EFFECT OF RELATIVE-HUMIDITY ON SPORULATION OF FUSARIUM-OXYSPORUM IN VARIOUS FORMULATIONS AND EFFECT OF WATER ON SPORE MOVEMENT THROUGH SOIL

Fusarium oxysporum f. sp. erythroxyli is being investigated as a mycoh erbicide for the narcotic plant coca. Sporulation of the fungus in sev en formulations containing different organic substrates and movement o f its propagules through soil were studied. The formulations were a gr anular wheat flour/kaolin (pesta); an extruded wheat and rice flour (C -6); and five alginate pellet products containing corn cobs, soybean h ull fiber, canola meal, rice flour, or rice flour plus canola oil. For mulations were incubated at 25 degrees C for 6 weeks in desiccators wi th various salt solutions to provide nine relative humidities (RH), ra nging from 100% (pure deionized water) to 0% (anhydrous CaSO4). Hyphae of F: oxysporum f. sp. erythroxyli grew out of alginate pellets with canola meal, rice, and rice plus canola oil as early as 24 h at 100% c onstant RH. Alginate pellets of rice plus canola oil and granular C-6 and pesta formulations consistently produced more microconidia, macroc onidia, and CFU than the other four formulations at all RH tested. The C-6 formulation 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 to 75%). The ef fect of percolating water on spore movement through soil was studied u sing a plant-pathogenic isolate of F: oxysporum f, sp. niveum. To dete rmine the effect of water percolation on propagule movement, formulati ons were placed on soil columns and artificial rain was applied. In ge neral, 10-fold fewer CFU were recovered at a 8- to 10-cm depth compare d with a 0- to 2-cm depth.