Phylloplane microorganisms as a potential biocontrol agent against Helminthosporium oryzae Breda de Hann, the incitant of rice brown spot.

摘要

Fifteen pathogenic isolates of Helminthosporium oryzae were established from 15 different rice growing areas representing nine districts: Madurai, Theni, Thanjavur, Thiruvarur, Nagapatinum, Tirunelveli, Trichy, Ariyalur and Cuddalore district of Tamil Nadu. The symptoms initially appeared on the leaves as small, oval, dark brown to black spots. Under favourable conditions, the fungus attacks grain and caused grain discoloration. The isolate, collected from Ammapettai of Thanjavur district was the most virulent (Grade 7.47, PDI 82.96) on rice plants followed by Trichy isolate I2 (Grade 7.26; PDI 80.74) while I15 (Cumbum) was the least virulent (Grade 1.8, PDI 20.00). The isolates of H. oryzae varied in size (length and width) of the conidia, colour and the number of cells per conidium. The maximum (39.1 micro m) length of the conidium was observed in I10 followed by I11 (37.3 micro m). The maximum (17.1 micro m) conidial width was observed in I8. The colour of the conidium varied from light brown (isolates I3, I6 and I14) to brown, while there was no appreciable difference in the conidial shape. The number of cells varied from 2 - 4 among the isolates. Six phylloplane microorganisms were tested against the virulent isolate of H. oryzae. Among them, Cladasporium spp. was very effective in inhibiting the mycelial growth and spore germination of H. oryzae followed by Penicillum spp. and Aspergillus flavus while Bacillus subtilis was least effective in inhibiting the mycelial growth and spore germination of H. oryzae..