Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/11/1998
Publication Date: N/A
Citation: Interpretive Summary: The soil-inhabiting fungus Fusarium oxysporum f. sp. erythroxyli has demonstrated potential for control of the narcotic plant coca. The ability of this fungus to sporulate on different formulations, and its movement through soil were studied. Formulations tested included wheat flour + kaolin (Pesta), an extruded wheat + rice flour (C6), and five alginate products containing ground corn cobs, soybean hull fiber, canola meal, ric flour, or rice flour + canola oil. Formulations were incubated at nine relative humidities from 100% to 0%. F. oxysporum grew out of alginate granules with canola meal, rice and rice + oil by 24 hours at 100% constant relative humidity. Granules with rice + oil, C6 and Pesta consistently produced more of both spore types and of fungal threads (hyphae) than other formulations. The C6 formulation produced the most spores and hyphae at low relative humidities. Canola meal granules produced the most spores under conditions of fluctuating relative humidity (100-75%). To assess the ability of fungal spores to move through soil, formulations producing spores were placed on top of soil columns and artificial rain was applied. In general, populations of F. oxysporum recovered were 10 times lower at a depth of 3-4 inches than in the top 0.75 inch. High clay content and small soil pore size reduced downward movement of the fungus. Dispersal by splashing water on the soil surface was also studied. Ten times less fungus was recovered 8 inches from the source than 4 inches from the source. This information will be used by scientists in determining which formulations are most likely to work under field conditions.
Technical Abstract: Fusarium oxysporum f. sp. erythroxyli has demonstrated potential for control of the narcotic plant coca. The ability of this fungus to sporulate from 7 formulations and propagule movement through soil were studied. Formulations included a granular wheat flour:kaolin (Pesta), an extruded wheat and rice flour (C-6), and five alginate pellet products containing corn cobs, soybean hull fiber, canola meal, rice flour, or rice flour + canola oil. Formulations were incubated at 25C for 6 wk in desiccators with salt solutions to provide 9 relative humidities (RH), ranging from 100% (pure de-ionized water) to 0% (anhydrous CaSO4). Hyphae of F. oxysporum grew out of alginate pellets with canola meal, rice and rice + canola oil by 24h at 100% constant RH. Alginate pellets of rice + canola oil, C-6 and Pesta formulations consistently produced more microconidia, macroconidia and colony forming units (CFU) than the other formulations at all RH tested. C-6 produced more propagules than the other formulations at low RH (<53%). Canola meal pellets produced more spores than three other formulations when exposed to fluctuating RH (100-75%). To determine the effect of water percolation on spore movement through soil, formulations were placed on soil columns and artificial rain was applied. In general, 10-fold fewer CFU were recovered at a 8-10cm depth compared to 0-2cm. High clay content and small pore size in the soil reduced downward movement of propagules in the soil. Splash dispersal of spores during natural rain (0.5-1.0mm droplets) was also studied. Ten-fold fewer CFU were recovered 20cm from the spore source compared to 10cm from the formulation.