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Article

Biological Characterization and Fungicide Sensitivity of Dactylobotrys graminicola Causing Oat Spikelet Rot in China

by
Ruifang Jia
,
Na Wang
,
Zhengqiang Chen
,
Shengze Wang
,
Kejian Lin
* and
Yuanyuan Zhang
*
Key Laboratory of Artificial Grassland Biohazard Monitoring and Green Prevention and Control, Ministry of Agriculture and Rural Affairs, Institute of Grassland Research, Chinese Academy of Agricultural Sciences, Hohhot 010010, China
*
Authors to whom correspondence should be addressed.
Agronomy 2024, 14(10), 2314; https://doi.org/10.3390/agronomy14102314
Submission received: 12 June 2024 / Revised: 19 September 2024 / Accepted: 25 September 2024 / Published: 9 October 2024
(This article belongs to the Section Pest and Disease Management)
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Versions Notes

Abstract

:
Oat (Avena sativa) is a significant cereal crop that is extensively cultivated in temperate regions and is suitable for growth at higher elevations. The damage degree and epidemic area of oat spikelet rot caused by Dactylobotrys graminicola are generally increasing and spreading. Mycelium growth rate method was used to identify biological characteristics and in vitro fungicide screenings of D. graminicola. The results show that sorbitol and casein tryptone were the best carbon and nitrogen source for the D. graminicola, respectively. The optimal temperature for mycelium growth and conidia production of the D. graminicola was 20 °C; meanwhile, an acidic environment was shown to be conducive to mycelia growth, and alkaline facilitated conidia production. Among the ten tested fungicides, 20% Pydiflumetofen showed the best inhibition rate, with an EC50 (concentration for 50% of maximal effect) value of 0.005 mg/L; 30% Difenoconazole Propiconazole and 35% Metalaxyl-M Fludioxonil also showed sufficient inhibitory effects against D. graminicola, with EC50 value of 0.05 mg/L and 0.04 mg/L. Furthermore, we used artificial inoculation to determine the effectiveness of fungicide control in field, Trifloxystrobin 10%-Tebuconazole 20% with more than 90% control effectiveness, followed by 20% Pydiflumetofen. The results of this study not only revealed the biological characteristics of D. graminicola, but also provided effective candidate fungicides for the prevention and control of oat spikelet rot disease.

1. Introduction

Oat (Avena sativa) belongs to the poaceae family, which is the sixth most important widely grown cereal crop in the world [1], with high nutritional value usually consumed as fodder and grains by livestock and human beings [2]. It has been broadly grown in northwest Europe, Australia, Russia, Canada, and China [3], between the latitudes of 40° N and 60° N. In recent years, the planting area of oat in China has been about 0.7 million hm2, providing a yield of 0.63 million tons [4], accounting for 2.8% of the total world output, with Chinese production ranked eighth worldwide. Yunnan province, Qinghai province, Gansu province, Inner Mongolia, and Tibet are the main oat production areas in China [5]. Rainfall in these areas is sparse and mainly concentrated in July to September. The occurrence of persistent rainfall during the harvest season leads to high humidity and high temperatures, which are important factors in the spread of oat diseases [6]. Oat spikelet rot (OSR) caused by D. graminicola was a new disease first reported in China in 2010 [7]; the disease occurs sporadically in the field in general, but in the heavily diseased field, the spikelet rot rate of it reaches 20 to 30% [8]. Under natural conditions, D. graminicola-infected host spikelets caused spikelet rot; meanwhile, infected wrapped spikelets flag leaf sheaths or inverted leaf sheaths to form a shuttle-shaped brown spot [9]. At present, the occurrence of spikelet rot caused by D. graminicola on Hordeum vulgare, Avena fatua, A. sativa, Triticum Aestivum, Secale cereale, and grass weeds in the high-altitude areas of Qinghai province, Gansu province, and Tibetin in China [10]. The complex host range makes it challenging to study the transmission pathways of the disease and develop effective prevention and control strategies.
Environment is one of the main factors of disease prevalence [11,12]; therefore, studying the relationship between biological characteristics of the pathogen and environmental factors is necessary. Due to the influence of environmental conditions, there are differences in the biological characteristics of different species or individuals of fungi [13,14]. Alpine pastoral areas are the main growing areas for oats, due to the sensitive environment, forming a unique habitat for plants and microbes. D. graminicola causes sheath rot of highland barley, which can survive for a long time under natural ecological conditions in high altitude and cold areas [15]. However, little is known about D. graminicola causing OSR.
Fungicides are widely screened and used to control oat disease [16]. Spraying fungicides are mainly used to control the major oat diseases, like rust, red leaf, and powdery mildew of oat in production [17,18,19,20]. Currently, the main strategy for controlling rust pathogens is the use of fungicides from the chemical groups of triazole and strobilurin [21]. Pre-seeding and foliar spraying treatment is the predominant chemical control of fungicides in oat red leaf management [22]. Triazole chemicals represented by triadimefon and difenoconazole are usually used in production to control powdery mildew of oats [23]. Over the last few years, the frequency of OSR epidemics has been substantially increasing and spreading in the alpine region of Qinghai-Tibet plateau of China [24]. However, previous studies indicated that only Mancozeb 70% and Carbendazim 50% were shown to be effective against barley sheath rot by inhibiting the mycelial growth of D. graminicola [15]. So far, there have been no reports of control measures for oat production areas and no reports of chemical fungicides to control OSR disease.
In addition, chemical control efficiency is strongly related to fungicide properties and pathogen resistance [25,26]. The screening of effective fungicides against pathogens isolated from a particular environment is needed. It is important to understand the biological characteristics of the pathogen as basic information of its disease epidemiology, as well as the sensitivity of local isolates to fungicides commonly used to control the disease. Our team found that OSR occurred to different degrees in Qinghai, Gansu, Yunnan, and Inner Mongolia, with incidence rates ranging from 5% to 25%, and we clarified that the pathogen was D. graminicola. The aim of the study was to assess the response of the pathogen to soil conditions and climatic factors, and to screen effective fungicides against the pathogen, in order to lay the foundation for the effective prevention and control of OSR disease.

2. Materials and Methods

2.1. Fungal and Antimicrobial Agents

Dactylobotrys graminicola GY-18 was collected from Shandan district, Zhangye city, Gansu, China. After being isolated and identified, it was stored at −80 °C in Key Laboratory of Artificial Grassland Biohazard Monitoring and Green Prevention and Control, Ministry of Agriculture and Rural Affairs. It was grown on Potato Dextrose Agar (PDA) for 24–48 h at 25 °C in dark conditions for further use. The 10 antimicrobial chemicals examined in this trial, with their common names and suppliers, are described in Table 1. All fungicides were purchased from Inner Mongolia Fusite Modern Agriculture Co., Hohhot, China. All chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China.

2.2. Biological Characterization of D. graminicola Strain GY-18 In Vitro

To determine the effect of temperatures on radial colony growth and spore production, strain GY-18 was inoculated on the PDA plate as described above, and then the colony was transferred to the central part of new PDA plate and placed in an incubator in the dark with the temperature set at one of the following values: 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C or 40 °C. After 7 days, the colony diameter (in millimeters) was measured using a Vernier caliper. The spores were eluted with 10 mL of sterile water, configured as spore suspension. The spore concentration was calculated using a Neubauer chamber. Three replicates were set up for each temperature treatment and the experiment was repeated three times.
To determine the effect of pH on mycelial growth and spore production, strain GY-18 was inoculated on the PDA plate as described above, and then the colony was transferred to the center of PDA plates with different pH values (4, 5, 6, 7, 8, 9, 10, 11) and placed in an incubator in the dark at 25 °C. Others were the same as above.
To determine the effect of carbon and nitrogen sources on mycelial growth and spore production, Czapek medium was used as the basal medium, and equal amounts of carbon (mannitol, xylose, soluble starch, sorbitol, carboxymethylcellulose sodium, inositol, fructose, glucose) or nitrogen (L-proline, ammonium chloride, glycine, casein tryptone, ammonium sulfate, potassium nitrate) sources were used to replace sucrose or sodium nitrate. Strain GY-18 was inoculated on the PDA plate as described above, then transferred to the center of the above medium and placed in an incubator in the dark at 25 °C. Others were as above.

2.3. Antimicrobial Activity to D. graminicola In Vitro

The employed fungicides were purchased from local distributors. The mycelial growth rate method was used to evaluate the antifungal activity of fungicides [27]. Different fungicides were dissolved in distilled water and then mixed with the PDA medium at different concentrations (Table 1). Afterward, a D. graminicola colony (with a diameter of 5 mm) was placed in the center of the PDA medium-containing plates and cultured at 25 °C for 7 days under dark conditions. Then, the colony diameter (mm) was measured using Vernier calipers. The rate of inhibition of mycelial growth of the pathogen per treatment was calculated.

2.4. Evaluation of Fungicides against Oat Spikelet Rot under Artificial Inoculation Conditions

The experiment was carried out at the grassland research institute’s experimental base in agricultural and animal husbandry intertwined areas, Chinese academy of agricultural sciences (Figure 1A). The test variety was Qinghai 444, which was obtained from the National Mid-Term Bank of Northern Forage Germplasm Resources, Hohhot, China. The seeding date was 13 June 2024. Drilling was carried out in rows spaced 50 cm apart, and the plot area was 25 m2. The experiment was set up with 11 treatments, and each treatment was set up with three randomly distributed replications, as shown in Figure 1B. During the oat booting stage, 100 oats were inoculated continuously using an injection inoculation method on 22 July 2024 (Figure 1C); two days after inoculation, a spray method was used to apply the fungicide and spray water as a control; refer to the fungicide label instructions for application rates (32.5% Difenoconazole Azoxystrobin 450 mL/ha, 30% Difenoconazole Propiconazole 450 mL/ha, 70% Mancozeb 2.25 kg/ha, 0.25% Fludioxonil 225 g/ha, 68% Metalaxyl-M Mancozeb 1.5 kg/ha, 20% Pydiflumetofen 750 mL/ha, 50% Kresoxim-methyl 225 mL/ha, 35% Metalaxyl-M Fludioxonil 450 mL/ha, 15% Triadimefon 900 g/ha, 10% Trifloxystrobin & 20% Tebuconazole 225 mL/ha). The number of diseased spikes was investigated at the oat filling stage, and the effectiveness of control was calculated based on the number of disease spikes.

2.5. Statistical Analysis

Mycelial growth inhibition/% = [(control colony growth diameter-treatment colony growth diameter)/control colony growth diameter] × 100. The logarithm of the set mass concentration was taken as the horizontal coordinate (x), and the probability value of the inhibition rate was taken as the vertical coordinate (y); the linear regression equation is y = a + bx, and the correlation coefficient r. The EC50 (concentration for 50% of maximal effect) values of different fungicides were calculated using Microsoft Excel 2003 and DPS V18.10 software.
Differences in the effects of temperature, pH, carbon, and nitrogen sources were analyzed using SPSS 17.0 software, and Duncan’s new complex range method was used to test the significance of differences.

3. Results

3.1. Effect of Temperature and pH

D. graminicola GY-18 was inoculated on PDA plates and placed on an incubator under different temperature conditions for 7 days. The results showed that GY-18 was able to grow in the temperature range of 10–30 °C (Figure 2A), but it has significant differences in colony diameters (Figure 3). GY-18 grew slowly at 10 °C and 30 °C, while the fastest growth rate was observed at 20 °C, with the average colony diameter reaching 77.35 mm. The growth rate was significantly different compared with other temperatures (p < 0.05). When the temperature reached 25 °C, mycelial growth began to be inhibited, and the average colony diameter was reduced to 66.66 mm, the growth of GY-18 completely stopped at temperatures lower than 5 °C and higher than or equal to 35 °C. By counting the number of spores, the results show that GY-18 was able to produce spores normally in the temperature range of 10 °C to 25 °C. Therefore, the optimum growth temperature of GY-18 was 20 °C, and temperatures that are too low or too high would inhibit its growth and spore production.
The results of the 7-day incubation of GY-18 under different pH conditions showed that it grew well in the range of pH 4–11, and there were differences in colony diameters under different pH conditions (Figure 2B and Figure 3), among which the average colony diameters of pH 4, 5, 6, and 7 could reach 57.07 mm, 55.10 mm, 55.48, and 54.61 mm. These were significantly different (p < 0.05) compared to the other pH conditions. At pH 4, the spore production of GY-18 was 5 × 104 spores/mL, indicating that acidic conditions are more favorable for the growth of GY-18, while alkaline conditions are good for GY-18 sporulation.

3.2. Utilization of Different Carbon and Nitrogen Sources

To exploring the utilization of carbon and nitrogen sources by GY-18, it was found that GY-18 could grow in all nine carbon and seven nitrogen source mediums supplied for testing (Figure 2C and Figure 4), and there were significant differences in the efficiency of utilization of different carbon and nitrogen sources. In the medium with inositol as a carbon source, the mycelial growth of strain GY-18 was faster, with an average colony diameter of 73.84 mm. This is a significant difference compared with other carbon source treatments (p < 0.05), followed by mannitol and sorbitol, with average colony diameters of 70.11 mm and 71.48 mm. The slowest growth was observed in the medium with carboxymethylcellulose sodium as a carbon source, with an average colony diameter of only 8.68 mm. Strain GY-18 was able to produce spores when soluble starch, sorbitol, fructose, and glucose were used as carbon sources. Therefore, strain GY-18 utilized sorbitol the best, but it was not able to utilize sodium carboxymethylcellulose as a carbon source.
The results of the growth measurement of GY-18 under different nitrogen source conditions showed that on the medium with casein tryptone as the nitrogen source, the mycelium of strain GY-18 was dense and grew fastest (Figure 2D and Figure 4), with an average colony diameter of 56.25 mm. On the medium with ammonium sulfate as the nitrogen source, the growth of GY-18 was the slowest, with an average colony diameter of 31.95 mm. Strain GY-18 did not produce spores on the medium treated with sodium nitrate and potassium nitrate as the nitrogen source, while strain GY-18 could produce spores in the rest of the nitrogen source treatments, and the largest amount of spores was produced in the casein tryptone treatment with a spore production rate of 2 × 105 spores/mL, which was significantly different from that of the other nitrogen source treatments (p < 0.05). Therefore, strain GY-18 had the best utilization of casein tryptone.

3.3. Fungicide Assays

D. graminicola showed different sensitivity to the ten selected fungicides (Figure 5). The growth of D. graminicola was significantly inhibited in vitro by ten agents, and this inhibitory effect was enhanced with the increase in concentrations. Among the ten tested fungicides, PYD (Pydiflumetofen) showed the highest inhibition rate, with an EC50 (concentration for 50% of maximal effect) value of 0.005 mg/L. This was followed by DP (Benzalconazole) and MMM (Metalaxyl-M Fludioxonil), which also showed an inhibitory effect against D. graminicola, with EC50 values of 0.05 mg/L and 0.04 mg/L, respectively. Moderate effects were observed with TT (Trifloxystrobin-Tebuconazole), FLU (Fludioxonil), and DP (Benzalconazole), which showed EC50 values of 0.25 mg/L, 0.31 mg/L, and 0.75 mg/L, respectively. In contrast, MAN (Mancozeb) and MMM (Metalaxyl-M mancozeb) showed low inhibition rates against D. graminicola with EC50 values of 8.28 mg/L and 13.96 mg/L, respectively. WP (Triadimefon) and KM (Kresoxim-methyl) showed the lowest EC50 values of 46.06 mg/L and 189.23 mg/L, respectively. Moreover, according to the regression equation, the slope of MMM was the largest at 8.3689, and that of KM was the smallest at 2.0665. This indicated that D. graminicola was the utmost sensitive to MMM and the least sensitive to KM (Table 2).

3.4. Efficacy Assays

A week before oat maturity, we investigated the effectiveness of different agents against spikelet rot of oat. It is clear that 10 fungicides have different preventive effects on OSR, among which 10% Trifloxystrobin-20% Tebuconazole (TT) has the highest preventive effect at 90.66%, followed by 20% Pydiflumetofen (PYD) at 88.52%. 32.5% Difenoconazole Azoxystrobin (DA), 20% Pydiflumetofen (PYD), 50% Kresoxim-methyl (KM), 15% Triadimefon (TRI), and 10% Trifloxystrobin-20% Tebuconazole (TT) showed more than 80% efficiency in preventing OSR in the field, which was significantly different from other fungicides at the 0.05 level. The efficacy of four fungicides, 30% Difenoconazole Propiconazole (DP), 70% Mancozeb (MAN), 68% Metalaxyl-M Mancozeb (MMM), and 35% Metalaxyl-M Fludioxonil (MMF), for the control of OSR in the field was from 65 to 75%. Fludioxonil (FLU) has the lowest preventive effect at only 56.42% (Table 3).

4. Discussion

The environment and nutritional factors where the plant is grown affects the growth of pathogens, which indirectly affects the development of the disease [11]. Low air temperature was previously shown to increase plant disease severity [28]. In this study, we characterized the influence of temperature on the pathogen, D. graminicola GY-18, mycelium growth, and sporulation quantity, and found that 15~20 °C was its optimal temperature range. This is consistent with Wang’s research on the optimal growth temperature of D. graminicola Gan-1131 isolated from barley. This shows that GY-18 is a cool-loving pathogen, and high altitudes and low temperatures may be more suitable for the spread and infection of GY-18. Oat and barley happen to be important nutritional resources in the alpine region of the Qinghai-Tibet plateau of China [29], which may be one of the reasons why oats are infected with D. graminicola. We also found that GY-18 has strong adaptability to different pH conditions, but it is more conducive to sporulation in alkaline environments, which may be related to the pH of the soil where the strain originated, such as the pH of soil in Shandan, Gansu province, which ranges from 8.5 to 9 [30]. Therefore, we suggest avoiding soil physicochemical imbalances caused by the long-term application of single fertilizers or long-term continuous cropping during oat cultivation. Carbon and nitrogen sources are fundamental components of microbial cell structure and are important functional nutrients [31]. In the interaction process between plants and pathogens, nitrogen becomes the target of competition between plants and pathogens [32]. In our study, GX-18 showed differences in the utilization of carbon and nitrogen sources. On PDA culture media with ammonium sulfate and ammonium chloride as nitrogen sources, the growth of GY-18 mycelium is significantly inhibited, indicating that GY-18 has a low utilization rate of ammonium sulfate and ammonium chloride. Ammonium sulfate and ammonium chloride are often used as nitrogen and phosphorus fertilizers [33], and the supply of nitrogen also has advantages and disadvantages in affecting diseases. When the nitrogen content is low, the sensitivity of tomato wilt disease bacteria increases [34], while high nitrogen conditions can also make plants highly sensitive to diseases [35]. The growth measurement results of GY-18 under different nitrogen source conditions indicated that the growth of GY-18 was significantly inhibited on the culture media of ammonium sulfate and ammonium chloride. Therefore, in the oat fields affected by GY-18 in the Gannan region of China, the fertilizer application rates with ammonium sulfate and ammonium chloride as the main nitrogen sources should be considered. Gautier [36] found that external carbon sources could alter the biosynthesis of fungal mycotoxins. Previous studies have found that with an increase in carbon dioxide, the nutritional content of disease-resistant wheat varieties changes significantly, including protein, starch, phosphorus, and magnesium [37]. In our study, we found that not all tested carbon sources supported mycelium growth and conidia production. GY-18 showed higher mycelium growth on sorbitol and more conidia production on fructose than on other carbon resources. For future studies, it will be important to investigate how other carbon resources influence the disease prevalence and to explore how they could be considered in oat breeding to provide new solutions for sustainable management of the disease.
Chemical control is one of the main measures for the prevention and control of oat disease [22]. Therefore, we conducted an in vitro screening of potentially effective fungicides against D. graminicola GY-18 (Figure 5). Among the ten tested pesticides, PYD, DP, and MMF which had mixtures of two components showed the higher inhibition rates, with EC50 values of 0.005, 0.040, and 0.050 mg/L, respectively. However, the control effect of DP and MMF on oat spikelet rot in field trials was average, indicating that the fungicides have a strong inhibitory effect on the pathogen under indoor conditions, but the control effect and the performance of the fungicides also have a great relationship [25], so the subsequent application of fungicides in the field, such as the concentration and the number of sprays, needs to be carried out in a more detailed study. Compared with DA and DP, whose active ingredients all include difenoconazole, the difference in the other active ingredients made a significant difference in the results of their trials in the field. While we still need further validation in the field, traditional chemical mancozeb showed moderate antibacterial effects against GY-18; the results were in accordance with previous studies which showed that mancozeb is effective against the barley sheath rot causal agent D. graminicola [15]. Except for mancozeb, for the other nine fungicides, no reports are available yet regarding their effects on OSR isolates.
Environmental factors may contribute to fungal resistance to fungicides [10]. Considering that the strains described in this study come from high-altitude and low-temperature environments, their biological characteristics and fungicide resistance may be different from other strains from other cultivation areas. Therefore, further studies are needed on the relationship and/or correlation between host disease incidence, control effectiveness, biological characteristics of pathogens at different locations, and the development of fungicide resistance. Overall, our study provides new insights into the occurrence of OSR in the region of the Qinghai-Tibet plateau, as well as D. graminicola biological characteristics and promising candidate fungicides for its management. As discussed above, further studies will be needed to develop effective and sustainable control approaches against OSR.

5. Conclusions

Oat spikelet rot is a new disease discovered this year and is gradually increasing in geographic distribution and severity of impact. We studied the adaptability of D. graminicola to nine different carbon sources and seven different nitrogen sources. Sorbitol and casein tryptone were identified as the optimal carbon and nitrogen sources for D. graminicola in this study. The ideal temperature for mycelial growth and conidium production was determined to be 20 °C. This indicated that low temperatures are more favorable for the spread of D. graminicola. Meanwhile, the results showed that D. graminicola grew faster under acidic conditions, and spore production was greater under alkaline conditions. Among the fungicides tested, 20% Pydiflumetofen exhibited the strongest inhibitory effect, followed by 30% Difenoconazole Propiconazole and 35% Metalaxyl-M Fludioxonil. Trifloxystrobin 10% & Tebuconazole 20% showed more than 90% control of oat spikelet rot after artificial inoculation with D. graminicola in the field. These findings not only shed light on the environmental conditions suitable for the growth and spread of D. graminicola, but also present potential fungicide options for managing oat spikelet rot.

Author Contributions

Conceptualization, Y.Z. and K.L.; methodology, R.J. and N.W.; software, R.J. and Z.C.; validation, Y.Z., K.L., N.W. and R.J.; formal analysis, N.W. and Z.C.; investigation, R.J., N.W. and S.W.; resources, Y.Z.; data curation, R.J.; data analysis, S.W.; data interpretation, S.W.; writing—original draft preparation, R.J.; writing—review and editing, R.J., Z.C. and Y.Z.; visualization, R.J.; supervision, K.L.; project administration, Y.Z.; funding acquisition, K.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Natural Key Research and Development Program of China (2022YFD1300802) and the Natural Science Foundation of Inner Mongolia Autonomous Region (2024QN03080).

Data Availability Statement

The data are contained within the article; further inquiries may be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Determination of efficacy of different fungicides against spikelet rot of oat in the field using artificial inoculation methods. Diseased nursery oat experimental area of grassland research institute’s experimental base in agricultural and animal husbandry intertwined areas (A). Experimental plot (25 m × 1 m): the red color represents the position where 100 oats were inoculated in a row; the reds are spaced 1 m apart (B). Oat inoculation period (C).
Figure 1. Determination of efficacy of different fungicides against spikelet rot of oat in the field using artificial inoculation methods. Diseased nursery oat experimental area of grassland research institute’s experimental base in agricultural and animal husbandry intertwined areas (A). Experimental plot (25 m × 1 m): the red color represents the position where 100 oats were inoculated in a row; the reds are spaced 1 m apart (B). Oat inoculation period (C).
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Figure 2. Effects of temperature, pH, carbon, and nitrogen resources on mycelium growth and sporulation capacity of D. graminicola GY-18. Colonial growth diameter and sporulation capacity at different temperatures (A). Colonial growth diameter and sporulation capacity with different pH (B). Colonial growth diameter and sporulation capacity with different carbon resources (C). Colonial growth diameter and sporulation capacity with different nitrogen resources (D). The bar means colony diameter; the dark spot means the number of conidia. Lowercase letters above the bar indicate significant differences (p < 0.05) among colony diameter; lowercase letters to the right of the black bar indicate significant differences (p < 0.05) among sporulation capacity. Data are mean ± SD (n = 3).
Figure 2. Effects of temperature, pH, carbon, and nitrogen resources on mycelium growth and sporulation capacity of D. graminicola GY-18. Colonial growth diameter and sporulation capacity at different temperatures (A). Colonial growth diameter and sporulation capacity with different pH (B). Colonial growth diameter and sporulation capacity with different carbon resources (C). Colonial growth diameter and sporulation capacity with different nitrogen resources (D). The bar means colony diameter; the dark spot means the number of conidia. Lowercase letters above the bar indicate significant differences (p < 0.05) among colony diameter; lowercase letters to the right of the black bar indicate significant differences (p < 0.05) among sporulation capacity. Data are mean ± SD (n = 3).
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Figure 3. Mycelial growth of D. graminicola GY-18 on PDA plates incubated for 7 days under different temperature and pH. ((A1): 5 °C, (A2): 10 °C, (A3): 15 °C, (A4): 20 °C, (A5): 25 °C, (A6): 30 °C, (A7): 35 °C, (A8): 40 °C; (B1): pH = 4, (B2): pH = 5, (B3): pH = 6, (B4): pH = 7, (B5): pH = 8, (B6): pH = 9, (B7): pH = 10, (B8): pH = 11).
Figure 3. Mycelial growth of D. graminicola GY-18 on PDA plates incubated for 7 days under different temperature and pH. ((A1): 5 °C, (A2): 10 °C, (A3): 15 °C, (A4): 20 °C, (A5): 25 °C, (A6): 30 °C, (A7): 35 °C, (A8): 40 °C; (B1): pH = 4, (B2): pH = 5, (B3): pH = 6, (B4): pH = 7, (B5): pH = 8, (B6): pH = 9, (B7): pH = 10, (B8): pH = 11).
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Figure 4. Mycelial growth of D. graminicola GY-18 on different carbon and nitrogen resource plates incubated for 7 days. ((A1): mannitol, (A2): xylose, (A3): sucrose, (A4): soluble starch, (A5): sorbitol, (A6): carboxymethylcellulose sodium, (A7): inositol, (A8): fructose, (A9): glucose, (B1): L-proline, (B2): ammonium chloride (B3): sodium nitrate, (B4): glycine, (B5): casein tryptone, (B6): ammonium sulfate, (B7): potassium nitrate).
Figure 4. Mycelial growth of D. graminicola GY-18 on different carbon and nitrogen resource plates incubated for 7 days. ((A1): mannitol, (A2): xylose, (A3): sucrose, (A4): soluble starch, (A5): sorbitol, (A6): carboxymethylcellulose sodium, (A7): inositol, (A8): fructose, (A9): glucose, (B1): L-proline, (B2): ammonium chloride (B3): sodium nitrate, (B4): glycine, (B5): casein tryptone, (B6): ammonium sulfate, (B7): potassium nitrate).
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Figure 5. Mycelial growth of D. graminicola GY-18 on PDA plates incubated for 7 days in the absence (CK) or presence of different concentrations of antimicrobial agents (10 antimicrobial agents in order from (A–J): DA, DP, MAN, FLU, MMM, PYD, KM, MMF, TRI, and TT. The last column is CK, and 1–5 were different concentrations (see Table 1 for details of the antimicrobial agent concentrations).
Figure 5. Mycelial growth of D. graminicola GY-18 on PDA plates incubated for 7 days in the absence (CK) or presence of different concentrations of antimicrobial agents (10 antimicrobial agents in order from (A–J): DA, DP, MAN, FLU, MMM, PYD, KM, MMF, TRI, and TT. The last column is CK, and 1–5 were different concentrations (see Table 1 for details of the antimicrobial agent concentrations).
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Table 1. The chemicals tested for antimicrobial activity against Dactylobotrys graminicola.
Table 1. The chemicals tested for antimicrobial activity against Dactylobotrys graminicola.
Fungicide NameAbbreviationFormulationRegistration NumberPlate Concentration (mg/L)
32.5% Difenoconazole AzoxystrobinDASCPD2015070710, 1, 0.1, 0.01, 0.001
30% Difenoconazole PropiconazoleDPECPD202113850.625, 0.125, 0.025, 0.005, 0.001
70% MancozebMANWPPD2006017924, 12, 6, 3, 1.5
0.25% FludioxonilFLUSDPD201500990.540, 0.18, 0.06, 0.02, 0.007
68% Metalaxyl-M MancozebMMMWGPD2008084632, 16, 8, 4, 2
20% PydiflumetofenPYDSCPD202200350.081, 0.027, 0.009, 0.003, 0.001
50% Kresoxim-methylKMWGPD200701241.62, 0.54, 0.18, 0.06, 0.02
35% Metalaxyl-M FludioxonilMMFSDPD201711390. 128, 0.064, 0.032, 0.016, 0.008
15% TriadimefonTRIWPPD20040283160, 80, 40, 20, 10
10% Trifloxystrobin
&20% Tebuconazole		TTSCPD2018432310, 1, 0.1, 0.01, 0.001
Table 2. Toxicity of 10 antimicrobial agents to D. graminicola on nutrient agar plates.
Table 2. Toxicity of 10 antimicrobial agents to D. graminicola on nutrient agar plates.
Agent aEC50 (mg/L)Regression Equation bR2
DA0.750 y = 0.54x + 5.06730.986
DP0.050 y = 0.7178x + 5.93920.977
MAN8.280 y = 1.176x + 3.91970.950
FLU0.310 y = 0.7056x + 5.36170.999
MMM13.960 y = 1.073x +3.77080.996
PYD0.005 y = 1.3237x + 8.09040.958
KM189.230 y = 1.2884x + 2.06650.916
MMF0.040 y = 2.323x + 8.36890.988
TRI46.060 y = 1.5726x + 2.38430.984
WT0.250 y = 0.4121x + 5.24740.998
a See Table 1 for details of antimicrobial agents. b x, concentration of antimicrobial agent; y, bacteriostatic rate.
Table 3. Efficacy of 10 agents for the control of spikelet rot of oats.
Table 3. Efficacy of 10 agents for the control of spikelet rot of oats.
Agent aDisease Spikelet Incidence (%)Control Effects (%)
DA8.05 ± 1.70 d87.39 ± 2.27 a
DP16.67 ± 4.61 c73.93 ± 6.36 b
MAN22.00 ± 6.00 c65.43 ± 9.09 b
FLU27.67 ± 7.77 b56.41 ± 12.45 c
MMM21.00 ± 4.36 c67.12 ± 5.66 b
PYD7.33 ± 1.15 d88.52 ± 1.28 a
KM8.00 ± 2.00 d87.42 ± 3.03 a
MMF19.67 ± 4.04 c69.24 ± 5.02 b
TRI10.33 ± 2.51 d83.84 ± 3.45 a
TT6.00 ± 2.00 d90.66 ± 2.72 a
Water63.67 ± 3.21 a-
a See Table 1 for details of antimicrobial agents. The letters in the control effects column indicate significant differences (p < 0.05) among different fungicide efficacies. Data are mean ± SD (n = 3).
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Jia, R.; Wang, N.; Chen, Z.; Wang, S.; Lin, K.; Zhang, Y. Biological Characterization and Fungicide Sensitivity of Dactylobotrys graminicola Causing Oat Spikelet Rot in China. Agronomy 2024, 14, 2314. https://doi.org/10.3390/agronomy14102314

AMA Style

Jia R, Wang N, Chen Z, Wang S, Lin K, Zhang Y. Biological Characterization and Fungicide Sensitivity of Dactylobotrys graminicola Causing Oat Spikelet Rot in China. Agronomy. 2024; 14(10):2314. https://doi.org/10.3390/agronomy14102314

Chicago/Turabian Style

Jia, Ruifang, Na Wang, Zhengqiang Chen, Shengze Wang, Kejian Lin, and Yuanyuan Zhang. 2024. "Biological Characterization and Fungicide Sensitivity of Dactylobotrys graminicola Causing Oat Spikelet Rot in China" Agronomy 14, no. 10: 2314. https://doi.org/10.3390/agronomy14102314

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