Potential of an indigenous fungus, Plectosporium tabacinum, as a mycoherbicide for control of arrowhead (Sagittaria trifolia)

An isolate of the indigenous fungus Plectosporium tabacinum was isolated from arrowhead (Sagittaria trifolia) in Yusung, Korea in 1990 and evaluated in laboratory and growth chamber tests as a potential mycoherbicide. The fungus grew comparatively slowly on potato dextrose agar and corn meal agar, attaining a diameter of 65 mm after 12 days at 25 degrees C. Conidia were mass-produced in shake-cultures or in a fermenter using potato dextrose broth containing yeast extract (0.5%, wt/vol) at 25 degrees C. When arrowhead seedlings at the 2- to 3-leaf stage were inoculated with conidial suspensions (2 x 10(7) conidia/ml) and incubated in a dew chamber for 18 h at 25 degrees C, the plants developed small, brown spots on the leaves and petioles in 2 days, and were blighted completely within 7 days after inoculation. This effect was consistent on arrowhead plants from the 2- to 5-leaf stage. Another arrowhead species, S. pygmaea, was as susceptible as S. trifolia to the pathogen. Several crops, including rice, barley, and wheat and 34 other common weed species, were immune. In small-scale field tests in paddy fields during the summers of 1992 and 1993, a mean reduction of 71.3% in the number of arrowhead plants was observed following a foliar spray of a conidial suspension (10(7) conidia/ml). These results indicate that P. tabacinum has potential as a selective mycoherbicide for arrowhead control.