Infiltration of Fungal and Bacterial Propagules into Soil

Abstract

Phytophthora megasperma zoospores and cysts and Serratia marcescens cells were infiltered during the establishment of a gradient of matric potential in horizontally positioned columns of soil. Tensiometers placed in the soil columns were used to record matric potentials (in situ). In columns wetted a distance of 65 cm, zoospores moved 35 cm behind the wetting front in sand, 44 cm in sandy clay loam, 48 cm in loam, and failed to move in silt loam soil. In the sand, sandy clay loam, and loam soils, matric potentials of −14.5, −18.4, and −16.2 mbars, respectively, were calculated for soil at the boundary between infested and noninfested soils. Zoospore cysts moved one‐half the distance zoospores did in each soil, respectively. The matric potentials associated with their boundary were −13.2, −13.4, and −12.0 mbars. Serratia marcescens cells were recovered close behind the wetting front in the first three soils but 48 cm behind in the silt loam. The matric potential 48 cm behind the wetting front was −33.5 mbars. Attempts were made to develop a predictive model for infiltration of biological propagules based on propagule size and soil moisture characteristic curves. Results indicated that infiltration of propagules occurred after soil pores with radii considerably larger than a priori estimates of the limiting pore radii were filled with water.

Mechanisms of biocontrol of soil-borne plant pathogens by Rhizobacteria

“…Siderophores mediate the limited amount of iron in the rhizosphere, deprive pathogens of iron and suppress their growth. Many reports have been published showing siderophore involvement in the suppression of plant pathogenic fungi (Baker, 1985;Baker et al, 1986;Bakker et al, 1986;1987;Becker and Cook, 1988;Cook and Weller, 1987;Elad and Baker, 1985a,b;Kloepper et al, 1980;Kleopper and Schroth, 1981;Loper, 1988;Scher, 1986;Scher and Baker, 1982;Schippers et al, 1987;Sneh et al, 1984;Weller and Cook, 1986;Weller et al, 1988;Wilkinson et al, 1981). Elad and Chet (1987) found that competition for nutrients between germinating oospores of P. aphanidermatum and bacteria was significantly correlated with suppression of disease in the greenhouse.…”

Effects of Flooding on Plant Disease

“…Phytophthora megasperma zoospores and cysts and Serratia marcescens Bizio cells were infiltered from the outflow of horizontal soil columns during the establishment of a gradient of ψ Γη (Wilkinson et al 1981). In soil columns wetted a distance of 65 cm, zoospores moved 35 cm behind the wetting front in sand, 44 cm in sandy clay loam, 48 cm in loam, and did not move in silty loam soil.…”

Calcium Interference with Zoospore Biology and Infectivity of Phytophthora parasitica in Nutrient Irrigation Solutions

“…Although direct evidence for a role of zoospores in the infection process has been difficult to obtain in soil, there is increasing recognition that these propagules are important for epidemic development of Phytophthora root rots in crop production (10,23,29), and zoospores have been demonstrated to be the major agents for spread of both Pythium aphanidermatum and Phytophthora capsici in recirculating nutrient systems in greenhouses (27,28). Zoospores also are transported more readily by bulk water flow through soil and other particulate materials than are nonmotile cells (33), and they can penetrate root mats in nutrient films (16). This maximizes the chance of infection from individual spores and increases the inoculum potential when zoospores aggregate at infection sites (26).…”