Introduction

Rice (Oryza sativa L.)  is the staple food crop for people of south, south-east and eastern Asia where 90% of the world’s rice is produced and consumed. It is grown in 114 countries across the world on an area of about 160 million hectares with annual production of 494.3 million tones and total supply of 711.5 million tonnes (Anonymous, 2016). The occurrence of grain discoloration has increased in South Gujarat in mid late and late varieties. It is major problem in rice cultivation as it reduces quality and quantity of rice production. It causes loss to producer and agro processors. The infected grain remain unfilled or discolored, become chaffy which are light in weight and during milling become powder or break resulting in poor recovery. Considering the importance of disease, a field experiment with different newer as well as combination of fungicides available in the market was laid out to test their efficacy against grain discoloration disease of rice.

Materials and Methods

A field experiment was laid out in randomized block design with six fungicides keeping three replications. Fungicides and their concentrations used for spraying to control the grain discoloration of rice are mentioned in Table 1.

Table 1: Fungicides and their dosage

Efficacy of each fungicide was compared with control plot, which was sprayed with water only. The gross plot size was 5.4×3.6 m² and net plot size was 5.1×3.2 m². with 15×20 cm². A popular rice variety Jaya was used for the study. Seeds were sown in the month of June and planted in July. Before sowing, healthy seeds were water soaked overnight and incubated in the gunny bags for better sprouting in the nursery. The land was prepared by puddling method. All standard agronomic practices were followed except using higher nitrogenous (150 kg ha^-1) fertilizer dose than the normal dose (N2:P₂O5:K₂O: 100:30:00). The first spray of fungicides on cv. Jaya was carried out at boot leaf stage and the remaining two sprays were carried out after 10 days interval. Ten hills from each treatment were randomly selected and labeled. These labeled plants were observed for disease incidence, discolored, unfilled, healthy grains and the yield of grain and straw per plot was also recorded.

Results and Discussion

Effectiveness of fungicides was compared with control, where no fungicide was sprayed. The percentage of healthy grains, discolored grains and unfilled grains were work out and presented in Table 2 and 3.

Table 2: Effect of fungicidal sprays on healthy and discolored grain

Table 3: Effect of fungicidal sprays on unfilled grain

3.1.  Healthy grains 

The results on effect of fungicides on healthy grains are given in Table 2. The treatment trifloxystrobin 25% + tebuconazole 50% found significantly superior which was at par with propiconazole 25 EC and carbendazim 50 WP during 1^st year and treatment propiconazole 25 EC during 2^nd year. While in 3^rd year, the treatment propiconazole 25 EC recorded significantly produced higher healthy grains which was at par with treatment trifloxystrobin 25% + tebuconazole 50%. In case of pooled results, the treatments trifloxystrobin 25% + tebuconazole 50% (75 WG) produced significantly higher healthy grain which was at par with propiconazole (25 EC). The year effect was found non significant.

3.2.  Discolored grains

 The spraying of fungicides significantly reduced the discolored grains than in control. The results on discolored grain are given in Table 2. The treatment T₁ found significantly superior which was at par with T₆, T₅ and T₄ during the 1^st year and treatment T₆ during 2^nd year. While in 3^rd year, the treatment T₆ recorded significantly reduced the discolored grain which was at par with treatment T₁. In case of pooled results, the treatment trifloxystrobin 25% + tebuconazole 50% (75 WG) (T₁) significantly reduced the discolored grain which was at par with propiconazole (25 EC) (T₆) and carbendazim 50 WP (T₅). The year effect was found non significant.

3.3.  Unfilled grains

The results on unfilled grain are given in Table 3. The spraying of fungicides significantly reduced the unfilled grain than in control. Among these fungicidal spray treatments, trifloxystrobin 25% + tebuconazole 50% (75 WG) (T₁) and propiconazole 25 EC (T₆) were at par. Both fungicides were found superior and significantly reduced the unfilled grains than the rest of fungicides. The year effect was found non significant. The present finding is more or less in line with earlier workers viz., Singh and Chand (1985) who reported that zineb, ridomil and carbendazim effectively manage the grain discoloration of rice. Sumangala et al. (2008) revealed that mancozeb at 0.3% (97.37% inhibition) was significantly superior among the non-systemic fungicides evaluated at three concentrations (0.1, 0.2 and 0.3%). Among the systemic fungicides, metalaxyl showed 98.48% inhibition of mycelial growth at 0.3% concentration followed by carbendazim (95.25% inhibition at 0.3%).  Hafiz et al. (2009) found that carbendazim was best followed by Topsin M, Dithane M-45 and Ridomil, respectively. Diseased grains treated with both of these fungicides showed maximum germination and least seedling mortality.

3.4.  Grain and straw yield

 The results on grain and straw yield of paddy affected by different treatments are given in Table 4. The results indicated that effect of different treatments was significant during all the individual years as well in pooled results. All the treatments were found significantly superior over control for grain and straw yield of paddy. During 1^st and 2^nd year, the treatment T₁ recorded significantly higher grain and straw yield which was at par with T₆. While in 3^rd year, the treatment T₆  recorded significantly higher grain and straw yield which was at par with treatment T₁. In case of pooled results, the treatments T₆ (propiconazole 25 EC) @ 1.0 ml l^-1) recorded significantly higher grain yield (5353 kg ha^-1) and straw yield (7011 kg ha^-1) which was at par with T₁ (trifloxystrobin 25% + tebuconazole 50%) @ 0.4 g l^-1) i.e. 5341 kg ha^-1 grain and 7001 kg ha^-1 straw yield.

Table 4: Effect of fungicidal treatments on yield parameters

Conclusion

Among the six fungicides screened against rice grain discoloration disease, trifloxystrobin 25% + tebuconazole 50% @ 0.4 g l^-1 and propiconazole  25 EC @ 1.0 ml l^-1 was found most effective against rice grain discoloration.

Acknowledgement

The authors express their gratitude to The Director of Research, Dean P.G. Studies, Navsari Agricultural University, Navsari, Gujarat for providing necessary facilities during the present investigations. Authors are also thankful to Indian Institute of Rice Research, Department of Plant Pathology, Hyderabad.

Anonymous, 2016. Fourth advance estimates of production of food grains for 2015-16, Department of Agriculture and Cooperation, Gujarat state, Gandhinagar, 102.

Hafiz Muhammad Imran Arshad, Junaid Ahmad Khan, Sumaira Naz, Salik Nawaz Khan, Muhammad Akram, 2009. Grain discoloration disease complex: a new threat for rice crop and its management. Pakistan Journal of Phytopathology21, 31−36.

Singh, R., Chand, H., 1985. Rice grain discoloration and its chemical control. International Rice Research Notes10, 16.

Sumangala, K., Patil, M.B., Nargund, V.B., Ramegowda, G., 2008. Evaluation of fungicides, botanicals and bio-agents against Curvularia lunata, a causal agent of gain discoloration in rice. Journal of Plant Disease Sciences3, 159−164.