Causal Agent Of Root Rot Research Articles

Identification of Fusarium spp. Associated with Chickpea Root Rot in Montana

Root rot caused by Fusarium spp. is a significant issue in the chickpea-growing regions of Montana. The specific Fusarium species responsible for the disease and their prevalence remain uncertain. A survey was conducted in 2020 and 2021 to identify Montana’s Fusarium species associated with chickpea. Four hundred and twenty-six Fusarium isolates were recovered from symptomatic chickpea roots across ten counties in the state. Isolates were identified by comparing translation elongation factor 1-α (TEF1-α) sequences in the FUSARIUM-ID database. Among the recovered isolates, Fusarium oxysporum was the most prevalent species (33%), followed by F. acuminatum (21%), F. avenaceum (15%), F. redolens (14%), F. culmorum (6%), F. sporotrichioides (6%), Neocosmospora solani (6%), F. equiseti (2%), F. torulosum (0.9%), F. gamsii (0.8%), F. proliferatum (0.2%), F. pseudograminearum (0.2%), and F. brachygibbosum (0.1%). The aggressiveness of a subset of 51 isolates representing various Fusarium spp. was tested on chickpea cv. ‘CDC Frontier’. A non-parametric variance analysis conducted on disease severity ranks indicated that F. avenaceum isolates were highly aggressive. This study reports for the first time that F. gamsii, F. proliferatum and F. brachygibbosum are causal agents of root rot in chickpea in the United States. This knowledge is invaluable for making informed decisions regarding crop rotation, disease management, and developing resistant chickpea varieties against economically significant Fusarium pathogens.

PRIMER REPORTE DE Macrophomina pseudophaseolina ASOCIADO A LA PUDRICIÓN DE RAÍZ EN CHILE APAXTLECO NATIVO (Capsicum annuum L.) EN GUERRERO, MÉXICO

<p><strong>Background.</strong> Chili is an important crop for Mexican culture. <strong>Objective. </strong>To identify the pathogen associated with the causal agent of root rot in a native chili pepper Apaxtleco in Guerrero, Mexico. <strong>Methodology.</strong> Root samples of diseased plants were taken from a chili plot in Apaxtla, Guerrero, and were taken to the Phytopathology Laboratory, at Colegio Superior Agropecuario del Estado de Guerrero (CSAEGRO), México. Subsequently, 1 cm root sections were made from healthy and diseased tissue, which were disinfected with 3% sodium hypochlorite for 1 min, and washed three times with sterile distilled water for 1 min, and dried with sterile absorbent paper, later, moistened sterilized paper was placed in the Petri dish and moistened with sterile distilled water and two slides were placed on it arranged in the shape of a cross and at each end of the slides and in the center of these, a piece of previously disinfected root was placed. The plates were kept at 28 °C ± 2 °C for 168 h. The purification of the pathogen was carried out using the hyphal tip and the identification was morpho-molecular. <strong>Results.</strong> The causal agent of root rot in Apaxtleco native chili plants was <em>Macrophomina pseudophaseolina</em>. <strong>Implications.</strong> Our result reveals the opportunity to improve the control of this pathogen at Guerrero, Mexico. <strong>Conclusion.</strong> <em>M. pseudophaseolina</em> causing root rot, in Apaxtleco native chili is reported for the first time.</p>

First report of Fusarium falciforme causing root rot and wilt on strawberry in Sinaloa, Mexico.

In Mexico strawberry production has great economic importance for the local and export markets as the country is the main strawberry supplier to the United States (SIAP, 2020). In 2022, strawberry plants with yellowing and wilting leaves, root rot and wilting, necrosis of vascular bundles and small fruits symptoms were observed in different commercial fields in the north-central Mexican state of Sinaloa, causing yield losses of about 10%. Typical Fusarium spp. colonies were recovered from all samples. They produced abundant white aerial mycelium with cream to orange pigment and branched septate hyphae (Fig. 1) (Leslie and Summerell, 2006). A total of 18 monosporic isolates were obtained by serial dilutions. The 18 isolates grown for 10 days on carnation leaf agar (CLA) produced hyaline microconidia with 0-2 septa, measuring 9.2 - 15.4 by 4.5 - 6.5 μm (n = 40) and hyaline macroconidia with three septa that measured 28.4 - 53.5 by 4.5 - 9 μm (n = 40). Chlamydospores were not observed. A fragment of the translation elongation factor 1-alpha (EF1-alpha) gene was amplified by polymerase chain reaction (PCR) using the primer pair EF-1/EF-2 (O'Donnell et al. 1998) from two monosporic isolates. The sequences were registered in the NCBI GenBank under accession numbers OR878541 and OR878543 (FRESIN178 and FRESIN194). BLASTn queries of NCBI GenBank identified the sequences as F. falciforme with 98% and 100% similarity to accession numbers OQ262968 and DQ246941 respectively. Fusarium ID database also identified the sequences as F. falciforme, is a member of the F. solani species complex (FSSC). Phylogenetic analysis revealed the partial EF1 sequences grouped with F. falciforme (Fig. 2). A pathogenicity test was performed on thirty strawberry plants (cv. Cabrillo) grown in sterile vermiculite. The plants were inoculated by immersing roots in 20 mL of a conidial suspension (1 × 105 conidia/mL) of isolate FRESIN194. Twelve uninoculated plants served as the control. All plants were grown for 60 days under greenhouse conditions (28 to 35°C). The assay was repeated twice. After 50 days, symptoms of root rot and wilting leaves like those observed in the field were observed. Uninoculated control plants did not develop symptoms. The fungus was reisolated from necrotic tissues of the inoculated plants and identified as F. falciforme by sequencing the EF1-alpha gene and morphological characteristics, completing Koch's postulates. Fusarium falciforme has been reported as the causal agent of root rot, stem rot, and wilt of tomato, papaya, chickpea, onion, common bean, and maize in Mexico (Díaz-Najera et al. 2021, Douriet-Angulo et al. 2021, Felix et al 2022, Tirado-Ramírez et al 2018, Vega-Gutiérrez et al. 2019a, Vega-Gutiérrez et al. 2019b). To our knowledge this is the first report of F. falciforme causing root rot and wilt on strawberry in Sinaloa, Mexico. This result provides useful information for the development and implementation of disease control strategies to mitigate damage caused by F. falciforme.

Identification and Fungicide Sensitivity of Fusarium spp. Associated with Root Rot of Scutellaria baicalensis in Shanxi Province, China.

Fusarium root rot is usually classified as an extremely destructive soilborne disease. From 2020 to 2021, Fusarium root rot was observed in production areas and seriously affected the yield and quality of Scutellaria baicalensis in Shanxi Province, China. Based on morphological characteristics and combined analysis of the internal transcribed spacer region of ribosomal DNA and translation elongation factor 1-alpha sequences, 68 Fusarium isolates obtained in this work were identified as F. oxysporum (52.94%), F. acuminatum (20.59%), F. solani (16.17%), F. proliferatum (5.88%), F. incarnatum (2.94%), and F. brachygibbosum (1.47%). In the pathogenicity tests, all Fusarium isolates could infect S. baicalensis roots, presenting different pathogenic ability. Among these isolates, F. oxysporum was found to have the highest virulence on S. baicalensis roots, followed by F. acuminatum, F. solani, F.proliferatum, F. brachygibbosum, and F.incarnatum. According to fungicide sensitivity tests, Fusarium isolates were more sensitive to fludioxonil and difenoconazole, followed by carbendazim, thiophanate-methyl, and hymexazol. In brief, this is the first report of Fusarium species (F. oxysporum, F. acuminatum, F. solani, F. proliferatum, F. incarnatum, and F. brachygibbosum) as causal agents of root rot of S.baicalensis in Shanxi Province, China. The fungicide sensitivity results will be helpful for formulating management strategies of S. baicalensis root rot.

Two novel heat-tolerant, culturable rhizosphere-inhabiting, plant growth-promoting ascomycete fungi associated with native plants in desert habitats of southwestern USA

During an investigations on Monosporascus cannonballus, the causal agent of root rot and vine decline of melons, in 1999, a previously unknown rhizosphere fungus was encountered in the desert soils of southern California. The fungus, herein named Desertella arida Stanghellini & Mohammadi sp. nov., was associated with roots of diverse plants including brassica (Sahara mustard (Brassica tournefortii), shepherd's purse (Capsella bursa-pastoris)) and plantain (Plantago ovata Forsk). The fungus forms extensive multinucleate, septate hyphae (6–17 μm in diameter) bearing hundreds of large spherical to pear-shaped unicellular asexual spores (50–120 μm in diameter), either singly or in large clusters. The spores are beige to cream-colored, thin-walled, and contain a dense, granular cytoplasm. Further investigation on the distribution of D. arida in soils of desert habitats in the southwestern USA led to the discovery of a second fungus belonging to a different species herein named Desertella americanense Mohammadi & Stanghellini sp. nov., in California, Arizona, Nevada, and Utah. The two species are morphologically similar. Spores from both fungi in native soil survived heat treatment up to 100 °C. Both species are culturable and colonized roots of monocots and dicots forming abundant hyphae and spores as early as 10 days post-inoculation. Desertella arida significantly enhanced shoot growth in broccoli, lettuce, Plantago ovata and flax. In conclusion, we discovered two desert-dwelling ascomycete fungi that were associated with the roots of native plant species in southern California. They were culturable on a synthetic medium, heat-tolerant and promoted growth on several crop species. These fungi appeared to exist in other neighboring states such as Arizona and Nevada.

First Report of Fusarium luffae Causing Leaf Blight on Loquat in Eastern China.

During May-June 2021 and 2022, leaf blight symptoms were observed on loquat leaves (Eriobotrya japonica cv. 'Mogi') in Jiangsu Province (Xuzhou municipality, 117.17° E, 34.13° N) in China. Approximately 10% of the leaves on the two hundred trees studied in a six-year-old loquat orchard exhibited round lesions that changed from light yellow to reddish-brown in 8-10 days. Approximately 3% of the infected leaves exhibited numerous lesions that coalesced, leading to expansive blighted areas. Twenty-five samples of symptomatic tissue, approximately 0.2 cm2 in size, were collected in May 2022 from five different trees (five samples per tree), sterilized in 2% NaOCl for 1 min, washed twice with sterilized ddH2O, and incubated at 26°C for 5 days on PDA medium containing 50 µg/mL chloramphenicol. Six isolates were obtained via single spore isolation. ITS (OQ954852-OQ954857), TUB2 (OQ968488-OQ968493), EF1-α (OQ971890-OQ971895), RPB1 (OQ971896-OQ971901), and RPB2 (OR037266-OR037271) genes were amplified using the ITS1/ITS4, T1/T22, EF1-728F/EF1-986R, RPB1-R8/RPB1-F5, and fRPB2-7CF/fRPB2-11aR primers, respectively (O'Donnell et al. 2010). The species was identified using the Fusarioid ID database (Crous et al. 2021), revealing that all obtained isolates showed high homology to representative F. luffae strains. Upon combining the ITS, TUB2, EF1-α, RPB1, and RPB2 sequences, the isolates showed 99.42%-97.85% and 99.59%-98.10% identity to F. luffae CGMCC 3.19497 (ex-type strain) and NRRL 32522, respectively. A molecular phylogenetic tree was constructed using MEGA X, with a selection of representative Fusarium strains. Microscope observations showed septate mycelium, microconidia (6.86 ± 0.91 µm length, 1.67 ± 0.24 µm width, containing 1 septum; number of observations = 21), fusiform macroconidia (15.88 ± 1.43 µm length, 1.66 ± 0.24 µm width, containing 1 septum; number of observations = 45), and linear chlamydospores (79.36 ± 28.36 µm length, 12.03 ± 3.37 µm width; number of observations = 152). These observations are consistent with the morphology of F. luffae (Wang et al. 2019). All isolates exhibited identical morphological characteristics. All isolates were evaluated for pathogenicity in vivo using healthy non-detached loquat leaves. A total of 15 leaves from 5 different three-month-old 'Mogi' loquat trees were used for each isolate. Experiments were performed three times. A suspension of 1 × 106 spores/mL obtained from a seven-day-old colony (10 mL per 15 leaves), was sprayed on non-wounded leaves for inoculation. Sterilized ddH2O was used in the control experiment. Inoculated trees were stored at 26°C and 70% relative humidity for four days. Leaf blight symptoms were observed in all inoculated leaves, and the symptoms were observed in all repeated trials. The pathogen was recovered, and its identity was confirmed by ITS sequencing and morphological analysis, fulfilling Koch's postulates. In recent years, F. luffae has been reported to cause fruit rot on muskmelon, flower rot on kiwifruit, soybean pod rot, and leaf spot on cherry in China (Yu et al. 2022; Zhang et al. 2022; Zhao et al. 2022; Zhou et al. 2022), demonstrating the host promiscuity of this pathogen. Although F. solani has been identified as the causal agent of root rot and fruit rot on loquat (Abbas et al. 2017; Wu et al. 2021), this is the first report of F. luffae causing leaf blight on loquat worldwide. This report will help to understand the pathogens affecting loquat orchards in China.

First Report of Curvularia spicifera, As New Causal Agent of Root Rot in Citrus Rootstock (Citrus aurantium) in Morocco

First Report of Curvularia spicifera, As New Causal Agent of Root Rot in Citrus Rootstock (Citrus aurantium) in Morocco

Antifungal and Plant-Growth Promotion Effects of Bacillus velezensis When Applied to Coastal to Pine (Pinus thunbergii Parl.) Seedlings

Fungal diseases such as root rot and leaf blight cause substantial losses in coastal pine (Pinus thunbergii Parl.) seedling production, which hinders afforestation/forest restoration programs. We isolated and identified Fusarium oxysporum and Alternaria alternata as the causal agents of root rot and needle blight diseases and investigated the biocontrol efficacy against the fungal pathogens and growth promotion of coastal pine seedlings using Bacillus velezensis CE 100. The bacterium produced the hydrolytic enzymes chitinase, β-1,3-glucanase, and protease enzymes, and the crude enzyme fraction of the biocontrol strain caused the deformation of the fungal cell wall and antagonized F. oxysporum and A. alternata, causing respective inhibition of spore germination by 91.0% and 85.9% and mycelial growth by 58.3% and 54.3%, at a concentration of 1000 µL/mL. Consequently, the bacterial treatment improved the survival rate of seedlings 1.9 times relative to the control group. The bacterium secreted indole-acetic acid (IAA) phytohormone and enhanced root growth and absorption of nutrients, which notably enhanced the biomass production of coastal pine seedlings. Therefore, these results provide evidence that B. velezensis CE 100 is an effective antifungal and growth-promoting bacterium that can facilitate the production of high-quality coastal pine seedlings for the restoration and establishment of coastal forests.

Phytophthora palmivora causes root and basal stem rot disease on macaw palm (Acrocomia aculeata) in Brazil

Macaw palm (Acrocomia aculeata Jacq.) is an oleaginous palm native to the American continent. It produces oil and has other important characteristics for the industry. In 2022, a severe disease causing basal stem rot, root rot, and plant mortality in a nursery and the field was detected on macaw palm plants in a farm, in João Pinheiro, Minas Gerais state, Brazil. From the rot symptomatic tissue of affected palms, two Phytophthora isolates were obtained by indirect isolation and were grown on PDA. Based on the morphological characteristics, particularly the coenocytic hyphae and papillate sporangia, the isolates were identified as Phytophthora palmivora. For phylogenetic analyses, the internal transcribed spacer (ITS) regions, β-tubulin gene (TUB), translation elongation factor 1-alpha gene (EF1-α), and two mitochondrial genes: cytochrome c oxidase subunit I (COXI) and cytochrome c oxidase subunit II (COXII), were amplified. Phylogenetic analyses confirmed that it is the species P. palmivora. Fulfillment of the Koch's postulates through pathogenicity test confirmed that P. palmivora was the causal agent of root rot and basal stem rot disease in macaw palm. This is the first report of this pathogen causing disease in macaw palms in Brazil.

Root rot Caused by Setophoma terrestris on Illicium verum in Yunnan Province, China.

Star anise (Illicium verum Hook. f.), a genus of star anise in the family Magnoliaceae, is an important cash crop of "medicinal and food" origin, mainly from China. In August 2021, root rot of I. verum was first observed on more than 80% of the plants grown within a 500 hectares area in Wenshan city, Yunnan Province. At the early stage of the disease, the phloem of the root was dark yellow-brown, and the leaves turn yellow. With further disease development, the whole root became black (Fig. 1a, 1b), and the leaves gradually fall off, affecting the growth, yield and eventually caused death of the whole plant. A total of 20 root samples were collected from typical symptomatic plant roots with 20 years old in Wenshan City (23°18'12″N, 103°56'98″E) and were cut into 2 × 2 mm pieces at the junction of infected and healthy tissue. Each sample was surface-sterilized with 3% NaClO and 75% alcohol for 60 s before rinsing three times with distilled water. The sterile filter paper (5×5 cm) was used to dry the tissue, and samples were cultured on potato dextrose agar (PDA) amended with streptomycin sulfate (50 μg/ml). Plates were incubated at 25°C in the dark in the incubator. From 9 isolates obtained in culture, 7 exhibited the morphology described by Boerema et al. (Boerema et al. 2004) for Setophoma sp. The hyphae were hyaline and septate (Fig.1c). After 14 days of culture on V8 juice agar, white round colonies are formed, but there is no groove in the middle of the colonies (Fig.1d), and transparent, oval, or cylindrical conidia were produced, 6.0-8.0 x 2.5 to 4.0 um (Fig.1e). DNA was extracted from a representative isolate BJGF-04 for molecular identification using a fungal genomic DNA extraction kit (Solarbio, Beijing, China). Polymerase chain reactions (PCRs) were performed with primers ITS1/ITS4 for the internal transcribed spacer (ITS) region (White et al. 1990) and primers T1/β-Sandy-R for the β-tubulin gene (TUB) region (Yang et al. 2017) and primers NL3/ LR5 for 28S large subunit rDNA (LSU) region (Hu et al. 2021) and NS1/ NS4 for 5.8S large subunit rDNA (SSU) region (Mahesha et al. 2021). Newly generated representative sequences were deposited in GenBank: ITS sequence (ON645256), TUB sequence (ON854484), and LSU sequence (ON644445), SSU sequence (ON644451). were sequenced and blasted, showing 99 to 100% sequence homology with known S. terrestris. Pathogenicity was performed using one-year asymptomatic plants of I. verum. A conidial suspension (1 x 106 conidia/ml) collected from V8 juice cultures with 0.05% Tween buffer was poured at a volume of 10 ml/plant. Three individual seedlings were used as replicates for each treatment, and sterile water was used as the negative control. All plants were placed in an artificial climate incubator at 25°C under 90% relative humidity. After 20 days, all inoculated plants showed symptoms identical to those described above, whereas controls remained healthy. Setophoma terrestris was reisolated from the infected roots, which was confirmed by morphological and molecular identification, which completed Koch's postulates. To our knowledge, this is the first report of S. terrestris as a causal agent of root rot on I. verum in China.

Preventing mycelial spread of Heterobasidion annosum in young Scots pine stands using fungal and viral biocontrol agents

Heterobasidion annosum is one of the most important causal agents of root rot of pines in Europe. The timing of cuttings to wintertime or stump treatment by control agents in summertime are used to prevent the spread of the fungus to new forest sites via aerial spores. However, there are no efficient control treatments for an already established infection except for changing the tree species to a resistant one, which often is not possible. In this study, we tested whether treating stumps around Heterobasidion disease centres by the biocontrol fungus Phlebiopsis gigantea could reduce the spread of the pathogen. In addition, we tested whether the infection of H. annosum by a debilitating mycovirus, HetPV13-an1, would affect the control efficacy. The results showed that the enlargement of disease centres was reduced by P. gigantea, and that this biocontrol effect was enhanced by the virus application. Furthermore, the results showed that the growth rate of P. gigantea varies not only between root systems, but also among different roots of a single stump.

First Report of Ceratobasidium sp. (AG-A and AG-G) Causing Root Rot and Stem Canker of Common Bean in Mexico.

Common bean (Phaseolus vulgaris L.), is a grain legume widely cultivated worldwide for its edible dry seeds and pods. In February 2021, root rot symptoms were observed in two common bean (cv. Azufrado Higuera) fields located in Ahome (25º96´19¨N, 109º33´42¨W) and Guasave (25º71´85¨N, 108º78´50¨W) municipalities in Sinaloa, Mexico. Diseased plants showed reduced growth, dark brown canker at the base of the stem, root rot, as well as the absence of secondary roots. The disease incidence was estimated up to 35%. For fungal isolation, symptomatic roots were surface sterilized with 1% sodium hypochlorite for 2 min, rinsed with sterilized distilled water two times, and blotted dry on sterile filter paper. Small fragments of diseased roots were placed on PDA medium and incubated at 25°C in darkness for 3 days. Rhizoctonia-like colonies were consistently obtained and 10 isolates were purified by the hyphal-tip method. Colonies on PDA were white initially and then turned brown after 15 days of incubation. The septate hyphae were 3.9 to 6.3 μm in width and branched at right angles with a septum near the point of branching. Microscopic examination by Safranine-O staining showed two nuclei per cell. The morphological features of the isolates resembled those of Ceratobasidium (Sneh et al. 1991). The two Ceratobasidium isolates were selected for molecular analysis and pathogenicity tests. The isolates were deposited in the Culture Collection of Phytopathogenic Fungi of the Faculty of Agriculture of Fuerte Valley at the Sinaloa Autonomous University (Accession nos. FAVF395 and FAVF396). For molecular identification, genomic DNA from each of the two isolates was extracted, and the internal transcribed spacer (ITS) region and partial fragments of the second largest subunit of RNA polymerase II (rpb2) gene were amplified and sequenced with the primer pairs ITS5/ITS4 (White et al. 1990) and RBP2-980F/RPB2-7cR (Liu et al. 1999), respectively. The ITS sequences (accession nos. ON630914 and ON630915) showed 99.66 and 99.01% identity with Ceratobasidium sp. (AG-A) from the USA (OM045887) and Ceratobasidium sp. (AG-G) from China (HM623627), respectively. Whereas, the rpb2 sequences (OM258171 and OM258172) showed 94.10 and 95.74% identity with Ceratobasidium sp. (AG-A) from Serbia (MT1267888) and Ceratobasidium sp. (AG-G) from Japan (DQ301701), respectively. A phylogenetic tree based on Maximum Likelihood and including combined ITS and rpb2 sequences data for Ceratobasidium spp. was generated. The phylogenetic tree grouped the isolates FAVF395 and FAVF396 within the Ceratobasidium sp. AG-A and AG-G clades, respectively. Pathogenicity tests for each isolate were performed by inoculating 10 healthy common bean seedlings (15-day-old) grown in pots. A total of 50 ml of a mycelial suspension adjusted to a concentration of 1 × 105 mycelial fragments/ml were directly placed on the stem base of each plant. Five uninoculated common bean seedlings were used as control. All plants were kept in a greenhouse for 15 days at temperatures ranging from 22 to 32°C. Root rot and stem canker symptoms appeared on inoculated seedlings after 10 days, whereas control plants remained symptomless. Fungi were reisolated from the infected roots and found to be morphologically identical to the isolates used for inoculation, thus fulfilling Koch's postulates. Ceratobasidium sp. has been previously reported as the causal agent of root rot of watermelon in Sonora, Mexico (Meza-Moller et al. 2014; Farr and Rossman 2022). To our knowledge, this is the first report of Ceratobasidium sp. causing root rot of common bean in Mexico. Further monitoring should be performed to quantify yield impacts and develop effective management strategies for this disease.

First Report of Fusarium acuminatum Causing Leaf Blight on Garlic in China.

In June 2021, leaf blight symptoms were detected on garlic plants (Allium sativum) in southeastern Jiangsu (Nantong municipality; 120.61° E, 33.25° N) in China. Two-month-old garlic plants exhibited leaf tip die back and light brown lesions in new and old leaves (Figure 1). The symptoms were observed in 40% of the plants in a 60-square-meters commercial field surrounded by rice fields, and were similar to those reported for Botrytis porri, Septoria allii and Stemphylium eturmiunum causing leaf blight on garlic (Dumin et al. 2021; Park et al. 2013; Zhang et al. 2009). Six samples of symptomatic tissue collected in Nantong municipality, approximately 1 cm2 in size, were sterilized in 2% NaOCl for 15 min and washed twice with sterile ddH2O. The pathogen was isolated from all collected samples on PDA medium, containing 50 µg/mL chloramphenicol, at 26°C. Pink colonies with orange pigmentation were observed after 7 days. Internal transcribed spacer (ITS), elongation factor 1-α (EF1-α), RNA polymerase II largest subunit (RPB1) and RNA polymerase II second largest subunit (RPB2) genes were amplified using ITS1/ITS4, EF1-728F/EF1-986R, RPB1-R8/RPB1-F5 and fRPB2-7CF/fRPB2-11aR primers, respectively. A total of 17 isolates were obtained, with nine of the isolates sharing the same sequences (strain NJC21), six of the isolates sharing the same sequences (strain NJC22), and the other two isolates showing different sequences (strains NJC23 and NJC24). The obtained sequences were submitted in GenBank under accession numbers OL655398-OL655401 (ITS), and OL741712-OL741723 (EF1-α, RPB1, RPB2). The obtained ITS sequences shared >99% homology to the ITS gene from F. acuminatum IBE000006 (EF531232), the EF1-α sequences shared 99% homology to the EF1-α gene from F. acuminatum F1514 (LC469785), the RPB1 sequences shared >99% homology to the RPB1 gene from F. acuminatum JW 289003 (MZ921675), and the RPB2 sequences shared 100% homology to the RPB2 gene from F. acuminatum NL19-077002 (MZ921813) or 100% homology to the RPB2 gene from F. acuminatum MD1 (MW164629). A phylogenetic tree was constructed using MEGA7 with related Fusarium strains (Figure 2). Microscope observations after incubation in potato-sucrose-agar (PSA) medium showed the presence of oval microconidia, fusiform macroconidia, septate mycelium and chlamydospores, and agree with the morphology of F. acuminatum (Marek et al. 2013). The pathogenicity was screened with two-week-old wounded and non-wounded garlic plants using a 1 × 106 spores/mL solution (20 µL). Sterile ddH2O was used in the control experiment. The inoculated plants were incubated at 26°C and 60% relative humidity for 3 days, detecting similar lesions compared to those observed in the field. The pathogen was recovered from 5 different lesions, from different plants, and its identity was confirmed by sequence analysis. Recently, F. acuminatum was reported to cause garlic bulb rot in Serbia (Ignjatov et al. 2017). Although F. acuminatum is well known as a causal agent of root rot (Li et al. 2021; Tang et al. 2021), F. acuminatum has also been found causing leaf blight on onion (Parkunan et al. 2013) and muskmelon (Yu et al. 2021). This is the first report of F. acuminatum causing leaf blight on garlic, demonstrating the host and tissue promiscuity of this pathogen. China is the largest producer of garlic in the world with nearly 20 million tons harvested in 2020. This report will help to better understand the pathogens that are affecting garlic production in China.

Population Genetic Analyses of Phytophthora cinnamomi Reveals Three Lineages and Movement Between Natural Vegetation and Avocado Orchards in South Africa.

Phytophthora cinnamomi is the causal agent of root rot, canker, and dieback of thousands of plant species around the globe. This oomycete not only causes severe economic losses to forestry and agricultural industries, but also threatens the health of various plants in natural ecosystems. In this study, 380 isolates of P. cinnamomi from four avocado production areas and two regions of natural vegetation in South Africa were investigated using 15 microsatellite markers. These populations were found to have a low level of genetic diversity and consisted of isolates from three lineages. Shared genotypes were detected between isolates from avocado orchards and natural vegetation, indicating the movement of isolates between these areas. The population from the Western Cape natural vegetation had the highest level of genotypic diversity and number of unique alleles, indicating this could be the point of introduction of P. cinnamomi to South Africa. Index of association analysis suggested that five of six populations were under linkage disequilibrium, suggesting a clonal mode of reproduction, whereas genotypes sampled from a recently established avocado orchard in the Western Cape were derived from a randomly recombining population. This study provided novel insights on the genetic diversity and spread of P. cinnamomi in South Africa. It also reported on the predominance of triploidy in natural occurring populations and provided evidence for recombination of P. cinnamomi for the first time. The presence of two dominant genotypes in all avocado production areas in South Africa highlight the importance of considering them in disease management and resistance breeding programs.

Biocontrol of Fusarium root rot in squash using mycorrhizal fungi and antagonistic microorganisms

BackgroundThe study amid to investigate the influence of Trichoderma album, T. harzianum, T. koningii, Bacillus subtilis (EF1) and Pseudomonas fluorescens against Fusarium solani, the causal agent of root rot in squash under in vitro conditions. Field experiment was conducted to evaluate the effects of arbuscular mycorrhizal fungi i.e., (Glomus intraradices, G. monosporum, G. etunicatu, AMF) and T. harzianum (TZ) as well as B. subtilis (BS) either as individual or combined treatment against Fusarium root rot of squash in two successive seasons of study 2020 and 2021 using New Eskandrani cultivar.ResultsTrichoderma harzianum caused the greatest reduction in mycelial growth of F. solani (75.17%), followed by T. album and T. koningii. Amongst the tested 4 cultivars (Sakata, Galaxy, New Eskandrani H1 hybird, Hollr Queen F1 hybrid) in glasshouse, Hollr Queen was the most resistant to the infection of F. solani with survival rate (84.92%), whereas New Eskandrani c.v was the most susceptible. Results of filed experiments proved that the combined inoculation of AMF + TZ + BS, AMF + BS, AMF + TZ, TZ + BS resulted in significant elevation of total chlorophyll, carotenoids, free phenolic compounds, free amino acids, total protein as well as the antioxidative enzyme activities (i.e. Superoxide dismutase, Peroxidase and Polyphenol-oxidase) and contents of macro and micro elements. Results further showed that the combined treatments caused a significant decrease in disease severity in both seasons with subsequent significant increase of plant growth parameters as well as total fruit yield/plant and total fruit yield/feddan.ConclusionIt could be concluded that the combined inoculations of the tested bioagents proved to have potentials in control of Fusarium root rot but large scale field experiments should be conducted before any ultimate conclusion or recommendation was drawn.

Evaluation of Durum Wheat Genotypes for Resistance against Root Rot Disease Caused by Moroccan Fusarium culmorum Isolates.

Fusarium culmorum is one of the most important causal agents of root rot of wheat. In this study, 10 F. culmorum isolates were collected from farms located in five agro-ecological regions of Morocco. These were used to challenge 20 durum wheat genotypes via artificial inoculation of plant roots under controlled conditions. The isolate virulence was determined by three traits (roots browning index, stem browning index, and severity of root rot). An alpha-lattice design with three replicates was used, and the resulting ANOVA revealed a significant (P < 0.01) effect of isolate (I), genotype (G), and G × I interaction. A total of four response types were observed (R, MR, MS, and S) revealing that different genes in both the pathogen and the host were activated in 53% of interactions. Most genotypes were susceptible to eight or more isolates, while the Moroccan cultivar Marouan was reported resistant to three isolates and moderately resistant to three others. Similarly, the Australian breeding line SSD1479-117 was reported resistant to two isolates and moderately resistant to four others. The ICARDA elites Icaverve, Berghisyr, Berghisyr2, Amina, and Icaverve2 were identified as moderately resistant. Principal component analysis based on the genotypes responses defined two major clusters and two sub-clusters for the 10 F. culmorum isolates. Isolate Fc9 collected in Khemis Zemamra was the most virulent while isolate Fc3 collected in Haj-Kaddour was the least virulent. This work provides initial results for the discovery of differential reactions between the durum lines and isolates and the identification of novel sources of resistance.

Pythium spp. Associated with Root Rot and Stunting of Winter Crops in North Carolina.

Annual double-crop rotation systems that incorporate winter wheat, clary sage, or a cover crop are common in eastern North Carolina. Stunting and root rot of clary sage (Salvia sclarea L.) reduce yields of this crop, especially in wet soils. Stunting and reduced stand establishment also afflict winter cover crops, including rye, rapeseed, and winter pea. Pythium spp. are causal agents of root rot of winter wheat in this region, but their role in root rot and stunting of other winter crops is not understood. During the growing seasons of 2018 to 2019 and 2019 to 2020, samples of clary sage, rye, rapeseed, and winter pea displaying symptoms of stunting were collected across eastern North Carolina, resulting in the recovery of 420 isolates of Pythium from the roots of all hosts. Pythium irregulare, Pythium spinosum, and the complex Pythium sp. cluster B2A were the species most frequently isolated from clary sage. P. irregulare and P. spinosum were aggressive pathogens of clary sage at 18°C and caused moderate root rot at 28°C. Koch's postulates confirmed that isolates belonging to Pythium sp. cluster B2A, Pythium sylvaticum, Pythium pachycaule, Pythium aphanidermatum, Pythium myriotylum, and Pythium oopapillum are pathogens of clary sage. P. irregulare (37% of all isolates) and members of the species complex Pythium sp. cluster B2A (28% of all isolates) constituted the majority of isolates collected from all hosts and were the species most frequently isolated from rye, rapeseed, and winter pea. In pathogenicity assays, isolates representing P. irregulare and P. spinosum caused slight to moderate root necrosis on rye, rapeseed, and winter pea. Isolates representing Pythium sp. cluster B2A caused slight to moderate root necrosis on rapeseed and clary sage, but no symptoms on rye or winter pea.

Identification of Root Rot Resistance QTLs in Pea Using Fusarium solani f. sp. pisi-Responsive Differentially Expressed Genes.

Pisum sativum (pea) yields in the United States have declined significantly over the last decades, predominantly due to susceptibility to root rot diseases. One of the main causal agents of root rot is the fungus Fusarium solani f. sp. pisi (Fsp), leading to yield losses ranging from 15 to 60%. Determining and subsequently incorporating the genetic basis for resistance in new cultivars offers one of the best solutions to control this pathogen; however, no green-seeded pea cultivars with complete resistance to Fsp have been identified. To date, only partial levels of resistance to Fsp has been identified among pea genotypes. SNPs mined from Fsp-responsive differentially expressed genes (DEGs) identified in a preceding study were utilized to identify QTLs associated with Fsp resistance using composite interval mapping in two recombinant inbred line (RIL) populations segregating for partial root rot resistance. A total of 769 DEGs with single nucleotide polymorphisms (SNPs) were identified, and the putative SNPs were evaluated for being polymorphic across four partially resistant and four susceptible P. sativum genotypes. The SNPs with validated polymorphisms were used to screen two RIL populations using two phenotypic criteria: root disease severity and plant height. One QTL, WB.Fsp-Ps 5.1 that mapped to chromosome 5 explained 14.8% of the variance with a confidence interval of 10.4 cM. The other four QTLs located on chromosomes 2, 3, and 5, explained 5.3–8.1% of the variance. The use of SNPs derived from Fsp-responsive DEGs for QTL mapping proved to be an efficient way to identify molecular markers associated with Fsp resistance in pea. These QTLs are potential candidates for marker-assisted selection and gene pyramiding to obtain high levels of partial resistance in pea cultivars to combat root rot caused by Fsp.

Biodiversity of the Fusarium fungi causing root rot of winter cereals in Belarus

Fusarium fungi are the main causal agents of root rot of winter cereals in Belarus. As many as 12 different species were identified, with occurrence being dependent on the cereal host species and weather conditions during the growing season. Lack of precipitation from April to July led to decreasing fungal biodiversity. Fusarium pathogen complex on wheat roots was formed by F. culmorum, F. avenaceum, F. equiseti, F. oxysporum, whereas F. equiseti and F. oxysporum prevailed on triticale and rye, and F. solani, F. avenaceum and F. equiseti dominated on barley root systems. The infestation of root with F. oxysporum increased under dry conditions. In contrast, F. culmorum was isolated from root system of wheat and triticale more frequently when rainfall was sufficient. For the first time, F. cerealis and F. tricinctum were isolated from triticale, and F. cerealis from rye only, in the Republic of Belarus.

Variability and inheritance in macadamia progenies to Phytophthora cinnamomi and P. multivora the causal agents of root rot and stem canker

Variability and inheritance in macadamia progenies to Phytophthora cinnamomi and P. multivora the causal agents of root rot and stem canker