Five genotypes showing differential field reactions to Alternaria leaf and stem blight were tested for their reaction to pathogen culture filtrate under in vitro conditions. The pathogen culture filtrate reduced in vitro germination, root and shoot growth and reduction was not uniform in all the genotypes. There was significant negative association between in vitro root growth and field disease score of genotypes suggesting the reliability of this trial for in vitro evaluation. The germination and shoot length in vitro did not show any definite trend to be reliable. Similarly, the detached leaf evaluation under in vitro did not show definite trend of association with field disease score. It is suggested to test a large number of genotypes with varying degree of resistance/susceptibility to confirm the results.