITS), MN326866 (tef), MN990457 (rpb2) and MN990456 (gpd). BLASTn queries of the obtained sequences (ITS, tef, rpb2 and gpd) showed 99-100% homology with the corresponding nucleotide sequences of B. sorokiniana (GenBank accession nos. GU480767, MF490855, LT715652 and MK558818 respectively). To fulfill the Koch’s postulates, twenty rice plants (cv. Basmati-385) were sprayed at 2 to 3 leaf stages by using the two representative isolates with a spore suspension of 105 spores/ml. SDW was sprayed on ten control plants. The plants were covered with polyethylene bags to keep the moisture contents and incubated at 25oC (±2oC) for 7 days. After a week, same symptoms as those described above were observed. In the repeated experiment, B. sorokiniana was re-isolated from the infected rice leaves and confirmed morphologically; fulfill the Koch’s postulates. With grave worry, the other species of the genus Bipolaris (B. oryzae, and B. victoriae) have also been found to the cause brown leaf spot of rice (Motlagh and Kaviani 2008). To our knowledge, this is the first report of Bipolaris sorokiniana causing brown leaf spot of rice in Pakistan. Because rice is highly consumable grain in Pakistan, so the rapid spread of this disease in the rice farming areas is of a serious concern.

First Report of Alternaria Alternata Causing Brown Leaf Spot on Apricot (Prunus Armeniaca) in Karbala Province of Iraq

During a survey in season 018, leaf spot symptoms were commonly observed on apricot (Prunus armeniaca) trees in the orchards of Al-Hussainiya district in Karbala Province of Iraq. The symptomatic leaves were gathered, the associated fungus was isolated and characterized relied on its morphological features and ITS-rDNA sequencing. The causative factor was found to be the fungus Alternaria alternata that caused distinguishable leaf spot symptoms on the inoculated leaves of apricot. Based on a review of previous references relatedof this disease in Iraq, this is the first report of the brown leaf spot disease caused by A. alternata in Karbala province of Iraq.

PATHOGENIC DISEASE OCCURRENCES IN PLANTATION SITES OF BASTAR DISTRICT, CHHATTISGARH, INDIA

The investigation on “Pathogenic disease occurrence in plantation sites of Bastar district, CG, India” revealed that the several disease of Tectona grandish and Eucalyptus globules trees species in the plantation site maintained by Bastar forest division (C.G.) During the survey of plantation sites, many trees were infected by pathogens. The infected teak species showed leaf spot, leaf blight, leaf gull, leaf brown spot, stem canker, powdery mildew etc. and affecting the growth and form of teak. Whereas in Eucalyptus trees showed stem canker, collar rot, leaf spot, leaf rust, brown leaf spot, disease and affecting the growth and forms of Eucalyptus. The survey was conducted at two plantation sites namely Titrgaon and Bastar in the region and incidence of pathogenic disease commonly found and casual organism/ pathogen were identified prescribed disease management was recorded. Management of immediate removal of infected plants helps to prevent the disease spread. Therefore, the present investigation was carried out for knowing occurrence and abundance of pathogens associated with Teak and Eucalyptus trees plantation in the Bastar district of Chhattisgarh.

Morphology and Molecular Characteristics of Alternaria sonchi Causing Brown Leaf Spot on Sonchus asper in Korea

During a disease survey on weeds and minor cultivated crops in Korea, a brown leaf spot disease was observed on Sonchus asper. Leaf lesions were round or irregular in shape, and grayish brown to brown with a purple margin. In severe infection, lesions enlarged and coalesced, resulting in blighting of the leaves. The isolates from these leaf lesions were identified as Alternaira sonchi based on morphological characteristics and phylogenetic analyses of Internal transcribed spacer region, Alternaria allergen a1, glyceraldehyde 3-phosphate dehydrogenase, RNA polymerase II, and translation elongation factor genes. This study provides a comprehensive description of the morphological characteristics and phylogenetical traits of A. sonchi causing brown leaf spot on S. asper in Korea.

The implication of leaf anatomical structure for the selective breeding of lilacs

The cultivars of the common lilac (Syringa vulgaris) grown in the south of the Russian Far East are not always winter-hardy and are often damaged by fungal diseases due to a very humid climate. A promising trend in the selective breeding of lilacs in Russia is the creation of new breeding material based on the gene pool of the broadleaf lilac (S. oblata) and its hybrids in order to introduce valuable adaptive traits into cultivars. The present work aimed to identify the traits of leaf anatomy in species and cultivars of Syringa resistant and susceptible to Pseudocercospora lilacis, the causative agent of brown leaf spot disease. The study was carried out on the living collection of the Botanical Garden-Institute, Far Eastern Branch, Russian Academy of Sciences (Vladivostok). The leaf anatomical structure of two Syringa species showing different degrees of resistance to P. lilacis in the monsoon climate of the Far East (resistant S. oblata and weakly resistant S. vulgaris, and also their hybrid cultivars) has been analyzed. The differences between species, subspecies, and cultivars are quantitative: they differ in the number of spongy mesophyll layers, the cell height in the first layer of palisade mesophyll, the cell height in the upper and lower epidermises, and the thickness of both mesophylls. The interspecific hybrids resistant or weakly resistant to P. lilacis (brown leaf spot disease) mainly retain the leaf anatomy structure of the maternal plant. One of the traits determining the resistance of hybrid lilac cultivars is an increased number of spongy mesophyll layers in the leaf blade. The study of leaf anatomy has shown that the four-layered spongy mesophyll leaf parenchyma correlates with the resistance of lilacs from the subsection Euvulgaris to P. lilacis. In S. oblata, this trait is inherited down the maternal line. To establish lilac cultivars resistant to fungal diseases, it is advisable to cross the two species (S. oblata and S. vulgaris) or their cultivars using one of S. oblata subspecies as a maternal plant.

Incidence of Alternaria Species Associated with Watermelon Leaf Blight in Korea

Alternaria leaf blight is one of the most common diseases in watermelon worldwide. In Korea, however, the Alternaria species causing the watermelon leaf blight have not been investigated thoroughly. A total of 16 Alternaria isolates was recovered from diseased watermelon leaves with leaf blight symptoms, which were collected from 14 fields in Korea. Analysis of internal transcribed spacer (ITS) region, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and RNA polymerase II second largest subunit (RPB2) were not competent to differentiate the Alternaria isolates. On the contrary, analysis of amplicon size of the histone H3 (HIS3) gene successfully differentiated the isolates into three Alternaria subgroups, and further sequence analysis of them identified three Alternaria spp. Alternaria tenuissima, A. gaisen, and A. alternata. Representative Alternaria isolates from three species induced dark brown leaf spot lesions on detached watermelon leaves, indicating that A. tenuissima, A. gaisen, and A. alternata are all causal agents of Alternaria leaf blight. Our results indicate that the Alternaria species associated watermelon leaf blight in Korea is more complex than reported previously. This is the first report regarding the population structure of Alternaria species causing watermelon leaf blight in Korea.

Use of Liming and Incidence of Diseases in Sugarcane

This study aimed to evaluate the incidence of red rot, brown leaf spot, and smut in ten sugarcane genotypes during two consecutive cycles, in the absence and presence of limestone. The experimental design consisted of randomized blocks with four replications, in the presence and absence of liming in the following sugarcane genotypes: G1 (RB002754), G2 (RB021754), G3 (RB041443), G4 (RB863129), G5 (RB93509), G6 (RB951541), G7 (RB962962), G8 (RB992506), G9 (SP79-1011), and G10 (VAT90-212) for genotype x environment interaction. The lowest incidences of red rot were observed in G3 (RB041443), G4 (RB863129), G8 (RB992506), and G9 (SP79-1011) for plant cane, and in G3 (RB041443), G4 (RB863129), G5 (RB93509), G8 (RB992506), and G9 (SP79-1011) for ratoon. All genotypes were susceptible to Colletotrichum falcatum, but limestone reduced its incidence in G3 (RB041443), G6 (RB951541), and G10 (VAT90-212) during the first growth cycle, and in G1 (RB002754), G2 (RB021754), G5 (RB93509), G6 (RB951541), G7 (RB962962), and G10 (VAT90-212) in the ratoon crop. Liming also reduced the incidence of brown leaf spot in G4 (RB863129), G6 (RB951541), and G9 (SP79-1011) in plant cane and G6 (RB951541) and G7 (RB962962) in the ratoon crop. Only the G9 genotype (SP79-1011) showed an incidence of smut. The genotypes had different incidence levels of red rot, brown leaf spot, and smut diseases, which varied in the presence of limestone. Limestone use reduced disease incidence as a function of genotype and cutting cycle.

Sustainability assessment of the resistance of smooth bromegrass varieties to the causative agent of helminthosporiosis on an artificial infectious background

Smooth bromegrass (Bromopsis inermis Holub.) is widespread perennial grass and high quality feed. It is characterized by hight frost resistance. The main direction in breeding work is breeding of varieties with high seed productivity and with increased resistance to diseases. The research was carried out using an artificial infectious background in the immunology laboratory in FWRC FPA (previously, the All-Russian Williams Fodder Research Institute). This research took place in Lobnya, Mytishchi district, Moscow region, in 2018 -2020 years. Long-term phytosanitary monitoring of crops showed that the most common disease of this culture is brown leaf spot (helminthosporium). Seed germination decreases by 21-41% to this patgen. 16 samples of smooth bromegrass was planted in the artificial infectious background to determine their disease resistance in 2018 According to the study carried out, it was found that the disease reaches its peak at the stage of seed ripening. Sample # 2 and sample # 12 on average exceeded the standard variety Fakelny by 12% for resistance to pathogens of helminthosporiosis (among the studied samples, according to three-year data). Sample # 2 and sample # 12 can be recommended for inclusion in the breeding process to create modern intensive type varieties.