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Article

Determination of the Resistance of Tolerant Hybrids of Buxus to the Pathogen Cylindrocladium buxicola and the Effect of Nutrition and Climatic Conditions on Leaf Color

by
Ivana Šafránková
1,
Jiří Souček
2,
Marie Machanderová
3,
Petr Salaš
4,
Jana Burgová
4,* and
Ludmila Holková
1
1
Department of Crop Science, Breeding and Plant Medicine Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1665/1, 613 00 Brno, Czech Republic
2
Czech Agrifood Research Center, Drnovská 507, 161 01 Prague, Czech Republic
3
JM GREEN s.r.o., Studenec 181, 675 02 Koněšín, Czech Republic
4
Department of Breeding and Propagation of Horticultural Plants, Faculty of Horticulture, Mendel University in Brno, Valtická 337, 691 44 Lednice, Czech Republic
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(10), 1256; https://doi.org/10.3390/horticulturae11101256
Submission received: 12 September 2025 / Revised: 11 October 2025 / Accepted: 15 October 2025 / Published: 17 October 2025
(This article belongs to the Section Plant Pathology and Disease Management (PPDM))
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Versions Notes

Abstract

Boxwood (Buxus sp.) plays a key role in historical gardens due to its evergreen foliage and resilience. However, recent outbreaks of disease caused by fungal pathogens such as Calonectria spp. (C. pseudonaviculata, C. henricotiae) and Pseudonectria spp. (P. buxi, P. foliicola), as well as pest pressures from Cydalima perspectalis, have led to significant losses. This study examined 100 boxwood plantings across the Czech Republic to evaluate pest and disease occurrence. Further, six modern boxwood cultivars from the groups of BetterBuxus® and NewGen® were tested in field trials under the climatic conditions of the Czech Republic, focusing on their resistance to abiotic stress and foliage color retention throughout the year. Laboratory trials confirmed all cultivars were susceptible to C. pseudonaviculata, with ‘Renaissance’ showing the slowest disease progression. Field assessments under two contrasting management regimes (“Minimalistic” and “Pampered”) indicated sporadic boxwood blight incidence but frequent Volutella blight outbreaks, particularly where plants suffered frost stress. Leaf color, an important esthetic trait, was evaluated using Munsell charts and measuring the relative chlorophyll content. ‘Skylight’ most closely matched Buxus sempervirens in the shade of green and winter color.

Graphical Abstract

1. Introduction

The evergreen boxwood (Buxus sp., Buxaceae) is one of the oldest and, until recently, has been the most commonly cultivated woody ornamental, whose popularity has been increased over the centuries by its resistance to pathogens and pests. At first, it provided a consistent appearance of parterres in chateau gardens and parks throughout the year, and later it was also used in private gardens and public green spaces, cemeteries, etc. [1,2,3,4]. Since the early 2000s, after the occurrence of both a new disease (boxwood blight) and pest (boxwood moth, Cydalima perspectalis), a decline in interest not only in new plantings of boxwood but also in its cultivation in nurseries was recorded.
The Invasive ascomycete fungi Calonectria pseudonaviculata [5] and C. henricotiae [6] have spread globally over the last two decades, driven by the trade in young asymptomatic plants and nursery stock [7,8,9], in which symptoms develop only after exposure to weather conditions favorable to the pathogen [10,11]. Boxwood blight occurs not only in Europe, e.g., Germany [9], the Czech Republic [12], Turkey [3], and Italy [13], but also in the USA [14], Canada [15], and New Zealand [16]. Initial efforts in disease control of the plants, based on the knowledge of inoculum characteristics, dispersal, as well as environmental effects and fungicide efficacy, have not reached the desired level. Ref. [9] report the effectiveness of fungicides on C. pseudonaviculata in field conditions to be 65–82%. Simultaneously, there has been an effort to find or breed cultivars resistant to boxwood blight, which would also meet the aesthetic requirements for plantings in historic gardens, especially its habitus and unchanging dark green leaf color throughout the year.
Pseudonectria buxi (DC.) Seifert, Gräfenhan & Schroers [17], and P. foliicola L. Lombard & Crous [18] are primarily found on Buxus sp. [18,19,20]. While P. buxi has been reported in many countries in Europe, Asia, and the Americas, P. foliicola has only been recorded in the Czech Republic, New Zealand, and the United States [18,20,21,22]. Both species penetrate the tissues of stems and leaves [23,24], which usually react to their presence by changing the color of the leaves on individual shoots or large parts of the bush [24].
In addition to pathogens, leaf color is also influenced by abiotic factors, especially low temperatures during the winter months. As a result of the accumulation of carotenoids in the tissues, the color of the leaves changes to orange, red, and various shades of brown [25,26]. The color change is specific for individual species and cultivars, influenced by location, exposure to sunlight, solar intensity, and the amount of available nutrients [27]. Although this is a reversible process, as the green color is restored after winter pigmentation, it is an aesthetically significant element that should be paid attention to when choosing a boxwood cultivar.
The objective of this applied study was to test the resistant and tolerant cultivars to the C. pseudonaviculata pathogen under the climatic conditions of the Czech Republic. Laboratory tests evaluating plant resistance to the C. pseudonaviculata isolate were conducted under favorable conditions. And an important part of this study was monitoring the color change in the leaves throughout the year in two variants of cultivation. The main aim of this was to provide valuable information for possible plantings and their care in historical gardens.

2. Materials and Methods

2.1. Screening

One hundred locations in the Czech Republic were selected and visited to examine the health status of boxwood plantings (Table 1). The presence of pathogens (Calonectria spp. and Pseudonectria spp.) and pests (e.g., Cydalima perspectalis, Monarthropalpus flavus, Psylla buxi, and spider mites) was assessed visually at the location. In the case of the occurrence of pathogens, a symptomatic plant sample was taken and placed in a humid chamber and left at laboratory temperature for further microscopical analysis. Molecular analysis was provided only for four isolates, including the isolate further used for artificial inoculation. The collected data were entered into the original map in the QGIS program. The base map shows the average annual temperatures and precipitation in each location in 2023.

2.2. Molecular Analysis

The identification of the pathogen (Calonectria and Pseudonectria) was also confirmed by sequencing analyses of two genomic regions, namely the ITS region (ITS1-5,8S DNA-ITS2) and the gene for LSU large subunit 28S RNA, at three monitored sites in the Czech Republic: Český Krumlov, Libochovice, Studenec, and Hodkov. DNA from infected boxwood leaves or derived mycelial cultures was isolated using the DNeasy Plant Mini Kit (Qiagen, Hilden, Germany) according to the standard protocol. Two DNA regions were sequenced; the coding for the ITS region was sequenced from ITS4/ITS5 primers and the LSU region from LR5/L0R primers. The corresponding ITS area (664 bp) and LSU area (922 bp) were amplified from specific primers, using Taq DNA Polymerase (Qiagen, Hilden, Germany). Reaction mixtures were prepared according to the standard protocol with the addition of 0.5 mM of each primer, 30–50 ng of genomic DNA, and a final concentration of Mg2+ of 1.5 mM. The PCR cycling consisted of an initial denaturation of 95 °C/3 min, followed by 40 cycles of 94 °C/15 s, 52 °C/15 s, and 72 °C/50 s for the ITS region and 40 cycles of 94 °C/15 s, 51 °C/15 s, and 72 °C/60 s for the LSU region. The resulting amplicons were separated on 1% agarose gels followed by GelRed staining. The amplified fragments were purified from agarose gel with the QIAquick Gel Extraction Kit (Qiagen, Hilden, Germany) and sequenced from the above-mentioned specific primers by the Sanger sequencing method. The obtained sequences were deposited in GenBank. The obtained sequences of the ITS region were deposited in GenBank under the numbers PV089704, PV089705, PV089706, and PV089707. The obtained sequences of the LSU region were deposited in GenBank under the numbers PV089814, PV089815, PV089816, and PV089817.

2.3. Plant Material

Simultaneously, six boxwood cultivars were selected for testing in the laboratory and open field. Four cultivars from the BetterBuxus® group (‘Babylon Beauty’, ‘Heritage’, ‘Renaissance’ and ‘Skylight’) and two cultivars from the NewGen® group (‘Freedom’ and ‘Independence’). Buxus sempervirens, a highly susceptible species, was selected as a control.

2.4. Laboratory Testing

Eleven plants (replicates) of three-year-old seedlings of the six cultivars were used to test the resistance to the pathogen Calonectria pseudonaviculata. An isolate from naturally infected fresh leaves of boxwood plants from Hodkov (GPS 49°47′2.55″ N, 15°8′57.95″ E) covered on the underside with freshly formed conidiophores with conidia was used for artificial inoculation of the seedlings. The seedlings were inoculated by spraying with a suspension of C. pseudonaviculata conidia (3 × 106 conidia × mL–1) from a smear of infected leaves. After inoculation, nine plants per cultivar were each placed in transparent plastic boxes (0.5 m × 0.5 m × 0.4 m) with the bottom covered with sterile hydrophilic foil moistened with 500 mL of distilled water. Until the end of the test, the plants were continuously irrigated with tap water as needed. The plants were incubated for 1 week at 23/18 °C and 94–100% RH, followed by 3 weeks at 20–23/18 °C and 80–90% RH.

2.5. Open Field Testing

Plants were planted in 2021 at three sites: Studenec (49°13′11.12″ N, 16°4′24.42″ E; 435 m a.s.l.; average annual temperature 7–8 °C, average annual precipitation 550–650 mm), Kroměříž (49°18′10.94″ N, 17°23′9.00″ E, 201 m a.s.l.; 8–9 °C, 550–650 mm), and Lednice (48°47′31.79″ N, 16°47′53.75″ E; 176 m a.s.l.; 9.2 °C, 479.7 mm). Two management variants, I “Minimalistic” and II “Pampered” (Table 1), were tested in three replicates. Ten plants for replicate and a total of 432 plants, including border plants, were planted randomly at each experimental site. At each site, a weather station was placed, and meteorological data (air temperature, relative air humidity, and leaf wetness) were automatically collected.

2.6. Pathogen Evaluation

Plants were assessed monthly (March–November) using the modified Horsfall–Barratt scale (Table 2) for pathogen and pest intensity (Table 2). Data were statistically analyzed.

2.7. Winter Coloring

The color of the leaves was evaluated using the Munsell Plant Tissue Color Charts, recording hue, brightness, and saturation. From each cultivar, variant, and repetition, two properly developed leaves (fourth leaf from the top of the shoot) were randomly selected and evaluated. A total of six leaves per cultivar and location. Simultaneously, the Normalized Difference Vegetation Index of each leaf was recorded using the PlantPen NDVI300 device (Photon System Instruments, Drásov, Czech Republic).

2.8. Statistical Analysis

The values recorded in 2023 and 2024 were statistically evaluated using TIBCO Statistica 14 software. Descriptive statistics (mean and standard deviation) were calculated for all measured parameters. Homogeneity of variances was tested using Cochran’s and Bartlett’s tests. Differences among the individual variants were assessed using analysis of variance (ANOVA) at a significance level of α = 0.05. When significant effects were found, post hoc comparisons were performed using Tukey’s HSD test.

3. Results

3.1. Screening

Survey results are mapped and available on an interactive map (https://www.zdravybuxus.com/mapy, accessed on 15 October 2025). Of the 100 boxwood plantings inspected, 17 cases of boxwood blight and 48 cases of Pseudonectria spp. infections (including four cases of Scolecofusarium ciliatum) were recorded. Cydalima perspectalis was recorded at 59 plantings. Only five stands appeared to be pathogen and pest free (Figure 1).

3.2. Laboratory Tests

All cultivars were susceptible to C. pseudonaviculata under laboratory conditions (Table 3). The first visible symptoms (leaf spots) appeared 4 days post-inoculation. Analysis of variance revealed significant effects of both cultivar (F (7, 225) = 43.15, p < 0.001) and time after inoculation (F (2, 225) = 13.43, p < 0.001) on disease severity. However, the interaction between cultivar and time was not significant (F (14, 225) = 1.21, p = 0.269), indicating that the pattern of symptom development over time was similar among cultivars. The control plants (Buxus sempervirens) showed the heaviest infection, statistically similar to ‘Freedom’ and ‘Skylight’. ‘Renaissance’ was least infected and showed symptoms first on day 18 after inoculation. Infection intensity was statistically comparable to the untreated control along with ‘Independence’ and ‘Heritage’. These findings indicate that, although all tested cultivars were susceptible to C. pseudonaviculata, the degree of infection differed significantly among genotypes.

3.3. Open Field Tests

Low temperatures were the most common and repetitive cause of damage, particularly at the Sudenec site (Figure 2). Table 4 shows the differences between individual sites based on the average temperatures reached, the lowest temperatures reached in a given month, and the number of days with temperatures below 0 °C (frost days).
The occurrence of boxwood blight was sporadic, detected only on ‘Freedom’ at Kroměříž in September 2023 and 2024 following rain periods with high humidity. Pseudonectria buxi was first recorded at Studenec (March 2023) on winter coloring shoots of ‘Heritage’. In May, Pseudonectria buxi was observed at the Lednice on various cultivars (‘Heritage’, ‘Babylon Beauty’, ‘Renaissance’ and ‘Independence’). Afterwards, Pseudonectria buxi was regularly detected at both sites. The highest intensity and frequency of damage were observed at Studenec, where damage to some cultivars (‘Heritage’, ‘Babylon Beauty’, and ‘Renaissance’) led to the dieback of infested shoots (Figure 3). The pathogen infestation preceded severe frost damage.

3.4. Winter Coloring

No tested cultivar matched the rich dark green color year-round of B. sempervirens. ‘Independence’ and ‘Skylight’ showed the most similar color compared to the control. Leaves of ‘Independence’ were of the highest intensity and saturation of dark green (Figure 4), and ‘Skylight’ maintained dark green color throughout the year at Studenec and Kroměříž. ‘Babylon Beauty’ showed the lightest coloration overall, even in the fertilized variant. ‘Heritage’ and ‘Freedom’ showed orange-brown coloration in winter months and persisted until the spring at Studenec (Figure 5). ‘Renaissance’ showed gradual, homogeneous color changes throughout the year with minimal variant differences. Only a slight difference between variants was observed. Orange-brown coloration correlated with the presence of Pseudonectria buxi.
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Figure 3. Intensity of Pseudonectria buxi infestation expressed using the modified Horsfall–Barratt scale (1–6, 1 = no infestation). M = “Minimalistic” variant, P = “Pampered” variant. Values represent means ± SD; error bars indicate within-treatment variability. Significant effects were found for site and cultivar (p < 0.001), while the effect of treatment variant was not significant (p = 0.67).
Figure 3. Intensity of Pseudonectria buxi infestation expressed using the modified Horsfall–Barratt scale (1–6, 1 = no infestation). M = “Minimalistic” variant, P = “Pampered” variant. Values represent means ± SD; error bars indicate within-treatment variability. Significant effects were found for site and cultivar (p < 0.001), while the effect of treatment variant was not significant (p = 0.67).
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Figure 4. Color shades of the monitored cultivars were recorded in May and November 2023 and 2024. Site: L—Lednice, S—Studenec, K—Kroměříž; blank spots indicate plants where it was not possible to record the color of the leaves due to frost damage.
Figure 4. Color shades of the monitored cultivars were recorded in May and November 2023 and 2024. Site: L—Lednice, S—Studenec, K—Kroměříž; blank spots indicate plants where it was not possible to record the color of the leaves due to frost damage.
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Figure 5. Assessment of color changes in foliage at the Lednice site (5 September 2024).
Figure 5. Assessment of color changes in foliage at the Lednice site (5 September 2024).
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Statistically significantly lower NDVI average values were achieved for ‘Babylon Beauty’ in both variants (Table 5). Also, the “Minimalistic” variant (Figure 6) achieved a statistically significant lower NDVI than “Pampered” over the years 2023–2024, which was particularly evident for B. sempervirens, reaching an average index of 0.64 (“Pampered” variant), significantly different from other tested cultivars. Only ‘Independence’ had a 0.01 lower average index in the “Pampered” variant. Cultivars ‘Renaissance’, ‘Skylight’, and ‘Heritage’ in the “Pampered” variant generally achieved higher average NDVI values. The lowest average value of the chlorophyll content was measured in ‘Heritage’ leaves (index = 0.44, May 2023, “Minimalistic” variant), and the highest in B. sempervirens (0.77, November, the “Pampered” variant).

4. Discussion

Since the last survey in the Czech Republic [28], the pests and diseases have spread significantly. Molecular analysis of symptomatic plant samples was not part of the project, however the genera of relevant pathogens (Calonectria and Pseudonectria) were confirmed by microscopic observation and their distribution demonstrated.
The primary objective of the project was to promote sustainable production by using resistant cultivars, thereby reducing pesticide use and minimizing their impact on the environment. While breeding and selection for resistant or tolerant varieties has long been a key part of integrated pest management (IPM) in agriculture and fruit and vegetable production, the focus in the breeding of ornamental plants and especially in woody plant production is primarily on aesthetic value. Only recently have initiatives and breeding programs by ornamental nurseries in Europe and the United States demonstrated progress towards selecting tolerant boxwood species [29,30]. Ref. [29] also recommend a two-stage selection process to effectively breed resistant boxwood to boxwood blight. They suggest eliminating highly susceptible cultivars by artificially inoculating and then field testing the more resistant seedlings under natural infection for several years. Such field trials can also be used to determine other important traits, such as growth habit, winter coloring, and winter hardiness.
Boxwood is unquestionably one of the most economically important ornamental crops. Its future likely depends on a combination of conventional and molecular breeding methods, alongside genetic engineering approaches [31,32,33,34]. As the laboratory tests demonstrated that none of the tested cultivars exhibited resistance to the pathogen Calonectria pseudonaviculata, which underscores the urgent need for continued breeding efforts and possibly biotechnological interventions. Moreover, field tests revealed a high incidence and severity of Volutella blight, highlighting its persistent threat to boxwood health. However, it is considered to be a secondary pathogen [35], occurring on senescent and damaged plant parts. It is possible that Pseudonectria species act as endophytes or latent pathogens in boxwood plants, with their outbreaks often triggered by physical damage or abiotic stress [11,36,37]. It is also important to note that pest infestations, such as those caused by Cydalima perspectalis, can increase a plant’s susceptibility to disease. Defoliation caused by caterpillars of this invasive moth damages leaf blades and weakens boxwood plants, and therefore increases their susceptibility to secondary fungal infections, including the pathogen Calonectria pseudonaviculata. This underscores the necessity of integrating disease resistance strategies and pest monitoring into breeding and cultivation programs [38,39,40].
This pattern aligns with the observed prevalence of Pseudonectria-infected plants at Lednice and Studenec, as well as the occurrence of Volutella blight on winter-discolored shoots of ‘Heritage’ at Studenec. Furthermore, [11] microclimatic conditions, primarily temperature extremes and humidity fluctuations, can significantly influence the susceptibility of boxwood to fungal infections.
Low temperatures were the most common cause of damage, which significantly limits the success of the introduction of any plant species [41]. Although no significant differences in abiotic damage intensity were found between “Minimalistic” and “Pampered” variants across 2023–2024. In the “Minimalistic” variant, all cultivars showed significantly higher damage than the B. sempervirens control. In the “Pampered” variant, only ‘Renaissance’ and ‘Skylight’ achieved low damage levels, comparable to B. sempervirens. ‘Babylon Beauty’ and ‘Independence’ showed the highest damage in both variants.
An important aspect for the possible use of new boxwood cultivars in garden and landscape architecture is the dark green color of the foliage throughout the year and the growth habit [29]. Winter coloring, also referred to as “winter bronzing”, can be undesirable and can change the aesthetic value of architectural work, especially of historical gardens. The visual assessment of leaf color change (Munsell charts evaluation) in boxwood was minimally affected by the variant, i.e., fertilization. The results are consistent with [42] presenting that fertilization had no effect on the results of their experiment and the leaf color change in the new cultivars (‘Freedom’ and ‘Independence’), where ‘Independence’ had the lowest level of winter color change.
On the contrary, differences between variants were observed by measuring the NDVI. The higher the NDVI, the less stressed the plants are [43]. In 2023, the monitored cultivars achieved higher average NDVI values than in 2024, most likely due to low temperatures in winter months, particularly at Studenec and Lednice. Also, plants of the “Minimalistic” variant often had lower NDVI values than in the “Pampered” one, which was mainly due to different plant care management. Based on these findings, it is advisable to provide the plants with sufficient nutrients in order to lower the level of winter color change.
These findings reinforce the importance of integrating abiotic stress and disease and pest resistance into breeding programs for boxwood to enhance their resilience and ensure sustainability in ornamental horticulture.

5. Conclusions

Testing of newly bred resistant and tolerant cultivars of boxwood (Buxus sp.) took place during the monitored period in 2023–2024. This is a very short period of time, which was taken into account when evaluating the results. And given the longevity of the plants, it would be advisable to continue the experiments. None of the tested cultivars bred for resistance or tolerance to boxwood blight proved to be fully resistant to Calonectria pseudonaviculata. This was demonstrated under laboratory conditions optimal for pathogen infection. Furthermore, in field conditions where no inoculation was performed, isolated occurrences of the pathogen were observed on ‘Freedom’. Based on the findings, the cultivar ‘Renaissance’ can be a relatively better option for planting in the climatic conditions of the Czech Republic. In laboratory experiments, it showed the highest resistance to the pathogen Calonectria pseudonaviculata. However, in field conditions, infestation with the pathogen Pseudonectria buxi was observed, especially in combination with abiotic stress caused by frost damage. In comparison to the commonly planted B. sempervirens, the cultivar does not achieve the same intensity of leaf color, and the shade changes throughout the year. Frost damage was observed on the cultivar, mainly due to insufficiently mature tissue in warm autumn. However, the damage was not deep, mainly affecting the tops of the shoots, and with sufficient nutrition the plants regenerated relatively well. Continued monitoring and implementation of advanced IPM are recommended to support sustainable use of boxwood in historic and modern gardens.

Author Contributions

Conceptualization, I.Š., M.M., and P.S.; methodology, I.Š., P.S., and M.M.; software, J.B.; validation, J.S., M.M., J.B., L.H., and P.S.; formal analysis, M.M., J.B., and J.S.; investigation, P.S., M.M., I.Š., J.B., and L.H.; resources, M.M., P.S., and J.B.; data curation, M.M. and J.B.; writing—original draft preparation, M.M., I.Š., and J.B.; writing—review and editing, P.S. and J.S.; visualization, M.M.; supervision, I.Š., P.S., and J.S.; project administration, M.M., P.S., and J.S.; funding acquisition, M.M., P.S., and J.S. All authors have read and agreed to the published version of the manuscript.

Funding

This article was created within the framework of institutional support for long-term conceptual development of the Czech Agrifood Research Center no. RO0425 and by project “SS05010079—Healthy Buxus”, which is co-financed with state support from the Technology Agency of the Czech Republic under the program “Prostředí pro život”.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

Author Marie Machanderová was employed by the company JM GREEN s.r.o. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Abbreviations

The following abbreviations are used in this manuscript:
BBBetterBuxus®
NGNewGen®
NDVINormalized Difference Vegetation Index
IPMIntegrated Pest Management

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Horticulturae 11 01256 g001
Figure 1. Occurrence of pathogens and pests of boxwood in the Czech Republic in 2023–2024.
Figure 1. Occurrence of pathogens and pests of boxwood in the Czech Republic in 2023–2024.
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Figure 2. Severe frost damage at the Studenec site, spring 2024.
Figure 2. Severe frost damage at the Studenec site, spring 2024.
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Figure 6. Winter coloring of model plant leaves, “Minimalistic” variant, Lednice, autumn 2023.
Figure 6. Winter coloring of model plant leaves, “Minimalistic” variant, Lednice, autumn 2023.
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Table 1. Description of the experimental variants.
Table 1. Description of the experimental variants.
Variant I “Minimalistic”
-
no irrigation
-
no additional fertilization
-
cut one time per year (end of May)
Variant II “Pampered”
-
drop irrigation for 1 h every second day
-
regular fertilization with water-soluble fertilizer:
Universol Green (4×; weekly 15 g/10 L, total 150 L; April)
Universol Blue (4×; weekly 15 g/10 L, total 150 L; June)
Universol Violet (4×; weekly 15 g/10 L, total 150 L; August)
-
cut twice a year (mid-June and end of vegetation)
Table 2. Modified Horsfall–Barratt scale—assessment of pathogen occurrence.
Table 2. Modified Horsfall–Barratt scale—assessment of pathogen occurrence.
Damage DegreeVolutella BlightBoxwood Blight
1healthy plants, no symptoms (0%)healthy leaves and stems, no signs of infestation (0%)
2loss of the leaf gloss, slight change in color, small spots on the edges of the leaves (1–5%)individual brown spots on leaves, no leaf drop, no stem lesions (1–5%)
3spots cover up to half of the leaf blade, leaves turn yellow (6–20%)spots on leaves cover up to one-half of the blade, do not necrotize, occasional leaf drop, occasional stem lesions (6–20%)
4leaves turn bronze, bark at the base of the stem cracks, occasionally peels off (21–35%)drop of primarily infected leaves, formation of spots on new leaves, black lesions on a third of the stem (21–35%)
5beginning of the dieback of the shoots, necrosis of the wood underneath the bark (36–50%)leaf spots and stem lesions up to half of the plant, severe leaf drop, especially of the inner parts of the plants (36–50%)
6dieback of infected shoots or entire plants (51–100%)new spots occurring on newly grown leaves, stems with numerous long black lesions, almost defoliated plants (51–100%)
Table 3. Disease severity after artificial inoculation with C. pseudonaviculata was evaluated using the modified Horsfall–Barratt scale under controlled conditions.
Table 3. Disease severity after artificial inoculation with C. pseudonaviculata was evaluated using the modified Horsfall–Barratt scale under controlled conditions.
CultivarTime After Inoculation (Days)The Presence of Symptoms (Score)Time After Inoculation (Days)The Presence of Symptoms (Score)Time After Inoculation (Days)The Presence of Symptoms (Score)
Buxus sempervirens41.09 ± 0.70 b82.36 ± 0.92 c182.82 ± 0.60 d
‘Babylon Beauty’41.18 ± 0.41 a81.36 ± 0.51 ab182.00 ± 0.63 bc
‘Skylight’41.82 ± 0.40 b81.91 ± 0.54 bc182.27 ± 0.47 bd
‘Renaissance’41.00 ± 0.00 a81.00 ± 0.00 a181.18 ± 0.40 a
‘Heritage’41.18 ± 0.40 a81.27 ± 0.47 ab181.36 ± 0.50 ac
‘New Gen Independence’41.14 ± 0.38 a81.29 ± 0.49 ab181.57 ± 0.53 abc
‘New Gen Freedom’42.20 ± 0.42 b82.10 ± 0.32 bc182.30 ± 0.48 bd
Buxus sempervirens—NC *41.00 ± 0.00 a81.00 ± 0.00 a181.00 ± 0.00 a
*—Negative Control plants. Data are mean ± SD; different letters a,b,c,d indicate statistically significant differences between cultivars in one-way ANOVA analysis (p < 0.05); score 1–6, 1 = no infestation.
Table 4. Temperature differences between locations.
Table 4. Temperature differences between locations.
SiteLedniceStudenecKroměříž
YearMonthAMT (°C)AMINT (°C)NFD (day)AMT (°C)AMINT (°C)NFD (day)AMT (°C)AMINT (°C)NFD (day)
202312.9−7.915.01.4−10.622.03.2−4.613.0
22.6−10.519.01.0−12.120.02.3−9.320.0
36.6−7.516.04.6−7.920.06.5−6.414.0
48.7−7.74.06.6−8.512.08.4−5.16.0
514.6−0.51.012.6−1.13.013.70.5N
619.55.2N17.71.8NNNN
722.78.0N20.75.8NNNN
820.77.5N18.83.8N20.47.0N
918.46.7N16.33.0N17.76.9N
1012.8−4.23.010.6−4.15.012.4−2.34.0
115.6−6.911.03.8−9.818.05.7−6.612.0
121.9−18.520.00.8−21.424.02.6−5.617.0
202410.6−13.224.0−1.0−14.328.00.3−15.125.0
27.2−3.88.05.3−5.39.07.3−4.36.0
39.0−5.29.06.8−7.014.08.9−5.08.0
412.3−2.66.09.7−6.113.012.0−2.16.0
516.83.0N14.50.9N16.62.6N
620.86.6N18.53.3N20.06.3N
723.38.4N20.65.8N22.39.1N
823.37.6N21.35.5N21.99.1N
916.5−0.11.014.9−1.72.016.11.5N
1010.8−0.81.09.2−1.35.010.5−0.11.0
113.1−5.319.01.8−7.323.03.6−3.618.0
121.3−7.622.00.0−8.625.01.2−8.323.0
AMT—average monthly temperature, AMINT—absolute minimum temperature, NFD—number of frost days. N = no temperature below 0 was recorded.
Table 5. The average NDVI values of the cultivars over the testing period (2023–2024).
Table 5. The average NDVI values of the cultivars over the testing period (2023–2024).
VariantTested CultivarNDVI
“Minimalistic”BetterBuxus® ‘Babylon Beauty‘0.54 ± 0.07 a
BetterBuxus® ‘Renaissance’0.58 ± 0.06 b
BetterBuxus® ‘Skylight‘0.59 ± 0.07 bc
BetterBuxus® ‘Heritage’0.58 ± 0.08 bc
NewGen® ‘Independence’0.60 ± 0.08 c
NewGen® ‘Freedom’0.59 ± 0.07 bc
Bxuxus sempervirens0.60 ± 0.08 c
“Pampered”BetterBuxus® ‘Babylon Beauty‘0.55 ± 0.10 a
BetterBuxus® ‘Renaissance’0.61 ± 0.06 bc
BetterBuxus® ‘Skylight‘0.61 ± 0.05 bc
BetterBuxus®’Heritage’0.61 ± 0.09 bc
NewGen® ‘Independence’0.59 ± 0.12 bc
NewGen® ‘Freedom’0.60 ± 0.08 bc
Bxuxus sempervirens0.64 ± 0.05 d
Data are presented as mean ± SD. Different letters indicate statistically significant differences between cultivars based on two-way ANOVA analysis followed by Tukey’s HSD test (p < 0.05). Significant effects were found for variant (p < 0.0001), cultivar (p < 0.0001), and their interaction (p < 0.001).
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Šafránková, I.; Souček, J.; Machanderová, M.; Salaš, P.; Burgová, J.; Holková, L. Determination of the Resistance of Tolerant Hybrids of Buxus to the Pathogen Cylindrocladium buxicola and the Effect of Nutrition and Climatic Conditions on Leaf Color. Horticulturae 2025, 11, 1256. https://doi.org/10.3390/horticulturae11101256

AMA Style

Šafránková I, Souček J, Machanderová M, Salaš P, Burgová J, Holková L. Determination of the Resistance of Tolerant Hybrids of Buxus to the Pathogen Cylindrocladium buxicola and the Effect of Nutrition and Climatic Conditions on Leaf Color. Horticulturae. 2025; 11(10):1256. https://doi.org/10.3390/horticulturae11101256

Chicago/Turabian Style

Šafránková, Ivana, Jiří Souček, Marie Machanderová, Petr Salaš, Jana Burgová, and Ludmila Holková. 2025. "Determination of the Resistance of Tolerant Hybrids of Buxus to the Pathogen Cylindrocladium buxicola and the Effect of Nutrition and Climatic Conditions on Leaf Color" Horticulturae 11, no. 10: 1256. https://doi.org/10.3390/horticulturae11101256

APA Style

Šafránková, I., Souček, J., Machanderová, M., Salaš, P., Burgová, J., & Holková, L. (2025). Determination of the Resistance of Tolerant Hybrids of Buxus to the Pathogen Cylindrocladium buxicola and the Effect of Nutrition and Climatic Conditions on Leaf Color. Horticulturae, 11(10), 1256. https://doi.org/10.3390/horticulturae11101256

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