Author(s): R. CHAKRABARTY AND H. KALITA

Abstract: A field experiment was conducted at Shillongani during rabi seasons of 2016-17 and 2017-18 in loamy soils of Central Brahmaputra Valley Zone (CBVZ) of Assam to study the diseases of rapeseed (Brassica campestris) and linseed (Linumusitassimum), their severity, yield loss and population of soil microorganism (fungi, actinomycetes and bacteria) under rice (Oryza sativa)-fallow and conventional system as well as under protected and unprotected conditions. In rapeseed, Alternaria leafblight (ALB) caused by A. spp.and collar rot caused by Sclerotiumrolfsii were the major diseases. The severity ofALB at 60 days after sowing (DAS) was higher under conventional system (26.60 and 29.23 % in 2016-17 and 2017-18, respectively) than in rice-land (24.17 and 24.06% in respective years). In conventional system, its severity was 17.23 % in 2016-17 and 19.67 % in 2017-18 under protected condition and 35.97 and 38.78 % in respective years under unprotected conditions. However, in rice-fallows, it was 15.97 and 16.23 % under protected and 32.37 and 31.89 % under unprotected conditions. Collar rot of rapeseed was observed only in the first year of study. The per cent severity was higher in rice-lands (0.92) than in conventional system (0.43). The yield loss ranged from 9.6-12.2 % under rice-fallow. In linseed, Fusarium wilt caused by F.oxysporum was the major disease. The severity of Fusarium wilt was slightly higher under conventional system (1.62 and 2.63 % in respective years) than in rice-lands (1.40 % and 2.18 %). Its severity was 0.31 and 1.01 % in rice-fallows under protected conditions and 2.49 and3.34 % under unprotected conditions in the years of experimentation, respectively. However, under conventional system, it was 0.53 and 1.27 % in protected and 2.70 and 3.98 % in unprotected conditions in the respective years. The seed yield of linseed in rice-lands (9.34 and 8.92 q ha-1) was higher than those in conventional system during both the years. Soil moisture was higher in rice-lands than in conventional system irrespective of crop grown during the growing period. Rice-lands registered higher population of bacteria and lower fungi and actinomycetes in soil at 90 DAS as compared to those under conventional.

DOI: 10.22271/09746315.2020.v16.i1.1292

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