Pea (Pisum sativum L.), commonly known as table pea, is a major leguminous vegetable crop belonging to the Fabaceae family. Among the fungal pathogens causing disease in peas, Rhizoctonia solani is particularly destructive, leading to root rot. This study assessed the in vitro effectiveness of seven fungicides carbendazim 50% WP, copper oxychloride 50% WP, tebuconazole 25.9% EC, hexaconazole 5% SC, propiconazole 25% EC, tebuconazole 50% + trifloxystrobin 25% WG, and thiophanate methyl 70% WP against R. solani at multiple concentrations. Complete inhibition of mycelial growth was observed with carbendazim, tebuconazole, hexaconazole, propiconazole, and the combination of tebuconazole + trifloxystrobin at 100, 150, and 200 ppm. Conversely, copper oxychloride at 500 and 1000 ppm was the least effective, followed by thiophanate methyl 70% WP.

Pea (Pisum sativum L.), an important legume of the Fabaceae family, is widely cultivated as a cool-season vegetable crop. It originated in the Mediterranean region and is consumed fresh, canned, or processed. Various types include garden, dry, edible-podded, and dwarf peas (Duke, 1981). Through symbiosis with Rhizobium, peas enrich soil nitrogen and support crop rotation. Optimal growth occurs in well-drained, light soils at 10-23 C and pH 5.5-7.0 (McKay et al., 2003). Nutritionally, peas are rich in protein (15.5-39.7%), vitamins (A, B-complex, C), minerals (Ca, P, K), and antioxidants (Clark, 2007). Dried peas offer even higher protein (22.9%) and carbohydrate (60.7%) content (Duke, 1981; Hulse, 1994).

Pea is a key crop in India, ranking fourth in area and fifth in global output (FAO, 2022). It spans 5.82 lakh hectares with 6.7 million tonnes yield annually (Anonymous, 2022a). Major growing states include Uttar Pradesh, Madhya Pradesh, and Rajasthan. In Rajasthan, 12,687 hectares produce 25,385 tonnes, with Jaipur alone contributing 7,801 hectares and 7,335 tonnes (Anonymous, 2022b). Low yields are mainly due to poor germination, nutrient deficiency, and especially diseases.

Pea crops are vulnerable to over 20 pathogens, including those causing Ascochyta blight, powdery and downy mildew, seedling blight, grey mold, root rot, white mold, anthracnose, rust, bacterial blight, soft rot, and viral diseases like pea mosaic virus and seed-borne mosaic virus (Gupta and Paul 2001).

Among fungal infections, root rot caused by Rhizoctonia solani is especially damaging. It can infect a wide array of host plants and persist in soil through sclerotia or saprophytic growth (Dube, 2013). The teleomorph is Thanatephorus cucumeris, and isolates are often categorized into anastomosis groups (AGs) based on hyphal fusion (Sneh et al., 1991). This pathogen attacks pea seeds, hypocotyls, and epicotyls (Acharya et al., 2014). Due to its capacity to survive in soil for up to six years, control becomes challenging.

Favorable conditions for disease development include warm and moist environments, especially affecting young seedlings (Cubeta and Vilgalys 1997). Incidence in India has been reported between 14.8% and 64.7% (Masoodi et al., 2016), and in Rajasthan, losses can go up to 72.98% (Sharma et al., 2016). Nationwide yield losses have ranged from 30% to 57% (Sharma et al., 2022).

Chemical intervention becomes necessary where root rot is prevalent. Therefore, this study focuses on evaluating the in vitro antifungal efficacy of certain fungicides against Rhizoctonia solani.

The effectiveness of seven fungicides (carbendazim 50% WP, copper oxychloride 50% WP, tebuconazole 25.9% EC, hexaconazole 5% SC, propiconazole 25% EC, tebuconazole 50% + trifloxystrobin 25% WG, and thiophanate methyl 70% WP) was assessed against the mycelial growth of Rhizoctonia solani at concentrations of 100, 150, 200, 500, 1000, and 1500 ppm (Table 1).

The poisoned food technique was utilized to evaluate the fungicidal activity. For each fungicide, a stock solution with an active ingredient concentration of 30,000 mg ml⁻¹ was prepared. Appropriate volumes were drawn from the stock and mixed with molten potato dextrose agar (PDA) to achieve the desired test concentrations. Twenty millilitres of the amended medium were poured into sterilized Petri dishes.

A 5 mm diameter mycelial disc was excised from a 15-day-old culture of R. solani using a sterile cork borer and carefully placed at the center of each plate under aseptic conditions. Control plates contained PDA without any fungicide. The experiment followed a completely randomized design (CRD) with three replications per treatment. All plates were incubated at 28 ± 1°C in a BOD incubator.

After 4 days of incubation, the radial growth of fungal colonies was measured. The percentage inhibition of mycelial growth compared to the control was calculated using the standard formula. Data obtained were subjected to statistical analysis under CRD.

I = C – T / C * 100

Where, I = Per cent mycelial inhibition of test pathogen, C = Radial growth (mm) in control, T = Radial growth (mm) in treated plates.

Table 1: Details of chemical fungicide and concentrations used in experiment.

Seven fungicides (copper oxychloride 50% WP, carbendazim 50% WP, tebuconazole 25.9% EC, hexaconazole 5% SC, propiconazole 25% EC, tebuconazole 50% + trifloxystrobin 25% WG, and thiophanate methyl 70% WP) were assessed in vitro against Rhizoctonia solani using the poisoned food method on PDA medium. Each treatment was tested at multiple concentrations and replicated thrice. The results (Table 2, Fig. 1) clearly demonstrated that increased fungicide concentrations were directly associated with greater inhibition of mycelial growth.

Complete suppression of the pathogen's mycelial growth was observed at 100, 150, and 200 ppm for carbendazim 50% WP, tebuconazole 25.9% EC, hexaconazole 5% SC, propiconazole 25% EC, and the combination product tebuconazole 50% + trifloxystrobin 25% WG. These fungicides showed significantly better performance compared to others. In contrast, copper oxychloride 50% WP recorded the least inhibition, with values of 46.11% and 64.07% at 500 and 1000 ppm, respectively. Thiophanate methyl 70% WP followed, showing 53.15%, 61.67%, and 64.26% inhibition at 100, 150, and 200 ppm, respectively.

The present findings align with those of Chanu et al. (2019), who reported complete suppression of Fusarium oxysporum f.sp. pisi by carbendazim. Similar results were obtained by Shivran et al. (2020), who demonstrated the efficacy of carbendazim against R. solani in clusterbean. Supporting this, Kumar et al. (2014) observed that both propiconazole and carbendazim were highly effective in managing web blight in black gram. In addition, Yadav et al. (2020) reported that the combination of tebuconazole and trifloxystrobin at 200 and 500 ppm significantly inhibited R. solani mycelial growth in vitro, and also performed best under field conditions by reducing disease incidence by 83.12% and enhancing seed yield by 84.71%. 

Table 2: Effect of fungicides on mycelial growth inhibition of Rhizoctonia solani.

  *Average of three replications of each concentration;  **Figures in parentheses are Arc sine percent angular transformed values.

Here, T1= Copper oxychloride 50%WP, T2 = Carbendazim50%WP, T3=Tebuconazole 25.9% EC, T4 = Hexaconazole 5%SC, T5 = Propiconazole 25%EC, T6 = Tebuconazole 50%+Trifloxystrobin 25% 75WG, T7 = Thiophanate methyl 70%WG, T8=Control

Fig. 1. Effect of fungicides on the mycelial growth of Rhizoctonia solani.

Conducting detailed studies on in vitro evaluation of fungicides helps in identification of effective chemical with its right dosage against Rhizoctonia solani.

Charanjeet Bhadu and C.B. Meena  (2025). In vitro Evaluation of Fungicides Against Rhizoctonia solani, the Causal Organism of Root Rot of Pea. Biological Forum, 17(7): 93-96.