A laboratory experiment was performed to study the persistence of imidacloprid from two formulations (Confidor 200 g litre-1 SL and Gaucho 700 g kg-1 WS), and its metabolism in three different soils (Gangetic alluvial soil of Kalyani, lateritic soil of Jhargram and coastal alkaline soil of Canning) of West Bengal following application at 0.5 kg and 1.0 kg AIha-1. Dissipation of imidacloprid in soil followed first-order kinetics and DT50 values ranged from 28.7 to 47.8 days. The shortest half-lives (28.7 and 35.8 days) were observed in the lateritic soil of Jhargram for both liquid and powder formulations. The formation of two metabolites of imidacloprid, imidacloprid-urea and imidacloprid-olefin, was first detected on day 30 of degradation at 28 (+/- 1) degrees C in all three soils.

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Collar rot disease caused by Sclerotium rolfsii attacks lentils at the seedling stage and reduces plant population considerably in the field. Although soil moisture and temperature influence disease development much, no concrete attempts to find the optimum level of moisture, temperature, and seedling age have been made in lentils. Here, we identified optimum soil moisture, temperature, and seedling age that allow successful infection by S. rolfsii and maximum seedling mortality in a controlled environment inside a plant growth chamber. Screening of one hundred and ninety genotypes for two consecutive years in the field identified some resistant genotypes. Ten genotypes were selected from earlier screening and further evaluated in sick plots at two different locations with different pH for three consecutive years. About 80% variation in disease resistance was due to genotypes, and minor infection of collar rot disease was observed in acidic lateritic soil than in neutral alluvial soil. Furthermore, low mycelial load in a selected resistant genotype was confirmed by quantitative real-time PCR using an S. rolfsii specific primer pair. The identified resistant genotypes will be helpful to breeding collar rot resistant cultivars and mapping disease resistance. In addition, the study improves the understanding of the development of collar rot disease, which is critical for expanding the area under cultivation in Asia, especially in rice fallows.

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