Abstract:
An experiment was carried out to study the cultural, morphological, and pathogenic
variability of different isolates of Sclerotium rolfsii infecting tomato crop under the
undulating red and lateritic zone of West Bengal. Cultural and morphological variability of
isolates were studied based on their mycelial growth rate, colony colour, mycelial
dispersion and appearance and sclerotia formation, colour, weight and number of sclerotia,
arrangement and maturity days of sclerotia using potato dextrose agar medium. Pathogenic
variability was studied based on pathogenicity test and host range study by soil infestation
method. All the ten isolates of S. rolfsii expressed significant differences with respect to
cultural, morphological, and pathogenic characters. In pathogenicity test, all the isolates
showed their pathogenic temperament to tomato plant where as in host range study, all test
crop species showed susceptible except wheat (Triticum vulgare) showed some extent of
resistance. Three isolates were found to be very fast growing (diam. > 9 cm), three were
fast growing (8-8.9 cm), three moderately fast growing (5-6 cm) and one was observed
slow growing (< 3 cm). Four isolates were white, one each of extra white and cottony
white, two isolates were light white and another two were dull white. The colour of
sclerotia ranged from brown to dark brown, shape ranged from spherical to oval and also
irregular, sclerotial weight ranged from 3.7 to 8.6 mg. Six isolates were observed scattered,
two peripheral and two were reported be central in Sclerotia arrangement. Sclerotia took a
range of 9 to 15 days after inoculation for maturity. A range of 154.0 to 395.0 sclerotia
production per plate was reported from the tested isolates.
