In vitro efficacy of fungicides against Alternaria alternata (Fr.) Keissler causing Alternaria blight of fennel

Introduction

Fennel is one of the important major seed spice crop, botanically named as Foeniculum vulgare Mill. belongs to the family Umbelliferae (Apiaceae) having chromosome number of 2n = 22. The generic name derives from the Latin "Foenum", which means 'hay', referring to the foliar structure. It is a well-known aromatic medicinal plant used in traditional medicine and also as spice and substrate for different industrial purpose (Telci et al., 2009) [12] . Vernacularly it is called Saunf or Badi Saunf. In India, its seeds are used for mastication and chewing alone or with betel leaves. Fennel is believed to be native of Southern Europe and Mediterranean region. It is widely cultivated throughout the temperate and subtropical region of the world (Kusuma et al., 2019) [9] . Fennel thrives well on drained loamy soil, which is rich in plant nutrients and lime. However, heavy soils are more desirable than light soils. Fennel is a cool season crop mainly grown during winter season in north India and does not thrive in south India except at higher elevation. A dry and cold weather favours higher seed production (Anon., 2020) [1] . Fennel is attacked by a number of diseases viz., Ramularia blight (Ramularia foeniculi Sibilla), powdery mildew (Leveillula taurica (Lév.) G. Arnaud, seedling damping off (Alternaria petroselini (Neerg.) E. G. Simmons), root rot (Fusarium solani (Mart.) Sacc.), Alternaria blight (Alternaria alternata (Fr.) Keissler and Alternaria petroselini (Neerg.) E.G. Simmons). Among them, Alternaria blight of fennel caused by A. alternata is a serious bottleneck in augmenting fennel production in Gujarat (Chaudhari and Patel, 1987) [3] . The disease manifests itself on all above ground plant parts in the form of angular, black depressed lesions on the basal leaves with small dark spots that soon developed into necrotic areas on the fennel stalks (Infantino et al., 2009) [5] . Looking to the regular occurrence of disease in moderate to severe form in Saurashtra region and the seriousness of the disease, it is necessary to study basic aspects of this disease particularly the efficacy of different fungicides in managing the disease under laboratory conditions intern to generate scientific information for its management under field condition and to minimize the crop losses caused by the disease.

Materials and Methods

The experiment was conducted in laboratory condition at the Department of Plant Pathology, College of Agriculture, Junagadh Agricultural University, Junagadh during the year 2024-25. Seven different non-systemic, systemic and readymixd fungicides each with three different concentrations were tested against A. alternata using Poisoned Food Technique of Bagchi and Das (1968) [2] using Potato Dextrose Agar as a germinating medium. The experiment was laid out in Completely Randomized Design (factorial concept) with three repetitions.

A. Collection of samples

Samples were collected from naturally infected fennel plant with Alternaria blight disease from Research Farm of Department of Plant Pathology, JAU, Junagadh.

B. Isolation and purification

Isolation of fungus was made by standard tissue isolation method on Potato Dextrose Agar (PDA) medium in Petri plate (90 mm diameter) and incubated at 28±1 ºC. The resulting fungal culture was purified by using the single spore isolation technique.

C. Fungicides used

D. Poison Food Technique

Appropriate quantity of each fungicide required was incorporated into autoclaved 100 ml PDA medium in 250 ml conical flask before solidification using digital balance and micropipette for solid and liquid formulation of fungicide, respectively. After thoroughly shaking on the vertex, the medium was poured into sterilized Petri plates (90 mm dia.) in equal quantity (20 ml per Petri plate) to form a uniform layer. The plates were then allowed to solidify. After solidification, an actively growing mycelial bit of 4 mm diameter cut with the help of sterilized corkborer were transferred under aseptic conditions in an inverted position in the center of the plate to make a direct contact with solidified PDA medium. Then Petri plates were incubated at 28±1 °C till the control plate attains full growth and observations were recorded on linear mycelial growth in treated and control plates. Inoculated Petri plates containing PDA medium without fungicides were served as control (Grover and Moore, 1962) [4] .

E. Observations noted

The percent growth inhibition of the fungus in each of the treatments were calculated by using the following formula (Vincent, 1947) [13] .

Where, I = percent inhibition of mycelial growth C = Average radial growth of fungus in control plate (mm) T = Average radial growth of fungus in treated plate (mm)

Results and Discussion

The observations on mycelial growth inhibition were recorded after nine days of inoculation.

A. Efficacy of non-systemic fungicides

The data presented in Table 1, Figure 1 and Plate I revealed that all non-systemic fungicides were capable of reducing the mycelial growth of test pathogen as compared to control. [11] and Rani at el. (2018) [10] . They found copper oxychloride 50 WP and mancozeb 75 WP as the most effective treatment against A. alternata. Whereas, chlorothalonil 75 WP showed the least effective as per finding of Kantwa et al. (2014) [7] and Rani at el. (2018) [10] while working with leaf blight of groundnut and pigeonpea, respectively.

B. Efficacy of systemic fungicides

The data presented in Table 2, figure 2 and Plate 2 revealed that all systemic fungicides were capable in reducing the mycelial growth of test pathogen as compared to control. Among different systemic fungicides tried in vitro, propiconazole 25 EC found significantly superior over rest of the treatments with 92.76 percent mean mycelial growth inhibition. Thiophanate methyl 70 WP exhibited 38.11 percent mean mycelial growth inhibition. The interaction effect between systemic fungicides and concentrations showed that propiconazole 25 EC and tebuconazole 25.9 EC each at 500 ppm concentration remained equally effective and significantly superior over rest of the treatments with 94.11 percent mycelial growth inhibition of test pathogen. Whereas, minimum mycelial growth inhibition was observed in thiophanate methyl 70 WP (27.97%) at 100 ppm concentration. The present findings were in close conformity with the results of Zade et al. (2018) [14] , Rani et al. (2018) [10] and Kommeta (2019) [8] . They reported propiconazole as the most effective treatment against A. alternata and carbendazim 50 WP and thiophanate methyl 70 WP as the least effective in controlling mycelial growth of A. alternata while working with Alternaria blight in soybean, pigeonpea and wheat, respectively.

C. Efficacy of ready-mixed fungicides

The data presented in Table 3, Figure 3 and Plate 3 revealed that all ready-mixed fungicides were capable in reducing the mycelial growth of test pathogen as compared to control. Among all ready-mixed fungicides tried in vitro, hexaconazole 4 + zineb 68 WP found significantly superior [8] and Jarwar et al. (2021) [6] , respectively. Which support the results of present findings.

Acknowledgement

AcknowledgementThe authors are highly thankful to the Director of Research and Dean, Faculty of P.G. Studies, Junagadh Agricultural University, Junagadh for providing the necessary facilities to conduct the experiments.

References

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