Background

Rice (Oryza sativa L.) is the staple food for more than 40% of the world’s population (Datta, 1981). Rice contributes with 21% to AGDP in Nepal (MOAD, 2017). Rice blast, caused by the Ascomycete fungus, Magnaporthe grisea Barr (Anamorph Pyriculariagrisea Sacc., synonym P. oryzae Cav.) is an important fungal disease of rice known to occur in most rice producing areas of the world (Ou, 1985). This disease can strike all aerial parts of the plant. Most infections occur on the leaves, causing diamond-shaped lesions with a gray or white center (Scardaci et al., 1997). This disease results in yield loss as high as 70-80% (Ou, 1985) when predisposition factors (high mean temperature, relative humidity higher than 85-89%, presence of dew, drought stress and excessive nitrogen fertilization) favor epidemic development (Piotti et al., 2005). Rice blast is most serious disease in both terai and hilly region, causing an average yield loss of 125 kg/ha in the hills and 112 kg/ha in the terai of Nepal (IRRI, 1996). Although blast diseases can be successfully controlled by fungicides and seed treatment with systemic fungicide, it disturbs the rice ecosystem, pollute the environment and induce resistant mutants of the pathogen (Prabhu and Filippi, 1993). One of the other approach, which is progressively being developed in compliance with sustainable environment issues during recent years is biological control. Trichoderma spp., the well-known antagonistic fungus are widely used in agriculture as a biofungicides (Mukherjee et al., 2008). Trichoderma viride showed antagonistic activity under in vitro, in vivo and field condition by inhibition of mycelial growth of P. grisea and minimum leaf blast severity (Sharma, 2006). The Trichoderma treated seed showed low disease intensity as compared to untreated seed reducing the disease intensity by 10-25% (Aravindan et al., 2016). In the present study, Trichoderma vride were tested for its efficacy against rice leaf blast diseases under field conditions.

1 Materials and Methods

The experiment was laid out in two factors factorial randomized complete block design during April to September 2017 with five replications and four treatment combinations. The treatments consisted combinations of factor A (two rice varieties namely, Sabitri and Radha 7) and factor B (Trichoderma viride, 5 ml/lit. and 0 ml/lit.). Individual plot size comprised of 6 m × 1 m, the row to row and plant to plant spacing was 20 cm. The space between two replications and border was one and half meters (Table 1).

Transplanting of seedlings were done during 1^st week of June, 2-3 seedlings/hill were transplanted with 20 × 20 cm of spacing. In case of treated plot, rice seedlings were dipped in the Trichoderma viride (10⁹ cfu/ml) solution of 5 ml/litre of water for 30 min. and dried under shade for 10-15 minutes before transplanting. FYM and N:P:K were applied at 6 ton/ha, and 100:30:30 kg/ha respectively. Total amount of phosphorus and potash and half amount of nitrogen were mixed in soil at the time of final land preparation. Remaining half doses of nitrogen was applied in two split doses; one at the tillering stage and the other at the head emergence stage. Weeding was done two times before the top dressing of urea.

10 plants were randomly selected from each plot excluding border line and tagged by a piece of ribbon for identification while taking data. The disease was scored three times at 5 days interval starting from the first appearance of leaf blast symptoms i.e. 75 days of sowing. It was taken on the basis of symptom appearance of the leaf blast which was graded in 0-9 scale (IRRI, 2002). The disease incidence and severity were recorded treatment wise by using the following formula:

The effect of disease severity on rice variety was integrated into area under disease progress curve (AUDPC) (Campbell and Madden, 1990). Area under disease progressive curve (AUDPC) determines the intensity and progress of disease development and calculated by using the following formula (Das et al., 1992).

Where, Yi = disease scored on first date, Ti = date on which the disease was scored, n = number of dates on which disease was scored. Data of disease scoring and then disease incidence and severity were tabulated in excel data sheet. The data were processed to fit into R-studio and analyzed using R 3.0.3 (Program, 2013). The ANOVA table was developed and different treatments were compared by Duncan’s multiple range test.

2 Results

2.1 Leaf blast incidence

Leaf blast incidence was found maximum at 80 DAT. Disease incidence was found least in Sabitri and Trichoderma viride treatment on this date.

Disease incidence was observed at 75, 80 and 85 DAT after the first appearance of disease symptoms. At 80 DAT, highest disease incidence was observed and it was significantly lowest in Sabitri in comparison to Radha 7. The disease incidence was almost three times more in Radha 7 than Sabitri. It was 11% and 32% for Sabitri and Radha 7 respectively (Table 2).

Application of T. viride was found significant in reducing the incidence of leaf blast disease. Disease incidence was almost two times less in T. viride treatment. It was 16% and 27% for treatment and non-treatment respectively (Table 3).

2.2 Leaf blast severity

Leaf blast severity was also found maximum at 80 DAT. The maximum severity of leaf blast disease was found significant (P<0.001) among both factors i.e. variety and Trichoderma viride. Disease Severity was found least in Sabitri and Trichoderma viride treatment (Table 4). It was significantly lowest in sabitri as compared to Radha 7. It was 1.472% and 3.864% for Sabitri and Radha 7 respectively.

T. viride treatment significantly reduced the percentage of leaf blast severity. In this study, T. viride was applied at 5 ml/lit of water and leaf blast severity in T. viride treatment and non-treatment was found 1.879% and 3.547% respectively i.e. leaf blast was 52.97% more severe in non-treatment than that of treated one (Table 5).

2.3 Area under disease progress curve (AUDPC)

The AUDPC value of leaf blast for both factor, variety and Trichoderma viride, and their interaction varied significantly (P<0.001) along with their mean AUDPC. The I, II and mean AUDPC value was least in Sabitri. The mean AUDPC value was 5.083 and 15.377 for Sabitri and Radha 7 respectively and differed significantly among Sabitri and Radha 7 (Table 6).

The I, II and mean AUDPC value was found significant among the T. viride treatment and non-treatment. T. viride was found efficient in reducing the AUDPC value for leaf blast disease. The AUDPC value was 6.104 and 14.356 in treated and untreated cases respectively (Table 7).

In the case of variety and Trichoderma viride interaction, AUDPC I value ranged from 1.632 to 15.976 with the least in Sabitri (1.632), followed by untreated Sabitri (3.743) and treated Radha 7 (4.886), and the highest in untreated Radha 7 (15.976). AUDPC II value ranged from 4.824 to 27.576 with the least in treated Sabitri (4.824), followed by untreated Sabitri (10.146) which was at par with treated Radha 7 (13.07), and the highest in untreated Radha 7 (27.576). Similarly, mean AUDPC value ranged from 3.228 to 21.774 with the least in treated Sabitri (3.228), followed by untreated Sabitri (6.938) which was at par with treated Radha 7 (8.980), and the highest in untreated Radha 7 (21.774) (Table 8).

3 Discussion

Disease incidence was observed at 75, 80 and 85 DAT after the first appearance of disease symptoms. The disease incidence was almost three times more in Radha 7 than Sabitri. It was 11% and 32% for Sabitri and Radha 7 respectively. Experiment by Chaudary et al. (2001) and Khanal et al. (2016) also presented the lowest incidence of blast disease in Sabitri.

Trichoderma treated was less affected with disease. This is in line with the result reported by the Kumar et al. (2017). Sharma (2006) also recorded minimum leaf blast severity with T. viride. Trichoderma were found effective in rice for controllong blast. Singh et al. (2012) also showed 23.30 to 30.55% disease incidence in Trichoderma treatment and 40.50 to 48.09% in non- treatment. This is in line with the findings of Khanal et al. (2016).

Sabitri showed lowest level of AUDPC value which is supported by Chaudhary et al. (2001) suggesting that Sabitri variety to be resistant to blast pathogen. This result also coincides with the findings of Chaudhary et al. (2005). The decreased AUDPC for sheath blight infected rice plants was also observed in the research findings of Franca et al. (2015) when sprayed with Trichoderma.

4 Conclusion

Trichoderma viride application was found efficient for leaf blast management and it is more effective when applied along with improved variety. The performance of Sabitri was found effective over Radha 7 for leaf blast disease management in Pyuthan district of Nepal.

Authors’ contributions

Each author has equal contribution to write this manuscript and conduct the experiment. All authors read and approved the final manuscript.

Acknowledgments

We would like to express our heartfelt thanks to Agriculture and Forestry University, Rampur, Chitwan and Nepal Agriculture Research Council, Khajura, Banke for providing financial and technical support to conduct this research.

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