ASSOCIATION OF PYTHIUM-COLORATUM AND PYTHIUM-SULCATUM WITH CAVITY SPOT DISEASE OF CARROTS IN WESTERN-AUSTRALIA

All 170 Pythium isolates from carrot cavity spot lesions from a field in Western Australia were found to belong to either P. coloratum or P. sulcatum. All isolates of P. coloratum produced large, brownish-black , water-soaked and depressed lesions on mature carrots inoculated with agar plugs colonized by the pathogen. In comparison, only a few isola tes of P. sulcatum produced lesions and these were small. In glasshous e trials, P. coloratum produced substantial and numerous lesions at an inoculum density of 0.5% (weight of millet seed-based inoculum/weight of soil), whilst P. sulcatum produced few and small lesions at inocul um densities of 0.8 and 1% and none at 0.5%. This is the first record of P. coloratum as a causal agent of cavity spot of carrots.