Assessment of plant growth promoter and biocontrol properties of plant growth promoting rhizomicroorganisms (PGPR) from tea soil against black rot disease agent of tea caused by Corticium theae Bernard in Bangladesh was done. The antagonistic microorganisms were isolated from rhizosphere soils of tea fields and cultured on different nutrient media. The isolates were screened for their antagonism against Corticium theae by dual culture technique. The microbial strains were inoculated with tea nursery soils by mixing with 50 g of decomposed cowdung. In tea plantations, the microbial strains were sprayed on diseased plants two times at 15 days intervals. Four different species of PGPR strains such as Bacillus, Pseudomonas, Streptomyces, Trichoderma were isolated from rhizospheric soil of tea. These PGPR strains enhanced plant growth in nursery and had a positive effect on the rate of increased in number of leaves, height of plants and girth of plants by 33, 43 and 3%, respectively. Lowest severity of black rot was found in plants treated with Trichoderma followed by Bacillus, Pseudomonas and Streptomyces strains. Trichoderma and Bacillus caused 16 and 14% reduction of disease severity while both Pseudomonas and Streptomyces strains reduced disease severity by 10%. All the PGPR’s have a great influence in reducing disease severity by 19% with optimistic relations. Radial mycelial growth of C. theae was also inhibited in similar trends. The biofertilizer showed comparatively lower response in reducing disease severity (8%) in comparison to PGPR’s. It can be concluded that Bacillus, Pseudomonas, Streptomyces and Trichoderma isolated from tea soil have their growth enhance capacity as well as decrease the disease severity of black rot in tea.

Only leaf reduction (Cultural measure), in treatment T4 [treated with leaf removal above 15 inches (38.10 cm) from ground level], maximum yield (2185.00 kgha-1) was found resulted 21.64% more over the control. T3 [10 inches (25.40 cm)] and T5 [20 inches (50.80 cm)] gave similar response having 20 and 20.68% increased yield over the control. The lowest severity (21.38 PDI) was found in T5 [20 inches (50.80 cm)] that was statistically identical to T4 [15 inches (38.10 cm)] and T3 [10 inches (25.40 cm)] having a decrease trend of 58.28%, 50.26% and 42.59% respectively. There is 92.99% impact of leaf reduction in reducing disease severity of red rust having a decrease trend of 7.2 PDI for removal of leaf by 5 inches (12.70 cm) from the soil level. Similarly there is 81.44% impact of leaf reduction in increasing yield of made tea (kg ha-1) having an increase trend of 103.01 unit for removal of leaf by 5 inches (12.70 cm) from the soil level. In leaf reduction (Cultural measure) with one round chemical application, treatment T13 [treated with leaf removal above 15 inches (38.10 cm) from ground level with one round of Carbendazim 50 WP] gave maximum yield (2,310.00 kgha-1) resulted 28.61% more over the control followed by T15 [20 inches (50.80 cm) with one round of Carbendazim 50 WP] and T14 [20 inches (50.80 cm) with one round of Copper-oxichloride 50 WP] having 28.18 and 27.69% increased yield of made tea.  Lowest severity (9.63 PDI) was found in T15 [20 inches (50.80 cm) with one round of Carbendazim 50 WP] having 41.21% reduction over control followed by identical PDI in T12 [15 inches (38.10 cm) with one round of Copper-oxichloride 50 WP], T13 [15 inches (38.10 cm) with one round of Carbendazim 50 WP] and T14 [20 inches (50.80 cm) with one round of Copper-oxichloride 50 WP] having 77.40, 77.31 and 77.79% reduction respectively. There is 78.24% impact in reducing disease severity of red rust having a decrease trend of 2.23 PDI for removal of leaf by 5 inches (12.70 cm) from the soil level with one round chemical fungicide application. Similarly there is 51.76% impact in increasing yield of made tea (kg ha-1) having an increase trend of 30.21 unit for removal of leaf by 5 inches (12.70 cm) from the soil level with one round chemical fungicide. From the benefit cost analysis it is projected that the treatment T3 [10 inches (25.40 cm)] received the highest marginal rate of return (1202.17%) followed by 1152.17% in treatment T4 [treated with leaf removal above 15 inches (38.10 cm). One round of systemic fungicides like Carbendazim 50 WP with this cultural practice gave 1034.21% and 1091.42% marginal rate of return respectively. Considering yield of made tea, disease severity and benefit cost analysis viewpoint, it can be concluded that, the cost effective treatment is removal of soil touching old leaves attached with tea bushes of MSK and LSK pruned sections within 10 inches (25.40 cm) to 15 inches (38.10 cm) from the soil level.