DISCUSSION
Thirteen imported hybrids, two local hybrids and two local high yielding varieties of rice seed were evaluated to determine the seed health status of imported hybrid rice seed in Bangladesh. A considerable amount of seed home pathogenic fungi and bacteria were observed by using blotter method, rolled paper towel method and agar plate method.
In total twelve pathogens were associated with the collected seed samples as detected by blotter method and agar plate method. The incidences of different pathogens were found to vary individually and independently among the hybrids and high yielding varieties of rice seeds.
In blotter method, 12 seed borne pathogens were identified. These were Xanthomonas spp., Rhizopus stolonifer, Aspergillus spp., Fusarium
moniliforme, Phoma sp., Bipolaris oryzae, Curvularia lunata, Penicillium sp., Alternaria tenuissima, Nigrospora oryzae, Chaetomium globosum and Tilletia
barclayana. It was observed that germination percentage of rice seeds varied significantly from 54.63% to 99.5%. The highest germination was observed in Hira-2 (99.50%) and the lowest germination was recorded in BRRI hybrid dhan-2 (54.63%). Germination percentage of Sonar Bangla-6, BRRI hybrid dhan-l and BRRI hybrid dhan-2 were below 80% that is lower than the national standard level of rice seed germination. The incidence of Xanthomonas spp.
ranged from 0.00 to 18.13%. The highest incidence was observed on Sonar Bangla-6 (18.13%) and no incidence was recorded on Hira-l and Hira-2. Bhutta and Ahmed (1994) reported that maximum seed infection due to Xanthomonas oryzae pv. oryzae was 11% and 12% in variety IRRI -6 at Lahore and Hydrabad, respectively. The incidence of Rhizophus stolonifer ranged from 0.00 to
19.75%. The highest incidence was recorded on BRRI hybrid dhan-I (19.75%) and no incidence was found in Hira-2 (0.00). The incidence of Aspergilllus .spp.
ranged from 0.00 to 12.00%. The highest incidence was observed on Hira-2 (12.00%) and no incidence was found in Hira-I, Richer-IOl , Moyna, Tia, Tinpata, Aloron. The incidence of Fusarium moniliforme ranged from 0.00 to 9.50%. The highest incidence was observed on ACI-l (9.50%) and no incidence was on Surma-I, Sonar Bangla-6, Richer-I 0 1, Moyna, Tia, Tinpata, Aloron, BRRI hybrid dhan-2, BRRI dhan-29. The incidence of Phoma sp. (0.50%) was observed only on Taj-l . The incidence of Bipolaris oryzae ranged from 0.00 to 18.00%. The highest incidence was observed on Aloron (18.00%) and there was no incidence was observed on Hira-2, ACI-l, Krishan-2, Sonar Bangla-6, Richer-I 0 I, Moyna, Tia, Tinpata, Aloron, BRRI hybrid dhan-2. The incidence of Curvularia lunata ranged from 0.00 to 4.25%. The highest incidence was observed on Aloron (4.25%) and no incidence was observed on Hira-I, Hira-2, Surma-l, Taj-l, Sonar Bangla-6, Richer-I 01, Moyna, BRRl hybrid dhan-l, BRRI dhan-29. The incidence of Penicillium sp. ranged from 0.00 to 1.75%.
The highest incidence was observed on Modhumoti-2 (1.75%) and no incidence was observed on Hira-l, Hira-2, ACI-l, Surma-I, Taj-l, Sonar Bangla-6, Richer-l 01,Moyna, Tia and BRRI hybrid dhan-2 . The incidence of Alternaria tenuissima ranged from 0.00 to.63%.The highest incidence (0.63%) was observed on Hira-l and most of the varities showed no incidence (0.00). The incidence of Nigrospora oryzae was observed only on Hira-l (0.25%). The incidence of Chaetomium globosum (1.25%) was observed only on Modhumoti- 2. The incidence of Tilletia barclayana (2.75%) was observed only on Richer- 101. The present findings were supported previous research reports (Ou, 1972;
Fakir and Ahmed, 1974; Hossain and Fakir, 1974 and Sharma et aI., 1992).
Sharma et al., (1992) detected 10 fungal species of fungi from the rice seeds where Fusarium moniliforme (Gibberella fujikuroi), Curvularia lunata (Cochliobolus lunata), Aspergillus flavus and Rhizopus spp. were the most
common. Of all the pathogens Xanthomonas spp., Rhizopus stolonifer ,Aspergillus spp., Bipolaris oryzae, Fusarium moniliforme were predominant. These pathogen were designated as predominant, because each of them constituted at least 5.0% of the total seed borne pathogens infection. Mian and Fakir (1989) reported that the most predominant fungi in order of prevalence were Helminthosporium oryzae, Curvularia lunata, Cladosporium cladosporioides, Aspergillus spp. and Trichoconis padwickii .
. In case of rolled paper towel method seed germination was
maximum
of 96.38% was recorded on Hira-l and the lowest of 8.25% germination was recorded on BRRI hybrid dhan-2. Percentage of Non germinated hard seed ranged from 1.63 to 86.50. The maximum percentage of hard seed was recorded on BRRl hybrid dhan-2 (86.50%) and the minimum percentage of hard seed was recorded on ACI-l (1.63%). Percentage of rotten seed ranged from 12.00 to 0.75. The maximum percentage of rotten seed was recorded on Sonar Bangla-6 (12.00%) and the minimum percentage of rotten seed was recorded on Hira-I (0.75%). Post-emergence mortality ranged from 0.00 to 4.38%. The maximum percentage of post emergence death recorded on Aloron (4.38%) and no post emergence mortality was recorded on BRRI Hybrid Dhan-2 (0.00%). Vigour index was ranged from 96.36-2329.28. Highest vigour index was in .Hira-1(2329.28) and lowest was in BRRI hybrid dhan-2 (96.36). These finding indicate that percent seed germination was decreased due to hard seed and rotten seed. Rotten seed and post emergence mortality of seedling were directly associated with seed borne pathogenic infection.
In agar plate method, 10 seed borne pathogenic infection were identified.
These were Xanthomonas spp., Rhizopus stolonifer, Aspergillus
flavus,
Aspergillus niger, Fusarium moniliforme, Bipolaris oryzae, Curvularia lunata, Penicillium sp., Alternaria tenuissima, Nigrospora oryzae .
The incidence of Xanthomonas spp. ranged from 1.63% to 15.13%. The highest incidence of Xanthomonas spp. was observed on Tinpata (15.00%) and the lowest incidence was observed on Hira-l(1.63%). The incidence of Bipolaris oryzae ranged from 0.00 to 15.13%. The highest incidence was observed on Aloron (15.13%) and no incidence was observed on ACI-l, Taj-l, Krishan-Z, Sonar Bangla-6, Richer-I 01,Moyna, Tia, Tinpata, BRRl hybrid dhan-2.The incidence of Fusarium moniliforme ranged from 0.00 to 7.63%.
The highest incidence was observed on ACI-l (7.63%) and no incidence was observed on Surma-I, Sonar Bangla-6, Richer-l 0 I, Moyna, Tia, Tinpata, Aloron, BRRl hybrid dhan-2, BRRl dhan-29. The incidence of Rhizopus stolonifer ranged from 0.00 to 3.00%.The highest incidence of Rhizopus stolonifer was observed on Tia (3.00%) and no incidence was observed on Hira-2, Modhumoti-2. The incidence ofAlternaria tenuissima ranged from 0.00 to1.63%. The highest incidence was observed on Hira-l(1.63%). The most of the varieties showed no incidence except Modhumoti-2 (1.50%), Krishan-2 (1.25%), Tinpata (1.38%). The incidence of Nigrospora oryzae was observed only on Hira-l (1.38%). The incidence of Curvularia lunata ranged from 0.00 to 6.38%. The highest incidence was observed on Aloron (6.38%) no incidence was observed on Hira-I, Hira-2, Surma-I, Taj-l, Richer-l 01, BRRl Hybrid Dhan-2, BRRI Dhan-29. The incidence of Penicillium sp. ranged from 0.00 to
1.88%. The highest incidence was observed on BRR! hybrid dhan-l (1.88%) and no incidence was observed on Hira-I, Hira-2, ACT-I, Surma-I, Taj-l , Richer-
t01, Sonar Bangla-6, Moyna, Tia, Aloron, BRRI hybrid dhan-2, BRRJ Dhan- 29. The incidence of Aspergillus flavus ranged from 0.00 to 6.50%. The highest incidence was observed on Hira-2 (6.50%) and no incidence was observed on Hira-I, Richer-I 0 1 Tia, Tinpata, Aloron. The incidence of Aspergillus niger ranged from 0.00 to 1.38%. The highest incidence was observed on Taj-
I
1(1.38%) and no incidence was observed on Hira-l , Hira-2, ACI-I, Sonar
Bangla-6, Richer-l 0 1, Moyna, Tia, Tinpata, Aloron, BRR! hybrid dhan-l, BRR! hybrid dhan-Z, BRR! dhan-28 and BRRl dhan-2. Of all the pathogens Xanthomonas spp., Bipolaris oryzae, Aspergillus spp, Fusarium moniliforme,
Rhizopus stolonifer were predominant.
The fungi and bacteria isoloated in the present studies comprise the genera Bipolaris, Rhizoctonia, Fusarium, Aspergillus, Penicillium, Alternaria, Nigrospora, Phoma, Chaetomium and Xanthomonas have also been reported in rice seeds by different scientists at home and abroad (Hossain. and Fakir, 1974;
Ribeiro (1980); Sing and Kang (1987); Basak and Mridha (1988); Fakir et al.(1990) Sharma et at.{l992), Ilyas and Javid (1995), Ali and Deka (1996).
Bipolaris oryzae, Trichoconis padwickii, Curvularia lunata, Nigrospora oryzae, Alternaria tenuis, Aspergillus spp. and Penicillium spp. were identified by Rahman et al. (2000) on BR 11.