Jl. Williams-woodward et Fa. Gray, Seasonal fluctuations of soil and tissue populations of Ditylenchus dipsaci and Aphelenchoides ritzemabosi in alfalfa, J NEMATOL, 31(1), 1999, pp. 27-36
Population dynamics of A. ritzemabosi and D. dipsaci were studied in two al
falfa fields in Wyoming. Symptomatic stem-bud tissue and root-zone soil fro
m alfalfa plants exhibiting symptoms of D. dipsaci infection were collected
at intervals of 3 to 4 weeks. Both nematodes were extracted from stem tiss
ue with the Baermann funnel method and from soil with the sieving and Baerm
ann funnel method. Soil moisture and soil temperature at 5 cm accounted for
64.8% and 61.0%, respectively, of the variability in numbers of both nemat
odes in soil at the Big Horn field. Also at the Big Horn field, A. ritzemab
osi was found in soil on only three of the 14 collection dates, whereas D.
dipsaci was found in soil on 12 dates. Aphelenchoides ritzemabosi was found
in stem tissue samples on 9 of the 14 sampling dates whereas D. dipsaci wa
s found on all dates. Populations of both nematodes in stem tissue peaked i
n October, and soil populations of both peaked in January, when soil moistu
re was greatest. Numbers of D. dipsaci in stem tissue were related to mean
air temperature 3 weeks prior to tissue collection, while none of the clima
tic factors measured were associated with numbers of A. ritzemabosi. At the
Dayton held, soil moisture plus soil temperature at 5 cm accounted for 98.
2% and 91.4% of the variability in the soil populations of A. ritzemabosi a
nd D. dipsaci, respectively. Aphelenchoides ritzemabosi was extracted from
soil at two of the five collection dates, compared to extraction of D. dips
aci at three dates. Aphelenchoides ritzemabosi was collected from stem tiss
ue at six of the seven sampling dates while D. dipsaci was found at all sam
pling dates. The only environmental factor that was associated with an incr
ease in the numbers of both nematodes in alfalfa stem tissue was total prec
ipitation 1 week prior to sampling, and this occurred only at the Dayton fi
eld. Numbers of A. ritzemabosi in stem tissue appeared to be not affected b
y any of the environmental factors studied, while numbers of D. dipsaci in
stem tissue were associated with cumulative monthly precipitation, snow cov
er at time of sampling, and the mean weekly temperature 3 weeks prior to sa
mpling. Harvesting alfalfa reduced the numbers of A. ritzemabosi at the Big
Horn field and both nematodes at the Dayton field.