Potentiality of fungal and bacterial antagonists against Fusarium pallidoroseum (Cooke) Sacc. Causing wilt of coriander in vitro

Introduction

Coriander (Coriandrum sativum L.) is a significant annual herbaceous plant native to the Mediterranean and Middle Eastern regions with a chromosome number of 2n=22. It is known by various names as Dhaniya in Hindi and Kotthamalli in Tamil. It is one of the oldest spices mentioned in history, with evidence of its use for more than 5000 years ago and referred to as "Spice of Happiness" by the Egyptians (Chahal et al., 2017) [5] . The crop is known to infect by various fungal diseases like, powdery mildew (Erysiphe polygoni DC.), wilt [Fusarium solani (Mart.) Sacc. or F. oxysporum f. sp. coriandrii] and root rot (Rhizoctonia solani Kuhn) (Lakra, 2001) [14] . Besides these, a novel reported wilt disease caused by Fusarium pallidoroseum (Cooke) Sacc. marks the first occurrence in Saurashtra region. Earlier, this fungus has been reported in West Bengal causing wilt disease of Chlorophytum nepalense (Bose et al., 2010) [4] , fruit rot disease of citrus in Gujarat (Baria et al., 2015) [3] and wilt disease of chilli in Kashmir (Wani, 2007) [25] . Since it is a new pathogen identified in the Saurashtra (Pithiya and Kanzaria, 2024) [19] , it is very necessary to develop an effective ecofriendly management strategy. Hence, the present study was framed in order to contribute new insights into disease management strategy against Fusarium pallidoroseum (Cooke) Sacc. causing wilt of coriander using fungal and bacterial antagonists in vitro by advocating the Materials and Methods given below.

Materials and Methods

A potentiality of seven fungal and six bacterial antagonists were evaluated against F. pallidoroseum in laboratory condition at Department of Plant Pathology, College of Agriculture, Junagadh Agricultural University, Junagadh. The experiment was laid out in Completely Randomized Design with factorial concept.

Potentiality of fungal antagonists against F. pallidoroseum in vitro

The potentiality of seven fungal antagonists viz., Trichoderma viride, T. harzianum, T. virens, T. koningii, T. hamatum, T. asperellum and T. viride NAU isolate-1 (2×10 6 cfu/g minimum) were tested against F. pallidoroseum using Dual Culture Technique of Morton and Stroube (1955) [16] with three repetitions. Twenty milliliters of sterilized melted potato dextrose agar (PDA) were poured aseptically in each 90 mm diameter Petri plate and allowed to solidify. Mycelial disc of four millimeters diameter of each antagonist and test fungus were cut with the help of sterilized cork-borer from the edges of actively growing culture were placed aseptically on the PDA medium in the same Petri plates, on opposite corners by keeping one cm distance from distal ends of Petri plates. A control plate was also maintained separately by placing two pathogens in the same plate, on the opposite corner. The inoculated plates were incubated at 28±1 °C in BOD incubator. The plates were observed periodically for the growth of the antagonist and test fungus.

Potentiality of bacterial antagonists against F. pallidoroseum in vitro

The potentiality of six bacterial antagonists viz., Pseudomonas fluorescens JAU isolate-1, P. fluorescens JAU isolate-2, Bacillus cereus, B. subtilis JAU isolate-1, B. subtilis JAU isolate-2 and B. thuringiensis were tested against F. pallidoroseum with four repetitions. The test fungus was dual culture plated with different six bacterial antagonist as described by Montealegre et al. (2003) [15] . Twenty milliliters of sterilized melted PDA (50%) + NA (50%) media were poured aseptically in each 90 mm diameter Petri plate and allowed to solidify. Mycelial disc of four millimeters diameter of test fungus was cut with the help of a sterilized cork-borer from the edges of actively growing culture and were placed aseptically in the center of PDA (50%) + NA (50%) medium containing Petri plates. A circular line made by dipping periphery of glass funnel of the size 60 mm diameter in a suspension of different bacterial antagonists (1×10 8 cfu/ml minimum) surrounding the fungal inoculum. The inoculated plates were then incubated for 72 h at 28±1 °C. A control plate was also maintained separately by placing pathogen in the centre of the Petri plate and the fungal growth was measured in all treatments and compared with control plate where the bacterial suspension replaced by sterile distilled water (Rupapara et al., 2019) [21] . The radial growth of the test pathogen was measured after five days of inoculation. The percent mycelial growth inhibition of the test fungus in each treatment by the fungal and bacterial antagonists were calculated by using the formula given here under (Vincent, 1947) [24] .

Where, I = Percent mycelial growth inhibition C = Mean radial growth of test pathogen in control plate (mm) T = Mean radial growth of test pathogen in treated plate (mm)

Statistical analysis

Statistical analysis was carried out as per standard methods as suggested by Panse and Sukhatme (1985) [17] .

Results and Discussion

The observations on mycelial growth inhibition were recorded after five days of inoculation. The results obtained are communicated here under.

Potentiality of fungal antagonists against F. pallidoroseum in vitro

The data presented in Table 1, Figure 1 The present study was in line with the results obtained by Karpe (2021) [12] . He reported least growth of F. oxysporum f. sp. coriandrii in presence of T. pseudokoningii in vitro.

The effectiveness of T. koningii also reported by Bammidi (2017) [2] , Patra and Biswas (2017) [18] and Charan et al.

(2021) [6] . Whereas, Ghaghara et al. (2019) [8] and Ram et al.

(2022) [20] revealed minimum growth inhibition of Fusarium spp. using Trichoderma hamatum which support the present findings.

Antimicrobial activity of fungal antagonists seems to be due to competition for food, production of antimicrobial compounds and mycoparasitism as suggested by (Sivan and Chet, 1989) [22] while employing T. harzianum for the control of F. oxysporum f. sp. vasinfectum and F. oxysporum f. sp. melonis in the cotton and melon rhizosphere, respectively. The role of secondary metabolites such as alkyl pyrones, iso-nitriles, polyketides, petaibols, diketopiperazines, sesquiterpenes and steroids in inhibition of microbial activities were also reported by (Howell, 1998) [10] . Sonkar et al., 2018 [23] showed trichodermin, viridin, harzinic acid, siderophore and gliotoxin as the toxic compound against Fusarium oxysporum. Similarly, Haran et al. (1996) [9] proposed the mycoparasitic activity of Trichoderma as one of the major mechanisms involved in their antagonistic activities against phytopathogenic fungi.

Potentiality of bacterial antagonists against F. pallidoroseum in vitro

The data presented in Table 2, Figure 2 and Plate II indicated that all the bacterial antagonists significantly inhibited the mycelial growth of F. pallidoroseum over control. The maximum mycelial growth inhibition of 63.92 per cent was observed in Bacillus cereus and was proved significantly superior over rest of treatments. The next effective treatment in order of merit was Pseudomonas fluorescens JAU isolate-1 with 61.11 per cent mycelial growth inhibition followed by Pseudomonas fluorescens JAU isolate-2 (55.22%). The treatment Bacillus subtilis JAU isolate-1 found moderately effective with mycelial growth inhibition of 40.06 per cent followed by Bacillus subtilis JAU isolate-2 (32.38%). Whereas, Bacillus thuringiensis found the least effective treatment with 27.94 per cent mycelial growth inhibition of F. pallidoroseum.

A more or less similar kinds of results were also reported by Charan et al. (2021) [6] . He reported the effectiveness Bacillus cereus in reducing mycelial growth of F. oxysporum f. sp. cumini in vitro. The effectiveness of Pseudomonas fluorescens and Bacillus subtilis also reported by Baria et al. (2015) [3] , Kumar et al. (2016) [13] and Jangir (2021) [11] , which support the results of present findings. The bacterial antagonists Pseudomonas spp. produces phenazines, phloroglucinols, dialkyl-resorcinols, pyoluteorin and pyrrolnitrin like compounds which act as mechanism of action in biological control (Chin-A-Woeng et al., 2003) [7] . Bacillus spp. produce several bacteriocins with antimicrobial activity such as amylolysin, amylocyclicin, amysin, subtilin, subtilosin A, subtilosin B and thuricin (Abriouel et al., 2011) [1] .

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