An Australian isolate of Alternaria crassa shows potential as a mycoherbicide to control the weed Datura stramonium

An isolate of Alternaria crassa obtained from Datura stramonium was tested for its potential as a mycoherbicide in south-eastern Australia. Sporulation of A. crassa in culture was greatest under the following conditions: on V-8 juice agar, with a 12 h photoperiod of 'Warm White' light, with cultures arranged in a monolayer, at 25-30 degrees C, at about 13 days after inoculation. Spores rather than mycelial fragments were required to kill seedlings of D. stramonium. Preliminary experiments indicated that a minimum dew period of 9 h and a spore concentration of 10(5)/mL were required to kill cotyledonary-stage seedlings of D. stramonium. In host range studies in the glasshouse, A. crassa killed or severely reduced the growth of all Datura species tested and other solanaceous weeds. Also, A. crassa caused disease symptoms on some crops and ornamental species, including four tomato and two eggplant cultivars, Petunia x hybrida 'Mardi Gras' and a soybean cultivar. Microscopic examination of the infection process after inoculation showed that spores germinated, formed appressoria and penetrated equally well on different species and so resistance was intracellular. This local isolate of A. crassa is potentially an effective mycoherbicide for D. stramonium and other solanaceous weeds in south-eastern Australia.