The efficiency of some bioagent fungi in reduction of wheat seed decay and seedling damping-off disease with heavy metals interaction

Madhi QH, Abass MH, Matrood AAA. 2021. The efficiency of some bioagent fungi in reduction of wheat seed decay and seedling damping-off disease with heavy metals interaction. Biodiversitas 22: 3984-3993. Biological control is an ecofriendly efficient measurement for disease control and heavy metals reduction in soils. The use of bioagent fungi such as Trichoderma koningii and Chaetomum globosum reduced the negative effect of pathogenic fungi that cause seed decay and the seedlings damping off wheat alone or by interaction with the concentrations of lead or cadmium, which increases the germination percentage of wheat seeds and reducing seedling damping off. It also reduced the severity index of wheat with pathogenic fungi and reduced the negative effect of interaction between heavy metals and pathogenic fungi on the severity index of the wheat. Results showed that T. koningii and C. globosum reduced the effect of the interaction of R. solani with 200 mg/kg lead to 57.7 and 55.4%, respectively and R. solani and cadmium 3 mg/kg with 60 and 61.6%, respectively. T. koningii and C. globosum also reduced the effect of the interaction F.solani with lead 200 mg/kg to 45.4 and 48.5%, respectively and F. solani and cadmium 3 mg/kg to 46.8 and 52.5% respectively. The bioagent fungi also increased the fresh and dry weight of shoot and root system, T. koningii significantly increased the fresh and dry weight of shoot in the presence of R. solani. The results also indicated that there was a high significant difference in the use of C. globosum in increasing the fresh and dry weight of shoot and root system. T. koningii and C. globosum significantly reduced the effect of interaction between the pathogenic fungi and low concentrations of lead and cadmium leading to an increase in the fresh and dry weight of shoot and root system. They also increased the plant height in the presence of pathogenic fungi as well as reducing the negative effect of the interaction between heavy metals and pathogenic fungi in the height of wheat plants. No significant interaction was observed between the low concentrations of lead and cadmium and pathogenic fungi in the presence of bioagent fungi. The results exhibited that bioagent fungi can reduce the negative effect of interaction of pathogenic fungi with lead and cadmium on the total phenols content of wheat leaves, and no significant difference was recorded in the treatment of low concentrations with the pathogenic fungi. Results showed that bioagent fungi can reduce the negative effect of the interaction of pathogenic fungi with lead and cadmium on the total phenols content of wheat plant leaves. No significant differences were recorded in the treatment of low concentrations with the pathogenic fungi in the presence of bioagent fungi. The two bioagent fungi increased the concentration of chlorophyll a and b, total chlorophyll and carotenoids reduced anthocyanin in leaves, and increased chlorophyll stability index compared to the control treatment.

First Report of Pod and Stem Blight and Seed Decay caused by Diaporthe longicolla on Soybean in Western Canada

In Oct. 2019, soybean plants (Glycine max) (cv. 24-10RY, R7 growth stage) with dry rot, necrosis, reddish-brown lesions, and small black fruiting bodies in linear rows were collected from fields in Manitoba (Carman, St. Adolph, Dauphin), Canada. The pods and seeds were shrivelled, small and some seeds were covered with whitish mycelium. Symptoms began as brown lesions, which darkened, elongated, causing wilt of the above stems then plant death. Microscopy showed that the fruiting bodies were pycnidia. Symptomatic stems were cut into 1-2 cm pieces and seeds surface-sterilized in 0.5% NaOCl, rinsed twice in sterilized H2O, air-dried on sterilized filter paper, and plated on PDA medium amended with 100 mg/L streptomycin sulfate at room temperature with 12-h fluorescent light/12-h dark for 3 days. The emerging hyphae were transferred using the hyphal tip method to new PDA petri dishes and incubated for 21 days (room T°). Mycelia of 20 isolates were dense, white and floccose with occasional green-yellow areas. Black stromata in concentric patterns or scattered as large masses were visible on the cultures’ back. Pycnidia formed solely or aggregated after 4-5 weeks of incubation on PDA. Alpha conidia emanated from pycnidia in creamy-to-yellowish drops and were hyaline, non-septate, ellipsoid to fusiform, and biguttulate. The average length and width of Alpha conidia were 5.5 μm and 1.5 μm, respectively (n = 30). No perithecia were seen. The cultures’ morphology was consistent with Phomopsis longicolla’s description (Hobbs et al., 1985). Seven isolates were selected for molecular characterization to confirm their identity by amplifying the ITS region with universal primers ITS4/ITS5 (White et al. 1990). All PCR amplicons were analyzed by electrophoresis through 1.5 % agarose gels and the size of PCR amplicons estimated using 1-kb plus DNA ladder (Thermo Fisher Sci., ON, Canada). PCR amplicons (~650 bp) were purified and sequenced in two directions by Psomagen Inc. (Rockville, MD, USA). ITS sequences were identical for all isolates, and GenBank searches (BLASTn: Altschul et al. 1990) confirmed species identity. ITS sequences (accessions MW466183-MW466189) were deposited in GenBank and matched the type sequence of Diaporthe longicolla strain ATCC 60325 (accession NR_144924) from G. max in USA with identities = 473/475 (99.6%) and gaps = 0/475 (0%). To confirm the pathogenicity of the seven isolates, the stems of V4-stage (four open trifolilates) soybean plants (cv. 24-10RY) were excised using a sterile scalpel. Mycelial plugs (9 mm in diameter) from 1-week-old culture of each isolate were placed over the wounded stems (Abdelmagid et al., 2019). Sterile PDA plugs were used on control plants. Six plants were used per isolate and control. Plugs of both treatments were wrapped with parafilm to avoid drying. The plants were incubated in a humidity chamber for 4 days and then in a greenhouse at 24:16°C day/night, 13:11-h light/dark cycle, and 70-80% relative humidity, and were irrigated as needed. Symptoms similar to those observed in the field were seen on the stems and seeds of all artificially-infected plants approx. 8 weeks after inoculation. Pods and seeds of inoculated plants were shrivelled and small. No symptoms were observed on control plants. Diaporthe longicolla was re-isolated only from the diseased plants and seeds. To our knowledge, this is the first report following Koch’s postulates to identify the causal pathogen of soybean pod and stem blight and seed decay in Western Canada. This will be instrumental in determining the causes of stem decay and contribute in properly dealing with soybean seed issues in Western Canada in the future.

Mitochondrial Genome Resource of Phomopsis longicolla, a Fungus Causing Phomopsis Seed Decay in Soybean

Phomopsis seed decay is one of the most devastating seed diseases reducing soybean seed quality worldwide. This disease is caused primarily by a seed-borne fungus, Phomopsis longicolla (syn. Diaporthe longicolla). As part of a genome sequencing project for P. longicolla, we present the mitochondrial genome resource of the isolate MSPL 10-6, one of the most aggressive field isolates. The circular mitochondrial genome is 53,646 bp long with GC content of 34.27%, and it encodes 14 common protein genes, 23 tRNA and two rRNA genes, and 10 introns. Forty-five SNPs and InDels also were identified during comparative analyses with another isolate. The mitochondrial genome sequence provides a useful resource for developing molecular markers for pathogen detection and for improvement of control strategies for the disease. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Diaporthe seed decay of soybean [Glycine max (L.) Merr.] is endemic in the United States, but new fungi are involved

Diaporthe seed decay can compromise seed quality in soybean [Glycine max (L.) Merr.] in the warm and humid production areas of the United States during crop maturation. In the current study, 45 isolates of Diaporthe were recovered from seed sampled from soybean fields affected by Diaporthe-associated diseases in eight U.S. states in 2017. The isolates obtained belonged to 10 species of Diaporthe based on morphology and phylogenetic analyses of the internal transcribed spacer, the partial translation elongation factor 1-alpha, and beta-tubulin gene sequences. The associated species included D. aspalathi, D. caulivora, D. kongii, D. longicolla, D. sojae, D. ueckerae, D. unshiuensis and three novel fungi, D. bacilloides, D. flavescens and D. insulistroma. One isolate each of the 10 species was examined for pathogenicity on seed of cv. ‘Sava’ under controlled conditions. Seven days post-inoculation, significant differences in the percentages of decayed seeds and seedling necrosis were observed among the isolates and the non-inoculated control (p<0.0001). While the isolates of D. bacilloides, D. longicolla, and D. ueckerae caused significantly greater percentage of decayed seeds (p<0.0001), the isolate of D. aspalathi caused the greatest seedling necrosis (p<0.0001) when compared to the non-inoculated control. The observation of new fungi causing Diaporthe seed decay suggests the need for a more comprehensive survey in the U.S. soybean producing areas since members of the genus Diaporthe appear to form a complex that causes seed decay.

The Efficacy of Ethaboxam as a Soybean Seed Treatment Toward Phytophthora, Phytopythium, and Pythium in Ohio

Phytophthora, Phytopythium, and Pythium species that cause early-season seed decay and pre-emergence and post-emergence damping off of soybean are most commonly managed with seed treatments. The phenylamide fungicides metalaxyl and mefenoxam, and ethaboxam are effective toward some but not all species. The primary objective of this study was to evaluate the efficacy of ethaboxam in fungicide mixtures and compare those with other fungicides as seed treatments to protect soybean against Pythium, Phytopythium, and Phytophthora species in both high-disease field environments and laboratory seed plate assays. The second objective was to evaluate these seed treatment mixtures on cultivars that have varying levels and combinations of resistance to these soilborne pathogens. Five of eight environments received adequate precipitation in the 14 days after planting for high levels of seedling disease development and treatment evaluations. Three environments had significantly greater stands, and three had significantly greater yield when ethaboxam was used in the seed treatment mixture compared with treatments containing metalaxyl or mefenoxam alone. Three fungicide formulations significantly reduced disease severity compared with nontreated in the seed plate assay for 17 species. However, the combination of ethaboxam plus metalaxyl in a mixture was more effective than either fungicide alone against some Pythium and Phytopythium species. Overall, our results indicate that the addition of ethaboxam to a fungicide seed treatment is effective in reducing seed rot caused by these pathogens commonly isolated from soybean in Ohio but that these effects can be masked when cultivars with resistance are planted.

Weed Seed Decay in No-Till Field and Planted Riparian Buffer Zone

Field management practices can alter the physical and chemical properties of the soil, also causing changes to the seed bank. Alterations can also occur to the soil microbial community, which in turn can increase or diminish the process of weed seed decay. In this research, the issue of seed degradation was studied in an undisturbed and a no-till soil, trying not only to uncover where seeds are more degraded, but also to investigate the microbial activities that could be involved in this process. Six different weed species, commonly found in northern Italy, were used: Abutilon theopharsti, Alopecurus myosuroides, Amaranthus retroflexus, Digitaria sanguinalis, Portulaca oleracea and Sorghum halepense. Seed decay was tested in two different sites, a no-till field and the adjacent buffer zone. Soil microbial activity was also measured using the Fertimetro, an approach based on the degradation of cotton and silk threads buried in the soil for one week. Degradation of the buried seeds was higher in the no-till field soil than in the buffer strip for all the studied species as was the microbial cellulolytic activity. Even though the buffer strip soil is an undisturbed habitat and resulted as having higher organic matter, the no-till soil conditions appeared more unfavourable to seed viability. Our findings suggest that no-till management can improve weed seed suppression in the soil. Moreover, cellulolytic microorganisms play an important role in seedbank longevity, so cellulolytic activity surveys could be used as an early monitoring bioindicator for weed seed suppression in soil.