Bio efficacy of fungicides against Ground nut root rot caused by Macrophomina phaseolina (Tassi.) Goid

Introduction

Groundnut production is affected both by biotic and abiotic stresses during different growth stages of crop. Diseases are one of the biotic stresses which cause a major constraint to groundnut cultivation (Vara Prasad et al., 2010) [5] . Among the diseases, dry root rot caused by Macrophomina phaseolina affect the crop at any growth stage and reduce the yield. Diseased plants showed yellowing, drooping of leaves and shredding of barks in the roots (Palaiah et al., 2019) [4] . In the infected area the pathogen produced a greater number of black coloured sclerotia (Ghosh et al., 2018) [1] . To combat the massive yield loss caused by this disease, there is a need to identify the best fungicide for the management of this disease.

Materials and Methods

Isolation, purification and maintenance of the pathogen Isolation of the pathogen was done on the PDA medium from dry root rot affected roots of the groundnut plant by using tissue segmentation method. Diseased roots were washed with the running tap water. Then, inside the laminar airflow chamber 2-5 mm size of diseased root tissues along with some healthy tissues were sliced out with the help of a sterilized blade. To avoid the surface contaminants, tissues were surface sterilized with 0.1 per cent mercuric chloride for about 30 seconds. After surface sterilization the tissues were washed three times with sterile water to remove the traces of mercuric chloride and blot dried in sterile blotter paper. The diseased root tissues were then transferred aseptically to the sterilized PDA medium and incubated at 28±3 °C for 6 to 7 days. Mycelial growth of the pathogen from the infected tissues was observed periodically. For maintenance of pure culture, fungal hyphae grown from the infected tissues were sub cultured by transferring it into fresh sterilized PDA slants by single hyphal tip method. Then the culture was stored at 5-6 °C and used for further studies.

In vitro evaluation of fungicides against the growth of M. phaseolina

In vitro evaluation of antifungal potential of different fungicides on the growth of M. phaseolina was performed through poisoned food technique (Nene and Thapliyal, 1993) [3] . Five different fungicides viz., carbendazim 50% WP, propiconazole 25% EC, carbendazim 12% + mancozeb 63% WP, tebuconazole 5% + trifloxystrobin 25% WG, azoxystrobin 23% SC were tested against groundnut dry root rot pathogen at the concentration of 500 ppm and 1000 ppm. Required quantities of fungicidal solutions were prepared and added into 100 ml PDA medium and mixed thoroughly. Then the poisoned media were poured into sterilized Petri plates separately. Then the Petri plates were inoculated with nine mm actively growing M. phaseolina culture and incubated at 25±7°C. Three replications were maintained for each treatment along with control. After incubation, the radial growth of the dry root rot pathogen was observed. The mycelial inhibition percentage was calculated using the Vincent formulae (Vincent, 1947) [6] .

Where, I = Per cent inhibition over control C = Growth in control T= Growth in treatment

Results and Discussion

In vitro evaluation of fungicides against the growth of Macrophomina phaseolina Five different fungicides viz., carbendazim, carbendazim + mancozeb, tebuconazole + trifloxystrobin, propiconazole, azoxystrobin were tested at 500 and 1000 ppm concentrations against M. phaseolina. Among all the fungicides tested, propiconazole and carbendazim + mancozeb were recorded complete inhibition of mycelial growth at both 500 and 1000 ppm concentration followed by tebuconazole + trifloxystrobin which exhibited maximum mycelial growth inhibition of 95.18 per cent and 96.29 per cent at 500 ppm and 1000 ppm concentration respectively. Whereas, azoxystrobin recorded least mycelial inhibition of 71.48 per cent and 81.48 inhibition at 500 ppm and 1000 ppm concentration respectively (Table 1 and Table 2; Fig 1 and Fig 2). Similar results were recorded by Khamari and Patra (2018) [2] and they observed complete mycelial inhibition (100%) of the pathogen at 1000 ppm and 99.60 per cent mycelial inhibition at 500 ppm concentration.

Conclusion

The results of present study revealed that the application of propiconazole 25% EC and carbendazim 12% + mancozeb 63% at 500 and 1000 ppm were completely inhibited the growth of ground nut root rot causing pathogen Macrophomina phaseolina.

Acknowledgement

AcknowledgmentThe authors acknowledge the Department of Plant Pathology, VOC Agricultural College and Research Institute, Tamil Nadu Agricultural University, Killikulam, Vallanad for providing facility to execute the work.

References

1. Ghosh T, Biswas MK, Guin C, Roy P. A review on characterization, therapeutic approaches and pathogenesis of Macrophomina phaseolina. Plant Cell Biotechnology and Molecular Biology. 2018;19:72-84.
2. Khamari B, Patra C. Evaluation of potentiality of different fungitoxicants against Macrophomina phaseolina, causing stem and root rot disease of sesame. International Journal of Chemical Studies. 2018;6(6):424-426.
3. Palaiah P, Narendrappa T, Mallesh SB. Screening of groundnut varieties and germplasm against collar rot, stem rot, and dry root rot diseases. International Journal of Current Microbiology and Applied Sciences. 2019;8(6):2321-2328.
4. Vincent JM. Distortion of fungal hyphae in the presence of certain inhibitors. Nature. 1947;159(4051):850.