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Article

Influence of pH on the Growth of Verticillium longisporum and Verticillium Stripe Severity in Canola (Brassica napus)

by
Yixiao Wang
,
Stephen E. Strelkov
* and
Sheau-Fang Hwang
*
Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2P5, Canada
*
Authors to whom correspondence should be addressed.
Horticulturae 2024, 10(6), 554; https://doi.org/10.3390/horticulturae10060554
Submission received: 3 May 2024 / Revised: 20 May 2024 / Accepted: 23 May 2024 / Published: 25 May 2024
(This article belongs to the Section Plant Pathology and Disease Management (PPDM))
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Abstract

:
Verticillium stripe, caused by Verticillium longisporum, is an emerging disease of canola (Brassica napus) in Canada. Studies were conducted to assess the impact of pH on both the growth of V. longisporum and its virulence on the canola host. Fungal growth was assessed by measuring the colony diameter following 14 and 21 days of incubation on potato dextrose agar at varying pH levels (4.7, 5.5, 6.5, 7.4, or 8.6). The results indicated that colonies of V. longisporum were approximately 16% greater in diameter at pH 7.4 and 8.6 compared with those at pH 5.5. The impact of pH on disease development at the seedling stage was investigated using a semi-hydroponic system with different pH levels of 4.4, 5.4, 6.3, 7.5, and 8.4 in half-strength Hoagland’s solution. Verticillium stripe was most severe at pH 7.5 and 8.4 after a 10-day period in the semi-hydroponic system. In a second inoculation experiment, canola seedlings previously inoculated with the fungus were transplanted into potting mix amended to four pH levels (5.6, 6.4, 7.2, and 7.8). The transplants were cultivated under greenhouse conditions and evaluated for Verticillium stripe severity at plant maturity. Disease severity was greatest at pH 7.8. This is the first study on the effects of pH on V. longisporum in canola. It suggests a substantial risk of increased disease severity and yield losses due to Verticillium stripe in regions with neutral to slightly alkaline soils.

1. Introduction

Verticillium longisporum (C. Stark) Karapapa, Bainbridge and Heale is the causal agent of Verticillium stripe, an emerging disease of canola (Brassica napus L.) in Canada. It was first identified in Manitoba in 2014 [1]. A national survey conducted by the Canadian Food Inspection Agency (CFIA) confirmed its presence in other provinces, including British Columbia, Alberta, Saskatchewan, Ontario, and Quebec [1]. Mature plants infected with V. longisporum typically exhibit unilateral streaking, peeling of the stem tissues, and the appearance of microsclerotia [2]. Yield losses attributed to V. longisporum have been reported to range from 10% to 50% [3]. The growing prevalence and incidence of Verticillium stripe across western Canada [4] have generated increasing concern in the canola sector. Given that the survival structures (microsclerotia) of V. longisporum can persist in soil for over 10 years [2], effective disease management strategies include minimizing soil movement, sanitizing field equipment, and implementing longer rotations without host crops. Such practices are not always practical, however, especially in the large acreage canola cropping systems of western Canada. Moreover, since no chemical controls or resistant canola cultivars are available [3], managing Verticillium stripe presents significant challenges.
Phenotypic diversity in the V. longisporum fungus is influenced by various parameters, including ambient temperature, relative humidity, and substrate or growing medium pH. Variations in these factors can affect the fungal growth rate, the pathogenicity, and, potentially, the disease incidence [5]. The pH of the soil can play an important role in the development of soilborne pathogens, influencing the severity of disease. For example, Sclerotinia stem rot (Sclerotinia sclerotiorum (Lib.) de Bary) is affected by pH in liquid media, with acidic conditions favoring sclerotium development [6]. Similarly, studies on Rhizoctonia solani J.G. Kühn have shown that its optimal growth pH is 6.0 [7]. The clubroot of canola, caused by the rhizarian parasite Plasmodiophora brassicae Wor., is favored in acidic soils [8]. While an increased temperature generally promotes mycelial growth in some Verticillium species [9], the effects of pH appear to be more variable [10,11,12]. For example, Verticillium dahliae Kleb. was reported to cause accelerated wilt symptoms on cotton at higher pH levels [13], while another isolate from pumpkins showed larger colony diameters at pH 5.2 [12]. The growth of V. alfalfae Inderb., H.W. Platt, Bostock, R.M. Davis & Subbarao, the cause of Verticillium wilt of alfalfa, was greatest at pH 6.0 [14]. While the effects of pH on other Verticillium species have been studied, little information is available regarding the pH sensitivity of V. longisporum and its impact on disease development in canola. An improved understanding of how pH influences this fungus and its pathogenicity could assist growers in implementing effective management strategies for Verticillium stripe. Therefore, the objectives of the current study were to: (i) evaluate the effects of pH on the radial growth of V. longisporum in vitro, (ii) assess the effects of pH on Verticillium stripe development at the seedling stage under semi-hydroponic conditions, and (iii) determine the effects of pH on Verticillium stripe severity and yield in canola at maturity under controlled environmental conditions.

2. Materials and Methods

2.1. Effects of pH on In Vitro Fungal Growth

A single-spore isolate VL43 of V. longisporum [15] was grown in Petri dishes (9 cm diam.) filled with potato dextrose agar (PDA). The cultures were incubated under darkness at room temperature (23 °C) for 28 days. A 5 mm diam. plug of a developing colony was transferred to the center of a 9 cm diam. Petri dish containing PDA amended to pH 4.7, 5.5, 6.5, 7.4, or 8.6. The pH value of the full-strength PDA medium was 5.5 ± 0.10. The medium at different pH values was prepared by adding 0.072 M HCl solution (pH 4.7 ± 0.01) or 0.1 M NaOH solution (pH 6.5 ± 0.02, 7.4 ± 0.01, and 8.6 ± 0.03), as necessary. The Petri dishes were incubated in darkness at room temperature. At day 14 and day 21, two measurements of colony diameter (growth) were taken at right angles to each other using a digital caliper. The average of the two measurements, minus the 5 mm diam. of the original agar plug, was then calculated. The experiment was arranged in a completely randomized design with five replicates (Petri dishes) per treatment and was repeated independently.

2.2. Effects of pH on Verticillium Stripe Severity under Semi-Hydroponic Conditions

Fungal cultures grown as described above were utilized to harvest conidial suspensions. Briefly, 10 mL of sterile distilled water was added to each Petri dish, and spores were gently dislodged using a sterile inoculating loop [15]. The spore suspension was then filtered through four layers of sterile cheesecloth to remove larger mycelial fragments. The concentration of conidia was estimated with a haemocytometer (Hausser Scientific, Horsham, PA, USA) and adjusted to 1 × 106 spores mL−1 with sterile distilled water.
Seeds of the V. longisporum-susceptible canola cultivar ‘Westar’ were placed on moistened filter paper in Petri dishes for 10 days to allow for germination. Roots of 10-day-old seedlings were soaked in a conidial suspension for 2 h. Non-inoculated controls were soaked in sterile water instead. After inoculation, 10 seedlings were placed on germination paper that had been moistened with half-strength Hoagland’s solution (pH 5.4 ± 0.15) or half-strength Hogland’s solution, the pH of which had been adjusted to 4.4 ± 0.14, 6.3 ± 0.12, 7.5 ± 0.12, or 8.4 ± 0.22 using 0.072 M HCl or 0.1 M NaOH. The paper with the seedlings was rolled up and tied with an elastic band in the middle of each roll [16]. Four rolls were placed in a 2 L glass beaker containing 1.5 L of the respective half-strength Hoagland’s solution. Inoculated and non-inoculated seedling rolls were placed in separate beakers. To prevent disease escapes, an additional 5 mL of the conidial suspension was added to the Hogland’s solution in each beaker for the inoculated treatments. The beakers were then incubated for 10 days in a growth cabinet at 28 °C with a 16 h photoperiod. The experiment was arranged in a split-plot design and repeated independently.
After 10 days of growth in the semi-hydroponic system, the seedlings were evaluated for disease severity using a 0 to 4 scale, where 0 = no symptoms and a normal root system; 1 = slight brown discoloration between the stem and root and reduced root size; 2 = a damaged stem, brown discoloration between the stem and root, and a reduced root size; 3 = a severely stunted seedling and minimal root development; and 4 = a dead seedling (Figure 1). In addition, the plant height was measured using a ruler, and the total plant biomass was determined by weighing on a balance.

2.3. Effects of pH on Verticillium Stripe Severity and Yields at Maturity

The effect of pH on Verticillium stripe severity and canola yields at maturity was assessed in a greenhouse using Sunshine Mix #4 growing mix (Sun Gro Horticulture, Vilna, AB, Canada) at various pH levels. Initially, the growing mix had a pH of 6.5 ± 0.24, which was adjusted by either adding 0.1 M HCl with a watering can to reduce it to 5.6 ± 0.27 or by incorporating hydrated lime (Graymont, Richmond, BC, Canada) to raise it to pH 7.2 ± 0.21 and 7.8 ± 0.16. The pH adjustments were performed on 40 L aliquots of the growing mix at a time, followed by thorough mixing in 53 L plastic tubs. Afterward, the original and pH-amended growing mixtures were stored for 7 days to ensure pH stability and then used to fill 0.38 L plastic pots for use in the experiments. Ten-day-old canola ‘Westar’ seedlings were inoculated with V. longisporum by dipping the roots in a conidial suspension (1 × 106 spores mL−1) for 2 h, as described above, and planted into the different pH potting mixtures at a density of one seedling per pot. The experiment was arranged in a split-plot design. Each treatment included four replicates consisting of 10 plants (pots) per replicate. The layout for the non-inoculated controls mirrored this arrangement. The greenhouse study was repeated independently.
Verticillium stripe severity was evaluated at plant maturity on a 0 to 4 scale, based on the amount of fungal microsclerotia on the entire plant, as described by Wang et al. [17]. Briefly, a rating of 0 = healthy plants with no microsclerotia visible; 1 = slight colonization by microsclerotia < 25%; 2 = moderate colonization by microsclerotia ≥ 25% to <75%; 3 = extensive colonization by microsclerotia ≥ 75%; 4 = severe colonization by microsclerotia and peeling of the stem epidermis. The plant height was measured using a ruler, as above. The seeds were harvested manually and weighed on a scale, with yields calculated for each replicate (10 plants).

2.4. Statistical Analysis

The data were analyzed with R v. 4.2.3: A Language and Environment for Statistical Computing (R Core Team 2013). The pH values were considered as fixed effects, and replicates were random effects. Inoculated and non-inoculated plants, the pH levels, and their interactions were considered as fixed effects. Replications within inoculated and non-inoculated plants (whole-plots), replications within pH levels (split-plots), and inoculated and non-inoculated plant interactions were considered as random effects.

3. Results

3.1. Effects of pH on In Vitro Fungal Growth

The results of the two independent repeats of the experiment were pooled, since they were not significantly different. At both time-points examined, the pH showed significant effects (p < 0.001). The mean colony diameter ranged from 35.9 mm to 42.2 mm across the different pH conditions after 14 days of incubation (Figure 2). The greatest average diameter was 42.2 mm and 41.9 mm, observed at pH 7.4 and 8.6, respectively. This was followed by an average diameter of 38.1 mm and 37.9 mm at pH 4.7 and 6.5, respectively. The smallest colony diameter, 35.9 mm, was obtained at pH 5.5 (Figure 2). Similar trends were observed after 21 days of incubation. At this time, the mean fungal colony diameter ranged from 54.7 mm to 62.0 mm across all pH conditions (Figure 2). The greatest colony diameter was again observed at pH 7.4 (60.4 mm) and 8.6 (62.0 mm), while the lowest was found at pH 5.5 (53.0 mm) and 4.7 (54.7 mm) (Figure 2).

3.2. Effects of pH on Verticillium Stripe Severity under Semi-Hydroponic Conditions

The results of the two independent repeats of the experiment were combined, as they were not significantly different. The mean Verticillium stripe severity ranged from 0.72 to 2.10 at the seedling stage across the various pH treatments in the inoculated plants. As expected, no disease symptoms were observed on the non-inoculated controls (Table 1). The most severe symptoms, with severities of 2.10 and 1.91 respectively, were observed on seedlings grown in Hoagland’s solution at pH 7.5 and 8.4. At pH 6.3, an intermediate Verticillium stripe severity of 1.59 was obtained, whereas the mildest disease, with severities of 0.72 and 1.19, respectively, was observed at pH 5.4 and 4.4 (Table 1). The mean plant height for the non-inoculated controls ranged from 77 mm to 84 mm, with no significant differences detected. In contrast, the inoculated plants had heights ranging from 56 mm to 66 mm (Table 1). The mean biomass for the non-inoculated controls ranged from 0.22 g to 0.27 g, while for the inoculated plants, it ranged from 0.10 g to 0.15 g (Table 1).

3.3. Effects of pH on Verticillium Stripe Severity and Yields at Maturity

The results of the two independent repeats of this experiment were pooled, as they were not significantly different. The mean disease severity for the inoculated plants across all pH treatments at maturity ranged from 0.33 to 1.58, with no symptoms of Verticillium stripe observed on the non-inoculated controls (Table 2). The most severe symptoms, with a disease severity of 1.58, were obtained at pH 7.8, followed by intermediate severity (1.24) at pH 6.5 and 7.2. The lowest disease severity, with a mean of 0.33 on the 0–4 rating scale, was observed at pH 5.6. In the non-inoculated controls, the plant height ranged from 58.4 cm to 113 cm, with the tallest and shortest plants obtained at pH 7.8 and pH 5.6, respectively (Table 2). At pH 6.5 and 7.2, the plant height was intermediate (79.6 cm to 87.5 cm) (Table 2). In the inoculated treatments, the plant height ranged from 54.2 cm to 93.7 cm, with the shortest plants observed at pH 5.6. No significant differences were detected for height at pH 6.5, 7.2, or 7.8, with values ranging from 85.4 cm to 91.4 cm (Table 2). The mean seed yield for the non-inoculated plants ranged from 0.88 g to 1.66 g, with the highest seed yield observed at pH 7.8 and the lowest observed at pH 5.6 (Table 2). The mean seed yield for the inoculated plants ranged from 0.61 g to 0.79 g, but there were no statistically significant differences among the pH treatments. The seed yield in the inoculated treatments was significantly lower than that in the non-inoculated treatments at pH 6.5, 7.2, and 7.8 (Table 2).

4. Discussion

Fungi generally demonstrate a wide tolerance to pH variations, with their optimal growth pH typically ranging between 5.0 and 6.0 [18,19]. For instance, previous research indicated that Fusarium oxysporum Schlecht. emend. Snyder & Hansen performed best at pH 6.3 [5], while R. solani exhibited optimal mycelial growth at pH 5.6 across various media [20]. This study represents the first attempt to assess the effects of pH on V. longisporum under diverse conditions. The findings provide evidence that pH influences the growth of this fungus and its capacity to cause disease on canola. Notably, V. longisporum displayed significantly smaller colony diameters when the pH was <6.5, suggesting poorer growth under acidic conditions. Conversely, the fungus showed the fastest in vitro radial growth at pH 7.4 and 8.6, indicating a preference for neutral to alkaline conditions. This preference was consistent, at least when assessed after 14 and 21 days of incubation. Furthermore, the influence of pH was reflected in the disease severity observed on canola, both at the seedling and adult plant stages. The symptoms of infection generally became more pronounced as the pH increased.
Similar pH effects have been documented with V. dahliae. In a study involving antirrhinum plants, disease symptoms progressed from mild to severe as the pH increased from 3.5 to 9.5 following inoculation with this fungus [21]. Additionally, other studies using V. dahliae isolated from cotton plants demonstrated comparable results, showing increased fungal growth, microsclerotia production, and severity of disease symptoms in alkaline conditions [10,13,22]. Furthermore, the growth of V. dahliae on tomato was favored at pH 8 [11]. In contrast, V. dahliae isolates recovered from artichokes, pumpkins, and other hosts were reported to show an optimal pH for fungal growth of around pH 5 [12,23]. Given the broad host range of V. dahliae, which infects over 300 plant species [24], the varying effects of pH on the growth, microsclerotia formation, and pathogenicity of different isolates may be due to their diverse host origins. Verticillium longisporum has a narrower host range, with an apparent preference for species in the Brassicaceae family [25]. As such, isolates of this fungus may exhibit reactions to pH that are more consistent. Unfortunately, at the time that this study was conducted, very few V. longisporum isolates that had been recovered from canola in western Canada were available, and only one was included in this study. As the pathogen becomes more widespread, it may be informative to evaluate a large collection of isolates from different regions of the Canadian Prairies to test this hypothesis. Other Verticillium species, such as V. alfalfae [14] and V. albo-atrum [26], showed optimal growth and sporulation at pH 6.
The severe disease development observed on the canola seedlings across various treatments under semi-hydroponic conditions suggests the potential of this system for studying Verticillium stripe. This system, based on a recently published hydroponic assay designed for investigating root architectural traits [16], appears effective for V. longisporum research. Additionally, similar systems may prove suitable. For instance, a hydroponics-based method was employed to screen for Phytophthora root rot resistance in chickpea, allowing for the more accurate observation of early host responses to infection [27]. Considering the consistent results observed for in vitro fungal growth and disease development on canola under greenhouse and semi-hydroponic conditions in this study, the semi-hydroponic system may be a valuable tool for the high-throughput screening of multiple isolates and/or host genotypes. It has the advantage of requiring less time and space compared to pot-based methods in the greenhouse.
In the semi-hydroponic conditions, the seedling height did not vary significantly across different pH levels in the non-inoculated treatments, and no clear trends emerged in the height of inoculated seedlings. However, inoculated seedlings were consistently shorter than non-inoculated ones across all pH levels tested. Conversely, in the greenhouse study at maturity, the plant height was the lowest at pH 5.6, irrespective of the inoculation status. There was also no significant difference in height between the inoculated and non-inoculated treatments at this pH level. These observed effects of pH on the height of canola in the absence of inoculum may reflect the pH preferences of canola itself. Baquy et al. [28] found that the plant height decreased as the soil pH declined from pH 7 to 4. Indeed, in this study, the seed yield at maturity was not significantly different between the inoculated and control plants when grown at pH 5.6, while at pH 6.5–7.8, the inoculated treatments had significantly lower yields. This likely further reflects the interactions between the pH optimum of the crop itself and the effects of V. longisporum infection. The growth of plants in acidic soils might be reduced due to pH-related toxicities and/or nutrient deficiencies [28]. While the plant biomass was recorded only in the semi-hydroponic study at the seedling stage, it was significantly lower in the inoculated vs. non-inoculated treatments; Cui et al. [15] also reported that dry weight decreased when plants were infected with this fungus.
The collective findings of this study suggest that V. longisporum exhibits faster growth and induces more severe disease symptoms under neutral to alkaline conditions. However, the mechanism(s) by which pH influences the growth or pathogenicity of this fungus remain(s) unclear and requires further investigation. Van Wyk and Baard [29] reported an increase in the conidial germination of V. dahliae, from 0% to over 60%, as the soil pH rose from 3.8 to 7.9. A similar phenomenon may occur in V. longisporum, wherein heightened germination at higher pH levels contributes to heightened disease severity. Nonetheless, this hypothesis does not account for the greater mycelial growth with increasing pH levels observed in the in vitro experiments.
Regardless of the exact mechanism(s), the preference of V. longisporum for higher pH conditions observed in this study may help explain the higher prevalence of Verticillium stripe in Manitoba [30] relative to Saskatchewan and Alberta [31,32]. The soil in most regions of Manitoba is neutral to alkaline [33]. Meanwhile, the majority of the more than 3 million ha of cultivated soils in the Prairies with a pH < 6.0 are found in the eastern and southwestern regions of Saskatchewan, as well as in central and northern Alberta [34,35]. Conversely, the widespread distribution of clubroot, caused by P. brassicae, in Alberta has been attributed to the prevalence of lower-pH soils in many regions of the province. This pathogen is known to favor acidic soils [8]. These observations underscore potential conflicting best management practices for these diseases; treatments for increasing the soil pH for clubroot mitigation [36] may inadvertently exacerbate the Verticillium wilt severity due to the preferred pH range of the respective pathogens. Similarly, several other important soilborne diseases of canola, including Sclerotinia stem rot [6] and Fusarium wilt (F. oxysporum) [5], are also favored by acidic soils. These factors should be taken into consideration when developing an integrated crop protection plan for canola.
Studying the pH effects on V. longisporum could offer valuable insights for growers and agronomists in devising integrated management strategies not just for Verticillium stripe but potentially for other diseases as well. To date, Verticillium stripe has been identified in Europe [37,38], North America [2,39], and Asia [40], where another significant disease of crucifers, clubroot, is also frequently reported [41]. Since clubroot development is favored in acidic soils, liming to increase soil pH is often recommended as a method for controlling this disease [41,42,43,44]. However, liming should be reconsidered in fields or regions where Verticillium stripe or other diseases favored by alkaline environments are also an issue.
This study investigated the impact of pH on V. longisporum and Verticillium stripe development in canola under various controlled environmental conditions. While some studies have explored the effect of pH on V. dahliae, to our knowledge, this is the first report on the influence of pH on V. longisporum in canola. The findings of this study suggest that neutral to alkaline environments promote pathogen growth, resulting in more severe disease symptoms. The observation that pH can profoundly affect the growth and virulence of V. longisporum may be valuable for growers, highlighting the potential importance of this parameter in Verticillium stripe development. Future research, particularly under field conditions, could further enhance our understanding of the pH effects on V. longisporum, thus facilitating knowledge-based disease management strategies.

Author Contributions

Conceptualization, S.-F.H. and Y.W.; methodology, Y.W.; data curation, Y.W.; writing—original draft preparation, Y.W.; writing—review and editing, S.E.S.; supervision, S.-F.H. and S.E.S.; funding acquisition, S.-F.H. and S.E.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was made possible by support from the Canola Agronomic Research Program (Project No. 2024.43), funded by SaskCanola, Alberta Canola, the Manitoba Canola Growers Association, and the Western Grains Research Foundation (WGRF). In-kind support from the University of Alberta is also gratefully acknowledged.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Horticulturae 10 00554 g001
Figure 1. Scale for evaluating the disease severity of canola seedlings inoculated with Verticillium longisporum. The seedlings were evaluated on a 0 to 4 scale, where 0 = no symptoms and a normal root system; 1 = slight brown discoloration between the stem and root, a reduced root size; 2 = a damaged stem, brown discoloration between the stem and root and a reduced root size; 3 = a severely stunted seedling and minimal root development; and 4 = a dead seedling.
Figure 1. Scale for evaluating the disease severity of canola seedlings inoculated with Verticillium longisporum. The seedlings were evaluated on a 0 to 4 scale, where 0 = no symptoms and a normal root system; 1 = slight brown discoloration between the stem and root, a reduced root size; 2 = a damaged stem, brown discoloration between the stem and root and a reduced root size; 3 = a severely stunted seedling and minimal root development; and 4 = a dead seedling.
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Figure 2. Mean diameter of Verticillium longisporum colonies after 14 or 21 days of growth on potato dextrose agar (PDA) at different pH levels. Means with the same uppercase letter or lowercase letter are not significantly different based on Tukey’s method at p = 0.05. The error bars indicate the standard deviation of the mean across replicates.
Figure 2. Mean diameter of Verticillium longisporum colonies after 14 or 21 days of growth on potato dextrose agar (PDA) at different pH levels. Means with the same uppercase letter or lowercase letter are not significantly different based on Tukey’s method at p = 0.05. The error bars indicate the standard deviation of the mean across replicates.
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Table 1. Effect of Verticillium longisporum inoculation on canola seedling height, disease severity, and biomass at various pH levels under semi-hydroponic conditions.
Table 1. Effect of Verticillium longisporum inoculation on canola seedling height, disease severity, and biomass at various pH levels under semi-hydroponic conditions.
Plant Height (mm) ***Disease Severity (0–4 Scale) ***Biomass (g 10−1 Plants) ***
pH ControlInoculatedControlInoculatedControlInoculated
4.4 ± 0.0181 ± 3.8 A59 ± 4.3 ab0 A1.19 ab0.27 ± 0.03 A0.11 ± 0.01 ab
5.4 ± 0.1084 ± 4.4 A66 ± 2.5 a0 A0.72 a0.27 ± 0.01 AB0.15 ± 0.02 a
6.3 ± 0.0282 ± 3.7 A56 ± 1.3 b0 A1.59 bc0.26 ± 0.01 AB0.12 ± 0.01 ab
7.5 ± 0.0179 ± 5.1 A56 ± 8.5 b0 A2.10 d0.24 ± 0.02 AB0.10 ± 0.03 b
8.4 ± 0.0377 ± 2.2 A59 ± 1.9 ab0 A1.91 cd0.22 ± 0.01 B0.11 ± 0.01 ab
Note: ‘Control’ refers to non-inoculated plants, while ‘Inoculated’ refers to seedlings inoculated with a Verticillium longisporum conidial suspension (1 × 106 spores mL−1). Plant height, disease severity, and biomass were assessed at 10 days after inoculation. Means in a column and category followed by the same uppercase or lowercase letter do not differ based on Tukey’s method at p = 0.05. Data are the least square means of four replications. Significant differences in height, disease severity, and biomass between inoculated and non-inoculated plants are indicated with three asterisks: ***, p < 0.001.
Table 2. Effect of Verticillium longisporum inoculation on the plant height, disease severity, and seed yield of canola at maturity under greenhouse conditions.
Table 2. Effect of Verticillium longisporum inoculation on the plant height, disease severity, and seed yield of canola at maturity under greenhouse conditions.
Plant Height (cm) Disease Severity
(0–4 Scale) ***		Seed Yield (g 10−1 Plants)
pH ControlInoculatedControlInoculatedControlInoculated
5.6 ± 0.2758.4 ± 3.9 C54.2 ± 1.7 b (n.s.)0 A0.33 c0.88 ± 0.13 C0. 79 ± 0.14 a (n.s.)
6.5 ± 0.2487.5 ± 5.8 B85.4 ± 5.8 a (n.s.)0 A1.24 b1.35 ± 0.07 B0.76 ± 0.02 a (***)
7.2 ± 0.2179.8 ± 9.4 B93.7 ± 6.8 a (*)0 A1.24 b1.50 ± 0.11 AB0.71 ± 0.03 a (***)
7.8 ± 0.16113 ± 5.5 A91.4 ± 3.5 a (***)0 A1.58 a1.66 ± 0.05 A0.61 ± 0.03 a (***)
Note: ‘Control’ refers to non-inoculated plants, while ‘Inoculated’ refers to seedlings inoculated with a Verticillium longisporum conidial suspension (1 × 106 spores mL−1). Plant height, disease severity, and biomass were assessed at plant maturity. Means in a column and category followed by the same uppercase letter or lowercase letter do not differ based on Tukey’s method at p = 0.05. Data are the least square means of four replications. Significant differences in height, disease severity, and biomass between inoculated and non-inoculated plants are indicated with asterisks: n.s., non-significant; *, p ≤ 0.05; ***, p < 0.001.
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Wang, Y.; Strelkov, S.E.; Hwang, S.-F. Influence of pH on the Growth of Verticillium longisporum and Verticillium Stripe Severity in Canola (Brassica napus). Horticulturae 2024, 10, 554. https://doi.org/10.3390/horticulturae10060554

AMA Style

Wang Y, Strelkov SE, Hwang S-F. Influence of pH on the Growth of Verticillium longisporum and Verticillium Stripe Severity in Canola (Brassica napus). Horticulturae. 2024; 10(6):554. https://doi.org/10.3390/horticulturae10060554

Chicago/Turabian Style

Wang, Yixiao, Stephen E. Strelkov, and Sheau-Fang Hwang. 2024. "Influence of pH on the Growth of Verticillium longisporum and Verticillium Stripe Severity in Canola (Brassica napus)" Horticulturae 10, no. 6: 554. https://doi.org/10.3390/horticulturae10060554

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