Oligomycins are macrolide antibiotics, produced by Streptomyces spp. that show antagonistic effects against several microorganisms such as bacteria, fungi, nematodes and the oomycete Plasmopara viticola . Conidiogenesis, germination of conidia and formation of appressoria are determining factors pertaining to pathogenicity and successful diseases cycles of filamentous fungal phytopathogens. The goal of this research was to evaluate the in vitro suppressive effects of two oligomycins, oligomycin B and F along with a commercial fungicide Nativo® 75WG on hyphal growth, conidiogenesis, conidial germination, and appressorial formation of the wheat blast fungus, Magnaporthe oryzae Triticum (MoT) pathotype. We also determined the efficacy of these two oligomycins and the fungicide product in vivo in suppressing wheat blast with a detached leaf assay. Both oligomycins suppressed the growth of MoT mycelium in a dose dependent manner. Between the two natural products, oligomycin F provided higher inhibition of MoT hyphal growth compared to oligomycin B with a minimum inhibitory concentration of 0.005 and 0.05 μg/disk, respectively. The application of the compounds completely halted conidial formation of the MoT mycelium in agar medium. Further bioassays showed that these compounds significantly inhibited MoT conidia germination and induced lysis. The compounds also caused abnormal germ tube formation and suppressed appressorial formation of germinated spores. Interestingly, the application of these macrolides significantly inhibited wheat blast on detached leaves of wheat. This is the first report on the inhibition of mycelial growth, conidiogenesis, germination of conidia, deleterious morphological changes in germinated conidia, and suppression of blast disease of wheat by oligomycins from Streptomyces spp. Further study is needed to unravel the precise mode of action of these natural compounds and consider them as biopesticides for controlling wheat blast.

Wheat, one of the most important food crops, is threatened by a blast disease pandemic. Here, we show that a clonal lineage of the wheat blast fungus recently spread to Asia and Africa following two independent introductions from South America. Through a combination of genome analyses and laboratory experiments, we show that the decade-old blast pandemic lineage can be controlled by the Rmg8 disease resistance gene and is sensitive to strobilurin fungicides. However, we also highlight the potential of the pandemic clone to evolve fungicide-insensitive variants and sexually recombine with African lineages. This underscores the urgent need for genomic surveillance to track and mitigate the spread of wheat blast outside of South America and to guide preemptive wheat breeding for blast resistance.

Wheat, the most important food crop, is threatened by a blast disease pandemic. Here, we show that a clonal lineage of the wheat blast fungus recently spread to Asia and Africa following two independent introductions from South America. Through a combination of genome analyses and laboratory experiments, we show that the decade-old blast pandemic lineage can be controlled by the Rmg8 disease resistance gene and is sensitive to strobilurin fungicides. However, we also highlight the potential of the pandemic clone to evolve fungicide-insensitive variants and sexually recombine with African lineages. This underscores the urgent need for genomic surveillance to track and mitigate the spread of wheat blast outside of South America, and to guide pre-emptive wheat breeding for blast resistance.

12Oligomycins are macrolide antibiotics, produced by Streptomyces spp., show biological activities 13 to several microorganisms like bacteria, fungi, nematodes and peronosporomycetes. 14 Conidiogenesis, germination of conidia and formation of appressoria are crucial for a successful 15 disease cycle and pathogenicity of the filamentous fungal phytopathogen. The goal of this 16 research was to evaluate the effects of two oligomycins, oligomycin B and oligomycin F along 17 with a commercial fungicide Nativo® 75WG on hyphal growth, conidiogenesis, conidia 18 germination, appressoria formation, and disease development of a worrisome wheat blast fungus, 19 Magnaporthe oryzae Triticum (MoT) pathotype. Both oligomycins suppressed the growth of 20 MoT mycelia depending on the dose. Between the two natural products, oligomycin F displayed 21 the maximum inhibition of MoT hyphal growth accompanied by oligomycin B with minimum 22 inhibitory concentrations (MICs) of 0.005 and 0.05 µg/disk, respectively. The application of the 2 23 compounds also completely halted the conidia formation in the MoT mycelia in agar medium. A 24 further bioassay showed that these compounds significantly inhibited MoT conidia germination 25 and induced lysis; if germinated, induced abnormal germ tube and suppressed appressoria 26 formation. Interestingly, the application of these macrolides significantly inhibited wheat blast 27 disease on detached leaves of wheat. This is a first report on the inhibition of mycelial growth, 28 process of conidia formation, germination of conidia, morphological changes in germinated 29 conidia, and suppression of blast disease of wheat by oligomycins from Streptomyces spp. A 30further study is needed to evaluate the mode of action and field trials of these natural compounds 31 to consider them as biopesticides for controlling this devastating wheat killer. 32 33 3 46 through G. Different isomers are highly selective for disrupting mitochondrial metabolism [3, 4, 47 8, 10]. Although the biological activities of oligomycins on fungi and peronosporomycetes have 48 been reported, nothing is known about the effect of these natural products on a notorious wheat 49 blast fungus Magnaporthe oryzae Triticum (MoT). The bioactivities of oligomycins to different 50 classes of fungal species indicates that their targets may involve varieties of cellular processes, 51 such as inhibition of mycelial growth of Cladosporium cucumerinum, Magnaporthe grisea, 52 Colletotrichum lagenarium, Botrytis cinerea, Cylindrocarpon destructans, Fusarium culmorum, 53 Erysiphe graminis and Phytophthora capsici [3, 11], lysis and motility inhibition of downy 54 mildew zoospores (Plasmopara viticola) of grapevine, and inhibition of motility of zoospores of 55 damping-off phytopathogen, Aphanomyces cochlioides [4]. 56 57 The wheat blast fungus MoT is one of the most damaging pathogens of wheat [12-15]. The 58 fungal three-celled, hyalin, pyriform conidium is bound to the host surface by an adhesive 59 secreted from the tip of the conidium [14, 16...

Faba bean (Vicia faba L.) is an underutilized promising grain legume commercially grown in central and northern part of Bangladesh (Yasmin et al. 2020). In January 2021, faba bean plants exhibiting symptoms of collar and root rot and yellowing of leaves were observed in thirty plots of an experimental field at the Bangladesh Agricultural University (24.75° N, 90.50° E), Mymensingh, Bangladesh. Infected plants had dark brown to black lesions on the roots, extending above the collar region. An average disease incidence and severity was 7.16% and 6.91%, respectively. Eight diseased plants were collected from the field by uprooting one plant from each of eight randomly selected experimental plots and surface disinfected with sodium hypochlorite (0.2%) for 3 min followed by 1 min in ethanol (70%), and then rinsed three times with distilled water and dried on sterile paper towels. Collar and root pieces (5×5 mm) of symptomatic tissues were placed on Potato Dextrose Agar (PDA). Plates were incubated at 25°C for three days and isolates were purified from single-tip culture. The isolates produced brown colored mycelia often with brown sclerotia. Under microscope, fungal colonies exhibited right–angled branching with constriction at the base of hyphal branches and a septum near the originating point of hyphal branch consistent with the description of Rhizoctonia solani Kuhn (Sneh et al. 1991). The isolates grew at 35°C on PDA (5 mm/24). Molecular identification of the isolates BTRFB1 and BTRFB7 was determined by sequencing the rDNA internal transcribed spacer (ITS) region using primers ITS1 and ITS4 (White et al. 1990). A BLAST search showed that the sequences (GenBank Accession nos. MZ158299.1 and MZ158298.1) had 99.28% similarity with R. solani isolates Y1063 and SX-RSD1 (GenBank Accession nos. JX913811.1 and KC413984.1, respectively). Phylogenetic analysis revealed that the present isolates grouped with R. solani anastomosis group AG-2-2 IIIB. To confirm pathogenicity, both isolates were grown individually on sterile wheat kernels at 28°C for 6 days (D’aes et al. 2011). Faba bean seedlings were grown in plastic pots containing sterile potting mix (field soil/composted manure/sand 2:2:1 [v/v]). Two-week-old plants were inoculated by placing five infested wheat seeds adjacent to the roots. Control pots were inoculated with sterile wheat kernels using the same procedure. Plants were placed in a growth room with a 16 h/8 h light/dark photoperiod at 25 ± 2°C after inoculation. Fifteen days after inoculation, typical collar and root rot symptoms were developed on inoculated plants, similar to symptoms observed in the field. Control plants remained non-symptomatic. Finally, six isolates of R. solani were isolated from the symptomatic plants and identified by morphological and molecular analysis. Rhizoctonia solani is the causal agent of seed and root rot, hypocotyl canker, and seedling damping-off diseases of faba bean in many other countries (Rashid and Bernier 1993; Assunção et al. 2011). To our knowledge, this is the first confirmed report of Rhizoctonia solani causing collar and root rot of faba bean in Bangladesh. This finding will be helpful for the development of management strategies to control this disease and to expand the production of faba bean in Bangladesh.