Background

Maize (Zea mays L.) is an important cereal crops in the world, used as food, feed and industrial products. It is the second most important staple food crop of Nepal in terms of area (849,635 hectares), production (1,999,010 t) and productivity (2.35 mtha^-1) and shares about 23.29% of the total cereal production contributing 7.46% in AGDP (MoAD, 2014). It is taken as a miracle C4 crop, has a very high yield potential with average yield of 4.71 mtha^-1 and ranks first among cereals followed by rice, wheat and millets (Anonymous, 2005). Maize crop suffers from 112 diseases reported from different parts of the globe resulting in considerable yield loss of which banded leaf and sheath blight (BLSB) caused by Rhizoctonia solani is the most important one causing significant yield loss (Saxena, 2002). It was reported for the first time from Srilanka (Bertus, 1927) under the name Sclerotial disease and causes direct losses resulting in premature death of the plant, stalk breakage and ear rot besides causing indirect losses by reducing the gross yield (Basta, 2003). The disease occurs in moderate to severe intensities every year in several countries resulting in significant loss in grain yield (Balla et al., 2000). Singh and Sharma (1976) estimated 40.5% loss in grain yield with 71% disease index. The indiscriminate use of chemicals for controlling the disease resulted environmental pollution, health hazards and the occurrence of different virulent race of the pathogen etc. Research for finding the most appropriate and readily available fungicide with the least effective dose for controlling the disease is the current need. Hence, an attempt was made to evaluate the most effective chemicals fungicides against the pathogen to manage the disease.

1 Materials and Methods

1.1 Isolation and maintenance of Rhizoctonia solani

The sclerotia collected from diseased plant of National Maize Research Program (NMRP, Rampur) and surface sterilized with 1% NaOCl solution for 30 sec and washed 3 times with distilled water. The PDA media was prepared, sterilized and poured 20 ml in each sterilized Petri dish. The sclerotia were then inoculated in the medium and incubated at 25 ± 1°C for 2-3 days. The fungal growth was further transferred to freshly prepared PDA medium for purification of pathogen and then incubated. The culture plate showing the typical Rhizoctonia growth was selected after 3 days and the mycelium was observed under the microscope and pathogen was confirmed.

1.2 Bio assay of fungicides by poisoned food technique

Four fungicides viz; Saff (Carbendazim 12% + Mancozeb 63% wp), Allcop (Copper oxychloride 50% w/w), Protector (Chlorothalonil 75% wp) and Vitavex power (Carboxin 37.5% + Thiram 37.5%) were weighed as 1 mg, 5 mg and 10 mg and simultaneously 1,200 ml culture media was prepared and placed on 15 conical flasks of 200 ml each containing 80 ml of media and the concentrations were made of 10 ppm, 50 ppm and 100 ppm as determined by Pearson Square method (Table 1). The different concentrations were incorporated and mixed well in conical flask containing PDA media at about 50°C and poured 20 ml in each Petri dish of 9 cm diameter.

The freshly growing mycelium from the selected culture plate was cut 5 mm with cork borer and inoculated at the centre of the Petri dish under aseptic condition in an isolation chamber. Controls were also maintained without any fungicides.

1.3 Experimental design and observation

In vitro experiment was conducted in Completely Randomized Design (CRD) with 13 treatments replicated four times. Mycelial radial growth was taken in 48, 72, 96 and 120 hours after inoculation for all treatments and the inhibition percent of mycelium by different concentrations of chemicals was calculated using the following formula given by Vincent (1927). 

Where I is the percent inhibition, C is the colony diameter in control and T is the colony diameter in treatment.

2 Results

Four chemical fungicides were treated with different concentrations (10 ppm, 50 ppm, and 100 ppm). All three concentrations showed significant percentage inhibition of mycelial growth as compared to control. All four fungicides significantly reduced the mycelial growth of pathogen in culture. The results showed that Copper oxychloride at 50 and 100 ppm was found most effective in inhibiting mycelial radial growth of the pathogen, followed by Vitavax, Chlorothalonil and Saff.

The percentage mycelia radial growth inhibition at 48 hours after inoculation (HAI) was found to be highest in case of Vitavax 10 ppm (34.267%), Copper oxychloride 50 ppm (89.73%), Vitavax 100 ppm and Copper oxychloride 100 ppm (89.73%) (Table 2).

Similar result was found at 72 HAI, the percentage mycelia radial growth inhibition was found to be highest in case of Vitavax 10 ppm (36.64%), Copper oxychloride 50 ppm (93.73%) and Vitavax 100 ppm (91.23%) were at par (Table 3).

At 96 HAI, percentage mycelial radial growth inhibition was found to be highest in case of Vitavex 10 ppm (23.88%), Copper oxychloride 50 ppm (94.44%) and Copper oxychloride (94.44%) and Vitavax 100 ppm (88.88%) were found to be more effective but statistically at par (Table 4).

At 120 HAI, Vitavax 10 ppm (7.77%) was found to have highest percentage radial growth inhibition along with Copper oxychloride 50 ppm (94.44%) and Copper oxychloride 100 ppm (94.44%) and Vitavax 100 ppm (86.66%) were at par (Table 5).

3 Discussion

We observed Vitavax was more effective in inhibiting mycelial growth of the pathogen at lower concentration (10 ppm) but Copper oxychloride was found the most effective in higher concentration (50 ppm, 100 ppm). Taware et al. (2014) also observed 44.79%, 49.99% and 56.29% inhibition by Copper oxychloride at 500 ppm, 1,000 ppm and 1,500 ppm respectively with the mean inhibition of 50.35% in the in vitro evaluation against Alternaria carthami by poisoned food technique. Harlapur et al. (2007) mentioned that Copper oxychloride 0.36% inhibit the mycelial growth of Exserohilum turcicum causing turcicum blight of maize by 54.14% in vitro.

4 Conclusion

All three concentrations of four fungicides significantly inhibited mycelial growth of Rhizoctonia solani compared to control. The results showed that Vitavax was more effective in inhibiting mycelial radial growth of the pathogen at lower concentration (10 ppm) but Copper oxychloride was found the most effective in higher concentration (50 ppm, 100 ppm). Since the effect of Copper oxychloride at 50 ppm and 100 ppm were observed statistically similar. Copper oxychloride 50 ppm can be used for better results at lower cost rather than 100 ppm with no significant different results. Application of Copper oxychloride and Vitavax in the field condition must be done for controlling banded leaf and sheath blight of maize (Rhizoctonia solani) before recommending to farmers.

Authors’ contributions

Each author equally contributed to collect data and write the manuscript. All authors read and approved the final manuscript.

Acknowledgments

Authors feel a great pleasure to express profound sense of gratitude and indebtedness to Institute of Agriculture and Animal Science, IAAS Rampur, Agriculture and Forestry University, Rampur. We would like to thank Sundar Shrestha, Madhav Dhakal, Lab technicians Sri Krishna Pandit and Chandra Prakash Sapkota for their continuous encouragement, valuable suggestions, continuous supervision, constructive criticism and excellent guidance for completing this work. 

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PMid:20343980