Efficacy of fungicides against Fusarium oxysporum f. sp. udum associated with wilt of pigeonpea

Introduction

Pigeonpea [Cajanus cajan (L.) Mill. sp.] belongs to family Fabaceae is an important legume of rainfed agriculture and cultivated as a sole crop, inter or mixed with cereals. It is good source of crude fibre, iron, sulphur, calcium, manganese, and water-soluble vitamins especially thiamine, riboflavin, and niacin. Pigeonpea is susceptible to over 100 pathogens, including fungi, bacteria, viruses, nematodes and phytoplasmas. Among various diseases, Fusarium wilt is a significant soil-borne disease affecting pigeonpea in India, causing yield losses of up to 67% at maturity and potentially 100% if the infection occurs at the pre-pod development stage (Kannaiyan and Nene, 1981) [6] . Hence experiment to find out effective fungicide against Fusarium oxysporum f. sp. udum was conducted under In vitro condition.

Materials and Methods

Efficacy of seven systemic fungicides and seven contact/combi fungicides were evaluated using the Poisoned Food Technique, as outlined by Nene and Thapliyal (1993) [7] . The systemic fungicides (referenced in Table 1) were tested at concentrations of 500 ppm and 1000 ppm, while the contact and combi fungicides listed in (Table 2) were tested at 2000 ppm and 2500 ppm. PDA medium, containing the appropriate amount of fungicide, was poured aseptically into 90 mm Petri dishes, where it solidified at room temperature. Each dish was inoculated aseptically with a 5 mm culture disc taken from an actively growing pure culture of a pathogen, placing the disc in the centre of the Petri dish on PDA. The plates were then incubated at 27 ± 2 °C. Three replicates of each fungicide concentration were prepared. Petri dishes with plain PDA (without any fungicides) and the pathogen culture disc were maintained as untreated controls. Observations on radial mycelial growth was recorded after seven days of incubation in all the replicated treatments. Percent inhibition of the test pathogen was calculated by applying the formula given by Arora and Upadhay (1978) [1] as follows,

Where, C = Growth (mm) of test fungus in untreated control plate. T = Growth (mm) of test fungus in treated plates.

Results

Effect of systemic fungicides on mycelial growth

The results indicate that all treatments of systemic fungicides at each concentration significantly reduced the mycelial growth of Fusarium oxysporum compared to the control. The fungus treated with Carbendazim 50% WP showed no mycelial growth. Tebuconazole 25.9% EC was the second most effective treatment, showing minimum mycelial growth compared to the control, followed by Propiconazole 25% EC, Thiophanate methyl, 70% WP, Difenoconazole 25% EC, Hexaconazole 5% EC and Azoxystrobin 23% SC. A similar pattern of mycelial growth inhibition was observed at the 1000 ppm concentration for all tested systemic fungicides. Results (Table 3, Fig 1 ) shows that all the treatments at all concentration were significant over the control in inhibiting the growth of test pathogen. At all concentration same trend of systemic fungicide were recorded in inhibition of mycelial growth. Carbendazim showed maximum inhibition of mycelial growth to the tune of 100% followed by Propiconazole, Thiophanate methyl, Difenoconazole, Hexaconazole and Azoxystrobin. The results of present investigation resembled with the finding of earlier records of many workers viz., Raju et al. (2008) [10] tested In vitro efficacy of five fungicides carbendazim, captan, dithane Z-78, thiophanate methyl, thiram against Fusarium oxysporum f. sp. udum and observed complete inhibition of mycelial growth of pathogen with carbendazim at all concentrations (100, 250, 500 ppm). These results were also supported by the observations of Mehta et al. (2010) [5] , Gupta et al. (2014) [4] , Patil et al. (2015) [9] and Arsia et al. (2018) [2] .

Conclusion

The results of the conducted experiment documented that, all tested systemic, contact and combi-product fungicide significantly inhibited the growth of the test pathogen compared to the untreated control in In vitro. However, among the systemic fungicides, Carbendazim 50% WP, Tebuconazole 25.9% EC, Propiconazole 25% EC and were most effective at both 500 ppm and 1000 ppm concentrations. In contact and combi-product fungicides viz., Carbendazim 12% + Mancozeb 63% WP and Tebuconazole 50% + Trifloxystrobin 25% WG combinations effectively inhibited the growth of Fusarium oxysporum f. sp. udum under In vitro experimental conditions.

References

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