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Article

Identification and Fungicide Control of Alternaria alternantherae Causing Leaf Spot on Celosia cristata and Alternanthera philoxeroides in China

by
Ya-Xin Xiang
1,
Jing Zhou
1,
Zhi Li
1,
Hai-Feng Liu
1,2,* and
Jian-Xin Deng
1,2,*
1
Department of Plant Protection, College of Agriculture, Yangtze University, Jingzhou 434025, China
2
MARA Key Laboratory of Sustainable Crop Production in the Middle Reaches of the Yangtze River (Co-Construction by Ministry and Province), Yangtze University, Jingzhou 434025, China
*
Authors to whom correspondence should be addressed.
Horticulturae 2026, 12(6), 750; https://doi.org/10.3390/horticulturae12060750 (registering DOI)
Submission received: 21 May 2026 / Revised: 9 June 2026 / Accepted: 16 June 2026 / Published: 20 June 2026
(This article belongs to the Special Issue Plant–Microbial Interactions: Mechanisms and Impacts)
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Highlights

What are the main findings?
  • We identified the fungal pathogen causing leaf spot on Celosia cristata and Alternanthera philoxeroides via morphological characteristics and multilocus phylogenetic analysis.
  • We assessed the pathogenicity of the fungal strains on two host plants, as well as their sensitivity to four fungicides.
What are the implications of the main findings?
  • This study reports Alternaria alternantherae as the causal pathogen of leaf spot on Celosia cristata and Alternanthera philoxeroides, and reveals differences between strains of the same species from the two different hosts.
  • This study recommends effective fungicides to control leaf spot on C. cristata based on in vitro and in vivo fungicide sensitivity assays.

Abstract

Celosia cristata and Alternanthera philoxeroides both belong to the family Amaranthaceae. Of the two species, C. cristata serves as a medicinal herb as well as an ornamental plant, whereas A. philoxeroides is a notorious invasive weed. In 2024, leaf spot symptoms were observed on C. cristata and A. philoxeroides in Jingzhou City, Hubei Province, China. Based on morphological characteristics and multilocus phylogenetic analysis using sequences of ITS, GAPDH, TEF1, RPB2, and Alt a 1, the pathogen isolated from both hosts was identified as the same species, Alternaria alternantherae. However, differences in morphology were observed between the strains from different hosts. Pathogenicity assays confirmed that this species can cross-infect both host plants. In addition, sensitivities of the pathogen to four fungicides (prochloraz, tebuconazole, azoxystrobin, and carbendazim) were tested in vitro and in vivo. The results revealed that the pathogen was highly sensitive to fungicides prochloraz and tebuconazole. These findings provide valuable insights into the management of leaf spot disease on C. cristata and the development of integrated control strategies for A. philoxeroides.

1. Introduction

Celosia cristata (Celosia argentea var. cristata), an annual erect herb of the genus Celosia in the family Amaranthaceae, is native to tropical regions of the Americas and Africa and is now widely cultivated worldwide. As a prominent bedding plant, it is distinguished by its striking inflorescences with diverse colors [1,2]. It also has a millennial history of use as a traditional medicinal herb [3]. In traditional Chinese medicine, its inflorescences are cool in property, sweet and astringent in taste, and clinically used to treat symptoms such as hemorrhagic conditions and topical disorders [1,4]. Modern phytochemical studies have identified various bioactive compounds in C. cristata, including saponin, glycoprotein, phenolic acids, phytosterol, and kaempferol, which exhibit hepatoprotective, antioxidant, immunomodulatory effects and potential for obesity management [5,6,7]. Additionally, C. cristata is an edible flower rich in vitamins, minerals, amino acids, and fatty acids [6], showing great potential as a raw material for functional foods and nutraceuticals.
Alternanthera philoxeroides, commonly known as alligator weed, is a perennial species in the same family. Native to South America, it was introduced to southern China in the 1930s as animal forage [8]. It has strong vegetative vigor and dispersal capacity across terrestrial, semi-aquatic, and aquatic habitats, relying exclusively on asexual propagation [9]. As one of the most damaging invasive weeds globally, it aggressively competes with crops for light, water, and nutrients, causing significant yield losses and economic losses [10,11,12].
Fungal diseases represent a major threat to plant health. Studies have shown that C. cristata is susceptible to multiple pathogens, such as Pseudomonas syringae (causing damping-off), Macrophomina phaseolina (causing stem base rot), and root-knot nematodes (suppressing growth and inducing gall formation) [13,14,15,16]. Meanwhile, A. philoxeroides, with its rapid proliferation, severely invades ecological niches and reduces biodiversity, presenting a great challenge for control [17]. Accurate identification of pathogens is essential for effective disease and weed management.
In September, 2024, an outbreak of leaf spot disease affecting both C. cristata and A. philoxeroides was observed in Jingzhou City, Hubei Province, causing plant death in severe cases. This study aims to isolate and identify the causal agents of the leaf spot diseases using integrated morphological and molecular biological approaches, and investigate the fungicide sensitivity of this pathogen in vitro and in vivo, providing a scientific basis for future disease management of C. cristata and control strategies of A. philoxeroides.

2. Materials and Methods

2.1. Sample Collection and Pathogen Isolation

Diseased plants of Celosia cristata and Alternanthera philoxeroides were observed in September, 2024, in Jingzhou City, Hubei Province, China (30°21′20″ N, 112°8′21″ E). Infected leaves of C. cristata exhibited yellowing and necrotic brown lesions, leading to wilting, and finally plant death (Figure 1A,B). Typical symptoms of A. philoxeroides leaves were circular to subcircular necrotic lesions with gray-white centers and purple-red margins, accompanied by chlorosis (Figure 1C,D). Diseased leaves of these two plants (ten leaves per plant) were collected for fungal isolation, and a random sampling method was employed to select leaves representative of disease incidence. Firstly, leaf tissues were surface disinfected after being cut into small segments (approx. 5 mm × 5 mm). Then, the tissue segments were placed onto Petri dishes with moistened sterile filter paper and incubated at 25 °C in darkness to induce fungal sporulation. After 24 to 48 h, abundant conidia resembling Alternaria spp. were observed on the samples under a stereomicroscope [18]. Conidia were singly transferred onto potato dextrose agar (PDA: Difco, Montreal, QC, Canada) plates using sterile glass needles and then incubated at 25 °C in darkness for 7 to 10 days. Resulting fungal colonies were subcultured onto fresh PDA plates 2–3 times for purification. Pure cultures were deposited in the Fungi Herbarium of Yangtze University in Jingzhou, China.

2.2. Morphology

To observe colony morphology of the fungal species, mycelial plugs (6 mm in diameter) taken from 5-day-old PDA cultures were transferred to the center of fresh PDA plates and incubated at 25 °C in darkness for 7 days. Colony characteristics such as color, texture, and size were recorded. To observe conidial morphology, the strains were also cultured on potato carrot agar (PCA) and V8 juice agar (V8A) plates at 22 °C under a cycle of 8 h light/16 h darkness for 7 days [19]. No sporulation was observed on those PCA plates, and manual sporulation induction was conducted: colonies were scraped and exposed to UV light for 2 h, then incubated at the same condition for an additional 48 h [18]. Conidiophores and conidia were photographed using a Nikon ECLIPSE Ni-U microscopy system (Nikon, Tokyo, Japan). Fifty mature conidia were randomly selected for dimension measurements [20].

2.3. DNA Extraction and PCR Amplification

Genomic DNA was extracted from fresh mycelia grown on PDA using a modified CTAB method [21]. Five primer pairs were used to amplify different gene regions: ITS5/ITS4 [22] for the internal transcribed spacer (ITS) of rDNA, gpd1/gpd2 [23] for the glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH), EF1-728F/EF1-986R [24] for the partial translation elongation factor 1-alpha gene (TEF1), RPB2-5F/RPB2-7cR [25] for the RNA polymerase II second largest subunit gene (RPB2), and Alt a1-4rev/Alt a1-4for [26] for the Alternaria major allergen gene (Alt a1). The PCR reaction was carried out in a total volume of 25 μL, containing 2.5 μL of DNA template, 1.25 μL of each forward and reverse primer, and 20 μL of 1.1× Taq PCR StarMix (Tsingke, Beijing, China). Amplification was performed using a BIO-RAD T100 Thermal Cycler (BIO-RAD, Hercules, CA, USA). The amplification protocols for ITS, GAPDH, TEF1, and RPB2 followed the procedure described by Woudenberg et al. [27], while the Alt a1 gene was amplified according to Lawrence et al. [26]. The PCR products were purified and sequenced by Tsingke Biotechnology (Beijing, China). All sequences were viewed and manually checked using BioEdit [28], and subsequently submitted to the GenBank database (accession numbers were included in Table S1).

2.4. Phylogenetic Analysis

Resulting nucleotide sequences were subjected to similarity searches via the BLASTn tool in NCBI website (https://blast.ncbi.nlm.nih.gov/, accessed on 15 December 2025). Reference sequences were obtained from the GenBank database based on high sequence similarities and previous publications [27,29,30]. A multilocus phylogenetic analysis was conducted using the One-click Fungal Phylogenetic Tool (OFPT) v1.9.0 [31]. Specifically, sequences of each genetic locus were aligned using MAFFT v7.520 [32], trimmed with TrimAl v1.2 [33], and the optimal nucleotide substitution model for each dataset was determined using ModelFinder v1.6.12 [34]. Phylogenetic trees were finally reconstructed through Maximum Likelihood (ML) analysis and Bayesian Inference (BI) analysis using IQ-TREE v1.6.12 [35] and MrBayes v3.2.7 [36], respectively.

2.5. Pathogenicity Assays

Pathogenicity of the fungal strains was evaluated on healthy detached leaves of C. cristata and A. philoxeroides. Prior to inoculation, leaves were surface-disinfected with 5% sodium hypochlorite for 2 min, followed by wounding of the leaf abaxial side using sterile needles. Mycelial plugs (6 mm diameter) obtained from PDA were then placed on wounded areas. Control leaves were treated with pure PDA plugs. Inoculated leaves were maintained on sterile plastic trays within humid transparent plastic containers at 25 °C in darkness. For conidial inoculation, a suspension (1 × 105 conidia/mL) was prepared using conidia harvested from PCA cultures as described in Section 2.2. The suspension was sprayed on living plants, while the control group was treated with sterile distilled water. Inoculated plants were covered with sterile plastic bags to maintain humidity and incubated at 25 °C. Disease development was assessed after 7–10 days by measuring lesion diameters. Each assay was repeated three times independently, with three detached leaves per replicate for the leaf assay, and three living plants per replicate for the plant assay.

2.6. Fungicide Sensitivity Assay

In vitro fungicide sensitivity of the fungal strains was tested on PDA. Four fungicides with different modes of action were used for the assay, including prochloraz (97% a.i., Anhui Guangxin Agrochemical Co., Ltd., Guangde, China), tebuconazole (97% a.i., Shandong Weifang Rainbow Chemical Co., Ltd., Weifang, China), azoxystrobin (98% a.i., Jiangsu Changqing Agrochemical Co., Ltd., Yangzhou, China), and carbendazim (98% a.i., Shandong Huayang Pesticide & Chemical Industry Group Co., Ltd., Tai’an, China). A six-concentration gradient (0, 0.01, 0.1, 1, 10, and 100 μg/mL) was established for each fungicide. After 7-day incubation at 25 °C, mycelial growth inhibition was calculated and effective concentration for 50% inhibition (EC50) values were determined. An in vivo fungicide sensitivity assay was conducted on healthy detached leaves of C. cristata and A. philoxeroides. Prior to pathogen inoculation, the leaves were surface-disinfected as previously described, and then sprayed with fungicide solutions (50 μg/mL, dissolved in DMSO). Control leaves were treated with same amount of DMSO. After air-drying for 2 h, 20 μL of conidial suspension (1 × 105 conidia/mL) was pipetted on the leaves for inoculation. Each assay was repeated three times.

3. Results

3.1. Fungal Strains

Fungal colonies obtained from diseased tissues of C. cristata and A. philoxeroides showed similar morphology. Therefore, representative strains from both hosts were selected based on morphology for further analysis (YzU 241887 and YzU 242139 from C. cristata; YzU 242140 and YzU 242141 from A. philoxeroides).

3.2. Fungal Morphology

On PDA, the colony of strain YzU 241887 was white, dense, and velvety, with yellow to pale yellow pigmentation on the reverse side (Figure 2A). Colony diameters ranged from 44 to 52 mm. On PCA, conidia were solitary, elongate-ovoid to elliptical, measuring 66–115 (−121.8) × 12.8–17.5 (−19.4) μm, with 5–8 septa (Figure 2B,D,E). The beak was filamentous, measuring 131–219 (−252.2) × 2.6–6 (−7) μm (Table 1). On V8A, conidia were solitary, elongate-ovoid to elliptical, with a smooth wall and a single beak, measuring 64–100 (−107) × 11.89–19.56 μm, with 4–8 transverse septa (Figure 2C). The beak was filiform, measuring 118.71–215 (−236.38) × 4–6 (−6.82) μm (Table 1).
The colony of YzU 242141 on PDA was pale yellow, irregular, and velvety, with the reverse side showing yellow pigmentation and white in the margin (Figure 3A). Colony diameters ranged from 44 to 49 mm. On PCA, conidia were solitary, elongate-ovoid to elliptical, measuring 63.45–104 (−127.03) × 13–18 μm, 5–7 transverse septa (Figure 3B,D,E). The beak was 56–160 (−214) × 3–7 μm in dimension (Table 1). On V8A, conidia were solitary, elongate-ovoid to elliptical, smooth-walled. Conidial dimensions were 65.8–105 (−113) × 14–19.2 μm, with 5–8 transverse septa (Figure 3C). The beak was filiform, 90–150 (−163) × 3–6 μm (Table 1).
Based on morphology, the two strains were similar to each other, with slight differences (Table 1), and were similar to A. alternantherae [27,37]. In addition, it could be distinguished from closely related Alternaria species by conidial size and beak length (Table 1).
Table 1. Morphological comparison of Alternaria alternantherae and its closely related species.
Table 1. Morphological comparison of Alternaria alternantherae and its closely related species.
SpeciesStrainConidiaMediumReference
Body (μm)SeptaBeak (μm)
A. alternantheraeCBS 124392(40–) 110 (–160) × (10–) 18 (–25) μm2–1460–225 μm (–400 μm) × 3.5–5.5 μmV8A[27]
EGS 52-03970–110 (–121.3) × 12–17 (–19.4) μm5–8131–200 (–225) × 3–5 (–6) μmPCA[38]
61–100 (–107) × 11–19 μm4–8125–205 (–236.4) × 4–6 (–3.7) μmV8A
YzU24188766–115 (−121.8) × 12.8–17.5 (−19.4) μm5–8131–219 (−252.2) × 2.6–6 (−7) μmPCAThis study
64–100 (−107) × 11.89–19.56 μm4–8118.71–215 (−236.38) × 4–6 (−6.82) μmV8A
YzU24214163.45–104 (−127.03) × 13–18 μm5–756–160 (−214) × 3–7 μmPCAThis study
65.8–105 (−113) × 14–19.2 μm5–890–150 (−163) × 3–6 μmV8A
A. celosiicolaEGS 42-01365–103 (–113) × 13–18 μm4–790–115 (–125) μmPCA[38]
70–105 (–115) × 14–20 μm5–7106–160 (–210) × 3–7 μmV8A
A. perpunctulataCBS 11526780–100 × 10–14 μm6–9100–210 × 2 µmPCA[27]
A. gomphrenaeMAFF 24676935–77 × 10–17 μm3–913–216 × 2–4 μmV8A[30]

3.3. Phylogeney

To clarify the taxonomic placement of the strains, a multilocus phylogenetic analysis was performed based on concatenated sequences of five gene regions: ITS, GAPDH, TEF1, RPB2, and Alt a1. A total of 71 strains were used for phylogenetic analysis, including 69 strains from Alternaria spp. Strains Pleospora tarda CBS 714.68 and Stemphylium herbarum CBS 191.86 were used as outgroup taxa. The dataset contained 2542 characters, including 496 bp for ITS, 572 bp for GAPDH, 239 bp for TEF1, 772 bp for RPB2, and 463 bp for Alt a 1. The maximum likelihood phylogenetic tree revealed that the four strains (YzU 241887, YzU 242139, YzU 242140, and YzU 242141) isolated in this study clustered within the Alternaria alternantherae clade with strong supports of 100% bootstrap value and 1.0 Bayesian posterior probability (Figure 4). Therefore, all isolates obtained from both C. cristata and A. philoxeroides were identified as Alternaria alternantherae.

3.4. Pathogenicity Assay

Pathogenicity tests were conducted using representative strains YzU241887 (isolated from C. cristata) and YzU242141 (isolated from A. philoxeroides) on detached leaves and living plants of C. cristata and A. philoxeroides. The results revealed that the two strains were able to infect both plants. On detached C. cristata leaves, the lesions caused by these two strains ranged from 10.37 to 15.78 mm (Figure 5A,B,D,E). On A. philoxeroides leaves, the lesion dimensions were 8.00 to 12.43 mm. Leaves in the control group remained healthy (Figure 5C,F). Symptoms on living plants of C. cristata and A. philoxeroides caused by the two strains were generally similar to those observed in the field, with lesion diameters ranging from approximately 5.8 to 30 mm on C. cristata (Figure 6A,C) and 1.46 to 4.74 mm on A. philoxeroides (Figure 6B,D). In control groups, both plants remained healthy (Figure 6E,H). The pathogen was reisolated from diseased leaves of both plants, and confirmed as A. alternantherae by morphology and TEF1 sequences. Thus, the Koch’s postulates were fulfilled.

3.5. Fungicide Sensitivity

An in vitro fungicide sensitivity assay was performed on strains YzU241887 and YzU242141 using the fungicides prochloraz, tebuconazole, azoxystrobin, and carbendazim. Similar fungicide sensitivity patterns were observed in these two strains, including mycelial growth phenotypes (Figure 7A,C) and mycelial inhibition rates (Figure 7B,D). However, quantitative differences in EC50 values were observed. EC50 values of strain YzU241887 were 0.057 μg/mL for prochloraz, 0.255 μg/mL for tebuconazole, 0.345 μg/mL for azoxystrobin, and 71.671 μg/mL for carbendazim. EC50 values of strain YzU2422141 were 0.008 μg/mL for prochloraz, 0.088 μg/mL for tebuconazole, 0.022 μg/mL for azoxystrobin, and 59.467 μg/mL for carbendazim. Both strains were sensitive to fungicides prochloraz, tebuconazole, and azoxystrobin, but less sensitive to carbendazim.
Fungicide sensitivity assays were conducted on detached leaves of C. cristata (Figure 8A–G) and A. philoxeroides (Figure 8H–N). The most severe symptoms were observed on the detached leaves of C. cristata and A. philoxeroides inoculated with only pathogen (Figure 8A,H) or pathogen with DMSO (Figure 8B,I). Detached leaves of two hosts treated with pathogen and fungicide carbendazim exhibited milder disease symptoms (Figure 8C,J). Leaves treated with pathogen and fungicide azoxystrobin showed significantly lighter disease symptoms (Figure 8D,K) than the previous treatment. No symptoms were observed on leaves treated with pathogen and fungicide prochloraz (Figure 8E,L) or fungicide tebuconazole (Figure 8F,M), similar to those without pathogen treatment (Figure 8G,N), indicating complete suppression of symptom development under the conditions tested.

4. Discussion

In this study, the fungal pathogen causing leaf spot on C. cristata and A. philoxeroides was isolated and identified as A. alternantherae based on morphology and multilocus (ITS, GAPDH, TEF1, RPB2, and Alt a 1) phylogeny. Sensitivities of the pathogen to four different fungicides (prochloraz, tebuconazole, azoxystrobin, and carbendazim) were also tested in vitro and in vivo, with prochloraz and tebuconazole showing the best control effect.
Most Alternaria spp. are saprophytic, commonly found in soil or decaying plant tissues, while others are pathogenic and cause diseases in economically important crops and ornamental plants [37,39]. In previous studies, Alternaria species have been reported on C. cristata, such as A. alternata and A. celosiicola [30,40]. In this study, A. alternantherae was found to be the pathogen causing leaf spot on Amaranthaceae plants C. cristata and A. philoxeroides. A. alternantherae has been reported to be pathogenic to C. cristata [41]. A. philoxeroides infection caused by A. alternantherae was first reported by Holcomb [42], and later confirmed by Barreto [43] and Akhtar [44] et al. Taxonomically, A. alternanthera is a large-spored species; it was originally classified in the genus Nimbya and subsequently reassigned to Alternaria by Lawrence [26].
Even though the pathogens from the two different hosts (C. cristata and A. philoxeroides) were the same species (A. alternantherae), differences in morphology, pathogenicity and fungicide sensitivity were observed between strains from C. cristata (YzU241887) and A. philoxeroides (YzU242141). Specifically, compared to strain YzU242141, strain YzU241887 had a narrower conidia body and longer beak (Table 1). Pathogenicity test revealed that strain YzU242141 produced more obvious yellow halos on A. philoxeroides leaves than strain YzU241887 (Figure 5 and Figure 6). In addition, according to the in vitro fungicide sensitivity assay, strain YzU242141 showed slightly higher sensitivity to the tested fungicides (prochloraz, tebuconazole, azoxystrobin, and carbendazim) than YzU241887. These indicate that long-term host adaptation may be associated with host-related phenotypic variation among conspecific fungal isolates, enabling pathogens to better adapt to host plants and field ecological conditions and further expand their host adaptability.
Of the two hosts, C. cristata is not only an ornamental plant but also a valuable medicinal and edible resource. Foliar diseases such as leaf spot significantly reduce the quality of C. cristata and lead to severe economic losses. Thus, effective disease control is important for this plant. In this study, four different fungicides were tested against its leaf spot pathogen A. alternanthera in vitro and in vivo. Among them, prochloraz and tebuconazole showed the strongest performance in controlling the disease. Therefore, these two fungicides can be considered promising candidates for future leaf spot management on C. cristata. A. philoxeroides is a highly invasive weed, posing serious challenges to ecological and agricultural management. Chemical control remains a primary strategy in weed management and plays an important role in ensuring stable crop production. Given the severe invasive threat of A. philoxeroides, there is an urgent need to develop green and sustainable control strategies. Overreliance on chemical herbicides not only promotes resistance evolution but also causes negative environmental impacts. Therefore, biological control approaches have attracted increasing attention. Previous studies have demonstrated the strong pathogenicity of A. alternantherae against A. philoxeroides, causing chlorosis, tissue necrosis, and plant death [45,46]. Demuner et al. [47] further identified virulence-related compounds, supporting its potential as a bioherbicide. Moreover, toxins and other secondary metabolites produced by this fungus also exhibit notable herbicidal activity [48,49,50], providing a theoretical basis for its development as a microbially derived herbicide. However, practical application would require comprehensive assessments of host specificity, environmental safety, and field efficacy.
These findings provide essential information for future management of leaf spot disease in C. cristata and for potential biological control of A. philoxeroides. Future research should focus on field evaluation of fungicides against C. cristata leaf spot, and on application techniques of bioherbicidal agents to facilitate practical implementation against A. philoxeroides.

5. Conclusions

In this study, A. alternantherae was identified as the causal agent of leaf spot on C. cristata and A. philoxeroides in China, based on morphology, multilocus phylogeny and pathogenicity tests. Isolates of this fungus from the two different hosts showed certain differences in morphological characteristics, pathogenicity, and fungicide sensitivity. In addition, prochloraz and tebuconazole were highly effective against the leaf spot disease, whereas carbendazim was ineffective. These results provide a basis for the management of the disease in the future.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/horticulturae12060750/s1, Table S1: GenBank accession numbers of fungal strains used for phylogenetic analyses in this study.

Author Contributions

Conceptualization, J.-X.D.; methodology, Y.-X.X., J.Z. and Z.L.; formal analysis, Y.-X.X. and J.Z.; Investigation, Y.-X.X.; data curation, Y.-X.X. and H.-F.L.; writing—original draft preparation, Y.-X.X. and H.-F.L.; writing—review and editing, H.-F.L. and J.-X.D.; supervision, J.-X.D.; project administration, J.-X.D.; Funding acquisition, J.-X.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (32270022).

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Natural symptoms observed on Celosia cristata (A,B) and Alternanthera philoxeroides (C,D) in Jingzhou City, China.
Figure 1. Natural symptoms observed on Celosia cristata (A,B) and Alternanthera philoxeroides (C,D) in Jingzhou City, China.
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Figure 2. Morphological characteristics of Alternaria alternantherae YzU241887. (A) Colony on PDA for 7 days at 25 °C; (B) conidia on PCA; (C) conidia on V8A. (D,E) Sporulation patterns on PCA. Scale bars = 50 µm.
Figure 2. Morphological characteristics of Alternaria alternantherae YzU241887. (A) Colony on PDA for 7 days at 25 °C; (B) conidia on PCA; (C) conidia on V8A. (D,E) Sporulation patterns on PCA. Scale bars = 50 µm.
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Figure 3. Morphological characteristics of Alternaria alternantherae Yz-U242141. (A) Colony on PDA for 7 days at 25 °C; (B) conidia on PCA; (C) conidia on V8A. (D,E) Sporulation patterns on PCA. Scale bar = 50 µm.
Figure 3. Morphological characteristics of Alternaria alternantherae Yz-U242141. (A) Colony on PDA for 7 days at 25 °C; (B) conidia on PCA; (C) conidia on V8A. (D,E) Sporulation patterns on PCA. Scale bar = 50 µm.
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Figure 4. Maximum likelihood phylogenetic tree of Alternaria spp. based on the combined gene sequences of ITS, GAPDH, TEF1, RPB2, and Alt a 1. Bootstrap support values > 70 and the Bayesian posterior probabilities > 0.70 are given at the nodes (BS/PP). Strains isolated in this study are in red. Strains Pleospora tarda CBS 714.68 and Stemphylium herbarum CBS 191.86 were selected as outgroup taxa.
Figure 4. Maximum likelihood phylogenetic tree of Alternaria spp. based on the combined gene sequences of ITS, GAPDH, TEF1, RPB2, and Alt a 1. Bootstrap support values > 70 and the Bayesian posterior probabilities > 0.70 are given at the nodes (BS/PP). Strains isolated in this study are in red. Strains Pleospora tarda CBS 714.68 and Stemphylium herbarum CBS 191.86 were selected as outgroup taxa.
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Figure 5. Pathogenicity of Alternaria alternantherae on detached leaves of different hosts. (A,B) Symptoms on detached leaves of Celosia cristata caused by strains YzU241887 (isolated from C. cristata) and YzU242141 (isolated from Alternanthera philoxeroides), respectively. (D,E) Symptoms on detached leaves of A. philoxeroides caused by strains YzU241887 and YzU242141, respectively. (C–F) Control leaves without inoculation.
Figure 5. Pathogenicity of Alternaria alternantherae on detached leaves of different hosts. (A,B) Symptoms on detached leaves of Celosia cristata caused by strains YzU241887 (isolated from C. cristata) and YzU242141 (isolated from Alternanthera philoxeroides), respectively. (D,E) Symptoms on detached leaves of A. philoxeroides caused by strains YzU241887 and YzU242141, respectively. (C–F) Control leaves without inoculation.
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Figure 6. Pathogenicity of Alternaria alternantherae on living plants of different hosts. (A,C) Symptoms on leaves of Celosia cristata caused by strains YzU241887 (isolated from C. cristata) and YzU242141 (isolated from Alternanthera philoxeroides), respectively. (B,D) Symptoms on detached leaves of A. philoxeroides caused by strains YzU241887 and YzU242141, respectively. (E,G) Control plants of C. cristata without pathogen inoculation. (F,H) Control plants of A. philoxeroides without pathogen inoculation.
Figure 6. Pathogenicity of Alternaria alternantherae on living plants of different hosts. (A,C) Symptoms on leaves of Celosia cristata caused by strains YzU241887 (isolated from C. cristata) and YzU242141 (isolated from Alternanthera philoxeroides), respectively. (B,D) Symptoms on detached leaves of A. philoxeroides caused by strains YzU241887 and YzU242141, respectively. (E,G) Control plants of C. cristata without pathogen inoculation. (F,H) Control plants of A. philoxeroides without pathogen inoculation.
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Figure 7. In vitro fungicide sensitivity of Alternaria alternantherae YzU241887 (A,B) and YzU242141 (C,D). (A) Sensitivity of strain YzU241887 to four fungicides at different concentrations; (B) inhibition rate of strain YzU241887 to four fungicides at different concentrations. (C) Sensitivity of strain YzU242141 to four fungicides at different concentrations; (D) inhibition rate of strain YzU242141 to four fungicides at different concentrations.
Figure 7. In vitro fungicide sensitivity of Alternaria alternantherae YzU241887 (A,B) and YzU242141 (C,D). (A) Sensitivity of strain YzU241887 to four fungicides at different concentrations; (B) inhibition rate of strain YzU241887 to four fungicides at different concentrations. (C) Sensitivity of strain YzU242141 to four fungicides at different concentrations; (D) inhibition rate of strain YzU242141 to four fungicides at different concentrations.
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Figure 8. In vivo fungicide sensitivity assay of Alternaria alternantherae YzU241887 (A–G) and YzU242141 (H–N) on detaches of Celosia cristata and Alternanthera philoxeroides, respectively. (A,H) Detached leaves of two hosts inoculated with pathogen only. (B,I) Detached leaves of two hosts treated with DMSO and pathogen. (C,J) Detached leaves treated with fungicide carbendazim and pathogen. (D,K) Detached leaves treated with fungicide azoxystrobin and pathogen. (E,L) Detached leaves treated with fungicide prochloraz and pathogen. (F,M) Detached leaves treated with fungicide tebuconazole and pathogen. (G,N) Detached leaves without pathogen treatment.
Figure 8. In vivo fungicide sensitivity assay of Alternaria alternantherae YzU241887 (A–G) and YzU242141 (H–N) on detaches of Celosia cristata and Alternanthera philoxeroides, respectively. (A,H) Detached leaves of two hosts inoculated with pathogen only. (B,I) Detached leaves of two hosts treated with DMSO and pathogen. (C,J) Detached leaves treated with fungicide carbendazim and pathogen. (D,K) Detached leaves treated with fungicide azoxystrobin and pathogen. (E,L) Detached leaves treated with fungicide prochloraz and pathogen. (F,M) Detached leaves treated with fungicide tebuconazole and pathogen. (G,N) Detached leaves without pathogen treatment.
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MDPI and ACS Style

Xiang, Y.-X.; Zhou, J.; Li, Z.; Liu, H.-F.; Deng, J.-X. Identification and Fungicide Control of Alternaria alternantherae Causing Leaf Spot on Celosia cristata and Alternanthera philoxeroides in China. Horticulturae 2026, 12, 750. https://doi.org/10.3390/horticulturae12060750

AMA Style

Xiang Y-X, Zhou J, Li Z, Liu H-F, Deng J-X. Identification and Fungicide Control of Alternaria alternantherae Causing Leaf Spot on Celosia cristata and Alternanthera philoxeroides in China. Horticulturae. 2026; 12(6):750. https://doi.org/10.3390/horticulturae12060750

Chicago/Turabian Style

Xiang, Ya-Xin, Jing Zhou, Zhi Li, Hai-Feng Liu, and Jian-Xin Deng. 2026. "Identification and Fungicide Control of Alternaria alternantherae Causing Leaf Spot on Celosia cristata and Alternanthera philoxeroides in China" Horticulturae 12, no. 6: 750. https://doi.org/10.3390/horticulturae12060750

APA Style

Xiang, Y.-X., Zhou, J., Li, Z., Liu, H.-F., & Deng, J.-X. (2026). Identification and Fungicide Control of Alternaria alternantherae Causing Leaf Spot on Celosia cristata and Alternanthera philoxeroides in China. Horticulturae, 12(6), 750. https://doi.org/10.3390/horticulturae12060750

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