Journal of Plant Pathology & Microbiology

Blast disease is one of the most devastating diseases of both the seasons that occurs in all rice growing areas. The disease, caused by Magnaporthe oryzae (Hebert) Barr., anamorph Pyricularia oryzae [1-3], is an important fungal disease of rice known to occur in most rice producing areas of the world [1]. Rice blast is the most common and destructive disease in irrigated rice of both temperate and subtropical areas of East Asia [4].

In Nepal, the disease causes 10%-20% yield reduction in susceptible varieties, but in severe case, it goes up to 80% [2]. Panicle infection causes complete yield loss [1]. Yield reduction by neck blast infection is twice as severe as the leaf blast [5]. Blast can be successfully controlled through the fungicidal spray and seed treatment with systemic fungicide [6]. Chemicals are commonly applied for controlling rice blast disease [7]. Biological control may be an approach of blast control which is also an eco-friendly and cost- effective measure.

Objective: To evaluate efficacy of fungicides and bio-agents against neck blast disease of rice.

An experiment was conducted to evaluate efficacy of fungicides and bio-control agent in management of neck blast by determining different parameters like disease incidence, disease index, Test weight and total grain yield, June to November 2014 in farm of plant pathology division, NARC, Khumaltar, Lalitpur. Disease scoring of neck blast was done after second application of the treatments, i.e. 75 days after transplanting selecting 10 hills of each plot following the standard scoring system developed by SES (2002). Diseases index (intensity) of neck blast was calculated by using the following formula from the data scored on a 0-9 scale above.

Similarly, disease incidence and total grain yield were computed using the formula as below:

Where, MC: Original moisture content of grains in percentage after harvesting.

Thousand grain weight (test weight) was also taken/plot and mean values/treatment were calculated.

The treatments significantly (P=0.05) reduced neck blast disease as compared to control (Table 1). Minimum disease severity (16.50%) was recorded with Tricyclozole, followed by Hexaconazole (26.5%), which were not significantly different to each other. while disease incidence was minimum with Hexaconzole (29.29%) and then in Tricyclazole (34.26%), which were also not considerably different to each other. T. viridae was least effective (50%) to reduce the disease.

Table 1: Effect of treatments on neck blast severity of rice in field at NARC, Khumaltar.

Tricyclazole and Hexaconazole were found significantly different with other treatments in reducing disease incidence, while in case of disease index Tricyclazole was significantly different with Kasugamycin, T. viridae and control, but Hexaconazole was significantly different with only T. viridae and control.

Test weight of rice genotypes differed significantly among the treatments. Tricyclazole had significantly highest test weight (29.03 g) than all the other treatments (Table 2). Hexaconazole had second highest (24.08 g) value.

Table 2: Effect of treatments on test weight and grain yield of rice in field at NARC, Khumaltar.

Total grain yield was statistically significant (P=0.05) among the treatments. It was highest in Tricyclazole (3.473 t ha^-1), followed by Hexaconazole (3.079 t ha^-1) and Kasu-B (2.631 tha^-1) (Tables 1 and 2). Minimum yield (2.411 t ha^-1) was obtained from T. viridae except control (1.878 t ha^-1).

Tricyclazole appeared better to control neck blast disease of rice than all other treatments. Though, T. viridae, bio-agent, appeared less effective to the Neck blast disease, it is quite comparable to other treatments. So, tricyclazole should be preferred as chemical fungicide and bio-agent can also be used as alternative to chemical fungicides to control the blast of rice in field. Thus, using minimum dose of appropriate fungicide or bio-agents, alternative to fungicide help in reducing health hazard by minimizing adverse impact on environment.

This study was conducted with the help of Nepal agriculture research council and Institute of agriculture and animal science. It is also acknowledged to Prof. Dr. Gopal Bahadur K.C., Ph.D., Prof. DR. Sundarman Shrestha and senior scientist Gopal Prasad Parajuli for his persistent encouragement, constant supervision, excellent guidance and invaluable suggestions.

During the course of experimental period, all the authors involved contributed their precious time and effort. Professor, Dr. Gopal K.C. was involved during experiment, initial from planning of experiment to till preparing manuscript. As well, Professor, Dr. Sundarman Shrestha had also involved and provided clear guidelines in conducting research in laboratory. Senior scientist, Mr. Gopal Parajuli had involved in creating a research environment and supervised in all step conducted in research process. Finally, Assistance. Professor, Mr. Prakash Ghimire had involved in all activities from planning for experiment, performing laboratory works, analyzing data and preparing manuscript.