Hydroponic seedling bioassay for the bioherbicides Colletotrichum truncatum and Alternaria cassiae
1995
Hoagland, R.E.
A rapid bioassay was developed to measure the bioherbicidal efficacy of spore preparations of the pathogens Colletotrichum truncatum (Schwein.) Andrus and W.D. Moore and Alternaria cassiae Jurair and Khan on hemp sesbania (Sesbania exaltata) and sicklepod (Cassia obtusifolia), respectively. The system uses 4-day-old dark-grown seedlings (grown hydroponically in paper towel cylinders) which were sprayed with spore suspensions. Shoot lengths were monitored non -destructively, and recorded over time under conditions of dark growth, 90-100% relative humidity and 25 degrees C. Shoot growth inhibition and stem collapse (mortality) were directly related to the spore concentration applied. Generally, at 10(3)-10(4) spores ml-1, these pathogens caused significant shoot growth inhibition within 25-30 h and seedling death within 40-50 h. This bioassay has been used to study herbicide-pathogen interactions, and may be extended to determine the bioherbicidal efficacy of different pathogen isolates, pathovars or spore formulations. This technique is more rapid, uses a lower inoculum volume, requires less space and is performed under more controlled bioassay conditions than conventional greenhouse methods. The data obtained are more quantitative than those obtained from bioassays relying on visual rating systems.
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