Turmeric (Curcuma longa L) is one of the most significant spice crops cultivated in India since antiquity. It is a member of the Zingiberaceae family of ginger and is also known as Indian saffron or Haldi. Rich in “curcumin,” its rhizomes are used for culinary, medicinal, religious, cosmetic and colouring reasons (Ravindran et al., 2007). Eighty percent of the world’s turmeric is produced, consumed and exported from India. Approximately 11 lakh tons of turmeric are produced annually worldwide. India exported 1.37 lakh tons of turmeric between April and October of 2024-2025. Bangladesh (26,285 tonnes), the United Arab Emirates (22,062 tonnes), Malaysia (6,419 tonnes), the United States (6,689 tonnes), Morocco (6,288 tonnes) and Iran (6,094 tons) are the main nations that import turmeric from India. In India, 2.91 lakh hectares (7.19 lakh acres) were planted with turmeric in 2024-2025. Maharashtra 0.78 lakh ha (1.93 lakh acres), Odisha 0.30 lakh ha (0.75 lakh acres), Tamil Nadu 0.24 lakh ha (0.58 lakh acres), Madhya Pradesh 0.26 lakh ha (0.64 lakh acres), West Bengal 0.19 lakh ha (0.47 lakh acres) and Telangana 0.16 lakh ha (0.41 lakh acres).The majority of turmeric cultivars on the market now are similarly vulnerable to serious diseases like leaf blotch (Taphrina maculans), rhizome rot (Pythium spp.) and leaf spot (Colletotrichum capsici). Turmeric foliar diseases reduce the size and weight of the rhizome by destroying the active photosynthetic surface. According to Hudge and Ghogul (2010), the leaf spot induced by C. capsici resulted in significant losses of 25.83 to 62.12 per cent fresh weight and 42.10 to 62.10 percent dry weight of mother and finger rhizomes, respectively. Farmers suffer significant financial losses as a result of the production drop brought on by leaf spot incidence.
       
Numerous external factors affect the growth and evolution of infections. Colletotrichum colonies exposed to light produced 1.70 times more conidia than colonies grown in total darkness. According to de Menezes et al. (2015), conidia grown in light exhibited UV tolerances that were at least twice as high as those grown in darkness. Light has an effect on Colletotrichum development, colony shape and virulence. This is important for the active production of melanin and for increasing virulence under different light wave lengths (Yu et al., 2013). Geographical location and nutrient availability had a significant impact on the growth, colony features, sporulation and spore dimensions of different isolates of C. lindemuthianum when exposed to cultural media (Narasimha et al., 2023). Potato dextrose agar and carrot dextrose agar were found to be the most efficient for C. capsici growth and sporulation among the twelve medium assessed (Joshi et al., 2024). According to Pillakathupu et al. (2021), soil modified with neem and goat dung was the most successful in lowering the severity of C. capsici illness.
       
Carbon sources had an impact on the proliferation of different Colletotrichum species. The best sugars for the growth of C. capsici were sucrose, lactose and glucose. Glucose, sucrose and fructose enhanced the growth of Colletotrichum gloeosporiosides and C. coccodes. (Shinde and Dilip, 2013). Arabinose had the highest dry mycelial weight (871.97 mg) of the nine carbon sources studied, followed by starch (575.38 mg) and sucrose (529.83 mg). After a 14-day incubation period, aspartic acid gained the highest dry mycelial weight (643.23 mg) among the six nitrogen sources, followed by sodium nitrate (390.87 mg) and ammonium sulphate (479.97 mg) (Sharma et al., 2025). For C. capsici, nitrogen sources like potassium nitrate, casein and calcium nitrate were found to be effective; for C. gloeosporiosides, peptone and potassium nitrate were appropriate; and for C. coccodes, peptone and sodium nitrate worked best (Shinde and Dilip, 2013).
       
Understanding the nutritional conditions and elements that affect a fungus’ mycelial growth is a prerequisite for any research that aims to comprehend the link between the host and the pathogen. The goal of the current investigation was to ascertain C. capsici’s morphological characteristics, sporulation on culture medium and growth on media containing different sources of carbon, nitrogen and organic extracts.

Isolation of Colletotrichum capsici
 
Turmeric leaves showed typical leaf spot symptoms were collected and pathogen was isolated.  The periphery of the lesions was cut into small pieces and surface sterilized with sodium hypochlorite (10.00 per cent) for 5-10 min. then washed with three changes of sterile distilled water. The sterilized bits were placed separately on potato dextrose agar (PDA) medium in Petri dishes. These plates were incubated at room temperature (28±2°C), observed the pathogen growth, identified the morphological characters and purified the Colletotrichum capsici (Plate 1).


 
Growth characters of C. capsici
 
Effect of light on growth and sporulation of C. capsici
 
The effect of light on growth and sporulation of C. capsici was studied on potato dextrose agar by exposing the pure cultures in Petri plate to 12 h. dark + 12 h. light, 6 h. dark + 18 h. light, 3 h. dark + 21 h. light, 18 h. dark + 6 h. light dark and 21 h. dark + 3 h. light. The plates were incubated at 28±1°C for seven days at continuous dark by covering with aluminium foil. The control plates were kept under natural light and dark conditions without covering aluminium foil. Observations on colony diameter and sporulation were recorded.
 
Growth of C. capsici on solid and liquid media
 
Eight different solid media viz., potato dextrose agar, potato dextrose agar + host leaf extract, Czapek’s Dox agar, Czapek’s Dox agar + host leaf extract, Richard’s agar, Richard’s agar + host leaf extract and rose bengal agar, rose bengal agar + host leaf extract were prepared separately and autoclaved at 1.4 kg/cm² pressure for 30 min. Nine mm culture disc of the virulent pathogen was placed at the centre of each sterile Petri plates containing different solid media separately and incubated for 10 days at room temperature (28±2°C) with three replications. The radial mycelial growth of the fungus was recorded in all the media. The same plates were also maintained at the same condition for some more days to observe the time period required for covering the entire plate. The above said media were prepared as broth @ 100 ml in 250 ml conical flasks separately and autoclaved as above. The flasks were inoculated with nine mm culture disc of 15 days old with three replications. Ten days after incubation, the mycelial mat of isolate was filtered through a pre weighed Whatman No.1 filter paper and dried in hot air oven at 60°C until a constant weight was obtained by subtracting the weight of the filter paper.
 
Growth on different carbon and nitrogen sources in solid and liquid medium
 
Richard’s agar medium containing different carbon sources viz., sucrose, mannitol, starch, cellulose and glucose @ 21.053 g of each per litre of medium was added separately and autoclaved at 1.4 kg/cm² pressure for 30 min. Nine mm culture disc of C. capsici was placed at the centre of the each sterile Petri plates containing the above said solid medium with different carbon sources separately and incubated for 15 days at room temperature (28±2°C) with five replications. Richard’s agar medium without any carbon source was served as control. The radial mycelial growth was recorded. The above carbon sources were used in Richard’s broth @ 21.053 g of each per litre of broth was prepared separately. One hundred ml broth of each carbon source was distributed uniformly into each 250 ml conical flask separately and autoclaved at 1.4 kg/cm² pressure for 30 min. and allowed to cool. Each flask was inoculated separately with 15 days old nine mm disc of C. capsici with five replications. Richard’s broth without any carbon source was served as control. Dry weight of mycelia was taken 15 days after inoculation. The above said procedure was followed for different nitrogen sources in Richard’s agar medium and broth. Sodium nitrate, ammonium sulphate, ammonium oxalate, ammonium dihydrogen phosphate and ammonium ferrous sulphate @ 1.385 g of each per litre of medium was added separately and sterilized. Inoculation of pathogen, incubation and recording of mycelial growth was done as above.
 
Effect of organic manure extracts on the growth of C. capsici in solid and liquid medium
 
The aqueous extracts of different organic manures viz., neem cake, farm yard manure (FYM), vermicompost, poultry manure and coir waste were prepared by suspending 30 g of each organic material in 100 ml of sterile distilled water in 500 ml conical flask for overnight. Then, the flasks were thoroughly shaken and content was filtered through double layered muslin cloth and autoclaved at 1.4 kg/cm² pressure for 30 min. The autoclaved extracts were individually added into previously sterilized molten Richard’s agar @ 10 per cent and 20 per cent and mixed thoroughly, poured into Petri plates and allowed to solidify. All the plates were incubated at 28±2°C after placing the nine mm discs of C. capsici with five replications. Richard’s agar without manure extract served as control. The radial mycelial growth of the pathogen was measured 15 days after incubation.
       
As mentioned above the same organic manures extracts at the rate of 10 per cent and 20 per cent concentrations were added to Richard’s broth individually.  Richard’s broth with distilled water served as control. The broth individually contained organic manure extract was poured in to 250 ml conical flasks @ 100 ml each and autoclaved at 1.4 kg/cm² pressure for 30 min. and inoculated with nine mm culture disc of C. capsici with five replications. The flasks were incubated for 15 days at room temperature (28±2°C). Inoculation of pathogen, incubation and recording of mycelial dry weight was done as above.
       
The per cent growth inhibition (PGI) of the pathogen was worked out for the above experiments by using the formula given by Vincent (1947).

 

 

Where,                  
C - Control.   
T - Treatment.
   
The above experiments were conducted in SRM College of Agricultural Sciences, Baburayanpettai, Chengalpattu District and Adhiparasakthi Agricultural College, Ranipet District, Tamil Nadu during 2024-2025.
                                             
Statistical analysis
 
The experiments were conducted by following completely randomized design (CRD). The statistical analysis of the experiment was done by the methods suggested by Gomez and Gomez (1984). Prior to statistical analysis of variance (ANOVA) the percentage values of the disease index were arcsine transformed. Data were subjected to analysis of variance (ANOVA) at significant level (P<0.05) and the means were compared by Duncan’s multiple range test (DMRT). 

Growth characters of C. capsici
 
Effect of light on growth and sporulation of C. capsici
 
The study on the effect of light on growth and sporulation of C. capsici showed the excellent conidia production under 3 h. dark + 21 h. light and continuous dark for seven days and the good sporulation was recorded in 6 h. dark + 18 h. light and continuous dark for seven days and in control. Poor conidia production was observed in 21 h. dark + 3 h. light and continuous dark for seven days (Table 1). An experiment conducted by Kommula et al. (2017) to understand the influence of light regimes on the growth of C. capsici revealed that alternate cycles of 12 hours dark and 12 hours light yielded a maximum colony growth. The findings of Unnithan et al. (2018) also pointed out that the performance of the pathogen under normal room conditions was a way better than in continuous darkness.  Maximum sporulation was recorded when C. musae culture was exposed to alternate cycles of 12 hours light and 12 hours darkness, continuous light and under normal conditions. Sporulation was good in continuous darkness (Prathibha et al., 2020).


 
Effect of different medium on the radial mycelial growth of C. capsici
 
The mean radial mycelial growth of C. capsici on different solid media was studied and it was ranged between 59.00 mm and 90.00 mm. Among the eight solid media, potato dextrose agar medium (PDA) was significantly superior and recorded the highest mycelial growth of 90.00 mm and this was followed by PDA + host leaf extract (HLE) as 87.00 mm, Richard’s agar (RA) as72.33 mm and least in Rose bengal (RBA) + HLE as 59.00 mm (Fig 1 and Plate 2). Czapek’s agar (CZA) individually and with host leaf extract and Richard’s agar alone and combined with host leaf extract showed on par results.




       
Among the tested media, PDA covered the Petri plate rapidly in eight days period, PDA with HLE covered in 10 days followed by Richard’s agar (12 days). Maximum period of sixteen days was taken by the pathogen in RBA + HLE (Fig 2).


 
Effect of liquid media on the dry mycelial weight of C. capsici
 
An experiment was conducted to identify the best liquid medium which supported the increased mycelial growth of the pathogen, C. capsici. Among the eight liquid media, potato dextrose broth (PDB) significantly encouraged the mycelial dry weight (657.66 mg) followed by PDB + HLE (631.00 mg), RB (600.66 mg), Czapek’s broth (CZB) (584.66 mg), Richard’s broth (RB)+ HLE (561.33 mg), CZB + HLE (554.00 mg), RB (543.33 mg), RBB + host leaf extract (466.33 mg) (Fig 3). In all the media, combined with host leaf extract was on par with individual medium except RBB and with host leaf extract.


       
According to Niren and Nakul (2019), out of twelve media used, OMA was found to be most suitable for heavy sporulation while PDA reproduced best mycelia and visible colony morphology (Oiuphisittraiwat et al. 2024). Least growth and sporulation recorded on synthetic media like CDA and RA.  Potato dextrose agar was the best for both radial growth (66.74 mm) and dry mycelial weight (264.74 mg) of Colletotrichum, whereas, host leaf extract agar significantly supported more sporulation 7.3 ×10⁴. The least mycelia growth of 39.32 mm, dry mycelial weight of 234.70 mg and sporulation 2.9 ×10⁴ were observed on Sabourband’s agar (Narasimha et al., 2023). 
 
Utilization of different carbon sources by C. capsici on solid and liquid media
 
The growth of the pathogen in different carbon sources amended RA medium exhibited significant differences between the treatments. Sucrose as carbon source prompted significant mycelial growth of 90.00 mm and the mycelial dry weight of 756.00 mg followed by glucose (85.66 mm and 733.00 mg). RA without any carbon source served as control and exhibited least mycelial growth of 69.66 mm and 459.33 mg (Fig 4 and 5 and Plate 3 and 4). Anil (2015) reported the maximum growth on maltose followed by glucose and sucrose. The maximum growth of the C. capsici isolate was obtained in sucrose, fructose and maltose (19 mm±00 mm) on isolate AUPEP-6 followed by glucose (16±1 mm), lactose (15.67±0.58 mm), whereas the least mycelial growth was observed on lactose (1.67±.58mm) on isolate AUPEP-9 (Messele et al., 2017).








 
Effect of different nitrogen sources on the growth of C. capsici on solid medium and liquid medium
 
The growth of the pathogen in different nitrogen sources amended Richard’s medium showed significant differences between the treatments. Ammonium oxalate as nitrogen source significantly increased the radial mycelial growth of 90.00 mm and mycelial dry weight of 834.33 mg followed by sodium nitrate 88.00 mm and 763.33 mg.  Richard’s medium without any nitrogen source recorded least growth of 70.00 mm (Fig 6 and Plate 5) and dry weight of 459.33 mg (Fig 7 and Plate 6).                             



   



         

Ammonium sulphate and ammonium dihydrogen phosphate were on par with each other in mycelial growth of C. capsici. Among the nitrogen sources, the pathogen preferred potassium nitrate followed by sodium nitrate and asparagines, lead nitrate and ammonium chloride supported least growth (Anil, 2015). The utilization of six different nitrogen sources by Colletotrichum isolates on the growth was significant. Sodium nitrate and ammonium dihydrogen phosphate (18±00 mm) supported the maximum growth followed by potassium nitrate (17±00 mm) and ammonium sulphate (16.67±.58 mm) on C. capsici isolate AUPEP-6. Potassium nitrate was found to be the least utilized nitrogen source on isolate AUPEP -9 (Messele et al., 2017).
 
Effect of different concentration of organic manure extracts on growth of C. capsici
 
The effect of five manure extracts at 10 and 20 per cent concentrations were tested on the mycelial growth of C. capsici. Among the five manure extracts tested, the neem cake extract showed the higher radial growth of 85.66 mm and 78.33 mm at 10 and 20 per cent concentrations against the control, which recorded 90.00 mm. Minimum radial growth of 59.33 mm and 53.33 mm was obtained in poultry manure extract amended medium at 10 and 20 per cent concentrations (Fig 8). Except coir waste extract, all the organic manure extracts at 10 and 20 per cent concentrations were equally effective in mycelial growth.


       
The mycelial dry weight of the pathogen in the above extracts at 10 and 20 per cent concentrations on liquid medium was also studied. In 10 per cent concentration, the weight varied from 348.00 mg to 728.66 mg. Coir waste exhibited the least weight of 348.00 mg. PDA without any manure extracts exhibited highest mycelial dry weight (769.66 mg). In 20 per cent concentration, the weight varied between 269.00 mg and 596.00 mg. (Fig 9). Reduction in survival ability of the pathogen correlated well with levels of concentrations of poultry manure which was more pronounced at three and five per cent levels (52-64 per cent) was reported by Shaikh et al., (2004).

Colletotrichum capsici causing leaf spot disease is most prevalent in the major turmeric growing areas of Tamil Nadu. The effect of light on growth and sporulation of C. capsici showed the excellent conidial production under 3 h. dark + 21 h. light and continuous dark for seven days. Poor conidial production was observed in 21 h. dark + 3 h. light and continuous dark for seven days. Potato dextrose agar and potato dextrose agar + host leaf extract media were supported the maximum radial mycelial growth (90.00 and 87.00 mm) in solid medium and maximum mycelial dry weight (657.66 mg and 631.00 mg) in liquid medium. Among the five different carbon sources tested in solid and liquid media, sucrose was identified as the best carbon source for maximum radial mycelial growth and mycelial dry weight (90.00 mm and 756.00 mg). Ammonium oxalate was identified as the best nitrogen source for maximum mycelial growth and mycelial dry weight (90.00 mm and 763.33 mg) among five different nitrogen sources tested in solid and liquid media. Poultry manure was identified as the best organic manure among others for the inhibition of growth of C. capsici and recorded the least mycelial dry weight of 327.33 mg and least mycelial growth of 59.33 mm and 53.33 mm at 10 and 20 per cent concentrations respectively.

Authors would like to thank the above Institutions for providing facilities to conduct this research work.
 
Funding
 
No source of funding for research.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.