UV treatment suppressed sclerotia germination and mycelial growth of Sclerotinia sclerotiorum
UV treatments (UV-B, UV-C and a combination of UV-B and UV-C) (Table 1) resulted in 1.06 to 1.66-fold reduction in sclerotia germination (Fig. 1a) and 1.37-4.47-fold suppression of mycelial growth (Fig. 1b, supplementary Fig. S3) compared to the non-irradiated controls. The results demonstrated a positive association between the suppression of sclerotia germination and mycelial growth with an increase in the cumulative UV dosages.
Significant suppression of sclerotia germination was observed from the treatment duration of 10 min and cumulative dosages of 3600 J/m² for UV-B (1.06-fold), 930 J/m² for UV-C (1.18-fold), and a combination of UV-B (3600 J/m²) and UV-C (930 J/m²) (1.33-fold) compared to the non-irradiated control (0 J/m²) (Fig. 1a). However, significant suppression of mycelial growth was observed with a shorter treatment duration of 5 min and cumulative dosage of 1800 J/m² for UV-B (1.37-fold), 465 J/m² for UV-C (2.52-fold), and 3 min for the combination of UV-B (1080 J/m²) and UV-C (280 J/m²) (2.66-fold), compared to the non-irradiated control (0 J/m²) (Fig. 1b).
The significant suppression of mycelial growth occurred at much lower UV dosages than those required for sclerotia germination, indicating higher susceptibility of mycelia. Besides, the combination treatment showed better suppression of sclerotia germination and mycelial growth than individual UV-B or UV-C treatments (Fig. 1). For a treatment duration of 5 to 15 min, the combination of UV-B and UV-C treatment showed 1.18-1.52-fold higher suppression of sclerotia germination compared to UV-B alone, and 1.08-1.27-fold higher suppression than UV-C alone. For mycelial growth, with similar treatment duration, the combination UV-B and UV-C treatment showed 2.22-3.10-fold higher suppression of mycelial growth compared to UV-B alone, and 1.21-1.26-fold higher suppression compared to UV-C alone.
UV treatment triggers ROS formation and lipid peroxidation in S. sclerotiorum
ROS staining of UV-treated mycelia using NBT showed the development of blue-purple colouration in UV-treated S. sclerotiorum mycelia (Fig. 2). The colour intensity increased with an increase in dosage, further confirming the additive effect of cumulative UV dosage on suppression of mycelial growth. Additionally, the ROS content in UV-treated mycelia was 1.15-2.58-fold higher than non-irradiated control (0 J/m2) (Fig. 3a). Significant accumulation of O2·– was observed from the treatment duration of 5 min with cumulative dosages of 1800 J/m² for UV-B (1.15-fold) and 465 J/m² for UV-C (1.42-fold) and the shorter treatment duration of 3 min for the combination of UV-B (1080 J/m²) and UV-C (280 J/m²) (1.71-fold) compared to non-irradiated control (Fig. 3a).
Another ROS, H2O2, also showed significant accumulation (1.33-2.69-fold) but at comparatively higher treatment duration (10 to 30 min) than O2·– (Fig. 3b). For individual UV-B treatment, significant changes were observed at 30 min with a cumulative dosage of 10800 J/m2 (2.21-fold) and individual UV-C treatment at 10 min with a cumulative dosage of 930 J/m2 (1.51-fold) compared to non-irradiated control (Fig. 3b). In contrast, the combination UV-B (1080 J/m2) and UV-C (280 J/m2) treatment, showed significant changes (1.49-fold) at lower treatment duration (3 min) compared to non-irradiated control (Fig. 3b).
To analyse the effect of UV-treatment on membrane damage of S. sclerotiorum, MDA was quantified in UV-treated mycelia (Fig. 3c). The result showed an increase in MDA content with an increase in cumulative UV dosages (Fig. 3c). Significant increases in MDA content were observed from the treatment duration of 15 min with a cumulative dosage of 5400 J/m² for UV-B (1.89-fold) and treatment duration of 10 min for the UV-C (930 J/m²) (1.60-fold) and the shorter duration of 5 min for the combination of UV-B (1800 J/m²) and UV-C (465 J/m²) (1.62-fold) compared to non-irradiated control (Fig. 3c).
UV treatment suppresses superoxide dismutase (SOD) enzymatic activity in S. sclerotiorum
To investigate the effect of UV treatment on ROS homeostasis, two major antioxidant enzymes, SOD and CAT, were quantified (Fig. 3d and e). The SOD activity was decreased with an increasing UV dosage, depicting UV-induced imbalance between scavenging of ROS activity and ROS production in UV-treated mycelia. A significant decline of SOD activity was observed from the treatment duration of 10 min with cumulative dosages of 3600 J/m² for UV-B (1.12-fold), 930 J/m² for UV-C (1.19-fold), and the shorter treatment duration of 5 min for the combination of UV-B (1800 J/m2) and UV-C (465 J/m2) (1.21-fold), compared to the non-irradiated control (0 J/m²) (Fig. 3d).
In contrast to the SOD, the antioxidant enzyme CAT increased with increasing in UV dosage (Fig. 3e). A significant increase of CAT activity was observed from the treatment duration of 5 min with cumulative dosages of 1800 J/m² for UV-B (1.14-fold), 465 J/m² for UV-C (1.20-fold), and the shorter treatment duration of 3 min for combination of UV-B (1080 J/m²) and UV-C (280 J/m²) (1.15-fold) compared to the non-irradiated control (0 J/m²) (Fig. 3e).
UV treatment showed significantly low disease severity and less chlorophyll damage compared to non-treated S. sclerotiorum inoculated tomato plants
To explore the effect of UV treatment on S. sclerotiorum-inoculated tomato plants, we quantified disease severity (Table 2) and photosynthetic pigments (Table 3). In our plant study, we treated the inoculated plants (3 DPI) at 50 cm from the UV light, a distance optimised in our previous study to avoid visible photodamage (Wong et al. 2024). Our previous study also reported that UV-C exposure for up to 10 min induces hormetic effects in plants, while higher dosages have deleterious effects on phenotypic and yield traits. Therefore, we selected five plant-friendly UV dosages that significantly suppress mycelial growth. The selected dosages were UV-B (3600 J/m²; 10 min), UV-C (930 J/m²; 10 min), and combinations of UV-B and UV-C [3600 J/m² and 930 J/m² (10 min); 1800 J/m² and 465 J/m² (5 min); 1080 J/m² and 280 J/m² (3 min)]. Disease scoring assessment of UV-treated S. sclerotiorum inoculated tomato plants showed highest disease suppression (81%) for the combination of UV-B (3600 J/m2) and UV-C (930 J/m2) and for individual UV-C (930 J/m2) treatments, compared to the fungal treated control [27-day post-fungal inoculation (DPI) and 14-day post-UV treatment, (DP-UVT)] (Table 2 and Fig. 4). Additionally, UV-treated S. sclerotiorum-inoculated tomato plants showed higher levels of photosynthetic pigments (Chl a, Chl b, and carotenoids) with the combination of UV-B (3600 J/m²) and UV-C (930 J/m²) (5.19-7.04-fold) and individual UV-C (930 J/m²) treatments (5.08-6.90-fold), followed by UV-B (1.22-2.14-fold) compared to the fungal treated control [27 day post fungal inoculation (DPI) and 14-day post-UV treatment, (DP-UVT)] (Table 2 and Fig. 4), indicating better plant recovery.
Table 2
Disease scoring analysis of UV-treated S. sclerotiorum inoculated Red Rock at 7-day and 14-day post of the last UV treatment.
| | Percentage of Sclerotinia sclerotiorum infection (%) |
| Non-irradiated control (0 J/m2) | Fungal treated control | | UV-B (3600 J/m2) | UV-C (930 J/m2) | UV-B and UV-C (3600 and 930 J/m2) | UV-B and UV-C (1800 and 465 J/m2) | UV-B and UV-C (1080 and 280 J/m2) |
| | | | First Sclerotinia Sclerotiorum symptom appeared (Starting Point of UV treatment) |
3 DPI | 0 ± 0.00 | 9.52 ± 0.82a | | 9.89 ± 0.82a | 9.99 ± 1.42a | 9.05 ± 1.65a | 9.55 ± 0.85a | 9.05 ± 2.18a |
| | | | Post-UV treatment |
20 DPI | 0 ± 0.00 | 66.18 ± 2.18s | 7 DP-UVT | 61.43 ± 1.42s | 15.88 ± 1.43t | 15.95 ± 0.83t | 35.33 ± 1.65u | 49.52 ± 2.98v |
27 DPI | 0 ± 0.00 | 88.57 ± 1.43p | 14 DP-UVT | 69.52 ± 2.18q | 16.57 ± 0.83r | 16.66 ± 1.43r | 38.57 ± 1.43s | 77.62 ± 4.13t |
Disease scoring analysis of UV-treated S. sclerotiorum inoculated Red Rock at 7-day and 14-day post of the last UV treatment. |
*DPI represent Day Post Fungal Inoculation |
**DP-UVT represent Day Post of Last UV Treatment of S. sclerotiorum inoculated tomato plants |
Data represented the mean values (n = 15) ± standard deviation, n indicates the number of biological replicates. Different alphabets indicate significant differences using One-way ANOVA, Tukey HSD comparison test p < 0.05. |
Table 3
Summary of photosynthetic pigments of UV treated S. sclerotiorum-inoculated Red Rock at 7-day and 14-day post of the last UV treatment.
| | Non-irradiated Control (0 J/m2) | Fungal treated control | | UV-B (3600 J/m2) | UV-C (930 J/m2) | UV-B and UV-C (3600 and 930 J/m2) | UV-B and UV-C (1800 and 465 J/m2) | UV-B and UV-C (1080 and 280 J/m2) |
| | | | | First Sclerotinia sclerotiorum symptom appeared (Starting Point of UV treatment) |
3 DPI | Chla (mg g− 1 FW) | 13.12 ± 1.25a | 10.28 ± 1.27b | | 10.22 ± 2.01b | 11.77 ± 1.82b | 10.98 ± 1.95b | 10.25 ± 1.08b | 10.55 ± 1.27b |
| Chlb (mg g− 1 FW) | 7.10 ± 0.95c | 4.32 ± 1.20d | | 4.42 ± 1.34d | 4.44 ± 1.21d | 4.68 ± 1.22d | 4.35 ± 0.98d | 4.49 ± 0.88d |
| Carotenoid (mg g− 1 FW) | 7.47 ± 1.30e | 4.85 ± 1.12f | | 4.82 ± 1.29f | 5.12 ± 1.26f | 4.79 ± 1.28f | 4.34 ± 1.02f | 4.81 ± 1.51f |
| | | | | Post-UV treatment |
20 DPI | Chla (mg g− 1 FW) | 13.21 ± 0.28g | 6.51 ± 0.88h | 7 DP-UVT | 7.11 ± 0.97h | 12.27 ± 0.21i | 12.65 ± 0.25i | 9.13 ± 0.64j | 5.83 ± 1.14k |
| Chlb (mg g− 1 FW) | 7.09 ± 0.92p | 1.87 ± 0.94l | | 2.98 ± 0.81mn | 6.07 ± 0.91q | 5.87 ± 0.85q | 3.94 ± 0.35no | 2.87 ± 0.34m |
| Carotenoid (mg g− 1 FW) | 7.21 ± 0.97t | 1.56 ± 0.78r | | 3.04 ± 0.93s | 6.27 ± 0.44u | 6.12 ± 0.28u | 3.66 ± 0.66s | 2.12 ± 0.24r |
27 DPI | Chla (mg g− 1 FW) | 13.78 ± 1.03x | 2.67 ± 0.66v | 14 DP-UVT | 3.27 ± 0.77v | 13.58 ± 0.94x | 13.86 ± 0.73x | 7.89 ± 0.64w | 2.91 ± 0.71v |
| Chlb (mg g− 1 FW) | 7.23 ± 1.10D | 1.02 ± 0.58D | | 2.18 ± 0.36B | 7.04 ± 1.17D | 7.18 ± 0.79D | 3.57 ± 0.43C | 1.64 ± 0.59AB |
| Carotenoid (mg g− 1 FW) | 7.22 ± 1.20G | 1.04 ± 0.44E | | 1.88 ± 0.45E | 7.14 ± 1.24G | 7.27 ± 0.77G | 3.61 ± 0.51F | 1.81 ± 0.46E |
Summary of photosynthetic pigments of UV treated S. sclerotiorum-inoculated Red Rock at 7-day and 14-day post of the last UV treatment. |
*DPI represent Day Post Fungal Inoculation |
**DP-UVT represent Day Post of Last UV Treatment of S. sclerotiorum inoculated tomato plants |
Data represented the mean values (n = 15) ± standard deviation, n indicates the number of biological replicates. Different alphabets indicate significant differences using One-way ANOVA, Tukey HSD comparison test p < 0.05. |
UV treatment improved fruit quality and bioactive compounds of S. sclerotiorum inoculated tomato plants
None of the fruit from UV-treated S. sclerotiorum inoculated tomato plants showed any visible disease lesions and all treated plants showed an increase in fruit yield (1.19-11.88-fold) and fresh weight (1.15-3.46-fold) compared to fungal treated control (Fig. 5). Among the UV treatments, the highest fruit yield (1.83-11.88-fold) and fruit fresh weight (2.03-3.46-fold) were obtained from plants treated with the combination UV-B (3600 J/m2) and UV-C (930 J/m2) compared to plants treated individually with UV-B or with UV-C (Fig. 5). All the fruit from UV-treated S. sclerotiorum inoculated tomato plants showed significant difference in fruit dry weight (2.32-3.60-fold) compared to fungal treated control, but no significant differences in fruit dry weight were found between the combination UV-B (3600 J/m2) and UV-C (930 J/m2) treatment and individual UV-B and UV-C treatment (Fig. 5).
All the fruits from UV-treated plants showed a significantly higher accumulation of bioactive compounds than the fungal-only-treated control, including total phenolic content, total flavonoid content, and ascorbic acid content (Table 4). Among the UV treatments, the highest accumulation of bioactive compounds, including total phenolic content (1.28-6.03-fold), total flavonoid content (1.29-5.39-fold), ascorbic acid (1.30-7.70-fold) and total antioxidant of (1.09-6.34-fold) was found in plants treated with a combination of UV-B (3600 J/m2) and UV-C (930 J/m2) compared to plants treated with only UV-B or only UV-C (Table 4).
Table 4
Summary of fruit bioactive compounds and total antioxidant activity of S. sclerotiorum-inoculated tomato plant treated with different cumulative UV dosages.
| Non-irradiated control (0 J/m2) | Fungal Treated Control | UV-B (3600 J/m2) | UV-C (930 J/m2) | UV-B and UV-C (3600 and 930 J/m2) | UV-B and UV-C (1800 and 465 J/m2) | UV-B and UV-C (1080 and 280 J/m2) |
Total phenolic content (mg CE/100g DW) | 101.33 ± 2.40a | 21.42 ± 2.61b | 89.23 ± 1.84c | 115.12 ± 1.17d | 129.22 ± 1.61e | 95.47 ± 2.26f | 75.83 ± 2.10g |
Total flavonoid content (mg CE/100g DW) | 125.10 ± 2.11a | 29.84 ± 1.28b | 109.62 ± 2.24c | 144.10 ± 1.18d | 160.84 ± 1.36e | 115.10 ± 2.12f | 85.72 ± 2.33g |
Ascorbic acid (mg /100g FW) | 52.47 ± 2.07a | 8.89 ± 1.04b | 34.82 ± 2.82c | 65.14 ± 2.21d | 68.42 ± 2.01d | 45.21 ± 2.34e | 23.89 ± 1.85f |
Total Antioxidant (DPPH) (%) | 88.38 ± 0.21a | 15.05 ± 1.57b | 75.38 ± 0.82c | 91.88 ± 0.28d | 95.38 ± 0.77e | 82.38 ± 0.43f | 70.08 ± 0.19g |
Summary of fruit bioactive compounds and total antioxidant activity of S. sclerotiorum-inoculated tomato plant treated with different cumulative UV dosages. |
Data represented the mean values (n = 15) ± standard deviation, n indicates the number of biological replicates. Different alphabets indicate significant differences using One-way ANOVA, Tukey HSD comparison test p < 0.05. |
UV treatment induced expression of defence-related genes in S. sclerotiorum inoculated tomato plants
Analysis of defence marker genes [salicylic acid (PR1, PR2 and PR5) and jasmonic pathway (PDF1.2, VSP2, PR3 and PR4)] showed differential expression patterns between UV-treated S. sclerotiorum-inoculated tomato plants and fungal treated control plants (Fig. 6). All the UV-treated fungal inoculated tomato plants showed significantly higher expression of all the defence marker genes compared to fungal treated control plants. The highest expression of defence marker genes [PR1 (7.44-18.10-fold), PR2 (6.76-8.20-fold), PR5 (4.96-7.01-fold), PDF1.2 (6.10-13.01-fold), VSP2 (4.19-7.05-fold), PR3 (5.16-6.78-fold), and PR4 (3.60-4.18-fold)] were observed at cumulative dosage for the combination of UV-B (3600 J/m2) and UV-C (930 J/m2) compared to individual UV-B and UV-C treatments at 7-day post-UV treatment, (DP-UVT) (20 DPI) and 14-day post-UV treatment (DP-UVT) (27 DPI). (Fig. 6). Besides, at 7 DP-UVT, defence marker gene PR1 showed the highest differential expression (18.10-fold) followed by PR2 (8.19-fold) and PR5 (7.00-fold), whereas, at 14 DP-UVT, PDF1.2 showed the highest differential expression (11.37-13.01-fold) followed by VSP2 (7.05-fold) and PR3 (5.16-fold) (Fig. 6).