Evaluation of Rice Varieties against Multiple Diseases Under Middle IGP of Bihar

An investigation was carried out to evaluate the susceptibility of rice cultivation to major field diseases like brown spot, sheath blight and bacterial leaf blight under middle Indo Gangetic Plain. The disease incidence and disease severity were observed at three different growth stages namely flowering, milk and maturity in boro seasons during 2015-16. The incidence of brown spot ranged from 8.93 to 17.83%, 16.67 to 25.67% and 18.33 to 28.33% at flowering, milk and maturity stages, respectively. The severity of brown spot in grade (0-9 scale) ranged from 5.13 to 10.33, 9.33 to 20.00 and 11.57 to 22.67, respectively at flowering, milk and maturity stages. The incidence of sheath blight of paddy ranged from 7. 03 to 16.50%, 13.13 to 22.67% and 19.67 to 35.67% at flowering, milk and maturity stages, respectively. The severity of sheath blight in grade (0-9 scale) ranged from 4.00 to 8.60, 8.33 to 13.93 and 18.33 to 34.33, respectively at flowering, milk and maturity stages. The incidence of bacterial leaf blight ranged from 5.00 to 14.00%, 11.43 to 21.00% and 17.00 to 34.00% at flowering, milk and maturity stages, respectively. The severity of bacterial leaf blight in grade (0-9 scale) ranged from 2.00 to 8.00%, 6.33 to 12.05% and 14.47 to 20.17%, respectively at flowering, milk and maturity stages. Among the varieties, the highest incidence and severity of Brown spot was recorded on Rajendra Bhagawati whereas it was lowest on 27P31 at all growth stages. In the case of Sheath blight, highest incidence and severity was recorded on Sambha Mahsuri whereas it was the lowest on CRL 193. Beside this in the case of Bacterial leaf blight, the highest incidence and severity was recorded on Kranti whereas the lowest was recorded on CRL 193. In general, it was observed that the incidence and severity of diseases increased gradually from flowering to maturity stage and the genotypes with the minimum incidence and severity of diseases gave the maximum yield.

Rice (Oryza sativa L.) is a major food crop of India. It is cultivated in an area of 43.95 million hectare with total production of 106.54 million tonnes and productivity of 2.42 t/ha. In Bihar, total area under rice is 3.26 million hectare and production is 8.24 million tonnes with an average productivity 2.52 t/ha (Directorate of Economics and Statistics, Govt. of Bihar, 2015). 'Boro' a term of Bengal origin refers to special rice cultivation in low land pockets during the months of November -May taking advantage of the residual water in field after harvest of kharif rice. The farmers innovated this rice cultivation with short duration photo period insensitive varieties to supplement a poor kharif harvest. The fact that boro rice gives much higher yields than kharif rice is mainly attributed to higher solar radiation and lower night temperatures throughout the crop growth in winter and favourable temperature during ripening. Generally boro rice crop is affected by more than 10 diseases and certain diseases are more common on hybrid rice varieties than on conventional varieties. Among the different diseases brown spot, sheath blight, blast, stem rot and bacterial leaf blight are considered important in various parts of rice growing areas of the world. Sheath blight is an important soil borne disease caused by Rhizoctonia solani that can cause up to 25% yield loss (Kumar et al., 2009). Bacterial leaf blight is caused by Xanthomonas oryzae occurs mostly during the wet season and in some areas of Asia, which can reduce crop yield by up to 50% (Latif et al., 2011). Brown spot of rice caused by Helminthosporium oryzae can reduce crop yield by up to 40%. However, rice genotypes may vary in their response to disease tolerance. Hence, the present experiment was undertaken to evaluate the performance of 30 rice genotype against three major rice diseases during boro season.

MATERIALS AND METHODS
The experiment was conducted with 30 rice genotypes (Table 1) in a randomized complete block design (RCBD) with three replicates at the ICAR Research Complex for Eastern Region Patna (25 o 30'N latitude, 85 o 15'E longitude and 52 m above mean sea level), Bihar during 2015-16 boro season. The climate of the experimental site is humid subtropical in nature characterized by the monsoon season from late June to late September and chilly winter nights and foggy or sunny days from November to February. Rice nursery was seeded on 06 December 2016. Sixty days old seedlings were uprooted from the seedbed very carefully and then transplanted in the main field with row to row spacing of 20 cm and plant to plant spacing of 15 cm. The crop was irrigated as per need on regular basis and fertilizers were applied @ 120, 50 and 50 kg ha -1 N, P 2 O 5 and K 2 O, respectively.

Assessment of the disease incidence
Each plot was visited on regular basis for recording observations. The disease incidence was recorded at three different growth stages of the plant viz., flowering, milk and maturity stage. Data were recorded visually by observing the symptoms.
Sixteen plants were randomly selected from each unit plot and the following parameters were considered for data collection. Number of tillers / plants Number diseased tillers / plants Percent leaf area diseased (LAD) Disease incidence was calculated by the following formula (Rajput and Bartaria, 1995): Disease incidence = Number of diseased tillers/ Total number of inspected tillers x 100 Assessment of the disease severity Sixteen plants from each unit plot were randomly selected and tagged for grading the severity of disease. The severity of three diseases viz. brown spot, sheath blight and bacterial leaf blight was recorded as per following IRRI recommended grading scale (Standard Evaluation System for Rice, 2002). The disease severity was recorded at flowering, milk and maturity stages of the crop. The grade of different diseases is presented in Table 2.
The crop was harvested on the maturity of the individual genotypes. The observations on growth parameters, yield and yield attributes were also recorded.

Isolation and identification of causal organism
The leaves from the diseased plants were collected from the field and cut into small pieces along with healthy portion. Cut pieces were sterilized by the surface disinfectants e.g. 0.1% mercuric chloride for 30 seconds. After sterilization the cut pieces were washed three times with sterile water. The cut pieces were then placed on sterile blotter paper to remove excess water. The cut pieces were then placed on the Potato Dextrose Agar plate. The plate were labelled and placed in the incubation chamber for 7 days at 25 + 2 o C. After 7 days of incubation, the fungi grown on culture media. A portion of culture was taken on slide and observed under microscope and identified the pathogenic fungi i.e. Helminthosporium oryzae, Rhizoctonia solani, with the help of relevant literature (Mew and Gonzales, 2002;Barnet and Hunter, 1972). In bacterial leaf blight causal organism Xanthomonas oryzae isolated on nutrient Agar media. A portion of culture was taken by inoculating needle on another Potato Dextrose Table 2. Disease severity scale of brown leaf spot, sheath blight and bacterial leaf blight

Analysis of data
The data on different characters were subjected to estimates of ANOVA (analysis of variance) by using statistical software OPSTAT.

Evaluation of rice varieties against disease incidence and severity
It was observed that under field conditions, the incidence and severity of brown spot disease were fairly significant. The incidence of brown spot ranged from 8.93 to 17.83%, 16.67 to 25.67% and 18.33 to 28.33% at flowering, milk and maturity stages, respectively. The severity of brown spot in grade (0-9 scale) ranged from 5.13 to 10.33, 9.33 to 20.00 and 11.57 to 22.67, respectively at flowering, milk and maturity stages (Table 3). At all the three growth stages, the highest disease incidence and disease severity was recorded in Rajendra Bhagawati whereas the least value was observed in 27P31. Rashed (2001), also reported that the incidence and severity of brown spot were observed 30.75 to 62.75% and 25.25 to 47.50%, respectively at 50 days after transplanting on the hybrids line 321H. The incidence and severity varied from 40.50 to 80% and 45 to 77%, respectively at 70 days after transplanting on the hybrids line 321H. Saifulla (1994) reported that mean brown spot severity ranged from 23.0 to 36.5% in IR9924-124 and IR9924-14. The incidence of sheath blight ranged from 7. 03 to 16.50%, 13.13 to 22.67% and 19.67 to 35.67% at flowering, milk and maturity stages, respectively. The severity of sheath blight in grade (0-9 scale) ranged from 4.00 to 8.60, 8.33 to 13.93 and 18.33 to 34.33, respectively at flowering, milk and maturity stages ( Table 4). In all growth stages, the highest incidence and severity was recorded on Sambha Mahsuri whereas the lowest incidence and severity was observed on CRL 193. The similar result was also reported by Alam (2007) The incidence of bacterial leaf blight ranged from 5.00 to 14.00%, 11.43 to 21.00% and 17.00 to 34.00% at flowering, milk and maturity stages, respectively. The severity of bacterial leaf blight in grade (0-9 scale) ranged from 2.00 to 8.00, 6.33 to 12.05 and 14.47 to 20.17, respectively at flowering, milk and maturity stage (Table 5). In all growth stages, the highest incidence and severity was recorded on rice cultivation 'Kranti' whereas the lowest incidence and severity of bacterial leaf blight was recorded on 'CRL 193'. These finding were supported by Akhtar et al., (2003) who found that BLB disease of rice prompted by Xanthomonas oryzae pv. oryzae has created a serious situation in all provinces of Pakistan viz., Punjab, Khyber Pakhtukhwa, Sindh, Baluchistan including Pakistan occupied Kashmir.

Grain yield and yield attributes
Plant height ranged from 76.8 to 118.3cm. The highest plant height (118.3 cm) was recorded in Jaymati and lowest (76.8cm) in RCPR 29. Number of tillers/hill ranged from 8.8 to 34.5. Maximum number of tillers was recorded in Arize Prima (34.5) and the lowest number of tillers was recorded in Annada (8.8). Number of panicle/hill ranged from 6.3 to 29.1. It was highest (34.5) in Arize Prima and lowest (6.3) in Annada. Weight of biomass/plant ranged from 23.6 to 88.4g. it was highest in Arize  Rai et al., (2003) who reported that maximum disease incidence and severity at maturity stage cause drastical yield loss.

CONCLUSIONS
Based on above findings it was observed that all the thirty rice varieties were susceptible to brown spot, sheath blight and bacterial leaf blight disease. In all growth stages, the highest incidence and severity of brown spot was recorded on Rajendra Bhagawati whereas the lowest incidence and severity was observed on 27P31. For sheath blight, the highest incidence and severity was recorded on Sambha Mahsuri whereas the lowest incidence and severity was observed in CRL193.
In case of bacterial leaf blight, the highest incidence and severity was recorded on Kranti whereas the lowest incidence and severity of bacterial leaf blight was recorded on CRL193. The findings indicate that minimum incidence and severity resulted in maximum grain yield. It was also observed that there was gradual increase in disease incidence and severity from flowering stage to maturity stage.