Biological Control of Taro Leaf Blight Caused by Phytophthora colocasiae (Racib.) and Storage Losses with Rhizobacteria

Abstract

Effect of seed treatment, soil application and foliar spray of rhizobacterial cultures that were isolated from Colocasia esculenta on Phytophthora blight was studied under polyhouse and field conditions. Under polyhouse conditions, when applied as seed tuber treatment, the antagonistic rhizobactcrial cultures S1B3, S11B4, S13B5 and S23BS reduced the Phytophthora blight disease severity. In these treatments there was no disease incidence compared to control where the disease severity was 2.92 on a 0-5 disease rating scale. In soil application, when rhizobactcrial cultures S4BS, S13B5 and S23BS were used, the disease incidence was nil compared to control where disease severity was 2.83 on a 0-5 disease rating scale. Foliar application with S1B4 and S11B3 reduced the disease severity to 0-0.33 rating compared to 2.66 in control. Under field conditions, tuber treatment with S1 B3, soil application of S13B5 or foliar application with S1B4 and S11B3 reduced the disease severity and increased the yield compared to untreated pathogen-inoculated control plants. Seed treatment with S1B3 resulted in tuber yield of 255g/plant compared to 95.42g in control. Soil application with S13B5 resulted in 232.65g/plant, while in foliar application with S1B4 or S11B3, yield were 274g and 605g per plant, respectively. These treatments promoted the plant growth also. These treatments were tested in the field and it was found that application of bacteria in combination (seed treatment, soil treatment and foliar spray) helped in reducing the leaf area damaged due to blight by 41% during the first peak of the disease spread and by 28% during the second peak of the disease spread. Rhizobacteria treatment also helped in reducing the storage losses. The storage loss of tubers harvested from rhizobacteria treated plots ranged from 4.14 to 21.24% compared to 26.02 and 21.78% in fungicide treated and control plots, respectively, resulting in 18 to 36% increased yield in the field trials.