Active Prevalence of Fusarium falciforme and F. acutatum Causing Basal Rot of Onion in Maharashtra, India

Over the past decade, there have been accumulating reports from researchers, farmers, and field extension personnel on the increasing incidence and spread of onion basal rot in India. Onion basal rot disease is mainly caused by Fusarium spp. This study aimed to validate the information on the active prevalence of F. falciforme and F. acutatum causing Fusarium basal rot (FBR) in Maharashtra. A survey was conducted, and the infected plants/bulbs were collected from fields of 38 locations comprising five districts of Maharashtra, namely, Nashik, Aurangabad, Solapur, Ahmednagar, and Pune, in 2023. This disease was prevalent in high-moisture and high-oil-temperature conditions and the symptoms were observed in most of the fields, with the FBR incidence ranging from 17 to 41%. The available data of basal rot incidence from 1998 to 2022 were analyzed, based on which the prevalence of FBR was 11–50%. Tissue from the infected samples of onion bulbs was used for the isolation. The identification was performed based on colony morphology and microscopic features and confirmed through molecular markers using ITS and Tef-1α gene primers. Of the ten Fusarium isolates collected from selected locations, six species were confirmed as F. acutatum and four as F. falciforme. The pathogenicity tests performed with onion seedlings and bulbs under moist conditions proved that both F. acutatum and F. falciforme independently could cause basal rot disease symptoms but with different degrees of virulence. Koch’s postulates were confirmed by reisolating the same pathogens from the infected plants. Thus, the active prevalence of FBR was confirmed in Maharashtra and also, to the best of our knowledge, this is the first report of F. falciforme and F. acutatum causing basal rot of onion independently in Maharashtra, India.


Introduction
Onion (Allium cepa L.), a fresh spice/vegetable, is consumed all over the world and India is globally the largest producer of onion with an overall production of 31.68 Mt [1].Though onion is primarily grown for food, it is also used as a traditional medicine in many Asian countries.Averaged over the quinquennial period of 2017 to 2022, India ranked first in area (1.37 million ha) and production (24.25 Mt) of onion in the world.However, the onion productivity (16.40 t/ha) of India ranked at the 90th position, being far lower than many other countries [1].
Fusarium is one of the most important genera of fungi due to its wide geographical distribution and morphological and genetic diversity, inciting a variety of plant diseases.Fusarium basal rot (FBR) is a seed-and soil-borne disease of Allium crops caused by a complex set of Fusarium species, viz., F. oxysporum, F. proliferatum, F. acutatum, and F. falciforme, in pre-as well as post-harvest conditions.
FBR is an economically significant disease of onion that causes considerable yield losses of up to 50% in the field and 30-40% during the post-harvest storage of bulbs [2].FBR generally occurs at all stages of Allium development [3]; however, seedlings and dormant or post-harvest bulbs are the most susceptible stages.Infected seeds and soil are the source of dispersal.This disease is widespread, particularly in the rainy season or in high-moisture conditions.The damage from basal rot is mostly recorded during storage [4].Primary infection by Fusarium spp.occurs when the fungus penetrates directly into roots or through wounds in roots or the basal parts of bulb scales [5][6][7].In the early stages of germination, the infection results in the delay of seedling emergence or a damping-off of the seedlings [8][9][10][11].Under field conditions, FBR-affected plants show symptoms of chlorosis, twisting, wilting, necrosis, bulb discoloration, and rot in the basal parts of the bulb and roots which become more noticeable during the plant's maturity [12,13].The disease outcome is the result of a host-pathogen interaction under the influence of environmental conditions.The diversity of Fusarium and Allium species and the occurrence of mixed infections enhance a multiplicity of FBR disease outcomes [14][15][16].
In India, the incidence of basal rot was first reported in Rajasthan by Mathur and Shukla [17], then in Coimbatore, Tamil Nadu [18].This disease is more prevalent in the southern region [19,20] of India.In India, since 1963, FBR has been known to be caused by Fusarium oxysporum f. sp.cepae [21], and in 2014, Ravi et al. [22] reported the association of F. proliferatum in basal rot in Andhra Pradesh [23] and then F. falciforme [13] and F. acutatum [24] causing FBR in Karnataka.
The Indian Council of Agricultural Research-Directorate of Onion and Garlic Research (ICAR-DOGR), the then National Research Centre for Onion and Garlic (NRCOG), Pune, Maharashtra, initiated sporadic surveys from 1998 to record the status of basal rot in Maharashtra, and the disease was recorded with variable intensity ranging from 11 to 50% [25][26][27].In Maharashtra, basal rot was reported to be majorly caused by Fusarium oxysporum f. sp.cepae until 2023 [28][29][30][31].
While going through the reports of F. falciforme and F. acutatum [13,24] causing basal rot (FBR) in Karnataka, we analyzed our samples collected from ten locations covering five districts, namely, Ahmednagar, Aurangabad, Nashik, Pune, and Solapur of Maharashtra, in 2023 and recorded that the basal rot incidence was caused by F. falciforme and F. acutatum.This indicates that the active prevalence of FBR in India is increasing day by day, which may become a major disease in years to come, making it an important issue for onion growers.The present study reports the prevalence and expansion of the FBR disease incidence caused by F. falciforme and F. acutatum in onion-growing regions of Maharashtra, India.

Survey and Sample Collection
ICAR-Directorate of Onion and Garlic Research, Pune, is the nodal agency in India with a mandate to plan, monitor, and evaluate the research on onion and garlic through independent and coordinated activities through its All-India Network Research Program on Onion and Garlic (AINRPOG), which currently has 28 centers located in different agroclimatic zones -.The PAN-India multilocational trials for improvement, production, and protection activities have been conducted since the inception of the institute.The various sorts of multidimensional data, including prevalent diseases of onion and disease incidence and severity, are collected in various research trials and the data so produced are documented every year in the Annual Report of AINPROG.The data on disease surveys of onion-growing areas of Maharashtra from 1998 to 2022 were collected from available reports [25][26][27], except for 2001 to 2006.Furthermore, a fresh survey was conducted in five different districts of Maharashtra, viz., Ahmednagar, Aurangabad, Nashik, Pune, and Solapur.A total of 38 villages from 11 blocks were surveyed in 2023 to understand the prevalence of basal rot.During the survey, samples from infected bulbs/plants were also collected from selective locations for the isolation and identification of pathogens.The percent disease incidence from each location was calculated using the following formula [32]: Disease incidence (%) = Number of infected plants Total number of observed plants × 100

Isolation and Identification of Isolates from Basal Rot Bulbs/Plants
Plants and bulbs showing symptoms of basal rot were collected from the surveyed locations, transported to the laboratory in sterile autoclaved bags, and processed for pathogen isolation using the method described by Rangaswamy, 1958 [33], and the subsequent cultural, morphological, and molecular characterization was performed using standard protocols.Briefly, the affected basal plate/bulb tissues were cut into small segments (approximately 5 mm long) and each piece was surface-sterilized by dipping in 1% sodium hypochlorite for 1 min and then washing thrice in sterile distilled water.Then, the infected tissues were placed on potato dextrose agar (PDA) in Petri plates and incubated at 25 ± 2 • C for 7 days.Single hyphal tips were transferred onto fresh PDA plates in such a way as to obtain a pure culture of isolates.The purification of cultures was performed by taking mycelial plugs (5 mm) from seven-day-old actively growing mycelia and placing them in 2% water agar plates.The plates were incubated for 48 h, and then observed under a compound microscope (Primostar, Carl Zeiss, Oberkochen, Germany) to locate the hyphal tip using the low-power objective.The hyphal tips were placed on PDA plates and slants to maintain as pure cultures.The pure cultures were stored at 4 • C for further studies.Thirty-eight total isolates were obtained from distinct samples.Among the 38 samples, 10 selective fungal isolates, named OGRDFW1 to OGRDFW10, from different districts were subjected to cultural, morphological, and molecular identification.The cultural and morphological characterization was performed using 7-day-old culture with a compound microscope (Primostar, Carl Zeiss, Oberkochen, Germany).

Molecular Identification of Fungal Isolates by Using Internal Transcribed Region and
Tef-1α Gene 2.3.1.DNA Extraction Based on morphological characteristics, ten Fusarium spp.isolates were grown in potato dextrose broth for mycelium production to be used for DNA extraction.DNA was extracted from mycelium harvested from broth media based on the cetyl trimethyl ammonium bromide (CTAB) method [34] with a slight modification.About 0.2 g of mycelium of each isolate was ground separately to a fine frozen powder in a sterile prechilled mortar and pestle using liquid nitrogen, after which a DNA extraction buffer (100 mM Tris HCl at pH 8.0, 1.4 M NaCl, 50 mM EDTA at pH 8.0, and 2% CTAB) was added.The RNA present with DNA was removed by RNase treatment.Quantification of DNA was performed by nano spectrophotometer (MicroDigital, Seoul, Republic of Korea).Working solutions of 25 ng/µL were prepared for optimization of polymerase chain reaction (PCR) by adding double-sterilized nuclease-free water.

Sequencing and Phylogenetic Analysis
The ITS and Tef -1α sequences obtained were BLAST-searched against the NCBI Gen-Bank database to confirm the identity of the strains.A phylogenetic tree was established from concatenated tef gene sequences using the Maximum Likelihood method in the molecular evolutionary genetics analysis tool MEGA ver.11 [35].

Pathogenicity Assay
The Fusarium spp.isolated from the host plants were cultured and tested for their pathogenicity to the onion cultivar Bhima Super.The seedling pathogenicity assay and the onion bulb inoculation assay was performed for ten isolates of Fusarium spp.(OGRDWF1 to OGRDFW10).Fifty-day-old seedlings were used for the pathogenicity assay and the experiment was conducted in controlled conditions under a net house.The experimental design was completely randomized and constituted in three replications.The seedling pathogenicity assay was carried out by dipping roots in the conidial suspension of ten Fusarium spp.isolates independently (10 6 conidia/mL) for 15 min and then transplanting them into pots containing sterilized potting mix [13,24].Each seedling was then drenched at the base with 5 mL of conidial suspension (10 6 conidia/mL).The control plants were treated with only sterile distilled water.According to Kalman et al. [36], the bulb pathogenicity assay was carried out by injecting a conidial suspension (10 6 conidia/mL) of the ten Fusarium spp.isolates independently into the basal plate of the bulbs (n = 40) and incubating the bulbs in moisture bags in the dark at 25 ± 2 • C for one week.After one week of incubation, external and internal disease symptoms were observed until 20 days and evaluated qualitatively, and the fungus from infected seedlings and bulbs was re-isolated and cultured to satisfy Koch's postulates.

FBR Incidence in Maharashtra
The analysis of reports of data from disease surveys of onion-growing areas of Maharashtra from 1998 to 2022 was carried out from available reports of ICAR-DOGR (1998-2020) and AINROPG (2021-2022) with missing years from 2001 to 2006, where the Fusarium basal rot (FBR) incidence varied from 11 to 50% (Figure 1).The disease incidence recorded during the fresh survey in 2023 of five different districts of Maharashtra, viz., Ahmednagar, Aurangabad, Nashik, Pune, and Solapur, varied from 17 to 41% (Figure 2).In our survey during 2023, we noticed that the highest disease incidence of 80.50% was observed in the village of Tejewadi in Ambegaon block followed by the village of Belhe in Junnar block of Pune district with an incidence of 78.50%.The lowest basal rot incidence (12.00%) was observed in the village of Niphad in Nashik district (Table 1; Figure 3).The highest average FBR incidence (40.64%) was recorded in Pune district followed by Ahmednagar (35.00%),Solapur (34.75%), and Aurangabad (23.67%), and the lowest average incidence of 17.17% was recorded in Nashik district (Figure 2).The native isolates In our survey during 2023, we noticed that the highest disease incidence of 80.50% was observed in the village of Tejewadi in Ambegaon block followed by the village of Belhe in Junnar block of Pune district with an incidence of 78.50%.The lowest basal rot incidence (12.00%) was observed in the village of Niphad in Nashik district (Table 1; Figure 3).The highest average FBR incidence (40.64%) was recorded in Pune district followed by Ahmednagar (35.00%),Solapur (34.75%), and Aurangabad (23.67%), and the lowest average incidence of 17.17% was recorded in Nashik district (Figure 2).The native isolates of Fusarium spp.were isolated from respective locations and designated as OGRDFW1 to OGRDFW10.

Isolation and Identification of Pathogens Causing Basal Rot
The disease symptoms observed on onion plants and bulb rot spreading from the onion basal plate upwards in the scales were selected and subjected to isolation and morphological identification (Figure 4).The isolates were purified and kept for incubation at 25 ± 2 • C.After 7 days of incubation, the isolates were preliminarily identified based on morphological characteristics.The radial growth of all the isolates varied from 64 to 80 mm mycelial growth at 7 days of incubation.The colonies of F. acutatum isolates showed white aerial mycelium that was purplish to pinkish in the center on both sides of Petri plates while the F. falciforme isolates showed white aerial mycelium on both sides (Table 2, Figure 5).When the cultures grew old, they became thick due to the growth of white aerial hyphal mats on the colony surface.Each isolate was observed with macroconidia and microconidia and their size was measured.
The macroconidia of F. acutatum were hyaline and falcate with bent apical cells with 1-2 septa measuring 18.2 to 20.3 × 2.4 to 3.7 µm (n = 40), while microconidia were ovoid and aseptate, measuring 3.6 to 5.8 × 3.2 to 4.3 µm (n = 40).The chlamydospores were round intercalary, hyaline, and single (Table 2, Figure 5).Macroconidia of F. falciforme were a li le bigger measuring 25.2 to 30.3 × 4.0 to 5.3 µm (n = 40), hyaline in color and falcate with slightly curved apexes with 2-3 septa, while the microconidia were 9.8 to 12.4 × 2.1 to 2.7 µm (n = 40), cylindrical to ellipsoid in shape, hyaline in color, and with 0-1 septa.The chlamydospores were round and intercalary, either single or in chains (Table 2, Figure 5).The colonies of F. acutatum isolates showed white aerial mycelium that was purplish to pinkish in the center on both sides of Petri plates while the F. falciforme isolates showed white aerial mycelium on both sides (Table 2, Figure 5).When the cultures grew old, they became thick due to the growth of white aerial hyphal mats on the colony surface.Each isolate was observed with macroconidia and microconidia and their size was measured.

Phylogenetic Relationship Based on ITS rRNA and Tef-1α Gene Sequences
Evolutionary history was inferred by using the Maximum Likelihood method and Tamura-Nei model.Initial tree(s) for the heuristic search were obtained automatically by applying Nearest Neighbor Interchange (NNI) algorithms to a matrix of pairwise distances estimated using the Tamura-Nei model, and then selecting the topology with the superior log likelihood value.The tree was drawn to scale, with branch lengths measured in the number of substitutions per site.This analysis involved 31 nucleotide sequences.Evolutionary analyses were conducted in MEGA11.The phylogenetic analysis based on Tef -1α sequences revealed that six isolates (OGRDFW1, OGRDFW2, OGRDFW4, OGRDFW5, OGRDFW6, and OGRDFW10) belong to F. acutatum, whereas four isolates (OGRDFW3, OGRDFW7, OGRDFW8, and OGRDFW9) belong to F. falciforme.Nodal robustness was targeted by the bootstrap method.The numerical value presented in the node indicates the bootstrap value.Based on the bootstrap values, isolates were clustered with F. acutatum and F. falciforme.The ITS sequences of four isolates and tef1 gene sequences of all ten isolates were submitted to GenBank (Table 3, Figure 6).

Pathogenicity Assay
The pathogenicity of six F. acutatum and four F. falciforme isolates was tested on seedlings and bulbs of a susceptible variety Bhima Super.All inoculated seedlings received infection and developed typical visible symptoms of FBR, viz., yellowing and wilting, and were all dead by 20 dpi (days post inoculation).And the inoculated bulbs also developed the soft rotting symptoms of FBR by 15 dpi and developed tissue decay of bulbs accompanied by the outgrowth of white hyphae on the bulb surface exhibited at 20 dpi, while the un-inoculated seedlings and bulbs remained healthy.The symptoms that developed in this inoculation assay were similar to those seen in naturally infected onion fields both on seedlings and bulbs.The pathogens F. falciforme and F. acutatum were reisolated as the original isolate, thus fulfilling Koch's postulates.

Pathogenicity Assay
The pathogenicity of six F. acutatum and four F. falciforme isolates was tested on seedlings and bulbs of a susceptible variety Bhima Super.All inoculated seedlings received infection and developed typical visible symptoms of FBR, viz., yellowing and wilting, and were all dead by 20 dpi (days post inoculation).And the inoculated bulbs also developed the soft ro ing symptoms of FBR by 15 dpi and developed tissue decay of bulbs accompanied by the outgrowth of white hyphae on the bulb surface exhibited at 20 dpi, while the un-inoculated seedlings and bulbs remained healthy.The symptoms that developed in this inoculation assay were similar to those seen in naturally infected onion fields both on seedlings and bulbs.The pathogens F. falciforme and F. acutatum were reisolated as the original isolate, thus fulfilling Koch's postulates.

Discussion
Fusarium basal rot (FBR) is an economically important disease, causing major loss in both pre-harvest and post-harvest conditions.Since the disease was reported, F. oxysporum f. sp.cepae has been known to be the causal agent of basal rot of onion [21,[37][38][39] in India.Shamyuktha et al. [39] recorded 27.00 to 74.33% F. oxysporum f. sp.cepae incidence in the Tirunelveli, Thoothukudi, and Tenkasi districts of Tamil Nadu.Muthukumar et al. [40] also reported a basal rot incidence varying from 10.12 to 24.87%, caused by F. oxysporum f. sp.cepae, in all surveyed locations of Tamil Nadu.Even recently, Thakare et al. [30] carried out a survey mostly in the locations covered in this study, in the Nashik, Pune, Solapur, and Ahmednagar districts of Western Maharashtra, and recorded the basal rot incidence caused by F. oxysporum f. sp.cepae with a range of 27.09 to 38.83%.In their survey, the Nashik district recorded the highest incidence, while Solapur recorded the lowest, whereas in our survey the Nashik district recorded the lowest disease incidence, and we did not record F. oxysporum f. sp.cepae in our collected samples.
Ravi et al. [22] observed the FBR incidence on onion bulbs in major growing areas of the Kadapa and Kurnool districts of Andhra Pradesh and reported F. proliferatum as the causal agent of FBR.Recently, F. falciforme [13] and F. acutatum [24] were also reported in Karnataka as causal agents of FBR.
In Maharashtra, basal rot, aka FBR, was reported to be caused by Fusarium oxysporum f. sp.cepae until 2023 [28][29][30][31].To understand the association and active prevalence of different Fusarium spp.causing basal rot in Maharashtra, a survey was conducted in five districts, viz., Ahmednagar, Aurangabad, Nashik, Pune, and Solapur of Maharashtra, in 2023 and the affected samples were collected and subjected to isolation and identification.Survey results revealed the presence of FBR incidence in surveyed locations of Maharashtra.The average incidence of FBR was the highest in Pune and the lowest in the Nashik district.After analyzing the basal rot incidence and the samples collected, it was revealed that, of the ten samples isolated and verified, four were caused by F. falciforme and six by F. acutatum.Our results are in agreement with Sarwadnya et al. [13], who also reported F. falciforme causing FBR in Karnataka.Bhat et al. [24] conducted a survey in the Bangalore, Bagalkot, Chitradurga, and Hassan districts of Karnataka and reported that FBR was caused by F. acutatum and F. falciforme.
The ICAR-DOGR (the then NRCOG), Pune, Maharashtra, initiated sporadic surveys from 1998 to record the status of basal rot from Maharashtra, and the analysis of the disease data revealed a variable intensity ranging from 11 to 50% [25][26][27].After going through the recent updates of reports from Karnataka to Maharashtra, the association of F. acutatum and F. falciforme in the previous year too could not be ruled out.
The plant and bulb samples collected from each of the 38 locations in the Ahmednagar, Aurangabad, Nashik, Pune, and Solapur districts were subjected to isolation.Pathogen diagnosis was carried out as described by Sarwadnya et al. [13] and Bhat et al. [24].Single hyphal tips were plated on potato dextrose agar and pure cultures were obtained, which were used for characterization.
The morphological characteristics of Fusarium spp.have been used in the past as the preferred method for species identification.The colonies of F. acutatum isolates had a white aerial mycelium with a reddish to pinkish center, but the isolates of F. falciforme displayed a white aerial mycelium on both sides.All these observations were found to be similar to those reported by Sarwadnya et al. [13] and Bhat et al. [24].Earlier, Kalman et al. [36] studied the morphology of Fusarium acutatum and observed fungal colonies of white aerial mycelium and growth rates ranging from 1.07 to 1.24 cm/day, and the size of the microconidia was 5.8-9.75 × 2.4-2.7 µm and macroconidia varied from 18.2 to 57.7 × 3.1 to 3.7 µm.
Since the Fusarium genus is complex, and morphological differences make it challenging to differentiate species [6,41], the isolates of the Fusarium spp.obtained from infected plants and bulbs of onion plants could not be differentiated morphologically; therefore, for further confirmation of identification, the Fusarium spp.isolates were subjected to molecular characterization using ITS1/4 and tef gene primers [13].The sequences were BLAST-searched in the NCBI database, confirming the identity of Fusarium spp.[42].The Tef1-α sequences were submitted to GenBank, which are available with the accession numbers of F. acutatum (OR102876, OR102877, OR102879, PP332885, PP332886, PP332890) and F. falciforme (OR102878, PP332887, PP332888, PP332889), respectively.The phylogenetic analysis clearly differentiated the species.The tef gene nucleotide sequences revealed that F. acutatum and F. falciforme clustered in a distinct phylogenetic clade from other species of Fusarium.Our findings are similar to those described by Bhat et al. [24] based on the multilocus BLAST analysis in the Fusarioid-ID database and showed that 14 isolates belonged to F. falciforme [13] and 12 belonged to F. acutatum.
In the pathogenicity assay, six F. acutatum and four F. falciforme were used on seedlings and bulbs of a susceptible 'Bhima Super' variety.The identity of the two species (F.acutatum and F. falciforme) as the causal agents of onion bulb and seedling rot disease was predominantly approved here using Koch's postulates [13].At 20 dpi, typical symptoms observed were yellowing, wilting, and death of seedling in bulbs; tissue decay with white mycelial growth on basal plates; and uninoculated plants remained healthy.Some earlier works studied the pathogenicity of Fusarium oxysporum f. sp.cepae on onion and observed the typical symptoms of yellowing and eventual dieback of the leaves, the drying of leaves, and, in the advanced stage, complete rotting of the basal portion of plants and the death of plants at 15 dpi [15,21,38,43,44].
The reports from Iran, Finland, and Burkina Faso suggest that F. solani and F. redolens typically result in lesions on seedlings, while they occur as asymptomatic infections on bulbs [10,45,46].Seedling age and growth stage have been proposed as major determinants of FBR presence on Allium spp.FBR tends to be more aggressive when infection establishes at an early stage of seedling development and on mature bulbs in storage [6,9,47,48].Le et al. [23] studied the co-infection of F. solani, F. proliferatum, and F. oxysporum on onion, where F. solani was highly virulent on seedlings while F. proliferatum and F. oxysporum severely affected both bulbs and seedlings in Vietnam.
As evident from the above reports, the causal agent for basal rot in Maharashtra was thought to be only caused by F. oxysporum f. sp.cepae until 2023 [30], and we have now found both F. falciforme and F. acutatum to be associated with FBR, which is the first report from Maharashtra and indicates the active prevalence of F. falciforme and F. acutatum.

Conclusions
There is a high probability that F. falciforme and F. acutatum contribute significantly to basal rot disease and were not reported earlier in Maharashtra.Although F. falciforme and F. acutatum have been previously reported in India, and the prevalence of the disease is now actively increasing in India.Though earlier report says that F. oxysporum f. sp.cepae is a major pathogen in causing FBR in Maharashtra.Our survey results showed that the F. falciforme and F. acutatum damage in onions ranged from 17 to 41%.Thus, the active prevalence of FBR was confirmed in Maharashtra, and to the best of our knowledge, this is the first report of F. falciforme and F. acutatum causing basal rot of onion independently in Maharashtra, India.

J 16 Figure 1 .Figure 1 .
Figure 1.Disease incidence of Fusarium basal rot disease in the Maharashtra state of India from 1998 to 2022.

Figure 1 .
Figure 1.Disease incidence of Fusarium basal rot disease in the Maharashtra state of India from 1998 to 2022.

Figure 2 .
Figure 2. Disease incidence of Fusarium basal rot disease in the Maharashtra state of India during 2023.

Figure 2 .
Figure 2. Disease incidence of Fusarium basal rot disease in the Maharashtra state of India during 2023.

Figure 3 .
Figure 3. Map showing the onion basal rot incidence in Maharashtra.

Figure 4 .
Figure 4. Varying symptoms of Fusarium Basal rot of onion: (a) FBR-infected field.(b) Single plant from the field with leaf dieback, ro ing of the basal plate, and loss of roots.(c) Intact infected plant and split open bulb showing soft watery decay.

Figure 4 .
Figure 4. Varying symptoms of Fusarium Basal rot of onion: (a) FBR-infected field.(b) Single plant from the field with leaf dieback, rotting of the basal plate, and loss of roots.(c) Intact infected plant and split open bulb showing soft watery decay.

Figure 6 .
Figure 6.Phylogenetic tree showing the relationship of 10 Fusarium isolates based on tef1-α gene sequence using the Maximum Likelihood method.The percentage of replicate trees in which the linked taxa clustered together in the bootstrap test (1000 replicates).Colletotrichum fructicola and Colletotrichum gloeosporioides were used as an out-group (* isolates included in this study).

Figure 6 .
Figure 6.Phylogenetic tree showing the relationship of 10 Fusarium isolates based on tef1-α gene sequence using the Maximum Likelihood method.The percentage of replicate trees in which the linked taxa clustered together in the bootstrap test (1000 replicates).Colletotrichum fructicola and Colletotrichum gloeosporioides were used as an out-group (* isolates included in this study).

Table 1 .
Survey locations in 2023 with their coordinates and FBR incidences.

Table 2 .
Morphological characterization and microscopic identification of Fusarium spp.isolates.

Table 3 .
BLASTN identification of the Fusarium spp.isolates from this study.