Forest ecosystems are vital for maintaining ecological balance, conserving biodiversity and supporting regional economies. Among temperate forest species, Cedrus deodara (deodar cedar) is a dominant conifer of the Western Himalayas, widely distributed in Jammu and Kashmir, India. It is valued for its ecological role in maintaining forest stability as well as for its economic importance through high-quality timber and soil conservation (Thakur and Tomar, 2020). Like other coniferous species, Cedrus deodara is susceptible to several fungal diseases which adversely affect plant health, seedling establishment and long-term forest productivity. Several fungal pathogens have been reported causing serious diseases in cedar and related conifer species worldwide. Root rot caused by Phytophthora cinnamomi has been reported as a major cause of drying and decline in Cedrus deodara in the North-Western Himalayas (Tapwal, 2010). Similarly, Dothistroma septosporum has been reported causing needle discoloration and premature defoliation in cedar species (Mullett and Fraser, 2016), while Lecanosticta acicola has been identified as the causal agent of brown spot needle blight in atlas cedar leading to premature needle shedding and decline in tree health (Schenck et al., 2022). Other fungal pathogens such as Diplodia pinea have also been reported causing dieback and stem cankers in conifer species, resulting in serious damage under favourable environmental conditions (Hlaiem et al., 2023).
       
Environmental factors play a crucial role in the development of fungal diseases in forest ecosystems. Temperature, relative humidity, rainfall and prolonged leaf wetness influence spore production, germination, pathogen survival and host infection. High humidity and frequent rainfall create favourable conditions for disease development and spore dispersal, while climatic fluctuations can stress conifer species, increasing their susceptibility to fungal infection (Pandey et al., 2023; Sharma and Sharma, 2024; Kumar and Pandey, 2024).
       
Fusarium graminearum is an important fungal pathogen, commonly known to cause severe diseases in cereal crops including wheat, barley and maize. The pathogen is responsible for diseases like Fusarium head blight, seedling blight, crown rot and root rot, resulting in loss of crop yield and grain quality worldwide (Xu et al., 2022; Jan et al., 2026). Because of its major economic impact and broad host range, it is regarded as one of the top ten fungal pathogens in plant pathology (Dean et al., 2012). Although the pathogen has been extensively investigated in agricultural crops, its occurrence in forest nurseries remains underexplored.
       
Recent observations in conifer nurseries of District Kupwara, North Kashmir, revealed serious needle blight symptoms associated with Fusarium graminearum. In our previous study, isolate CN16 was isolated from symptomatic Cedrus deodara needles, identified as Fusarium graminearum through morphological and molecular characterization and its pathogenicity was confirmed through pathogenicity testing and fulfilment of Koch’s postulates (Jan et al., 2026). However, the epidemiology of this disease and the environmental factors influencing its development remain poorly understood. Building upon this previously established pathogen-host association, the present study was undertaken to: (i) assess the incidence and intensity of needle blight in Cedrus deodara nurseries of District Kupwara, North Kashmir; (ii) investigate the epidemiology of the disease using the previously characterized Fusarium graminearum isolate CN16; (iii) evaluate the effects of temperature and relative humidity on spore production and germination under laboratory conditions; and (iv) examine the relationships between disease development and field meteorological variables, including temperature, relative humidity, rainfall and wind speed.

Survey and assessment of needle blight disease
 
Field surveys were conducted during 2023 and 2024 in four nurseries located at Zachaldara, Reshwari, Diver and Chowkibal in District Kupwara, North Kashmir, to assess needle blight of Cedrus deodara. In each nursery, three 1 × 2 m² plots were randomly selected independently in each study year, with each plot containing 100 two-year-old seedlings. Thus, different sets of two-year-old seedlings were assessed in 2023 and 2024. Each plot was considered a sampling replicate and disease incidence and intensity were assessed at the plot level. Disease incidence was determined by counting the number of seedlings showing one or more characteristic needle blight symptoms, including chlorotic spots, browning, necrotic lesions, premature needle shedding, or associated needle damage. A seedling was considered infected when one or more needles or whorls exhibited visible symptoms. Disease incidence was calculated as the percentage of infected seedlings out of the total number of seedlings assessed in each plot using the following formula:

 
For each plot, 100 two-year-old seedlings were assessed. Disease intensity was assessed visually at the whorl level using the 0-4 rating scale of Skilling and Nicholls (1974). Each whorl was assigned a disease severity rating based on the proportion of needles within the whorl exhibiting visible disease symptoms (Table 1).


       
The percentage of disease intensity was determined using the expression:

Isolation and identification of Fusarium graminearum
 
The Fusarium graminearum isolate CN16 used in the present study was obtained from symptomatic needles of Cedrus deodara during the previous investigation (Jan et al., 2026). For isolation, approximately 5-mm needle segments from the advancing margins of lesions were surface sterilized with 70% ethanol, rinsed three times with sterile distilled water, air-dried under aseptic conditions and placed on potato dextrose agar (PDA). Emerging fungal colonies were purified by hyphal-tip transfer and maintained on PDA. Morphological identification was based on colony and microscopic characteristics. Colonies exhibited rapid growth with yellowish-brown to reddish-brown pigmentation and dense, woolly mycelium. Microscopic examination revealed septate, branched hyphae and hyaline, slightly curved, 3-5-septate macroconidia measuring approximately 30-40 × 5-8 µm, consistent with Fusarium graminearum (Jan et al., 2026). Molecular identification of isolate CN16 was previously performed using the internal transcribed spacer (ITS) region and translation elongation factor 1-alpha (TEF1-α) gene. The ITS region was amplified using ITS1 and ITS4 primers and the resulting sequences were compared with reference sequences using BLASTn. The ITS sequence showed 99% similarity with reference sequences of Fusarium graminearum and was deposited in GenBank under accession number PX116986. TEF1-α was additionally amplified and sequenced for taxonomic confirmation and phylogenetic analyses based on ITS and TEF1-α sequences placed isolate CN16 within the Fusarium graminearum clade (Jan et al., 2026). The pathogenicity of the same isolate CN16 on Cedrus deodara was previously confirmed through artificial inoculation and fulfilment of Koch’s postulates (Jan et al., 2026). Therefore, the present study used the previously characterized isolate CN16 for the laboratory epidemiological experiments described below.
 
Effect of temperature on spore production and germination
 
Spore production at different temperatures
 
The effect of temperature on spore production of Fusarium graminearum isolate CN16 was evaluated under laboratory conditions. Actively growing 5-mm mycelial discs from 7-day-old PDA cultures were transferred to fresh PDA plates. The plates were incubated in BOD incubators at seven temperature regimes (10, 15, 20, 25, 30, 35 and 40°C). Three replicate plates were used for each temperature treatment in a completely randomized design (CRD), with each plate considered an experimental unit. After 7 days of incubation, spores (conidia) were harvested from each plate by flooding the colony surface with 10 mL of sterile distilled water containing one drop of Tween-20 and gently scraping with a sterile glass rod. The resulting suspension was filtered through two layers of muslin cloth to remove mycelial fragments. Spore concentration (spores mL^-1) was determined using a haemocytometer.
 
Spore germination at different temperatures
 
To assess the effect of temperature on spore germination, a standardized conidial suspension of isolate CN16 was prepared from cultures incubated at 25°C and adjusted to 1 × 10⁴ conidia mL^-1 using a haemocytometer. Aliquots (0.1 mL) of the suspension were placed onto thin layers of 2% water agar in cavity slides. Three replicate sets were used for each temperature treatment, with three slides prepared for each replicate. The germination values obtained from the three slides within each replicate were averaged to obtain one replicate value. The inoculated slides were placed in moist chambers lined with moist filter paper and incubated at 10, 15, 20, 25, 30, 35 and 40°C. After 12-24 h of incubation, the slides were examined under a compound microscope. Spores showing visible germ-tube emergence were considered germinated and germination percentage was calculated as the proportion of germinated spores relative to the total number of spores counted.
 
Effect of relative humidity on spore production and germination
 
The influence of relative humidity (RH) on spore production and germination of F. graminearum isolate CN16 was studied under controlled laboratory conditions. Seven RH levels (50, 60, 70, 80, 90, 98 and 100%) were established and maintained using sealed desiccators containing saturated salt solutions. RH conditions were verified using a thermometer-hygrometer.
 
Spore production at different RH levels
 
For spore production, PDA plates of isolate CN16 were incubated at 25°C for 5 days to obtain actively sporulating cultures. The plates were subsequently placed in sealed desiccators maintained at the respective RH levels and exposed for 48 h. Three replicate plates were used for each RH treatment in a completely randomized design (CRD), with each plate considered an experimental unit. Spores were harvested from the colony surface by flooding each culture with 10 mL of sterile distilled water containing one drop of Tween-20 and gently scraping with a sterile glass rod. The resulting suspension was filtered through two layers of muslin cloth to remove mycelial fragments and spore concentration (spores mL^-1) was determined using a haemocytometer. The spore concentration obtained from each plate represented one replicate value.
 
Spore germination at different RH levels
 
For spore germination, a standardized conidial suspension of 1 × 10⁴ conidia mL^-1 was prepared. Aliquots (0.05-0.1 mL) of the suspension were placed on clean glass slides coated with a thin film of water agar or 1% gelatin. Three replicate sets were used for each RH treatment, with three slides prepared for each replicate. The germination values obtained from the three slides within each replicate were averaged to obtain one replicate value. The slides were placed inside desiccators maintained at the respective RH levels and incubated at 25±2°C. After 24 h, the slides were examined microscopically and germinated and non-germinated conidia were counted. Germination percentage was calculated as the proportion of germinated conidia relative to the total number of conidia counted.
 
Effect of meteorological factors on disease development
 
The influence of weather factors on needle blight development was studied during 2023 and 2024 at the SKUAST-Kashmir nursery, Wadura. Six naturally infected six-year-old Cedrus deodara plants were monitored fortnightly from February to November without fungicide application. Disease severity was assessed using a 0-5 rating scale.
       
Meteorological data, including temperature, relative humidity, rainfall and wind speed, were obtained from the university observatory at SKUAST-Kashmir, Wadura. Disease intensity was recorded at 15-day intervals from the first fortnight of February to the first fortnight of November during 2023 and 2024. Meteorological data corresponding to each 15-day observation period were matched with the disease-intensity values recorded for the same period. These paired observations were used for correlation and multiple regression analyses.
 
Disease development rate
 
The logarithmic infection rate (r) was calculated following Vander plank (1963):

 
Where,
r = Logarithmic infection rate (unit/day)
x₁ = Disease intensity at time t₁
x₂ = Disease intensity at time t₂
t₂ - t₁ = Time interval between successive observations
where (x₁) and (x₂) are disease intensities at times (t₁) and (t₂), respectively.
 
Statistical analysis
 
Experimental data were subjected to analysis of variance (ANOVA) and treatment means were compared using critical difference (CD) at the 5% level of significance. Percentage data were subjected to arcsine transformation, whereas spore count data were square-root transformed prior to statistical analysis.  For the field-weather analysis, disease intensity was recorded at 15-day intervals on six plants and expressed as the mean disease intensity for each observation interval. Correlation and multiple regression analyses were performed using the interval mean values from 36 observation intervals (18 intervals in each year) to examine the association between disease development and meteorological variables. The temperature and relative humidity experiments were conducted in a completely randomized design (CRD) with three independent replicate plates per treatment, while three slides were used for each replicate in the germination experiments and their values were averaged. The variation among replicates within treatments was considered the experimental error. All statistical analyses were performed using OPSTAT statistical software.
       
Disease incidence and intensity data expressed as percentages were subjected to arcsine transformation before analysis. A two-way analysis of variance (ANOVA) was performed to assess the effects of location, year and their interaction. The transformed values were used for statistical analysis, whereas original percentage values are presented in the tables for biological interpretation. Treatment means were compared using the critical difference (CD) at the 5% level of significance.

Symptomatology of needle blight disease
 
Field surveys during 2023 and 2024 revealed typical needle blight symptoms on Cedrus deodara seedlings in District Kupwara. Initial symptoms appeared as small yellow spots (0.1-0.7 mm) on needles, which enlarged (0.7-1.5 mm) during May-June, causing greenish-yellow discoloration (Fig 1). By late June, black fungal fructifications developed on infected needles. Severe infections resulted in needle browning, premature needle drop, reduced seedling vigour and stunted growth. Similar symptoms caused by Fusarium graminearum have also been reported in cereal crops (Taheri, 2018).


 
Disease incidence and intensity in nurseries
 
Field surveys conducted during 2023 and 2024 revealed significant variation in needle blight incidence among locations and years, whereas disease intensity differed significantly between years but not among locations given below (Table 2).


       
Disease incidence was comparatively higher during 2023 than 2024, with an overall mean incidence of 35.08% and 31.58%, respectively (Table 3). Across both years, disease incidence ranged from 28.99% to 36.16%. The highest pooled disease incidence (36.16%) was recorded in Reshwari, followed by Diver (34.16%), whereas the lowest incidence (28.99%) was observed in Zachaldara.


       
Mean disease intensity was recorded at 17.95% during 2023 and 15.91% during 2024 (Table 4). Across all surveyed locations, pooled disease intensity ranged from 15.57% to 18.35%. The highest disease intensity (18.35%) was recorded in Reshwari, followed by Chowkibal (17.43%), whereas Zachaldara recorded the lowest intensity (15.57%). The comparatively higher disease incidence and intensity recorded during 2023 may be attributed to relatively favourable environmental conditions supporting pathogen development and disease progression.


 
Effect of altitude on disease incidence and intensity
 
The correlation analysis revealed a positive relationship between altitude and needle blight severity associated with Fusarium graminearum in Cedrus deodara nurseries (Table 5). In 2023, disease incidence showed a moderate positive correlation with altitude (r = 0.60), which was stronger in 2024 (r = 0.93). The pooled correlation coefficient is 0.67.


       
Similarly, disease intensity exhibited a strong positive correlation with altitude in 2023 (r = 0.75), while a moderate positive relationship was observed in 2024 (r = 0.59) while the pooled intensity correlation was 0.90. However, none of these correlations was statistically significant at the 5% level. These results therefore indicate an observed positive association between altitude and disease incidence and intensity, because the analysis was based on only four locations. The apparent association may be related to environmental conditions such as temperature and moisture regimes at different elevations. The observed positive association is broadly consistent with previous reports suggesting that elevation-associated environmental conditions may influence the occurrence of needle-colonizing fungal pathogens (Van Maanen et al., 2000; Gourbière et al., 2001).
 
Effect of temperature on spore production and germination
 
Temperature significantly influenced both spore production and germination of Fusarium graminearum under laboratory conditions (Table 6). No spore production or germination was recorded at 10°C, indicating no detectable spore production or germination under the laboratory conditions tested. A significant increase in spore production was observed at 20°C, reaching 315.66 spores, although germination remained limited at 10.0%. The highest spore production was recorded at 25°C (344 spores), which also coincided with the maximum germination percentage (36.6%). Beyond 25°C, both spore production and germination declined sharply. At 30°C, spore production decreased to 216.3, while germination dropped to 5.0%. Further increases in temperature resulted in a pronounced reduction in reproductive activity. At 35°C, spore production was limited (126.6) and germination was completely inhibited. Similarly, at 40°C, only 59.3 spores were production, with no germination observed.


       
Under the laboratory conditions tested, spore production and germination were highest at 25°C, whereas lower and higher temperatures resulted in reduced or no detectable germination. These findings agree with Leslie et al., (2006), who reported optimum growth and sporulation of Fusarium spp. at 20-28°C.
 
Effect of relative humidity on spore production and germination
 
Relative humidity significantly influenced spore production and germination of Fusarium graminearum (Table 7). Maximum spore production and germination were recorded at 98-100% RH, while both parameters declined progressively with decreasing humidity. At 60% RH, spore production and germination were greatly reduced and no spore activity was observed at 50% RH. Prolonged incubation (4 days) further enhanced spore production and germination under favourable humidity conditions. Overall, high relative humidity (≥90%) was essential for optimum spore production and germination and the observed differences were statistically significant (p = 0.05).


       
These findings indicate that high relative humidity (>90%) favours spore production and spore germination of Fusarium graminearum under the laboratory conditions tested. Prolonged moisture availability may promote hydration of conidia, metabolic activation and successful germ tube emergence. Similar observations have been reported by Griffin (1996); Madhavi and Krishna Murthy (2019), who reported that atmospheric moisture plays a critical role in fungal physiology, spore germination and infection establishment. The present findings suggest that prolonged humid conditions may favour fungal disease development under natural conditions (Rotem, 1994).
 
Effect of weather parameters on disease development
 
Needle blight development caused by Fusarium graminearum was monitored during 2023 and 2024 to assess its association with weather factors (Fig 2 and 3). In both years, disease intensity remained low during February-March under cool, dry conditions. Disease increased gradually from April-May with rising temperatures (13-19°C) and moderate relative humidity, followed by a sharp increase during June-August when temperatures (22-24°C) and humidity were high. Peak disease intensity was recorded during September-October and remained high until November, indicating that warm temperatures and high relative humidity favored disease development.




       
The most rapid increase in disease intensity occurred between June and August, when temperatures peaked at 24-27°C, relative humidity remained moderately high and rainfall events were more frequent than early-season periods. Disease intensity continued to rise through September and October, reaching its highest levels, even as temperature gradually declined, suggesting a lag effect between favourable weather conditions and visible disease expression (Nagaraju et al., 2025). The field observations were broadly consistent with the laboratory findings. Disease development was most pronounced when field temperatures were approximately 22-27°C, while the laboratory experiment recorded maximum spore production and germination at 25°C. This overlap suggests that temperatures around 25°C may favour fungal reproductive activity and disease development under the conditions observed in the present study. However, the laboratory optimum should not be interpreted as a field epidemiological threshold, as disease development under natural conditions is influenced by multiple interacting factors, including relative humidity, rainfall and wind speed. By November, disease intensity stabilized at a high level, while temperature, rainfall and wind speed declined.
       
The seasonal progression of disease clearly demonstrated that moderate temperature and sustained humidity strongly influence disease establishment and progression under natural conditions. Similar findings were reported by Skilling (1974), who demonstrated that cool and humid environmental conditions together with prolonged needle wetness create favourable conditions for conifer needle infection and disease progression.
 
Correlation and regression analysis of meteorological factors
 
Correlation analysis revealed variable associations between meteorological factors and disease intensity and infection rate of needle blight caused by Fusarium graminearum (Table 8). Temperature exhibited a significant positive correlation with disease intensity (r = 0.41), indicating that increasing temperature within favourable range promoted disease development. However, temperature showed a significant negative correlation with infection rate (r = –0.58), suggesting reduction in new infection establishment during advanced disease stages.


       
Correlation analysis showed that relative humidity had weak positive associations with disease intensity (r = 0.15) and infection rate (r = 0.04), while rainfall showed a weak negative association with disease intensity (r = -0.11). Wind speed was strongly negatively correlated with disease intensity (r = -0.75) but showed a moderate positive correlation with infection rate (r = 0.32). In contrast, studies on other conifer needle pathogens have reported stronger relationships between moisture-related variables and disease processes. For example, relative humidity and rainfall were reported to influence spore abundance of Lecanosticta acicola on eastern white pine (Wyka et al., 2018). However, in the present field dataset, the weak correlations observed for relative humidity and rainfall suggest that their direct relationships with disease intensity were limited, highlighting differences between pathogen-host systems and between spore production and disease development. Multiple regression analysis showed that the weather parameters collectively explained 56.78% of the variation in disease intensity (R² = 56.78%), with positive regression coefficients for temperature and relative humidity and negative coefficients for rainfall and wind speed (Table 9).


       
The regression model for infection rate explained 35.04% of the total variation (R² = 35.04). Temperature and relative humidity had negative effects on infection rate, whereas rainfall and wind speed contributed positively, indicating their role in the initiation and spread of new infections rather than overall disease severity. Similar relationships between weather factors and forest fungal diseases have been reported by (Sinclair and Lyon, 2005; Pampanagouda et al., 2019; Nagaraju et al., 2025).

The present investigation provides an epidemiological assessment of needle blight caused by Fusarium graminearum on Cedrus deodara in District Kupwara, North Kashmir, building upon the recently reported occurrence of this pathogen-host association. Disease incidence showed significant variation among locations and years, whereas disease intensity varied significantly between years but not among locations. Higher disease intensity was generally recorded at some high-altitude nurseries and a positive association between altitude and disease incidence and intensity was observed. Laboratory studies demonstrated that temperature and relative humidity strongly influenced fungal reproductive development, with maximum spore production and germination observed at 25°C and relative humidity above 90%. Field epidemiological observations, together with correlation and regression analyses, indicated that meteorological conditions, particularly temperature, were associated with disease development under natural conditions, while the relationships with relative humidity, rainfall and wind speed varied in strength. These findings provide baseline information for disease monitoring and may contribute to the development of future forecasting and management strategies for Cedrus deodara needle blight under temperate Himalayan conditions.

There is no conflict of interest declared by any of the authors.