Even in the same anastomosis groups, eg, AG4, there
are both isolates sensitive and less sensitive to pencycuron. The regeneration
of colonies from protoplasts of R-C significantly decreased by the osmotic shock
in the presence of pencycuron, while such effect was canceled by washing
off the chemical prior to the osmotic shock. However, in Rh-131, the application
of the chemical appeared to stimulate the regeneration from protoplasts. Further
the measurement of optical density of protoplasts suspensions was performed to
elucidate the effect of pencycuron on the osmotic stability of protoplasts in a
short period. The optical density of suspensions of R-C protoplasts rapidly
declined in a short period of incubation by the osmotic shock in the presence of
pencycuron, but the effect on Rh-131 protoplasts was not statistically
significant regardless of the presence or the absence of the chemical. In the
first year of the experiments, 7 methods, including 1 with soil disinfection at
planting, were applied in Aug In the following year, R solani stem and stolon
infection on potato plants were assessed in Jun Soil treatment at planting with
pencycuron resulted in the lowest disease severity in the following year. At the
lowest dosage the treatment promoted the total counts of seedborne fungi at 8%
seed moisture content, but 3 and 5 g/kg exerted an inhibitory effect. At 16%
moisture, pencycuron enhanced seedborne fungi at all 3 doses after most
treatment periods, while pencycuron + captan had the reverse effect. Seeds with
16% moisture content lost viability more rapidly than those with 8% moisture,
the effect being more marked as storage time increased. Based on inhibition of
mycelial growth of the pathogen by different concentrations of pencycuron, the
average EC50 of sensitive isolates of R solani AG-4 was 0.02 micro g/ml. Tenfold
concentrations of 0.02 micro g/ml were used as discriminatory concentrations to
detect the sensitivity of 403 isolates of R solani AG-4 to pencycuron. 27.94% of
isolates were resistant to pencycuron. The EC50 of R solani AG-4 KHL 2-1, KHL
15-3, KHL 8-2, KHL 14-1, PLKT 4-1 and KHL 9-1 isolates were 0.0224, 0.0225,
0.0680, 0.0627, 0.1130 and 0.2241 micro g/ml, respectively. In this study, both
temperature and pH had a significant effect on the sensitivity of mycelial
growth of R solani to pencycuron at 0.2 micro g/ml. The responses of the
isolates to pencycuron could be distinguished as resistant, moderately resistant
and sensitive when they were cultured on potato dextrose agar at 20-24 degrees C
and pH 5.4. Different components of the media could also change the sensitivity
of R solani AG-4 to pencycuron. When R solani AG-4 had pectin as a carbon
source, the sensitivity of its hyphae to the fungicide was markedly reduced.
However, the results indicated that each of 8 nitrogen sources in a modified
medium did not affect the sensitivity of R solani AG-4 to pencycuron. These
experiments indicated that both soil- and tuber-borne inoculum must be
considered in any program aimed at controlling R solani. Tuber treatments of
either a 20 min dip in 2% formaldehyde, sprays with pencycuron, iprodione or a spore suspension of 10-6 spores/mL
of Verticillium biguttatum or a dust with tolclofos methyl were most effective
if planted in soil fumigated with 500 L/ha metham sodium or soil with low levels
of R solani. A commercial formulation of Trichoderma harziannum and T koningii
applied as a dust at 1.3 g/10 kg seed was in most cases ineffective when treated
seed was planted into either fumigated or unfumigated soil. The incidence of
progeny tubers with sclerotia varied between sites and ranged from 85% in an
unfumigated soil planted with infected tubers to 2% in a fumigated soil planted
with pencycuron-treated tubers.
Yangzhou pioneer chemical CO., LTD
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