The influence of soil moisture, temperature, crop plant, flooding, and
addition of plant residues and CaCO3 on survival of phialospores of C
halara elegans in organic soil was studied. The extent of survival of
phialospores (number of propagules recovered from artificially infeste
d soil) was monitored over a 19-wk duration using a semiselective medi
um (TB-2RBA). Survival was significantly greater (P less-than-or-equal
-to 0.01) in soil maintained at a constant soil moisture level (matric
potential of about -50 J/kg) than when moisture level gradually decli
ned to about -900 J/kg; propagules could be recovered from both soil m
oisture treatments for up to 19 wk. The presence of carrot plants did
not significantly influence propagule survival when compared with fall
ow soil, and propagules of C. elegans could be detected after 19 wk of
soil incubation at 20 C. The presence of onion seedlings, however, de
creased recovery of the pathogen to an undetectable level after 15 wk.
When soil was flooded and maintained at 4 C, survival was comparable
to that in nonflooded, fallow soil. However, with increasing temperatu
re (15, 20, or 25 C), recovery of phialospores from flooded soil was s
ignificantly reduced (P less-than-or-equal-to 0.01) and no propagules
were detected after 12 wk. In nonflooded soil at constant soil matric
potential of about -50 J/kg, survival was reduced significantly only a
t 30 C and not at any of the lower temperatures tested. Addition of pl
ant tissues of alfalfa, carrot, rye, and onion all significantly reduc
ed the extent of survival of phialospores compared with the fallow con
trol, with onion tissues having the most pronounced effect. The additi
on of CaCO3 had no effect. The results from this study indicate that p
hialospores of C. elegans can survive in organic soil for periods grea
ter than 19 wk, especially under moist and cool conditions. Survival o
f phialospores was reduced significantly by the presence of onion seed
lings, flooding the soil at 25 C, and addition of plant residues. Thes
e findings could have application for reducing inoculum of C. elegans
under field conditions.